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Thread: Weird audio Amp problem...

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    Weird audio Amp problem...

    I built a busking Amp for the demonstration of my whistling to good music. It consists of:
    1) electret Mic PreAmp,
    2) ETI-486 Howl-round Stabilizer,
    3) Pedal Reverb and a
    4) 100W (class D) Amp running on a 11.1V LiPo.

    Problem: When I turn the system on, the whistling volume is moderate, yet then when I turn it briefly off/on, the volume goes suddenly quite high and then gradually weakens.
    I don't know what is causing it gradual drop? Maybe it has something to do with an old electrolytic? - Thank you in advance for any suggestions, Jo

    Here's a sample of my inherited whistling, which I care to maintain (even now at age 77):
    https://app.box.com/s/u68q3fn26jtwb9673xbfc751mef4wq6e

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by jjj View Post
    I built a busking Amp for the demonstration of my whistling to good music. It consists of:
    1) electret Mic PreAmp,
    2) ETI-486 Howl-round Stabilizer,
    3) Pedal Reverb and a
    4) 100W (class D) Amp running on a 11.1V LiPo.

    Problem: When I turn the system on, the whistling volume is moderate, yet then when I turn it briefly off/on, the volume goes suddenly quite high and then gradually weakens.
    I don't know what is causing it gradual drop? Maybe it has something to do with an old electrolytic? - Thank you in advance for any suggestions, Jo

    Here's a sample of my inherited whistling, which I care to maintain (even now at age 77):
    https://app.box.com/s/u68q3fn26jtwb9673xbfc751mef4wq6e
    What is the model of the 100watt class D amp and why are your turning it off/on briefly? If the amp exhibits no other problem than this I thing you could be upsetting the SMPS Oscillation pattern. If you turn it off then wait 5 or 10 seconds does it still exhibit said behavior?

    nosaj

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    Old Timer J M Fahey's Avatar
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    Agree and add: divide and conquer.

    Start by connecting your preamp straight to power amp, what happens now?

    Post the relevant schematics, we know nothing about your system.

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    Juan Manuel Fahey

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    That's the Amp...
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    Ola amigo... estuve 15 anos en St'go de Chile y ahora habla un poquito chileno. (Una broma para ti: "Mi amigo que fue catholico se puso lutherano, porque le gusta el utero y ano!"

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    Don't forget the joker g1's Avatar
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    Which LiPo are you using?
    It sounds like maybe you are hearing a peak surge at turn on/off that the battery cannot sustain for long.

    Or maybe you need the 'voltage up pcb' mentioned on the amp picture you posted. What is your speaker impedance?

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    Old Timer J M Fahey's Avatar
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    That amplifier can put some 15W RMS into 4 ohms, being optimistic.

    That said, with good speakers it´s quite acceptable.

    Measure the battery while playing, IF it´s poorly charged and drops heavily under load, that may explain your problem.

    If not,there is a problem with your mic preamp, we need its schematic.

    For now, forget the other pieces of equipment (anti feedback and reverb) .

    Te felicito, recordás muy buen Español.
    Claramente por haber vivido en Sudamérica y no sólo estudiarlo en la escuela

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    Juan Manuel Fahey

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    Quote Originally Posted by J M Fahey View Post
    That amplifier can put some 15W RMS into 4 ohms, being optimistic.

    That said, with good speakers it´s quite acceptable.

    Measure the battery while playing, IF it´s poorly charged and drops heavily under load, that may explain your problem.

    If not,there is a problem with your mic preamp, we need its schematic.

    For now, forget the other pieces of equipment (anti feedback and reverb) .

    Te felicito, recordás muy buen Español.
    Claramente por haber vivido en Sudamérica y no sólo estudiarlo en la escuela
    =====================
    Soy de origen aleman. Egualmente, tu ingles es incredible... por un gaucho de la Pampa. - Una senorita ofrece a un caballero un mate y el caballero contesta: "Un mate cebados con esos lindos manos es una delicia de matear!" (Esto aprendi de mi tutor de espanol.) Otro chiste: Una (fea chichona) senora de aseo pregunta a su jefe: "Que profesor, Ud. quire casarse conmigo? El profesor contesta: "Si, porque hecho me cuenta, que me viene mas barato de casarle que pagarle por hora..." Otro mas: En un negocio visto un aviso que dice: "Si algun le habla mal de mi preguntele cuanto me debe..." Mi senora Elsita es chilena y hablo cada dia en chileno con ella. Por eso tengo pratica; 'sipo' (si pues... cachai?) - Como te parece mi silbido heredado?
    Back to work:
    Yes, good idea: I'm going to connect my MM to monitor the 5A2 LiPo battery while turning on the PA to see if the voltage drops after a while. I also bought some Ali-Express voltage step-up circuits and will try them in case the battery has a voltage drop. The Mic Preamp is just an ordinary electret Mic circuit. Maybe el culpable es the old electrolytic condenser ...which is almost as young as I'm?
    I even added a PB switch to the Mic so, that I can "revive it" again, but that causes a nasty switching noise. If I can filter this switching noise out that'll OK too, because I can always find a dead point in the melody, where I can "revive it" the volume loss again.
    Of course it would be better to find the problem and finish the madness once and for all. Maybe I have to pay for an electronics technician to locate the flaw.
    Well let's see how I go.

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    Quote Originally Posted by g1 View Post
    Which LiPo are you using?
    It sounds like maybe you are hearing a peak surge at turn on/off that the battery cannot sustain for long.

    Or maybe you need the 'voltage up pcb' mentioned on the amp picture you posted. What is your speaker impedance?
    Thx for the helpful reply. I just now monitored the battery on turn on etc: it showed a steady 12.56V !! The speaker is a "Pioneer" 8 Ohm speaker model.

    I swapped my old two transistor electret PreAmp for the below China PreAmp circuit. It works just as good, but the main problem still exist. I am now almost sure that the culprit is that 100W Class D Amp. Tomorrow I'm going to power this Amp with a voltage step-up circuit to 14 V or so and then see if the volume remains steady.

    How about this dual Mic AD633 circuit, will it effectively cut down on feedback? That would be great, for then I can eliminate the bulky ETI howlround eliminator. I'm not quite sure how it effectively works.
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    Last edited by jjj; 01-24-2019 at 10:50 AM.

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    Old Timer J M Fahey's Avatar
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    Thanks
    Chilean ladies are beautiful, I almost married when I was there.

    Now back to the hardware problems

    Quote Originally Posted by jjj View Post
    I'm going to connect my MM to monitor the 5A2 LiPo battery while turning on the PA to see if the voltage drops after a while.
    ............
    I just now monitored the battery on turn on etc: it showed a steady 12.56V !!
    Ok:
    1) please post exact battery name/model or even better a direct link to the one you have.
    I googled 5A2 LiPo battery and all I found were drone capable ones, all 3.7V (so you either are using a pack of 4 or bought some prepackaged ones) and only 850mAH which is a red flag, that´s about 1 hour autonomy feeding a 15W amplifier.

    I also bought some Ali-Express voltage step-up circuits and will try them in case the battery has a voltage drop.
    They can´t do magic or pull power out of thin air; if main battery exhausts and drops, "boosted" voltage also will.
    If anything, it will drop even harder.
    IF you need higher voltage, add an extra 3.7V cell in series.
    The Mic Preamp is just an ordinary electret Mic circuit. Maybe el culpable es the old electrolytic condenser
    Please post the actual circuit.
    Can´t suggest you measure a couple voltage points if I don´t know what points you have to begin with.

    I even added a PB switch to the Mic so, that I can "revive it" again, but that causes a nasty switching noise.
    That stinks of poor biasing or voltage leakage which mess with operating point(s).
    maybe in the preamp, maybe some leak misbiases the power amp ... just guesses until we see a schematic.

    You won´t have the Class D amplifier one, but post a couple sharp and well illuminated closeups, specially showing the input and output areas.

    Just guessing based on poor to zero data:

    * your mic preamp may be poorly biased or leaking or missing a ground reference.
    That typically "starts" ... sort of ... but slowly drifts until it cuts out ... then switching ON-OFF "resets" it.

    If I can filter this switching noise out that'll OK too, because I can always find a dead point in the melody, where I can "revive it" the volume loss again.
    Of course it would be better to find the problem and finish the madness once and for all.
    That´s the point.
    Maybe I have to pay for an electronics technician to locate the flaw.
    Ok,the Forum takes USD, GBP, Yen, Renminbi, Euro and Chilean Pesos... which one will it be ?

    I swapped my old two transistor electret PreAmp for the below China PreAmp circuit. It works just as good, but the main problem still exist. I am now almost sure that the culprit is that 100W Class D Amp.
    Probably.
    We NEED those PCB closeups to suggest some measuring points, also show how is speaker connected.
    MAYBE some DC is leaking through some input capacitor and shifts amp bias, maybe you connected speaker wrong and amp can´t stand that for long.

    I >>>GUESS<<< (lacking data ) that your amp uses a floating/balanced/bridge output and you MAY be connecting speaker wrong, grounding one of its terminals.
    In that case one half amp will be shorted, maybe not exploding because of internal protection but overheating and now and then muting it.

    But we need more data to proceed. Entendés huevón culiáu?

    Really, "you are our eyes" .....

    Tomorrow I'm going to power this Amp with a voltage step-up circuit to 14 V or so and then see if the volume remains steady.
    If amp drifts or self blocks or battery dies no step up circuit will help you.
    How about this dual Mic AD633 circuit, will it effectively cut down on feedback? That would be great, for then I can eliminate the bulky ETI howlround eliminator. I'm not quite sure how it effectively works.
    Those are very specialized circuits, very poor audio quality , they are meant for special communications problems such as tank or fighter jet crews, noisy factories/mines, etc. , practically unusable for singing.

    That said, the Grateful Dead used a similar circuit, but it was fully passive and works only with dynamic microphones: they taped a second Shure SM57 element a couple inches away from the one they were singing into (practically swallowing it) , and connected both in series but out of phase.



    Ambient noise was picked up by both and almost cancelled, voice got to one very strong, and quite weaker to the other, so its cancellation was minimal.
    But it´s a very tricky setup.

    Of course, they NEEDED it because otherwise they "might" have had a feedback problem


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    Juan Manuel Fahey

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by J M Fahey View Post
    That said, the Grateful Dead used a similar circuit, but it was fully passive and works only with dynamic microphones: they taped a second Shure SM57 element a couple inches away from the one they were singing into (practically swallowing it) , and connected both in series but out of phase.

    Ambient noise was picked up by both and almost cancelled, voice got to one very strong, and quite weaker to the other, so its cancellation was minimal.
    But it´s a very tricky setup.
    Any mention of the wall of sound, plus a photo, rates a thumbs up. However there's a bit of disinformation involved. Unless it was an early, cheap experiment, dual SM57's weren't used. Matched pairs of Bruel & Kjaer condenser instrumentation mics were the norm, plus a "balance box" on the stand between them. Despite the cost & reputation of those unbelievably expensive B&K's, resulting sound quality wasn't as good as you'd imagine. Some nights yes and others, well, ....... the less said the better. What to do for your band? Best stick with an old fashioned - single - SM57 or 58. One per customer.

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    Enjoy. Every. Sandwich.

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    Well, it sounds like everything in my little PA is bad, but I don't think it's really ...that bad. Today I changed the Mic PreAmp for a China made one and it sounds as good as my old two transistor electret Mic circuit. Yet the main problem is still not solved. I then changed the 100W Amp for another China made Amp and that too didn't cure the main problem. - So now the problem can only be in the reverb unit or the ETI howlround reducer.
    It's still all the same: after I turn on the power switch of the PA, the sound volume is moderate, yet the moment I quickly turn off and on again the switch, the PA suddenly doubles its amplification volume.
    To counter this phenomenon I inserted a small speaker Pot (with a tiny heat sink on it) to curb the volume. The resistance to the speaker (including its 8 Ohm speaker) is 43 Ohm. I don't think that has something to do with the main problem or has it?
    So, since I cannot find the cause of the problem I'm planning to settle for next best option: a type of push button on the electret Mic, which allows me to kick start the PA every 20 seconds or so. I got to think of some kind of circuit, which first briefly disconnects the loudspeaker and then turns off and on again the power to the PA. Maybe I can even automate it with an China off/on timer?
    Otherwise the setup is truly great sounding and maybe one day I might meet an electronic expert, who admires my whistling and so, he might be willing to check it out. Until then I have to put up with what is available to my limited electronic knowledge.
    It was very nice having met you wonderful people... Warm Regards, Jo from Townsville in tropical N. Australia

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by jjj View Post
    Well, it sounds like everything in my little PA is bad, but I don't think it's really ...that bad.
    Nobody said that, it has a problem we are trying to solve.
    Yet the main problem is still not solved.
    Well, it won´t solve on its own, that´s for sure.
    I then changed the 100W Amp for another China made Amp and that too didn't cure the main problem.
    Read above.
    - So now the problem can only be in the reverb unit or the ETI howlround reducer.
    WHAT "reverb unit or the ETI howlround reducer"
    You were asked to:
    For now, forget the other pieces of equipment (anti feedback and reverb) .
    It's still all the same: after I turn on the power switch of the PA, the sound volume is moderate, yet the moment I quickly turn off and on again the switch, the PA suddenly doubles its amplification volume.
    To counter this phenomenon I inserted a small speaker Pot (with a tiny heat sink on it) to curb the volume. The resistance to the speaker (including its 8 Ohm speaker) is 43 Ohm. I don't think that has something to do with the main problem or has it?
    Who knows? You have not tested it as asked to.
    So, since I cannot find the cause of the problem
    You haven´t even tried
    I'm planning to settle for next best option: a type of push button on the electret Mic, which allows me to kick start the PA every 20 seconds or so. I got to think of some kind of circuit, which first briefly disconnects the loudspeaker and then turns off and on again the power to the PA. Maybe I can even automate it with an China off/on timer?
    Ever heard of Rube Goldberg?
    He consistently designed very complex setups to solve very simple problems, such as:


    That said, happy whistling

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    I built a busking Amp for the demonstration of my whistling to good music. It consists of:
    1) electret Mic PreAmp,
    2) ETI-486 Howl-round Stabilizer,
    3) Pedal Reverb and a
    4) 100W (class D) Amp running on a 11.1V LiPo.

    Because I already changed 1) and 4) without success, the problem can only be either in the ETI-486 Howl-round Stabilizer or the Mooer Pedal Reverb. The thing I still need to find out if the signal from 2) output is adequate or too low? If it's too low that might explain the problem.
    Yet, it still is quite weird that a kick restart suddenly overdrives the signal. - This is why I won't be able to cure the problem unless I settle for the kick start mode.

    Well, the last weeks I already added a PB switch on electret Mic for it and it truly helped me to maintain good performance. The only annoying thing is the switching noise... When I whistle in public I usually meet lots of people. Chance, I might meet the right person able to solve my problem. End of problem!
    My head is now spinning around ...how to get rid of that ugly switching noise?
    A double PB switch, where on press one contact disconnects the speaker and the other contact disconnects and reconnects the power supply. Maybe the speaker need to be disconnected a fraction earlier? It has to be happen all in about 1 second. - Life isn't' meant to be easy!

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by jjj View Post
    I built a busking Amp for the demonstration of my whistling to good music. It consists of:
    1) electret Mic PreAmp,
    2) ETI-486 Howl-round Stabilizer,
    3) Pedal Reverb and a
    4) 100W (class D) Amp running on a 11.1V LiPo.

    Because I already changed 1) and 4) without success, the problem can only be either in the ETI-486 Howl-round Stabilizer or the Mooer Pedal Reverb. The thing I still need to find out if the signal from 2) output is adequate or too low? If it's too low that might explain the problem.
    Yet, it still is quite weird that a kick restart suddenly overdrives the signal. - This is why I won't be able to cure the problem unless I settle for the kick start mode.

    Well, the last weeks I already added a PB switch on electret Mic for it and it truly helped me to maintain good performance. The only annoying thing is the switching noise... When I whistle in public I usually meet lots of people. Chance, I might meet the right person able to solve my problem. End of problem!
    My head is now spinning around ...how to get rid of that ugly switching noise?
    A double PB switch, where on press one contact disconnects the speaker and the other contact disconnects and reconnects the power supply. Maybe the speaker need to be disconnected a fraction earlier? It has to be happen all in about 1 second. - Life isn't' meant to be easy!

    So lets simplify this a little bit. Remove the pedal reverb. Then see if your problem still exists, If it does remove the ETI-486.
    I really think your going to introduce more issues trying to accomadate the on/off issue.

    nosaj

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    Don't forget the joker g1's Avatar
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    Is the electret mic preamp designed to be running at the voltage you are running it at?
    It sounds like you have added a push-button disconnect for the electret and it temporarily cures your problem? The explanation is a bit confusing.

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    Lifetime Member Enzo's Avatar
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    Whenever I see a symptom of a repressed output that springs to life at power down, my first thought is an unterminated DC voltage somewhere. For example, a missing/open resistor at a transistor base. Or a tube grid. If your preamp uses op amps, check the output pins for DC offset. For that matter, make sure the power to the IC is right. If you are running single sided off a battery, did you include a good voltage reference at half voltage?

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    Quote Originally Posted by nosaj View Post
    What is the model of the 100watt class D amp and why are your turning it off/on briefly? If the amp exhibits no other problem than this I thing you could be upsetting the SMPS Oscillation pattern. If you turn it off then wait 5 or 10 seconds does it still exhibit said behavior?

    nosaj
    The model is: "China garbo"/ Chip: TPA3116 D2
    Yes, you are right... if I turn it off and wait for about 10 seconds and then turn it on, the volume doesn't jump high and then slowly lowers, but the volume level is fairly modest. So, the the rapid power turn off/on must be "upsetting the SMPS Oscillation pattern" and that explains the momentary volume raise. These things I wouldn't know. The stupid thing is, that I actually like this higher volume level, but don't know how to obtain it.
    OK then. The question now is: since this is a 100W Amp any higher voltage should deliver more volume; am I right? I'll try to raise the voltage with this one and see if it's any good:
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    Last edited by jjj; 01-26-2019 at 10:00 AM.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by jjj View Post
    The model is: "China garbo"/ Chip: TPA3116 D2
    Yes, you are right... if I turn it off and wait for about 10 seconds and then turn it on, the volume doesn't jump high and then slowly lowers, but the volume level is fairly modest. So, the the rapid power turn off/on must be "upsetting the SMPS Oscillation pattern" and that explains the momentary volume raise. These things I wouldn't know. The stupid thing is, that I actually like this higher volume level, but don't know how to obtain it.
    OK then. The question now is: since this is a 100W Amp any higher voltage should deliver more volume; am I right? I'll try to raise the voltage with this one and see if it's any good:
    Let me start off by saying this, you are doing the same thing I have been guilty of many times here. If you want to fix this follow JM Fahey instructions closely, do not go left unless instructed to or right for that matter. Do only what is asked of you and nothing more than reporting back.

    You are bouncing all over the place without really answering any questions or responding with any test. What you will find is if you don't help yourself by helping us help you. You will still have the same problem. This is not like other music forums out there, There are real techs from the benches here, not people who might postulate on unreal possibilities.

    So lets get this show on the road, go back to JM Fahey's lasy post and please answer the questions, Then G1, then Enzo.

    If there is a language barrier please state so we can work with what we know, there are many multiple language people here that can and do help.

    Our main goal and possibly motto should be "We can help you get it fixed and if you want more , Help you understand"
    The journey of a thousand miles starts with one step, some people never make that first step out of fear though.

    nosaj
    You can do it, I have faith

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    I have no doubt that you are all experts in electronics and that's why I begged you for help. Enzo helped me in the past and I never forgot him, too.
    I read all the posts and at the same time made sure that I checked out if any of these suggestions/ possibilities might apply. Your previous post happened to fit my problem and that's why I discarded other possible causes. I also understand that it is almost impossible to guess the problem, unless one has all the detailed Info.

    But at least we got near enough to what is causing it and that's what I was looking for and I am truly grateful for this help. - You are also right that I should reply to each question, because it serves to narrow down and diagnose the problem. On the other hand I at least changed the electret Mic PreAmp and the 100W Amp and so, knew where I was heading.
    Tomorrow I'm going to open the system box again and increase the 100W Amp's voltage to about 18V and observe if the sound volume increases to the desired level and remains steady. - I'll let you know of the result. I really trust that it might resolve the problem. Of course it then still will suddenly raise the volume level if I turn the system rapidly turn off & on again, because that's the nature of this class D Amps, I learnt and I should avoid it.
    Besides, I did the same kind of "labor of love", you good people do, for many years, teaching youngsters philosophical insight while performing in public and they were very grateful. I wrote several philosophical books, titled: "A Guide To Personal Contentment" and "Grandpa's Insight"

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    My victory celebration came too early...
    I just finished to add that (shown) voltage up circuit and adjusted it to 22V. It all looks good, but.. but when switch the system on the full sound volume of the 8 Ohm speaker is still only moderate. Yet, when I then turn the power switch fast off + on the sound volume goes "through the roof" (very loud) and I have to curb the volume with that speaker Pot. This high volume level then takes about 20 seconds to gradually return back to the moderate sound level.
    So, the 22V voltage increase results in no significant sound volume increase/ change from the normal 11.1V battery supply. How disappointing!
    That make me wanting to go back to the sound volume "kick start" idea of quickly turning off and on the power supply. During whistling I can easily find a spot in the melody where I can for 1 second "kick start" the system. The only problem with that how to silence the switching noise?
    In three steps:
    1) A press onto a tiny push switch at the Mic disconnects the speaker
    2) A push button press then turns off & on the power supply
    3) and another press onto the tiny push switch (from 1) reconnects the speaker

    There surely are better ways of achieving it with just one press on a push button. In all it would make me already happy.
    I don't know why this class D Amp causing me all these problems. Maybe I should rather use a small car Amp? With this unit I tried to build a small unit for room size performance. My big unit busking unit has a 30+30W Sony car Amp and a stereo tube PreAmp (which I build) and there I haven't got this kind of problems with the very same components (i.e. Electret Mic PreAmp, => ETI-486 Howl-round Stabilizer => Pedal Reverb).

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  22. #22
    "Thermionic Apocalypse" -JT nickb's Avatar
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    I suggest you take the output from each section one at a time to an external known good amplifier in order to isolate where the problem occurs i.e mic preamp, reverb, howl suppressor, power amp input. Is there a preamp with tone/ volume somewhere in this?

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    Old Timer J M Fahey's Avatar
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    Tomorrow I'm going to open the system box again and increase the 100W Amp's voltage to about 18V and observe if the sound volume increases to the desired level and remains steady. - I'll let you know of the result. I really trust that it might resolve the problem.
    Who asked for that experiment?
    Of course it then still will suddenly raise the volume level if I turn the system rapidly turn off & on again, because that's the nature of this class D Amps, I learnt and I should avoid it.
    No, it´s not the nature of Class D amps, there are millions of them around and nobody reports that.
    In fact, I don´t even think the problem lies in the Class D amp, go figure.
    My victory celebration came too early...
    Why that doesn´t that surprise me?
    That make me wanting to go back to the sound volume "kick start" idea of quickly turning off and on the power supply.
    Please be my guest.

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  24. #24
    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by jjj View Post
    My victory celebration came too early...
    I just finished to add that (shown) voltage up circuit and adjusted it to 22V. It all looks good, but.. but when switch the system on the full sound volume of the 8 Ohm speaker is still only moderate. Yet, when I then turn the power switch fast off + on the sound volume goes "through the roof" (very loud) and I have to curb the volume with that speaker Pot. This high volume level then takes about 20 seconds to gradually return back to the moderate sound level.
    So, the 22V voltage increase results in no significant sound volume increase/ change from the normal 11.1V battery supply. How disappointing!
    That make me wanting to go back to the sound volume "kick start" idea of quickly turning off and on the power supply. During whistling I can easily find a spot in the melody where I can for 1 second "kick start" the system. The only problem with that how to silence the switching noise?
    In three steps:
    1) A press onto a tiny push switch at the Mic disconnects the speaker
    2) A push button press then turns off & on the power supply
    3) and another press onto the tiny push switch (from 1) reconnects the speaker

    There surely are better ways of achieving it with just one press on a push button. In all it would make me already happy.
    I don't know why this class D Amp causing me all these problems. Maybe I should rather use a small car Amp? With this unit I tried to build a small unit for room size performance. My big unit busking unit has a 30+30W Sony car Amp and a stereo tube PreAmp (which I build) and there I haven't got this kind of problems with the very same components (i.e. Electret Mic PreAmp, => ETI-486 Howl-round Stabilizer => Pedal Reverb).
    Something occurs to me that is in analogy form but I'm not sure if this is possible.

    To me this seem like a carborated engine, similar to pumping the gas before starting giving it an inrush of gas an air to make the engine rev.. which it goes back to normal after the excess gas has burned off.

    So first off stop turning it off then on real fast. Turn it on feed a sine wave signal into it with a dummy load in place of the speaker and take an AC voltage measurement, if we can get roughly 85 watts out of the amp, you have no problem with it and have created a problem where there was none.

    nosaj

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  25. #25
    Old Timer J M Fahey's Avatar
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    Oh, he will never get that amount of power out.

    Just 15W into 4 ohms with straight 12V from battery, and maybe 70W RMS from a *stiff* overrated 26V power supply, none of that cheesy booster fed from a puny underrated battery nonsense, simply because that´s what voltage swing allows.

    The test should be to feed whatever´s needed (think 500mV to 1V RMS or so) to Class D amp until it just clips, first check that it holds output steady, then turn it on-off many times to see whether there is a volume surge (I bet none will be found ) and then start checking for the real problem.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Oh, he will never get that amount of power out.

    Just 15W into 4 ohms with straight 12V from battery, and maybe 70W RMS from a *stiff* overrated 26V power supply, none of that cheesy booster fed from a puny underrated battery nonsense, simply because that´s what voltage swing allows.

    The test should be to feed whatever´s needed (think 500mV to 1V RMS or so) to Class D amp until it just clips, first check that it holds output steady, then turn it on-off many times to see whether there is a volume surge (I bet none will be found ) and then start checking for the real problem.
    Well I just kinda pulled that number outta my a$$ for a rough estimate I guess I should start doing the math.

    nosaj

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    Test result: If I ran the same setup with my Sony car Amp and I haven't' got this problem. Yet, since I tried to create a small traveler's unit with the same components I ran into 1000 problems. To me the components (i.e. electret Mic PreAmp, ETI-486 Howl-round Stabilizer and the pedal Reverb work fine, only the 100W Amp doesn't' deliver to my expectations. Maybe the pedal Reverb's output is too low?
    - I'm about to give up, because my electronics knowledge is limited and thus, unable to locate the problem with this 100W Amp. Yet, at least it works to my satisfaction in that "kick-start" method. I now already returned all as it was before and chose one tiny switch and push button, which I glue to the Mic.
    Three fast presses then will "kick-start" the system until one good day on which I meet an electronics expert, willing to have a look at it.
    Thus, best is I pack it up and send it to you. How much will cost me your expertise ? I can compensate your efforts with all my inherited musical expertise/ recordings. Albeit my wife calls me "Einstein", I can't possibly be perfect at everything...
    For years I tried to miniaturize this setup... now I gotten old and I'm still at it and never will give up hoping for success! - I wished I could buy such a small/ compact, fairly powerful travel unit, but most of them (on AliExpress and eBay) lack proper reverb. are either too big or too expensive.
    I'll show you a Pic of the Mic with the 2 "kick-start" switches...

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  28. #28
    Don't forget the joker g1's Avatar
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    Quote Originally Posted by jjj View Post
    Test result: If I ran the same setup with my Sony car Amp and I haven't' got this problem.
    And the whole system including the sony amp was running off the LiPo that you are now using?

    If so, maybe the new amp requires a different signal level than the sony. Or maybe the new amp is just defective.

    If you were not running the system with the sony amp off the same LiPo, you need to test it like that.

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  29. #29
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    Yes, the Sony Amp runs on the same 11.1V LiPo battery as well. It could be that the 100W Class D Amp. needs a stronger signal. In that case I would need to amplify the strengthen the reverb signal. Yesterday I lifted the voltage for the 100W Class D Amp to 22V and the output volume to the 8Ohm remained almost the same. It could be that a weak input signal is causing it?
    Today I wired that said "kick-start" idea to the Mic and it works a charm...
    Here's the Pic of it:
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  30. #30
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by nosaj View Post
    Well I just kinda pulled that number outta my a$$ for a rough estimate I guess I should start doing the math.

    nosaj
    Oh, don´t worry with that, I thought you were referring to the published spec for that class D amp, which IS advertised as a "100W amplifier"

    Just check the very first post:

    4) 100W (class D) Amp running on a 11.1V LiPo.
    I was answering to *that*.

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    Yes, it could be that the 100W needs a stronger input signal. That's why it acts so weird with a weak signal. In that case I would need to amplify the strengthen the reverb signal. The Chinese sell some low Watt PreAmps. (Maybe 2W might suffice?) Yet, then again it might be something else? Maybe even me!
    Well, for now I found a poor, yet satisfactory solution, which at least enables me to happily perform until I personally meet an admirer of my musical art, who's willing and able to check out what's wrong with it.
    So, I'm truly grateful for all your wonderful help... in this case it's just me who's unable to help myself.
    One final question:
    how can I automate this power "kick-start" madness? The Chinese sell cheap timers with RLY. The problem there's that the speaker needs to be first disconnected and reconnected last.

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    Last edited by jjj; 01-28-2019 at 07:08 AM.

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    The last 4 days it was raining non-stop here in Townsville Qld.4814 and that gave me a chance to investigate the problem further.
    Result: After I disconnected the ETI Howlround (which I built) the problem is no more. It worked for 20 years, but now I ask myself what has gone wrong wit it?
    What might causing it. At that time I only added a 12V negative voltage generator, albeit it should have been +/-15V.
    I (twice) tried to upload the magazine in which the ETI Howlround is featured, but this forum's application rejects its upload.

    Here's a box.com upload of it: https://app.box.com/s/em8ggpmmp1pwfh3y1dyq5tlwt8s1mzom

    I also included a Pic of my improvised hardware...
    Maybe this cheap Frq shifter will do the job:
    https://www.aliexpress.com/item/Free-Shipping-1pc-AD303-frequency-shift-anti-whistle-module-Microphone-howling-suppressor/1568429213.html?spm=2114.search0104.3.1.6bfa6b0ap3QhyA&w s_ab_test=searchweb0_0,searchweb201602_3_10065_10068_101 30_10547_319_317_10548_10696_453_10084_454_10083_433_106 18_431_10307_537_536_10131_10902_10132_10133_10059_10884 _10887_321_322_10103,searchweb201603_54,ppcSwitch_0&algo _expid=ea2a3542-8545-4cd4-817d-a79a45b520eb-0&algo_pvid=ea2a3542-8545-4cd4-817d-a79a45b520eb&transAbTest=ae803_5
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  33. #33
    Old Timer J M Fahey's Avatar
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    Result: After I disconnected the ETI Howlround (which I built) the problem is no more. It worked for 20 years, but now I ask myself what has gone wrong wit it?
    Which was suggested .... ummmmm ..... in post #3

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  34. #34
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Just the relevant section from the magazine:

    Howl.pdf


    This thread's a hoot (pun intended)!

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