Advice needed on first cab build. Smaa single speaker type.

[tonequester]

tonequester here. I'm new to this part of the forum. A little backgroung info on what i'm trying to do. I'm working on a way to "re-amp" a Blackstar HT-1R, 1 Watt, studio/practice amp, through a solid state (kit built) power amp with an out put of 20-30 Watts. I'll be using the 4-16 ohm speaker output jack on the back of the "tube amp". I have an Eminence, 150 W., 32 Ohm speaker. If buy another of these, and hook them in parallel I will have 16 Ohms, which would work with the Blackstar, but I'm going to re-amp with a s.s. power amp. Do I need to make sure the power amp is designed to work with EXACTLY 16 Ohms. Also, what would be considered a "good" size for the cabinet, with two 15",150 Watt speakers. Open back or closed ? Any Opinions welcome, thanks.......tonequester.

[Chuck H]

JMHO, but... Chasing the usefulness of that 32 ohm speaker by buying another one is a waste of money. You could probably get a well known and respected, proper guitar amp speaker for the same price. That is, unless you've heard this 32 ohm speaker and like it's tone above all others. The SS amp DOES need to be designed with the intended ohmage in mind IF you want to get the full wattage out of it. If you run the SS amp into too low a load it may over dissapate. If you run it into too high a load it won't deliver the intended power. The cabinet size is somewhat pedantic WRT guitar amps. Accidental resonances and peaks are part of why certain cabinets sound good with certain amps. Remember that a guitar amp is intentionally coloring the sound. And absolutely NOT trying to reproduce it accurately. That said... There are cabinet designs for roughly 30 watts that are known to sound a certain way for guitar tone. A VOX AC30 with a pair of Celestion Blues (or cheaper, but not considered as good, a pair of V30's) comes to mind. There are also many 1x12 cabinet designs that are very popular and should work well for amps from 20W to 50W.

Point is... If your going to spend money on a speaker for guitar, buy a guitar speaker. Don't try to make the 32 ohm speaker useful by correcting it's load with another 32 ohm speaker (unless you like that speaker, as noted).

Another note... If your feeding signal from the "host" amp to the supporting amp properly, the tube amp should be oblivious to the needs of the SS amp. So the SS amp and it's speaker load is the only formula you need to consider.

[tonequester]

tonequester here.



Thanks Chuck. Your reply is as always, based in common sense. Sometimes i try to "think' to much, and in doing so forget common sense. The only strange thing about the 32 Ohm speaker is that I'm sure that I got it as a guitar amp speaker. It may have been someones mistake,but it came from an amp that was parted out. I don't even recall what the amp was. I guess that I should have known that 32 Ohms would not be used for a stock speaker. after considering your reply, I am now inclined to perhaps buy two more of the Weber speakers that I have used to replace the stock Blackbird in my HT-1R. I really like the tone, and their price is hard to beat. I can get a couple of 12" Alnico speakers(guitar) in 4 or 8 Ohms for about $50.00 a piece. Weber claims that all 15" speakers suffer from "cone rub' at high volume. I have no idea if this is hype or true, but a couple of 12's would probably do me fine, and fit a cab that is not too big to lug around. I figured that the s.s. amp and the load would be the main consideration, thanks for confirming that. I'm checking out multiple methods of matching tube, s.s., and speaker cab. It seem that depending on what method one chooses, that alone can run anywhere from a few bucks to $500.00. I figure you can guess which direction I will try to begin with. I know that a simple load resistor is the cheapest way to go, with probably the least in positive results. The Ultimate Adaptor appears to do everything including wiping your nose,
but at $499.99 it exceeds the cost of the tube amp kit and the s.s. kit amp combined. I'm looking at the "middle road". When I find a possibility, I'll definitely post it. I know that I need something that not only will satisfy impedance matching needs, but also give some control over signal strength. Those are things that the Ultimate Adaptor apparently does among other things. Thanks again for the reply. I always look forward to your comments as you are quite good at blending "theory" with common sense. You like me, don't like to waste money if it is
possible not to do so. Have a great day Chuck H ! tonequester.

[Chuck H]

I think your talking about the Ultimate Attenuator. Also known as the Ho attenuator as this is the name of the designer and a name they were also sold under by him. This next bit is a very important consideration. I met the Ultimate attenuator guys at the 2009 NAMM show. I loaned them an amp and they loaned me an attenuator. Both to the benefit of our personal exhibits since there was an 85dB limit on sound levels. The attenuator I had brought (a cheapy L-pad thingy) sounded like crap and the amp they brought (and old HiWatt) did too. Both booths sounded much better for the trade. Anyhoo... I'm told that the Ultimate uses a flat 30 ohm resistive load for all amps and then re amps with a SS power amp. At face value that 30 ohm load seems too high. But if you look at speaker impedance curves you'll see that the "load" they're rated at only occupies a very small frequency range in the low mids. All other frequencies being higher. Sometimes MUCH higher. So the nominal impedance of a speaker is really no where near it's rating. It's much higher. This same train of thought was used by other makers of resistive attenuators too. The Kendrick/Trainwreck/Dr.Z Airbrake, for example, uses a 32 ohm load. The idea being that it should still be safe for the host amp and sound more like a speaker at frequencies outside of the rated load. And it seems to work. These attenuators don't blow up amps and players seem to prefere their tone to other models. So...

You could build a simplified version of the Ultimate/Ho type attenuator by using a power resistor for the load and use a voltage divider from that resistor to feed the SS amp. You could even include an EQ in the SS preamp if you like. At that point you'd have, basically, a 30 watt version of the Ultimate/Ho attenuator for a fraction of the cost. The Ultimate/Ho attenuator has been refined for players tastes over the years and has a good rep. That, no doubt, is how they can charge so much money for such a simple concept. It's also worth noting that the Ultimate/Ho design is good for amps up to 250 watts!!! So all that capability is wasted on small amp like yours. Also, you intend to use your unit as an amplifier, not just an attenuator. Which should be a simpler design. In fact, if you only want to use the SS amp for boosting volume, you could just use a voltage divider at the SS amp input and let the host amp speaker be the load. So this raises an important question about your goal with this project. Do you plan to silence the host amp, and then use the SS amp as the only power amp feeding a speaker? This would have the benefit of giving you infinite volume control from whisper quiet up to 30W. Or do you only want the SS amp to be a satellite wattage bump for more power? When your functional goals are clear the design will be too.

EDIT: Part of the point being, there is no sense in using something like the Ultimate/Ho attenuator, capable of 250W, to pad your little amp down to preamp levels to feed a 30W SS amp!?! Why not just use something lika 22ohm/50 watt load resistor as the host amp load, then voltage divide an input level signal from the load resistor, then feed one stage of SS preamp, then a volume control and simple EQ, then to another SS preamp stage that feeds the SS power amp. Then you could plug any amps speaker output, up to fifty watts, directly into your unit and use your unit to attenuate or amplify the signal up to 30W. The divider off the load resistor would need to be made variable so that you can adjust the feed signal for amps of different wattages. And you'll have the benefit of added EQ! Easy peezy lemon squeezy. A $20 panel meter could be added to tell you when the divided signal is optimal for your SS amp making adjustment a simple visual thing. Also include protection diodes to avoid damage to the SS amp input in case the adjustment is wrong for the host amp in use. But the host amp, as long as it's plugged into your unit, will always be safe because it's hooked directly to the load no matter what. Now THIS would be a truely useful gear tool.

Something like this:

[Austin]

You can hook up that 32 ohm speaker to the blackstar amp, it won't hurt it. You could take the signal for the ss amp directly off the speaker leads instead of a resistor too. 1 watt into 32 ohms = about 5 volts swing, 1 watt into 8 ohms = about 2 volts

Ohm's Law Calculations With Power


But I think this idea is lame and that you should just build a tube amp because they are easy and fun and sound nice. You can do it, it is very easy. Don't even buy some expensive kit, just buy the parts yourself and put it together. One single el84 or a 6v6 capacitor coupled to a single 12ax7 with both sides in cascade. You don't even need a volume knob. Less than 100 bucks in parts.

[Chuck H]

But I think this idea is lame

Well... Don't hold back!

...you should just build a tube amp because they are easy and fun and sound nice. You can do it, it is very easy. Don't even buy some expensive kit, just buy the parts yourself and put it together. One single el84 or a 6v6 capacitor coupled to a single 12ax7 with both sides in cascade. You don't even need a volume knob. Less than 100 bucks in parts.

Except that he already has a low watt amp now!!! Your proposal won't get him to 30W as intended. And if you can build even the most bare bones 30W tube amp, domestically, for under $100 your better at this than I am!

Chassis - $30
Tubes - $50
OT - $30
PT - $50
knobs, pots, jacks, switches, filters, pilot, lead wire, components, board and eyelets, misc. screws and other hardware, possible cosmetic appointments and rubber feet!!! Probably another $50 easy! And no one can buy this stuff in town anymore. It's all on line shopping. So there's going to be at least $40 in shipping charges!

We're up to $250 on a conservative guestimate. I'll bet it actually can't be done for less $300. Unless you pay your workers with a bag of rice and a fish head. And low ball everything to death until the amp needs to be re engineered to keep it from failing with such low spec and quality parts.

Just sayin'

[tonequester]

tonequester here.



Hey Austin ! Thanks for the reply to my post. You're idea on building an amp from parts is a definite for me in the time frame of no more than a year, tops. I've had some experience with repairs and mods with tubes, but never a build from scratch. Perhaps I lack confidence or am overly cautious, but at the same time, this first time, I want to minimize the chance of getting something wrong and not being to have a usable amp in the very near future. The MOD 102 kit is only $250.00, and I should end up with a usable amp relatively fast. The on-line support feature may well be needed in my first attempt. You gents here on the forum ALL seem to have much more in-depth knowlege and experience than I do. because of about three months of participation, I feel that I'm much better prepared than I was when I first posted. I have you and a dozen more like you to thank for the increase. However, I'm not as "quick" as I used to be. Often, I don't "see the light of day" until several of you explain something in detail, from several angles. Other times I get what is being explained pretty quick, only to have it completely change my directiion. I'm pretty good at cutting back other areas of my life in order to save what I need tto do a project. I just have the need not to waste what I spend on a given project .I guess I have to "hedge my bets". With good folks like you helping me out, I'll get there. I will say that I now know what it feels like to be "remedial" at something.
Thanks so much for your advice. Every reply you make to one of my posts(the other "guys" also) I now print off for further scrutiny. I started out with a folder. I think I'll end up with an encyclopedia. Have a great one Austin 1 tonequester.

[tonequester]

tonequester here.


Greetings Chuck ! Easy, peezy, lemon, squeezy ! That's just what the doctor ordered for "a tinker, a tailor, and a so-so man" like me. Between you and my friend Austin
I have everything that I need in the mentoring department. Unbridled enthusiasm, reasonable approach, knowlege and experience. I printed off this whole post for consideration. It's made me think and rethink already, and as you pointed out ; What do I want, is the biggest question I can ask. As usual your thumbnail was excellent. I believe that this is exactly what I was trying to form in that great void that IS my mind. The load resistor would be easily incorporated in the inexpensive s.s. power amp(kit). The idea of using a panel meter for adjustment of the input signal is great ! A few bucks worth of protection diodes is a must. Your diagrams are worthy of a textbook. I don't see anything more to consider, other than figuring out the values needed, and ordering the s.s. kit. As for the tube amp kit(MOD 102), It's always been a project to stand on it's own. The $250.00 seems very reasonable for a beginner build. I don't expect a" wall of sound" from it. It should be about twice as loud as the HT-1R, and it will be all tube. I don't expect it to be in need of re-engineering and failure from low spec or parts quality issues. It should serve it's purpose. That being an introduction to the building of tube amps. If I do alright on it, then it's time to "gear-up" to build my best take on an all-purpose amp
with plenty of guts, usable for most occasions. Thanks for correcting me on the Ultimate Attenuator. I couldn't remember "Attenuator" to save my soul as I typed the post. I'm glad to know of your experience with it, and the prospect of approximating it's performance. If I were swimming in cash, I wouldn't pay 500.00 for the thing, but buying the critical parts to approximate it's performance is another thing. Silencing the host amp has been my take on this experiment. I felt that the whole volume thing, as you so eloquently put it : "This would have the benefit of giving you infinite volume control from whisper quiet up to 30 W"., was best addressed by s.s. My only requirements here are : the output consideration(app. 30 W.), and clean colorless amplification
of the input. It's not hard to find a number of kits that will fit this bill. I've done plenty of s.s. projects, so a kit is just an easy and inexpensive way to an end result here. I don't believe I could build one of the s.s. amps that I've been looking at from parts, for anywhere near the kit price. I can get a kit using a well known I.C., F.E.T.s, Mosfets, or Darlington transistors for
well under $75.00, depending on the extras and the power supply needs. Probably the only truly irritating thing about them, is that none seem to come with a power supply, most don't offer one as a seperate kit, and some of the ones that are required are hard to find. Thanks for putting this whole thing in a better light for me, not to mention pretty much how to go about doing it. I just got a box from Stew-Mac(5-way sw.,volume and tone controls), this week I order the pick-ups. By the end of next week I should have finished upgrading my Kramer. That being done, it will be time to tackle this experiment, especially as I now have my Blackstar back(un-attached speaker included). In 2-3 weeks I should have my s.s. power amp kit. I'm leaning to one based on the LM1875 monolithic I.C. It's proported to be 30W. music power, and 20W. RMS, into 8 Ohms. It's considered a beginner's build, so it should go together quickly, even with the modifications that you suggested. I'll be checking into load resistors, a proper panel meter, and perhaps another cheap kit....a "drop in" equalization module. I've seen a couple of simple
bass, midrange, treble controls in module form for around $8.00 to $10.00 bucks. There might be some that are more sophisticated that I haven't taken notice of. Despite wanting no coloration from the s.s. amp, some means of compensation seems only sensible. One can always leave the settings for flat response. Good enough for me. Lemon squezzy ! I'd never guessed
that a man with the true talent befitting a died in the wool Yanker, would be so quotable as well ! I think that this kind of thing comes fairly easy for you, whatever time that you've put into thinking about my mad schemes, I appriciate it, no end. Here's wishing you all the best. Long may you reign as the "Head Yanker" of the forum ! Sincerely, tonequester.

[J M Fahey]

Just curious, what is the DC resistance of that Eminence speaker?.
Also post the resistance shown in the multimeter screen when you join red and black test probes.
Thanks.

[tonequester]

Eninence speaker D.C, resistance

tonequester here.


Hi JM. I just got your post and had a meter handy. The meter is NOT a True Rms meter, but I"m guessing that this won't be a problem. The speaker checks out at 26.8 Ohms. When probe to probe, the reading is .2 Ohms. The meter used always shows .2 Ohms when checked lkie this. I hope this is useful to you. Thanks for the reply, and interest. tonequester.

[J M Fahey]

Thanks.
Just checking that the speaker was *really* 32 ohms .
Many Manufacturers use a general purpose label and hand write with Sharpie or something data such as impedance, power, serial number or date, so it *might* have been a mistake, but you just confirmed it.
Weird.
What was that speaker originally used for?
I'm intrigued because I actually make speakers, and from experience know that 32 ohm coils mean real thin wire, *very* hard to wind, or car audio type 4 layer coils, which I dislike.

[tonequester]

tonequester here.

Good day JM. The speaker is about 30 years old. When I first started to "experiment " with electronics I was pumped up because I had taken a chance on a Fender Princeton
(circa 1960), I was actually trying to get a deal on a Vox AC30, but they were all out of my price range. The guy offered me the Princeton for like $250.00. When he tried to demo it for me, all it did was buzz. He immediately offered me $50.00 as is. I took the chance, and got lucky. There was an intermittently bad groungd to chassis which I fixed. I got the "bug". I started to
scrounge for anything electronic to salvage. A friend had an old amp that was shot, all rusted up, with insulation rotted on all the wires. I scrapped what I could from it and got that speaker.
I couldn't read any specs on it, but checked the D.C. resistance and found it to be 32 Ohms. It was of course not stock for the amp, a Peavy I think. I put it in my junk pile and forgot about it untill I stumbled upon it not long ago. Back when I salvaged it, I didn't realize that it was a little uncommon, but nonetheless figured it would come in handy some day. I was surprised to find that it is still made after all this time. It is an Eminence, model mm-55-220, and if I remember correctly, it is rated at 100 W. Now you know everything that I know about it. I don't know if you caught my post about how I had to repair a thumb size hole in the cone. I found a method of doing so on the internet, and decided to give it a try. I used alternating laminates of soft paper towels, and regular paper, with a flexible fabric glue in between laminates. I did a laminate per day uintil I had 6 layers, and then spray painted it black,carefully avoiding the logo. Darned if it doesn't play fine, and I put some serious volume through it. I had never considered a re-cone. I just figured it would cost me more than the odd-ball was worth to me.
Austin replied to the post after I had patched it. He claims that Eminence will re-cone it "cheap". I haven't checked into this, yet. I still wonder at it's value to me. The thing weighs in at over 5lbs. That's the whole Shee-bang ! Have a great day JM. tonequester.

[J M Fahey]

Googled a little and found this, explaining the 32 ohm speakers.
Replacing the Suitcase Speakers
I bet the original speaker in your amp died and the salesman must have thought "hey !! a 12" speaker is a 12" speaker" and replaced it with some old pullout he had lying around.
Just your luck that it happened to be a weird 32 ohm one.
Maybe it pays to sell it for good $$$ to the Rhodes guys and/or exchange it for a couple "normal" 8 ohm guitar Eminences.
Win-win situation.

[tonequester]

tonequester here.


Thanks JM. At least I have some idea of what probably happened. I appreciate your time in checking this out. I believe that I'll contact the Rhoads guys to see what kind of deal they might be willing to make. Even if they would only swap for one 8 Ohm, 12" it would leave me better off than I am with this odd-ball. As it is, nobody else would be interested in the speaker if just for the fact that I patched the cone. However, the article said that the voice coil is no longer made, so I must have misunderstood the info I found leading me to think the speaker is still made. Perhaps Rhoads guys will be interested. Thanks again for clearing up the "mystery". I probably have several other odd-ball items electronic that could, considering their age, be of some value to somebody. I guess that I'm just a rat-packer at heart. Have yourself a great day. tonequester.

[tonequester]

tonequester here.


Greetings, and thanks to everybody who has replied to this post. The info has been very useful, all around ! I'm trying to determine the voltage output of my HT-1R,
Blackstar. It's one Watt RMS output. If I understand this correctly, The square root of(1W. X 8 Ohms load) would give me...2.828 V. I take it that this would be an RMS voltage. I intend to use a W. x 30 Ohm load resistor to "feed" a s.s. power amp. A potentiometer will be placed after the power resistor for adjustment of signal level, with a panel meter to be able to actually see what's going on,relating signal strength to perceived.In selecting a pot would it be best to use peak voltage instead of RMS ? Chuck H wasgood enough to come up with this circuit for me and has first hjand experience with the Ultimatate Attenuator. This circuit is a sort of no frills version of the expensive attenuator. The s.s. amps input sensitivity is 100mv. @
4.7 Khz. just for the record. The s.s. amp is in kit form, and inexpensive. The kit does not give any specs related to max. input signal. It's input impedance is 150kOhms.
Any tips or opinions are welcome. Thanks for all of the help already given here.