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**Enzo** · 08-09-2012, 09:38 PM

An attenuator intended for between amp and speaker is by its nature a low impedance device - your measures 13 ohms resistance. You can't expect your signal generator to drive that, any more than it could drive a speaker directly. The generator can;t drive a 13 ohm load, so it loads it down to almost nothing. Yes that is attenuation, but not from the action of your circuit, but merely from the "weight" of your circuit on the generator. That is like asking your automobile to tow a railroad train.

**tonequester** · 08-10-2012, 03:13 AM

tonequester here.

Greetings Enzo, and thanks for the reply. However, there are some problems. First, I just got done hooking up my my "signal generator" to a small(2" x 3"), 8 Ohm speaker
and had no trouble driving it. The volume was of course no where ear shattering, but had the tone been a song, I could have easily understood the lyrics across the room. There are other issues, and it's my fault for not being more specific about what I'm doing. I said in my post that I had "jury rigged" a signal generator, and I meant "JURY RIGGED". I used a cassette deck to record an organ tone as close to 1500hz as was possible, I ran a short length of wire to the negative(6V.D.C.) battery terminal with an alligator clip on the other end. I cut off the same length(10") of stereo ear phone cable(with the stereo plug attached. This wires conductors were about half of the "guage" of the wire used for the negative connection. I soldered the dual conductors together so that the stereo plug became a mono plug. I plugged this into the cassette decks headphone jack. The voltage across the two conductors was miniscule(with a small D.C. component) with the unit turned on "pause". No tape was rolling. When the tape "rolled", there was enough noise to cause a small rise in voltage(A.C.). When the recorded tone came on, the voltage increased to 1.71V.A.C. I did average this from fluctuations of no more than 80 to 90 millivolts. So, I don't know why, but my "signal generator" does drive a speaker. I just now had a thought, so I plugged my headphones into the "generator". The volume was not ear-splitting, but I don't listen to music, or my guitar through them at any louder volume. That's how it stands on the "signal geneator". Now about the "loading" or "attenuation". I should have been more specific about the "circuit" concerning the resistance measurements. Also I made a mistake when typing up the post, using the wrong figure for total resistance. I've double checked my figures and math now and this is how the "circuits' resistance breaks down. The wiring I used came to a total of 1.2 Ohms. The rest of the "circuit" came to a total of 7.5 Ohms. Still a load I guess. Instead of 7.5 Ohms resistance, how about I call it 8 Ohms impedance instead. i believe now, that I should.
Does this make a big difference( and I truly don't know myself). I'm still wondering why a reduction in signal voltage by 98.83%, as directly fed into the 15W. s.s. amp didn't all but shut the thing down. I am just guessing here as I don't have any means to check sound levels before and after "loading" or "attenuating", but I would have guessed the volume was attenuated by about 25%. I apologize for the mistake I made concerning total resistance, which I did check. I also apologize for relying on that resistance measurement, without mentioning that instead of a total of 8.7 Ohms resistance, it should be stated as 1.2 Ohms resistance and 8 Ohms impedance. Before you have a fit over what impedance was "presented" to the amp, it
was 8 Ohms(the amps own speaker). I know that this all may seem pretty weird, but I believe that I've approached attenuation in a novel fashion. I'd like to tackle one thing at a time,
so I won't get too detailed about the "circuit". I will say this. I have been able to attenuate the signal voltage by over 98%. In doing so the frequency remained exactly the same. These aren't
bad starting points, but they ARE just that. I also don't want to look the COMPLETE fool by putting some hair-brained circuit in it's entirety on this forum, only to be given a bunch of crap for it, or made the forum "court jester". I hope my earlier post(now corrected) can now be addressed. I do know that I can't get where I want to go with simple resistance, I just mis-read my chicken scratching. It won't happen again. Thanks for your trouble in replying to info, that was in error. tonequester.

"

**Enzo** · 08-10-2012, 04:07 AM

Why don't you draw up a schematic of your circuit, and a drawing of how you intend it to be connected to the rest of the world, and post that. If you lack a scanner or drawing software, perhaps draw it large on paper and photgraph it, upload the photo. DOn't worry about looking foolish, ther are many schematics people submit with glaring errors, just as there are some wonderful ones. It isn;t like you will have to look us in the eye at breakfast tomorrow or at work or something. It matters how you intend to use it. The circuit to attenuate the output of the amp on its way to the speaker is not the same as a circuit to attenuate a hot signal before it goes to the amp input.

You seem focused on frequency. A bunch of resistors attenuating a signal won;t change its frequency. Perhaps you are thinking of the frequency RESPONSE of the system changing? That is not the same thing as changing frequency. Turning your tone controls over to extremes on an amp will change the frequency response of an amp, but a note remains the same note regardless. Freq response means the relative amplification of the various frequencies, so one amap may emphasize the low notes while another might emphasize the high ones, but neither changed the notes themselves. AM I anywhere near your thinking? Or am I missing the point?

**Chuck H** · 08-10-2012, 05:46 AM

I know your just as interested in the theory of operation as you are in the use of the projects. Maybe we can get further into it when more information is garnered. In the mean time, if it's an attenuator between an amp output and a speaker your interested in, Here is a simple resistive model I designed. It has some advantages over other inexpensive attenuators. Like being infinitely variable and ofering a more constant load. This diagram is for an 8 ohm load up to twenty watts (for a guy here that wanted to use it with a 5E3). Circuit values and rating could be changed to idealize it for different purposes or wattages. It could be used as is with a four ohm load. You can safely use it with a sixteen ohm load but I think it may detriment tone.

Attached Files

**tonequester** · 08-10-2012, 06:22 AM

tonequester here.

Enzo. You are not missing the point. I'm not very good at MAKING a point.. You are right in that I don't have access to a scanner, not do I even know how to upload a photograph. I've had maybe 5 months experience with using my first computer. All I know is what I've been able to figure out by myself. Even the "Dummies" books weren't basic enough for me. However, I will draw something up, and try to Google up how to do the upload thing. I may be having a go at attenuation like nobody has been foolish enough to try before.
My basic idea is this : The last thing that "colors" your tone is the speaker, of course(not counting things like bouncing the sound off of the ceiling). At this point, just before the speaker
the "hot" signal will include the fundamental(s) and harmonics that we want to hear(hopefully). Why can,t attenuation work at this juncture ? As for being "hung up" on frequency, I'm not.
However, the biggest complaint about attenuators, is that they alter the sound. The alteration in sound concerns problems with the overall frequencies one wishes to faithfully reproduce.
Attenuators are victims of opinion to some degree. Inevitably, some think that Brand X sounds great, while others have complaints. I expect this. However, I also believe that the few that I've checked out myself are not exactly "linear" in their operation/results. I have" heard" that resistance does not affect frequency. I have also "heard" that resistance increases when frequency increases. I know what capacitors and inductors can do to tone. I understand the LCR circuit and it's tuning. I've also "heard" enough to know that "active" circuitry can boost
frequency(probably cut as well),where the RCL circuits are about "rolling off' frequencies. So, I'm not hung up on frequency here per se, but it seems to me that the ideal attenuator would be one that attenuated signal strength down where the amp could only produce what everybody keeps calling "bedroom' level(another opinion) volume, which is itself not so easy to determine. Then it must faithfully reproduce the fundamentals plus second, and third order harmonics of a 24 fret guitar. It's my understanding that low E is 83hz and that the high E string at the 24th fret is 1175hz. So, just to be safe the attenuator should be as close to linear between 50hz and 4000hz. I only used a test frequency to see if I got blown out of the water on my
first try. It was the less than expected attenuation of volume with a greatly smaller "hot" signal that took me by surprise. An idiot ought not be surprised at anything, but I keep forgetting that I'm an idiot. I had an Ohmite wirewound rheostat, brand new, checked out for accuracy at 25 Ohms. I tried this alone(adjustable power resistor). I got less attenuation with it than I did
with my "concoction'. Now if a single value power resistor is so good(as some say) as an attenuator, the proper value rheostat would be even better. Mine evidently was not a high enough value to do the job. However, if the power resistors(adjustable or not) are really that good, why are a dozen other attenuators of varying design complexity(active and passive) being sold
at places like Musicians Friend in the price range from $49.95(simple L-Pad), to the Ultimate Attenuator at $699.00 ? I do not see my "concoction" coloring the sound, but putting it at as close to the end of the signal chain assures that any coloration it might produce(frequencies gained or lost) would not be amplified. Attenuating the signal before the amps input is turning your guitar down. I wish to operate the amp at full "volume" with out ending up as deaf as Pete townsend. I have very good headphones, but they don't sound nearly as good as the speaker i have installed in my amp. This could be the phones,. the speaker, or it could be EMULATED OUTPUT/headphone "circuit" in the amp. I don't want to attenuate this. Maybe what I'm trying to do is impossible. I'll find out in do time as I continue to tinker and tweek it. If for some reason you know it to be impossible to attenuate the "hot" signal on a tube amp(pre-speaker),
I'd appreciate it greatly if you can find time for one more reply.If it is impossible, I would also like to know why. Sorry to take up so much of your time. I hope it isn't a total waste.
I want you to know that I truly appreciate, and feel honored, everytime you reply to one of my post. I never take what you reply with in a bad way. you are among a few on this forum that
I consider instructors. Some others are ALMOST in as much need of instruction as I am. Everybody is great in any case. Don't feel like you have to get right back to me. I'll be here a tinkering whenever you get the time. I will remember to attempt to learn how to upload drawings here, as I have wished i could do this several times already. Those thumbnail pictures and schematics are way cool ! have a great day Enzo ! tonequester.

**Chuck H** · 08-10-2012, 06:57 AM

Just FYI... If you want to use headphones and have it sound like your amp, truely sound like your amp, that indeed may not be possible. But, you can build an active load attenuator that will simulate a guitar speaker. Just not your exact speaker. Since speakers have a complex impedance you would need to simulate this in a dummy load if you want to capture the amps responses to variable damping, voltage peaks @ frequency, etc. But this sort of attenuator can get expensive because of the very large inductors needed. My own personal version of the attenuator outlined above uses an active load instead of a resistive load. The returns are small. At moderate levels of attenuation the resistive vs reactive loads are indiscernible to the human ear. Partly because the actual speaker still has some influence on the complex impedance. At very high attenuation levels the reactive load is better. But still not by a huge amount. IMO not by enough to warrant the extra expense. BUT, if headohones is the goal, and you want it to sound like a guitar speaker, a reactive load may be your only option. It's important to realize here that it's not the frequency balance were dealing with. But rather the way the amplifier behaves when playing into a load of a fixed impedance vs a complex impedance. You could build the attenuator above. At full attenuation you can remove the speaker load and plug in a pair of headphones. Though you wouldn't have volume control for the headphones!!! That could be rigged up on a switch though, with another pot that only operates in "headphone" mode. If the tone is too dissimilar for you, you could then take it to the next level and build a reactive load. But don't you have enough projects going yet???

**tonequester** · 08-10-2012, 07:02 AM

tonequester here.

Greetings Chuck. Thanks for the reply, and the circuit. It looks very interesting. I'll give it a much more thorough "pondering" in the morning and get back to you, most likely with some questions. I actually have a 25 Ohm rheostat. I bought a couple of power resistors at the "Shack" yesterday, but when I got home I had mis-read the values. Do you need any 100 Ohm, 10Watters ? ! I don't know which is failing faster, my eyes, or my frigging brain. I believe I'll probably build your circuit(with your permission) and give it a try. My idea is bizarre in the extreme. I even did a patent search out of curiosity, and among those granted for attenuators, my "idea" was NOT mentioned ! Surprise, surprise ! However, Edison mentioned
"one percent inspiration and 99% perspiration". I haven't broke a sweat yet. The best thing is that I'm tinkering with salvage that didn't cost me a dime......so far. Thanks again for the
interest in what will probably pan out to be yet another insane idea. Glad I have you and Enzo to keep me grounded. Have a great day. I'll "catch' you again soon. tonequester.

**Enzo** · 08-10-2012, 07:02 AM

Well here, let me confuse you further. It is one thing to reduce the sound level without changing the overall freq response, but your ears are not linear either. Go google up "fletcher-munson curves" to see how your ear responds. That is why stereo receivers have a "loudness" button. The less loud a sound is, the more limited is your ears' response to it.

And remember that in a guitar amp, the single largest variable in tone is the speaker. And once more, speakers are not linear either. They are mechanical systems, and can respond differently when run at polite levels versus when they are run LOUD.

Please be sure you understand the use of the term frequency here. A-sharp is a note, it has a frequency, same with B-natural. And all the others. The frequency is the note, or vice versa. All your EQ and tone controls and speaker effects change the frequency RESPONSE, meaning that in one system, given a dead even input, maybe the A-sharp comes out a bit louder than the B-natural, while in another system the B-natural comes out a shade louder than the A-sharp. However, in none of them is the B-natural turned into an A-sharp. If your guitar is in tune, and you change amp and speakers, the guitar will still be in tune, even if the tone is different. Frequency is the notes, frequency response is the relative loudness of each note compared to the others. Your tone controls or your attenuators or anything else that changes the sound will not change the frequency of the sound, it will change the frequency response of the sound. SO an active circuit can boost a frequency relative to another, not boost frequency. You turn up the treble control you get more treble, not different notes of treble.

[QUOTEI had an Ohmite wirewound rheostat, brand new, checked out for accuracy at 25 Ohms. I tried this alone(adjustable power resistor). ][/QUOTE]

HOW did you try it? If you put it in parallel with a speaker, it won;t have a lot of effect, put it in series with a speaker it will have a larger effect.

Resistors are fine attenuators - electrically. WHy do they sell fancier things than resistors? Because they can. Every one of them touts itself as the best in some way. But really, the amplifier and speaker work together, they react to one another. An amplifier reacts differently to a speaker than it does a resistor. Those fancier attenuators have L and C elements addded in to make the amp react more like it does to a speaker, because a speaker is not a pure resistance.

**tonequester** · 08-10-2012, 06:00 PM

repluint to a reply, attenuation

tonequester here.

Hey Enzo. Thanks once again for the reply and subsequent info. In all honesty, you did not confuse me at all with your reply. I have looked at the Fletcher-Munson curves. It's not too hard for me to understand what they mean and how they apply. I get the loudness controls being a compensation circuit to address the percieved volume "problem". I'm pretty well up to speed on tuning, having done so almost daily for 32 years. i started out taking classical lessons and learned a lot at that time. My teacher insisted on using a 440hz tuning fork. I now use a good quality digital that has guitar, bass, and chromatic functions. I understand fundamentals and the orders of harmonics from this time as well. I've always been a Hi-Fi "nut",even before I began guitar lessons. I actually designed and helped to build a couple of high 5-way
speakers for my brother in law(a woodworker who built the cabs out of amaranth, or purpleheart, with plexi-glass fronts). I learned about loudspeakers, proper phase, crossovers, etc., back then and continue to study these things. No speaker is linear, as you said, and some are much more colse to being so than others. As far as the rheostat(25 Ohms) is concerned, i realized that a parallel connection would not "get it". I hooked it up in series. While it had definite control over attenuation, it was not enough of a load at maximum to get the desired effect. If I had to guess, perhaps 100-150 would be a better match under the conditions my "experiment" was caried out under. I also realize that "hype" is a major factor in the music electronics business. often there is more hype than facts to be had. Also the differences in human perception of sound come into play. I have heard those who say a load resistor of X value works great on it's own. Others say it sounds like S___. It's the same for RCL circuits, active circuits, and combinations of the two. In considering price, there are often added bells and whistles that certainly increase the cost, and may or may not be necessary.
I realize that there are those who will spend $1000.00 on the latest "hot" deal, without one shred of detailed info or fact involved. "Guys on the forum said it was the s___."
I even wonder how many dollars worth of equipment this forum has been rwsponsible for selling. In all honesty, I believe that my little idea concerning attenuation has a 99.9% chance of being so-much junk. Like I've said before, I don't lack for time or curiosity. These things are always a chance to kearn something new, and I've always been
much more into the experimental side of things technical, than into theory(probably to my eternal downfall). I'm going to keep playing with the "thing" because these things
keep my mind active and prevent depression. Chuck H, I believe, was the person who asked me if I didn't have enough projects going. For someone like me, I can't have enough. Not putting in 40+ hours a week at a job, leaves a great hole in ones life. If I were rich.....I'd travel. I don't travel. I do what I can do, and enjoy it.
I really appreciate your replies and all of the information you have given me. I feel with your comments on any given concern, all "angles" are better covered, and I know that you know of what you speak. I, for my part....listen. I,m sure that you are not only a great tech, but that you would make a great instructor for techs. I believe thats nthe best comment I can make about you as i "know" you. tonequester. P.S. Sorry for the length, bipolars never know when to shut up.

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