Resonance cap in NFB?

[defaced]

In other words, a schematic would really help

[daz]

I don't have one. But all you have to do is look at a marshall 2204 and envision a .0033 cap, a 22k R, and then a 50k pot all in series in place of the 100k R in the schematic.

[defaced]

You're running Windows right? It's got Paint on it. Take the schem Chuck uploaded, modify it to be what you have, and repost it. It doesn't have to be pretty, it has to be what you're trying to do.

Edit: you could make a schem in PowerPoint or download a copy of Google SketchUp

[daz]

[Chuck H]

Hows this? The only difference I made (to both) was to change the old type presence circuit for the one that keeps DC off the pot. And instead of indicating a 0V rail I marked it as ground.

[daz]

What does that do differently? I mean, what would the sonic results be opposed to they way i have it now?

[Chuck H]

OK. I don't want a big wrong or right thing going on here. But if you actually have your amp wired like the modified schematic you posted you should review it.

If your asking what the differences are between the different presence circuits that I posted then I can tell you.

The stock 2204 uses a 4.7k resistor as a voltage divider for the feedback loop. This is paralleled by the .1 "presence" cap in series with a 22k pot. This circuit keeps DC voltage off of the pot so it doesn't sound scratchy while your adjusting it.

In the older style Marshall presence control (in my first schematics) the 5k pot takes the place of the 4.7k resistor as the voltage divider for the feedback loop. The extra 300 ohms of the pot makes little difference in this circuit. The .1 "presence" cap is mounted on the pot in such a way that the pot can act as both the presence adjustment and the voltage divider for the feedback loop. This is a simpler circuit. But it allows DC on the pot. So the adjustment is scratchy sounding.

The only real sonic difference (other than the pot being scratchy or not) I can imagine would be that with the stock 2204 circuit the presence is always on just a little. The .1 cap can not be completely removed from the feedback loop. With the other circuit you turn the presence knob to 0 and the .1 cap is out of the loop.

HTH

Chuck

[daz]

So what you're saying is i have it wired the *right* way as it is? I mean, i DO have the 4.7k R that you say keeps the pot from sounding scratchy. and as far as having a bit of presence even when all the way down, thats fine with me because i usually don't turn it all the way down, and when i do it's as "off" as i'd ever want it. Anything more than that i just pull the switch and defect the NFB altogether anyways. Thats also a great tone. So as i've been saying, it's already about as perfect as i could ask for. As it is i get more sounds out of it then i've ever gotten from any amp including multi channel amps.

So today i'm finishing off the faceplate which is turning out real nice with just a kinko's copy of a layout i did in a graphic app and mounted it under clear plexiglass. Gonna redo the color and font tho because it's not quite what i had in mind. Then a couple cab fixes that also didn't come out exactly as planned and this baby is locked up and done.....FINALLY !

[Chuck H]

I agree. I never have a presence control on 0 anyhow. Especially on Marshall type amps. It's just part of the sound. I've never tried the 2204 type presence circuit for myself. The scratchy pot doesn't bother me. But if I were going to sell an amp I might use it just because rotating the adjusment wouldn't raise any eyebrows.

As for how your amp is wired, the way you modified the schem shows a 4.7k resistor in a place it should never be. Probably just a typo kind of thing since you would surely know it if you actually wired it that way. So no big.

I'm glad your liking the amp. I didn't know you had the loop on a bypass switch. Pulling that switch is all the comparison you need to know if you like the amount of feedback your using. So, FWIW, I never said your circuit was wrong. I said it was unusual. That doesn't mean bad. I never infer. I'm a straight shooter.

When Dr.Z came out with an ultralinear amp it raised alot of hackles. It too was unusual. So I suppose that puts you in good company.

Oh, and I'm sorry for the "bad loser at Monopoly" comment. It was called for But I shouldn't have done it anyway.

We're all here to learn what we need and help where we can.

Chuck

[Steve Conner]

Will you guys please quit arguing over subjective tone? We live in a universe where people pay good money for Peavey 5150s and Vox Deacys. Like I've said 100 times but nobody probably listened, the holy grail of tone doesn't exist. There is no ultimate tone, just your favourite tone.

To make a real, objective, testable point, the 4.7k resistor in Daz's schematic doesn't do anything because both ends are connected to ground.

[Enzo]

Either that or it is in series with the speaker.

[daz]

This is what i get for trying to appease defaced who seemed determined to get me to post a schematic. The placement of the 4.7k is indeed a typo because if a schematic is drawn way different than what i'm used to i have to stare at it a while to see it correctly. So i'll just say it again....look at a 2204 and in place of the 100k resistor coming off the OT put a .0033uf, 22kR, and 50k pot in that order. Thats exactly how mine is wired and it works flawlessly. No scratchy pot or anything like that. I'm not trying to keep this thread going, i'm just answering what i've been asked.

[rathmann]

daz - i think part of the issue is that folks here are very generous with sharing their knowledge and really like to assist in getting others to expand their own understanding as well. sure, someone could just give you the simple straight answer to a question, but then you'll just keep returning and ask the same questions over and over (I'm not implying you've done that. It's just what tends to happen when folks don't understand some of the underlying concepts of tubes and amps.) Your original question was answered very early on. *No, the order with which a cap and resistor are connected when in series does not make a difference.* The thread should have ended there.

But I think Chuck H was trying to be helpful by pointing out that the circuit was unusual. He never said it was "wrong" or "bad" nor did he make any comments about the amp's actual tone. (How could he, having never heard the amp?) An unusual circuit could be either 1) an innovative new approach 2) an uncommon but tested design 3) a misrepresentation or misunderstood analysis of what the actual circuit is 4) something hacked together by a drunken one-arm pirate and his clever parrot assistant. Point being - you've made it very clear in your posts that you DON'T have a lot of theoretical or technical knowledge about this stuff, and so I believe Chuck H wanted to make sure what your were describing was actually the circuit, and if so point out that, being somewhat unorthodox, your mileage may potentially vary from the norm.

Further - text-based communication is fraught with holes, uncertainties, ambiguities, multiple meanings, and misinterpretations compounded by the fact that it can be loaded with implications, assumptions, and be emotionally charged - not very good on a technical forum discussing the very specific, unambiguous subject matter of electrical circuits. The best language we could possibly use for this is the schematic.

"look at a 2204 and in place of the 100k resistor coming off the OT put a .0033uf, 22kR, and 50k pot in that order." First off, you've assumed people know what a 2204 is and that they have a schematic (and it's possible you or a person your working with has an incorrect copy). It's good to help people to help you. Post the schem or a link. Write one up yourself. Taking the time to understand your circuit well enough to draw it out will go a long way to helping you gain a more fundamental understanding. Sure, someone else could look it up, but why should they? You're not paying anyone for their time, so you'll get more in return the more you put into the question.

Arguing about subjective experiences does not really endear one to those who can best be of assistance. It is in your best interest to be understood, not "right". Interesting take on the boy who cried wolf fable, btw.

[Chuck H]

Will you guys please quit arguing over subjective tone?

I'm glad your enjoying the thread Steve

Who's arguing? I only became argumentitive in one post. And that was personal. A moment of weakness. And I appologized...Kind of. Other than that I absolutely and unequivocably NEVER said to Daz 'your amp sounds bad', 'must sound bad', is constructed wrong' or anything of the sort. I pointed out that it was unusual. Unusual does not mean bad or wierd. It means not usual. Sheesh.

I knew he had some trouble with the tone of a previous build and JUST IN CASE this MAY have been part of the problem, I simply tried to make him aware of it. It was always his option to try it and see or simply disregard it. I never intended to upset him so much. But I have been known to be clumbsy in conversation.

the 4.7k resistor in Daz's schematic doesn't do anything because both ends are connected to ground.

No, it's in series with the speaker/s. But you'll notice that I stepped as gently as possible over the error.

Chuck