Ultrapath

[dcoyle]

By the way, if your switch is just hanging out while you try the circuit, make sure you put a little tape over the contact lugs, they have full B+ on them.

Dan

[tedmich]

please post clips of ULTRAPATH cap in and out and don't (initially) tell us which is which!!


(science!)

PS he'd use it:

[J M Fahey]

Oh, I DO know.
You would be stunned by the thousands of wild experiments I have made, a few of which I posted here.

Many by accident, others on purpose, even knowing beforehand they would not work or work bad, not "to try accepted knowledge to see whether it's true or not" BUT to listen what such a mistake sounds like.
Then I remember that sound and retrieve it when it appears again to help with/speed up troubleshooting.

Tons of times I have listened to what an amp sounds like, opened it and went straight to the bad part , even suggested possible faults here to posters who describe what they hear, who later answer: "yes, it was that, but how did you know???? "

And many times did (still do) decouple to +V , because it was closer while going to the proper ground was inconvenient.

But I consider it a kludge which sometimes helps, not a "sound improvement" by any means.

[Mike Sulzer]

I could answer what the difference is, by quoting the Olsen article, but really I can't say he's attributing the reason for change correctly. I can say there is a difference and it is less distorted.

I didn't find noise to be a problem, at all.

For the trouble of a temporary spst switch and a 30ufd cap hanging outside the chassis I was able to try it, and find out for myself. It was noticeable enough to me to think it might be of interest to others. If you have a Champ type amp check it out, otherwise one is just speculating. The Olsen article also shows how to implement it on cathode biased push pull, but I haven't tried it.

Mike S. and JMF, I have tremendous respect for you, based on your posts, but I would say that those who dismiss an idea ahead of time, based on one objection, don't really get a chance to see if there was something else going on that was interesting. If you think you are saving your self or others time by not checking out something, fine, but you don't really know, do you?

I could give a rip if any one thinks well or poorly of ultrapath, I am just reporting what I heard.

Cheers.

Dan

The Olsen article is about removing electrolytic capacitors from the signal path. This could be done in a straight forward way by replacing the cathode bypass and the final power supply capacitor with non-electrolytic capacitors. The ultra path circuit supposedly accomplishes this in a simple elegant way. Actually, in merely connecting the bypass capacitor to the B+ it puts an electrolytic capacitor in series (in the path back to signal ground) that was not there to start with. And, yes, this capacitor has the residual power supply ripple across it. (Olsen thinks it does what he wants because he does not understand how circuits work, at all, not even a little bit.)

I do not know about you, but when I see an idea that looks like nonsense, and looks even more like nonsense when you examine it more closely, I do not try it. There are too many good ideas to try.

[dcoyle]

J M Fahey,

I have no doubt of your vast experience or prowess, as I said, I know that from your posts. I am unclear what you are asserting, though.

I never said it was a "sound improvement", nor that it was better. In my first post I say I hear it as less distortion with no valuation. What confuses me is whether you are saying you can imagine from your engineering knowledge what it must sound like without trying it, which seems incurious, or are you saying you have tried it and decided that it is dominated by noise or only "sometimes" helps? I did not assert it ever helps, or that it should be used, only that it was there.

If you think it sometimes helps, why is it a kludge?

Dan

[tedmich]

J M Fahey,

I have no doubt of your vast experience or prowess, as I said, I know that from your posts. I am unclear what you are asserting, though.

I never said it was a "sound improvement", nor that it was better. In my first post I say I hear it as less distortion with no valuation. What confuses me is whether you are saying you can imagine from your engineering knowledge what it must sound like without trying it, which seems incurious, or are you saying you have tried it and decided that it is dominated by noise or only "sometimes" helps? I did not assert it ever helps, or that it should be used, only that it was there.

If you think it sometimes helps, why is it a kludge?

Dan

no clips yet?

[dcoyle]

Mike Sulzer

You don't have to try it, I can see why you wouldn't, but I would comment that there is a history, particularly in electronics, of inventors or popularists of ideas not understanding why they worked, from Faraday to Deforest to Hafler and UL.

I could care less about any of the tout's statements as to elegance, efficacy or cause, as I said. I simply mention it as audible and characterized it as less distorted. If you try it and don't hear it that way, great, I'd like to learn from you, again. If by "looks even more like nonsense" you mean there is no effect, I haven't found that to be the case. Audible and slightly less distorted.

Dan

[dcoyle]

Mike, you say you're conservative in what you explore, but i gotta ask, is this wildly less plausible than a single turn pickup?

Dan

[dcoyle]

"no clips yet?"

I don't have that ability.

Dan

[Mike Sulzer]

Mike, you say you're conservative in what you explore, but i gotta ask, is this wildly less plausible than a single turn pickup?

Dan

Yes, wildly less plausible. There is nothing implausible about a single turn pickup; it just has very low impedance, which I think is inconvenient, but you can use a transformer.

[nickb]

The problem I have with this is power supply noise. The (expensive) capacitor to the cathode couples this noise straight to into the tube, giving it the full gain of the stage. The magnitude effect depends on the (grid) source impedance. The solution is to improve the power supply which adds further expense. Of course once you have improved the caps in the power supply you don't get the same incremental benefit of the expensive oil /film one. What's the point in getting 1dB less in distortion if the price is 2dB of noise? On balance it seems that the conventional approach is the right one.

[Mike Sulzer]

The problem I have with this is power supply noise. The (expensive) capacitor to the cathode couples this noise straight to into the tube, giving it the full gain of the stage. The magnitude effect depends on the (grid) source impedance. The solution is to improve the power supply which adds further expense. Of course once you have improved the caps in the power supply you don't get the same incremental benefit of the expensive oil /film one. What's the point in getting 1dB less in distortion if the price is 2dB of noise? On balance it seems that the conventional approach is the right one.

1. Exactly. And if that is not audible, then either the listening test is no good, or the power supply is essentially perfect.

2. Exactly again.

But the real flaw is in the initial idea of the circuit, which claims (Olsen article) to be completing the circuit, the loop around the tube and transformer using only high quality components. But the signal ground has been left out of this, meaning that the cathode resistor has been bypassed with the series combination of the oil filled capacitor and the power supply electrolytic, exactly what they say is to be avoided.

It seems to me that the electrolytic in the power supply have such a low impedance that they are not a problem. But it you insist they are, ultra path does not get them out of the cathode bypass path.

But the best laugh of all is the claim in the originally referenced article that you adjust the cathode resistor for minimum distortion, thus demonstrating that the idea works. Obviously even without the ultra path capacitor, for some given level of input signal, you can adjust the cathode resistor for minimum distortion. In any case, I would not trust these people to make either a listening test or a measurement.

Edit: why am I confident that the power supply electrolytic is good enough? First consider the cathode resistor; it has a value of about 1K, If it is bypassed with a value that gives a reasonable low frequency pole, then we need to consider the value of any series resistance in this electrolytic, possibly with a nonlinear component. Suppose this component is significant.

Now consider the plate resistor (or equivalent transformer primary impedance). It might be 100K, and the value of the power supply capacitor could be larger than that of the cathode bypass capacitor. Thus the relative size of the nonlinear series capacitor is less, possibly 100 times less in a high quality supply. So I think here is no need to worry about the supply electrolytic, and if there is concern it should be with the cathode bypass capacitor.

[dcoyle]

Again, I have not suggested that the explanation offered in any paper is correct, nor any "approach is the right one", nor that it is an improvement for guitar amps. I cited the papers to give credit for the idea and to give a link of how to hook it up. What I did say was that I had tried it and there was a difference, which sounds slightly less distorted, and had anyone else tried it?

I've learned no one has tried it, except maybe JM Fahey, and several folks are not going to try it.

The solen film cap (30 ufd /400v ) I used is $11.35, the atom sprauge that was there (100 ufd / 100v ) is $3.95, so it's only $7.40 more, not really "expensive" for most of us.

No other cap was changed.

For anybody that is curious about this effect and wants to see if the noise goes up or if the effect doesn't exist, as I believe Mike S. is saying below, try this. On a single ended, cathode bypassed (champ) type amp: 1. disconnect the lead of the positive terminal of the anode bp cap and connect it to one output of a spdt switch, 2. run a wire from the central pole of the switch to the cathode, where you just disconnected the electrolytic cap, and 3. run a wire from the other output of the switch to the 25 or 30ufd film cap, and connect the other end of the cap to the place where the B+ connects to the output transformer. Tape anything you might touch during switching.

What I hear is slightly less distortion in one position and no change in noise.

Dan

[Mike Sulzer]

"if the effect doesn't exist, as I believe Mike S..."

What I wrote was that I believe that changing the cathode bypass capacitor is a bigger effect than making a change in the power supply caps. If that is true, then you might be hearing the better cathode bypass capacitor, even though you are connecting it to the power supply. If so, a lower voltage less costly capacitor from the cathode to ground might do as well or better, but I really do not know what you are hearing, and I think it is strange that you cannot hear any increase in hum.

[uneumann]

For anybody that is curious about this effect and wants to see if the noise goes up or if the effect doesn't exist, as I believe Mike S. is saying below, try this. On a single ended, cathode bypassed (champ) type amp: 1. disconnect the lead of the positive terminal of the anode bp cap and connect it to one output of a spdt switch, 2. run a wire from the central pole of the switch to the cathode, where you just disconnected the electrolytic cap, and 3. run a wire from the other output of the switch to the 25 or 30ufd film cap, and connect the other end of the cap to the place where the B+ connects to the output transformer. Tape anything you might touch during switching.

What I hear is slightly less distortion in one position and no change in noise.

Dan

At the risk of yet another line of inquiry... how about a measurement? Can you put a scope on the B+ point where you tie the film cap? I'd say AC couple it at about 1V/div (or thereabout). When you're playing do you see any signal there? If there is anything in the range of a volt or more, then it will have an impact on the cathode voltage and likely on the amp tone. If there is no signal there, I'm at a loss for what could cause any difference.

My 2 cents of theory: A class A stage should show little or no signal at that B+ point - until you hit stage overdrive. It's possible that at that point, if the clipping is asymmetric, you'll see a change in current draw from the PS. Once that happens B+ may rise or fall - which may impact the cathode bias (and distortion) depending on the time constants involved.