Manzamp!

[John_P_WI]

The small cap is most likely a poly with a much lower esr, quicker and faster than the elytic. Nothing special, it works.

[matt h]

(deleted)

[groovtubin]

The use of the small bypass cap in parallel with the large bypass cap on a cathode isn't new, or novel. Similar to how they're used in hifi circles putting a small value film cap in parallel with the electrolytics in the power supply. Different responses/different frequencies, de-harshing the 'lytic, better clarity.

I don't accept those type of explanations its like saying 'it just happens' I need to see the math. If something happens in a circuit, it happens because of some pre-determined set of rules. I don't pretend I know them all, but here's what I do know.

They are not at different frequencies. You look at the network in it's entirety, R1//(C1+C2), not independently R1//C1 and R1//C2.
The paralleling of two capacitors increases the total dielectric area and consequently the amount of capacitance and in the network that is seen as one equivalent capacitance.

C1=Q1/V and C2=Q2/V where Q is the charge. Q=Q1+Q2. The voltage across each capacitor is the same, therefore C = C1+C2

The cutoff frequency point of the network is 1/(2*Pi*R1*(C1+C2)) where C1 and C2 are in Farads and R is in ohms. There isn't two different cutoff points.

The only difference is the charge time for each capacitor in this case is vastly different.

The audio effects of which I'm struggling to visualize. I do know that I would discount it as insignificant in any circuit design calculations....but that doesn't mean I'm right to do so.

Mike Soldano ran a .05 cross 2nd stage cathode in clean side of a Yamaha T-100...killer clean sound, n i look at it like this, it sounded like the value! Very fendery wet mids...wonder where he got it from Alan? Most likely HIFI world..?

respectfully, jim@Omegaamps

['67_Plexi]

The small cap is most likely a poly with a much lower esr, quicker and faster than the elytic. Nothing special, it works.

That one. When I said frequency/response I wasn't talking about the audio signal dumping through it but I certainly didn't make that clear, tried to get there with bringing up power supplies, but fell flat. I think of it more akin to a refresh-rate of a monitor (which, herp derp, expressed in, y'know, frequency and response time)

What I do know, is that if you can avoid electrolytics as bypass caps, the sonic effect is noticeable-- the single most notable change of any cap swap I've ever encountered. I figured popping in the little film alongside the 'lytic was just an attempt to get some of that.

Agreed they do. At high frequencies electrolytics look like an inductor and resistor in series to the circuit. The capacitance of the electrolytic is frequency dependent and decreases with increasing frequency.
The effect in a signal chain position is very noticeable. They are noisy too. One of the best mods you can do to any Boss pedal is replace all the 1uF electrolytics in the signal chain with film caps.
I just couldn't imagine the effect being noticeable in a cathode bypass position with a film capacitor that small. I asked Cliff Chase, the owner of Fractal audio and one of the best engineers I know. He re-iterated the above, but also agreed with me that 0.01uF seems way too low 'for HF take over duties' and thought it was probably there for stability reasons rather than sonic. You would need a much lower value film cap for high frequency duties where the electrolyitic stops acting like a cap. I'll look at some electrolytic specs and figure the exact value. I think we have somewhat of an answer, even if the value seems a bit off. I'm also going to try a listening test too in a bypass position. I've been using tant caps in bypass positions for years and only recently started using electrolytics and to be honest didn't hear any noticeable difference, but its difficult to compare between two different amplifiers, it really needs to be done in the same amp at the same time.

Thanks guys. Interesting thoughts.

['67_Plexi]

After a couple more discussions with Cliff, we have an agreement on its purpose.

At that value it's not being used for 'tonal' purposes. It's definitely stability.

Because its on the first gain stage, the inductive action of the electrolytic could couple high frequencies in to the cathode which would be amplified by further gain stages. There will be a resonant frequency which if the gain is high enough could cause an oscillation. Putting that small cap. will reduce the resonant frequency and the magnitude of resonance.

It might be a good option for any high gain first stages.

[Synchu]

That is an extremely useful discussion and joy to read.
Thanks for that!
Niki

[jon]

It seems that the build shots from this amp are no longer linked on the site. Did anyone happen to save them. I would be much appreciated if someone could message me a zip file of them.

Jon

[lovetone]

Would it be a possibility that a file could be created in the files section with the build images?

This was a very interesting build I and I guess others might like to try some time.

[caphead]

I remember this thread from near it's beginning and the thing which impressed me the most was how ic-racer took this one picture: http://personalpages.manchester.ac.uk/s ... zamp02.jpg
.... and turned it into a verifiable schematic. This to me is beyond amazing and I'd like to find a photo-zoom program that works this well on my Windows 7 clunker of a pc What ic-racer said a couple posts into this thread was:

Aldus Freehand c1992

I keep an old iMac up and running because, frequently the older software is easier to use and runs faster. Plus I have a lot of old software. I like Macintosh, but I'm disappointed that my new 27" iMac can run Windoze but not 68k Macintosh software!

Would any of you more computer savvy individuals on this forum know of a program (preferably free, but I'm not holding my breath on this detail) which would have a similar non-pixelated zoom characteristic as the Aldus program ic-racer used? I've tried a whole bunch of those 'free trial period' photo zoom programs but nothing so far has been all that much better than the 'Windows Photo Gallery' program which came stock on this PC. I'm pretty good at creating schematics from gut-shots but this ability is limited by the quality of the pictures I have to work with.......

[Gainzilla]

Hey Caphead,

The software you're talking about is vector illustration software. The most commonly used in professional circles is Adobe Illustrator. The drawings are vector, and when exported as a .pdf are fully scalable with no quality loss. You can get a creative cloud membership for under $20/mo (I think), which gives you access to literally ALL Adobe software.

A good free alternative is Inkscape (http://inkscape.org/). Should be able to output as .pdf, is free, and is available for Windows or Mac.

LMK if you have any questions.

Cheers!

[caphead]

Awesome, thank you Gainzilla! I will give these options a shot (the free Inkscape one first, my funds getting tighter as xmas nears ) Although I do have adobe 'creative cloud' somewhere on my PC but I doubt it's the fully featured one your talking about.

[Gainzilla]

Cool, I think I have some component libraries for illustrator, and they should work for Inkscape as well (they're just all on a "parts" layer or something). LMK if you want those.

Btw, I used your universal layout in a build last year, and really liked it! Well, there are pros and cons. There are other layouts that make better use of the board-space, but the components are so logically/proximally placed that lead dress is less of an issue. Also, it makes for a tidy build.

Cheers!

[BigBear333]

Where did the inspiration for the .05uf cap on pin 7 of the PI come from? I do not see that implemented in other builds - was that a circuit tweak after it was built?

[Mark]

I wonder what has become of this amp?

Is Iceracer still using it?

Did he mod it after some months of use or leave it as is?

It's the Dumble that gets the least love it seems.

Just curious.

[10thTx]

This is still one of my favorite YouTube amp demos:

https://www.youtube.com/watch?v=FGUPyKYz3Xo

With respect, 10thtx