Issues with the Maestro FZ-1S (low fuzz volume) - DIY version of GGG

Started by CosmicEffect, January 14, 2023, 11:34:08 AM

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CosmicEffect

Quote from: duck_arse on January 19, 2023, 08:50:03 AM
more to the previous - a few things.

if you have a three pole switch, you should probably wire the pedal as true bypass.
wiring the whole board with black is cool, as they say, but does no favours to those debugging/inspecting.
very much check your solders on R14, the holes look dry of solder.
what are the markings on C6, please? I always suspish caps when I can't see the writing, esp when there is only one of that kind on-board.
also suspish blue resistors when they only have 4 bands. please measure the resistance of R2.

but nevermind all that. I'd bet on the fact [!!] that the two greencaps at C10 and C11 are not the correct values. they should be 680pF, but I'd bet on at least 68nF being fitted. can you please confirm the markings on them?

and having gone all over your board this evening, I again say - you need a rethink on your layouting. my opinion only, but none of your far flung placements make sense. group a transistor and it's biasing parts in a lump, then link the lump to the next lump. you will end up with a less pretty pattern of parts, but also a much much less complicated mess of traces and vias.

Thank you for these additions!
I will indeed re-check the value of the components, see if they correspond to the labeling.

Concerning the layout of the components on the PCB, keep in mind that this is one of my first PCBs and that I do not yet know the design rules of electronic boards. I am aware that this may seem absurd to some experts.

But I will take your comments into account for my next designs.

Also, I have already wired the pedal in true bypass. The footswitch you see at the bottom left of the photo is the fuzz switch (I didn't have a mini switch yet, so I put this one to do the tests)

duck_arse

I wouldn't worry too much about the expert, it seems he's left the room to us bozos.
" I will say no more "

pacealot

Does this mean that it's safe once again for an idiot like myself to post my dumb, uneducated, and unscientific observations?  :icon_eek:

If so, then I can confirm that bmsiddall's approach to the 47K resistor at Q4's base worked great for me as well; I think I used a resistor/pot combo (I believe something like a 25K linear pot and a 56K resistor, but YMMV of course), but in any case I was able to get it to work through a very useful range of gating, from none at all to a much more pleasant and less abrupt cut-off than the stock 47K provided. This worked consistently well with a handful of different trannies of medium-ish gains (300-400 hFE or so) and types (2N3391s, BC109Bs, even in a PNP positive ground version with 2N5138s and 2N5087s).

My ignorant non-EE-capable assumption is that that resistor sets the turn-on point of Q4, yes? Close? No?

In any case, I really enjoy this circuit and think it's a great platform for some very useful mods, and it hasn't really been widely explored to its full potential yet.
"When a man assumes, he makes an ass out of some part of you and me."

antonis

Quote from: pacealot on January 19, 2023, 03:23:39 PM
My ignorant non-EE-capable assumption is that that resistor sets the turn-on point of Q4, yes? Close? No?

Yes.. :icon_wink:
(but, as it is, only for incoming signal positive waveform..)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

pacealot

"When a man assumes, he makes an ass out of some part of you and me."

Lino22

One more comment. I built a few of these, and the biggest annoyance is their sustain, that is really short and tends to end suddenly in the middle of a note. You will help this by Q3 Hfe about 700. Q3 feeds the square wave generator of Q4 and has a major impact on the sustain. The sustain will never be smooth, but can be adjusted to be musically useful.
When you put up with this, it sounds very rich and lushy. I was thinking about building it without the useless Balance feature.
When the core started to glow and people started yelling, he promptly ran out the door and up a nearby hill.

antonis

ΙΜΗΟ, the issue is located on Q4 bias rather than on Sustain pot itself..

Q3 stage gain is strongly dependent on Sustain pot setting and signal frequency..
There might be cases where the combination of low Q3 stage gain with note decay level can't force Q4 into active mode..


"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

duck_arse

perhaps one of the have-built-it blokes would be so kind as to do some transistor voltage measures for us to look at.
" I will say no more "

pacealot

Indeed, can do — let me dig around to pull it out and then I will post them forthwith and/or toot sweet.

Another thing I tried that helped "sustain" (or at least provided more saturation) is putting a large-ish (anywhere from 10µF to 47µF)  'lytic cap in parallel with the 470Ω Q3E resistor, as per many gain stages we all know and love. This proved more efficacious for me than swapping out for higher hFE trannies (not that that hurt either). But yes, the Q4B resistor change is specifically to deal with the very issue raised by Lino22.
"When a man assumes, he makes an ass out of some part of you and me."

pacealot

Okay, some voltages from my version (using 2N3391s for all four transistors here, roughly 300-400 hFE, and a pair of noisy old CS3710s as the clipping "diodes"/transistors):

Supply: +8.74V (after power filtering)

Q1B: +2.47
Q1C: +8.71
Q1E: +1.985

Q3B: +0.568
Q3C: +1.059
Q3E: +0.024

Q4B: +0.403
Q4C: +7.79
Q4E: 0V

(I read Q2 last, as it's the output stage)
Q2B: +1.058
Q2C: +4.97
Q2E: +0.546

These readings are with the stock 47K resistor value from Q4B to ground, which has significant gating. With different values, the only readings that changed significantly were those on Q4B and Q4C (Q3C dropped ever so slightly as that resistor value increased, but not by more than a couple of mVs). Here are those readings:

Q4B-to-ground resistance ~59K (dialed in to the least audible gating and loudest noise/hum):

Q4B: +0.499
Q4C: +2.7

Q4B-to-ground resistance ~72K (max resistance of 47K resistor plus 25K pot — significant gating again):

Q4B: +0.534
Q4C: +0.074
"When a man assumes, he makes an ass out of some part of you and me."

duck_arse

interesting, and so competently done. we just need Cosmic to come back wiv his new readings now.
" I will say no more "