MkII bias and general pointers (calling JakeFuzz, Timbo, and mgwhit!)

[timbo_93631]

Sorry, late to the party!  Glad to hear it is working out for you.  My best MKII tips are to put a small 220-470 ohm resistor in series with the -9v power going to the board, this can help quiet down a noisy build and make sure to filter the power too, lower gain in Q1 is good, and a little more leakage is ok in Q3, and sometimes helpful as you described.  FWIW I didn't have to do anything special to get the nice 1590a MKII stomptown (Jon) is selling to work great, see my comments in his FS ad here. 

[Cortexturizer]

100, 0.04
74, 0.03
56, 0.121
102, 0.032
128, almost no leakage?

I measured the Ge trannies that I have left, and the clip was recorded with this combination

56, 0.121
102, 0.032
128, ...

I tried other combiantions but they either produced no sound, or sounded pathetic.

[Effectsiation]

I feel like I end up writing this once a month, probably because there's so much misinformation out there about biasing a Tone Bender MKII compared to a Fuzz Face:

David Main (of D*A*M) measured vintages ones and said he found between 7.9-8.6 volts on Q3's collector.

Thanks Scruffie for posting those measurements with the other transistors too!

[Bret608]

Sorry, late to the party!  Glad to hear it is working out for you.  My best MKII tips are to put a small 220-470 ohm resistor in series with the -9v power going to the board, this can help quiet down a noisy build and make sure to filter the power too, lower gain in Q1 is good, and a little more leakage is ok in Q3, and sometimes helpful as you described.  FWIW I didn't have to do anything special to get the nice 1590a MKII stomptown (Jon) is selling to work great, see my comments in his FS ad here. 

Thanks Tim! Based on the tone you were getting in the clip you posted, his board is worth picking up. I've about got my build squared away but for a little extra noise and static when I play with the volume pot. I think I have enough trannies to do another though if the mood strikes me! 

[ummagumma]

@Cortexturizer
now here's a just a 'random' thought...
did you happen to wonder that you are dealing with temperature unstable semiconductors and the fact that you are working in extreme temperatures of 40°C/104°F got something to do with it!?!
try to cool it down and see what 'll happen.   

[Cortexturizer]

[soundcloud]https://soundcloud.com/kuato-design-stompboxes/tb-mkii-professional-first[/soundcloud]

So i started from scratch, made another one, and this one is killer. It is incredibly quiet, still unboxed.
I used this combo

56, 0.121 [unknown transistor from smallbear purchased ages ago]
74, 0.03 [gt308V]
100, 0.04 [gt308V]

What you can hear in the clip is the new circuit with Attack maxed and playing with the volume pot. I start with the tele deluxe bridge pickup rolled back to almost zero, you can hear how nice this thing cleans up. And the bias was set by ear, and when I measured it it was 4.5V! Ha! I tried higher values of course but I am undecided whether I like em. Haven't even tried this on an amp.
I did the following mods:
replaced 470R resistor with 1k5 for lots of volume and that low mid thing
put a 100K trimpot in series with a 10K resistor as Q1's base resistor [this is great for fine tunning]
put a 100R resistor from the emiter of Q3 to Attack pot [probably should put a liiiiiiitle more cause there's still a slight buzz when Attack maxed]
25K as a Q3 biasing trimpot
220n PIO instead of the 100n cap on schematics

Pretty satisfied.

@ummagumma
Haha de si matoriiiiiii
Ma nesto sam zeznuo pri samoj izradi...prihvatio sam tvoj savet od odavno...bolje napraviti novo nego provesti vecnost gledajuci gde je greska. A vec sam pola vecnosti trazio gresku...no sad odlucih da ga napravim opet i radi uber i neverovatno je tih, ne mogu da verujem koliko. Pozdrav care

[Bret608]

That sounds great! I played through mine again this morning and am now extremely pleased. I wish I had a way to record so I could share too, but then again unleashing my poor playing on you all may not be too friendly!

I was not getting any extraneous noise or crackle when I tweaked my guitar's volume pot. Two things that may have made the difference: first, I dialed back the volume knob to where it was just above unity rather than utterly slamming the amp's front end. Also, it was a bit cooler here this morning than it was last time I played with the circuit. This ties back to what ummagumma said--I think any perceived instability in the circuit on my part is an artifact of playing it unboxed in a warm house in the summer.

[Cortexturizer]

Okay I think I got this mastered now. Here's a clip

[soundcloud]https://soundcloud.com/kuato-design-stompboxes/wooz[/soundcloud]

Attack close to max, and playing with the volume knob. It has the most sustain ever.
I biased it by ear. For the Q1 base resistor now I have a 100k and a 100k trimpot in series. Still a 25K trimpot for the Q3 collector. I biased the two by ear and this is what came out.

I am absolutely satisfied with the sound now.

Oh, and I put the cap that goes from Q1 to Q2, normally a 100n, well I put it to be a 10n. I made it for a friend and we felt it had too much bass, so I decided to cut some there.

What do you think guys?

[Cortexturizer]

And I suddenly realised that I just used a battery that measured 6.14V!!!
I had two of them, exactly alike, on my desk, and I thought I got a brand new one, but no, what I got is the old one which was standing there for months.
So go figure...What an incredible improvement in sound. From a dead battery.
Oh to hell with this, I'm done for tonight.

[Cortexturizer]

No, I am not done.
I just tried the brand new battery and it behaves the same, just has a buzzier sound, which is to be expected, since the bias is higher.
So, with my battery being 6.4V, I got 2.8V on Q3 collector and 0.16V on Q1 base.
With the battery on 9.3V, I got 4.9V on the Q3 collector, and 0.16V on Q1 base.

I prefer the first sound. Did Hendrix used to give batteries to his rodey and get em when they were way down? Heh.

[ch1naski]

Hey cortex,
Maybe you could throw a voltage sag potentiometer into the circuit.
I know the zygote has one built into the circuit..... Have not tried it, but it could be set up to give you your preferred dead battery sound.

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[midwayfair]

I prefer the first sound. Did Hendrix used to give batteries to his rodey and get em when they were way down? Heh.

The Fuzz Face clone on my board has external voltage and bias. I regularly run it closer to 5V. Also, the Selmer Buzz Tone ran on a 3v battery. (I think the Maestro did, too?)

If you were using an adapter, I'd tell you to just order a 6V regulator (those exist), but in this case, a 10-25K pot in series with the -9v source is probably less wasteful (electronically). It's not like there's a danger of overheating. Or you can just use a trimmer or -- best -- a fixed resistor that drops the voltage however much you need.

[Cortexturizer]

Both wonderful ideas, and I can't believe I haven't thought of the voltage sag thing and I've known about it forever.
And yeah, Maestro did run on 3V.
I'm gonna put a trimmer inside definitely.
How do you like the sound guys?

[Bret608]

I think it sounds great! I love that a few changes to the part values lend such possibilities for tailoring the sound and response to your particular setup.

[ch1naski]

I can never even see the sound clip links on my mobile device.....grrr. It just looks like empty space in the post

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