Tonebender MK II - low output, sounds thin??

[azrael]

Source Voltage: 8.99, battery

Q1
8.06v
0.07v
0.00v

Q2
0.16v
0.08v
0.00v

Q3
7.50v
0.14v
0.07v

Built it using this layout:
http://www.fuzzcentral.ssguitar.com/mkII.php

And I'm using SB172's for the germanium transistors, their gains are 70-70-100, from Q1-3, respectively.

Anything else you need to know?

I believe Q3's voltage is higher now due to temprature, it measured at 7v exactly yesterday. I read that's where it should be. I can't get it to 4.5v, anyway. Only go as low as 6.5 or so.

Isn't Q2 kind of low, though?

I'm asking here because it fuzzes up fine, but I have the volume and fuzz maxed out, and I feel like it's thin, and definitely needs more output. Also, rather noisy, doesn't like non TB-pedals in front of it. Thoughts?

[petemoore]

Q1
8.06v
0.07v
0.00v

Q2
0.16v
0.08v
0.00v

Q3
7.50v
0.14v
0.07v

Built it using this layout:
http://www.fuzzcentral.ssguitar.com/mkII.php

And I'm using SB172's for the germanium transistors, their gains are 70-70-100, from Q1-3, respectively.

Anything else you need to know?
  Assumin collectors is on the tops.
  Q1 has collector of...looks like somethin' high, depedns on supply V.
  I believe Q3's voltage is higher now due to temprature, it measured at 7v exactly yesterday. I read that's where it should be. I can't get it to 4.5v, anyway. Only go as low as 6.5 or so.
Isn't Q2 kind of low, though?
  It's base should be connected and = Q1C.
I'm asking here because it fuzzes up fine, but I have the volume and fuzz maxed out, and I feel like it's thin, and definitely needs more output. Also, rather noisy, doesn't like non TB-pedals in front of it. Thoughts?

[azrael]

really? I was seeing other people's Q1 around 8v, thought that was fine.

Any ideas as to what the problem could be?

[trjones1]

Your voltages look  fine to me.  FWIW, I dialed the bias of mine in by ear and it just happened to end up around 4.5V.  I think it totally depends on the transistors you use and the temperature when you take the readings, which effects the bias a lot. 

For more output, increase the size of the resistor that goes from 9V to the output capacitor.  Go up to 1.5k or 2.7k, if you want a lot of output.  You might have to adjust the resistor to Q3's collector to keep your bias right.

[petemoore]

Q1 has collector of...looks like somethin' high, depedns on supply V.
  Say the supply happens to be 9v, that's 1 volt of + swing [minus the 'elbow room' voltage the transistor requires], if the battery is 8.06, that's basically connected t supply.
  Q3 collector [which is a FF's Q2] should be at 1/2 or so of battery supply, this stage is also near to running into the supply rail.
  Audio probing will tell more about how Q1 works [it should boost a lot] and Q's 2 and 3 [should be a pre-boosted FF].

[mac]

Q2 is low, meaning it is leaky so you need a higher value trimmer at Q3 to get 4.5v.
What value are you using at Q2C, 47k or 100k.
If your ge is leaky 100k is too much, so replace it for a 47k and test if you can lower Q3 collector.

In a recent post about Si TB MKII, 7v at Q3 sounded the best to me. Salt and pepper to taste

mac

[azrael]

I read that some people put a trimmer to replace the 100K at Q2, so I tried that. I'm going to try and bias it again. I'll let you know how it goes.

[azrael]

No real difference, couldn't get it higher than .28v on Q2's collector.

Any other ideas?

How would I know if Q2 was leaky? I bought it as a matched set from another user here.

I'd really like to cut down on this hiss happening here, and make this a usable pedal.

[azrael]

Hmm...Well, I plugged it in again, sounds good! Not thin like the other day, not sure why.

I still would like to cut down on some noise. It is prettty darned noisy. I have my noise gate behind it, turned up pretty high.

I'm thinking about shielded wire for the I/O wires...Any other ideas?

[mac]

You need to read RG's fuzz face article at Geofex.com. There is a simple method to test your germs.
About noise and hiss, try bypassing the power supply at different points in your pcb if possible with a big cap. It can also be a transistor issue.

mac

[azrael]

The germaniums were sold to me by another user here, I forget his name, but they were held in high regard by other buyers. I have the germanium tester on a perfboard somewhere, I'll see if I can find it.

bypassing the power supply with a cap? Could you explain a bit more.

[azrael]

FWIW, here's a pic of the pedal's wiring:

The only difference is that there is now a 100K trimpot on Q2.

[mac]

bypassing the power supply with a cap? Could you explain a bit more.

A 22uf to 100uf from vcc to gnd.

I have a lot of 2sb172, they sound really good.

mac

[azrael]

Okay, so just attach one end of the cap to ground, and touch it to different points and see what happens?
What exactly should this do?

[azrael]

Just tried another set of Germaniums I have, some 2SB405s and an A103. I forget what the third. Not as aggressive, I'm gonna tweak it a bit.

But! The point being, it's MUCH quieter. Is it possible it's just the 2SB172s I got are noisy?? I got them from DIYSBer any.

[mac]

Just put the big cap between batt (+) and (-). It will shunt any nasties coming from the batt to gnd.

Try replacing one 2sb172, then another, to check if one is noisy.

I guess those 2sa103, 2sb405 are Matsush*ta transistors.

mac

[azrael]

Good idea, I will try some substitution, for sure.

These ones are actually Sanyo 2SB405s? I got em from a guy in Brazil. 


And thank you for the elaboration on the cap thing. I actually liked the sound of the other transistors better, it was just way too noisy. If I can make them work, I would rather use them.

[mac]

These ones are actually Sanyo 2SB405s? I got em from a guy in Brazil

Latin America is a good source of jap transistors. Lots of sanyo, toshiba, matsushitas, hitachis.

mac

[any]

haven't been around for ages, so sorry for not getting back to you.
I've sent you a PM with my email address if you'd like to sort out a refund/replacement.

Cheers