Tone Bender MKII - Original Layout - What do you think?

Cliff Schecht · February 09, 2009, 03:57:08 AM

The word (well, company) Matsushita gets edited.

yeeshkul · February 09, 2009, 04:05:40 AM

yeah, that's what i expected. After inserting an old Czech OC75 with massive leakage for Q2 the VQ2C vent down to 250mV and VQ3C went up for almost 3 volts.
Matsupoota rulez!

yeeshkul · February 09, 2009, 04:13:36 AM

actually i made a little testing board for FF/TB circuits with bunch of trimpots. I will make a separate thread out of it, i see it makes sense. Especially if you are up to building more than one unit.

Nitefly182 · February 09, 2009, 04:17:12 AM

So you think the transistors are crappy? I figured the small bear stuff was the best way to go for something like a tonebender but I guess not. So based on what you are saying, I need to reduce the Q2C resistor and crank up the bias resistor in order to get those voltages around 1v and 4.5 volts for Q2 and Q3?

yeeshkul · February 09, 2009, 04:32:43 AM

I am not saying anything like smallbear stuff is crappy. I have really great experience with that shop. The guy behind it is an extremely helpfull man. Leaky transistors can bes used in TB circuit. The originals were leaky as well i bet. Q1 even must be leaky to bias itself. Just use 47k for Q2C and bigger trimpot to push down the Q3 bias (to at least 7V) and rock on

.

EDIT: measure the trannies, put the results up here and i will tell you the possible best choice for the setup.

Nitefly182 · February 09, 2009, 01:06:23 PM

Im about to give up. I have built two tonebenders and none of them would bias up in any way. I cant get anything good out of this pedal and its exactly like the layout posted about halfway down the first page. I dont know what it is but I just cant make a tonebender work for some reason. The only change I made was putting a trim pot in place where the original pedals had an 8.2k resistor so I worked around the bias mod on that layout. All the wiring is exactly the way it should be. I just dont get it.

Electric Warrior · February 09, 2009, 01:23:12 PM

did you connect the bias 2 and bias 3 traces? or did you lay it out like in Chris first layout?

edit: oh, I can see from your picture that you did it the right. don't give up. you've got such a neat looking board..
maybe it's the trim pot. try to connect only two legs.

yeeshkul · February 09, 2009, 01:36:42 PM

Nitefly if you can'y reach 4.5V at Q3C even with 50k trimpot, there is something else that must be wrong. Leaky electro cap? Did you measure them? Cold soldering spot? Measure everything first. Post the voltages.
By the way i posted my test circuit here http://www.diystompboxes.com/smfforum/index.php?topic=74130.0

Don't give in without the fight

Man i was so many time right on the edge of throwing that bloody thing out of my window and it always turned to be fine in the end. I am talking in general now. It is gonna be fine, TB is too simple not to come out right.

sharkminusbear · February 09, 2009, 08:45:51 PM

Nitefly, your build puts mine to shame, your's looks awesome.

I used a 25k linear pot for my bias and I was able to get the collector on Q3 (OC75) to around 4.5 easily . I happen to like it biased differently depending on how I feel though... sometimes I got for a higher bias.

I ordered the tonebender set from smallbear and was not impressed with the combo, it sounded too smooth and modern for my taste. I ended up using one of the OC76's they sent me in Q2, but I salvaged 2 OC75's from my BYOC. It's got this nice gorwling breakup now with that sweet germanium sounding decay on notes.

If you can't get the bias below 9v with a 50k pot, then I think something else is going on.... oh hey, you said all you did was put a trimpot in place of the 8.2k? I put a 470R resistor there and then used the bias pot method from Electric Warrior's layout. Maybe you could throw a 470R in there and just connect the leads of the trimpot with wires from the bias strips on the board?

Dunno if this is right or wrong, I'm new at this stuff.

yeeshkul · February 10, 2009, 02:06:55 AM

Quote from: sharkminusbear on February 09, 2009, 08:45:51 PM
Maybe you could throw a 470R in there and just connect the leads of the trimpot with wires from the bias strips on the board?

470R is there already ini? That one is supposed to be there all the time and people just change it for 1k when the want more volume out of the device.
Nitefly check out if the trimmer used is connected well (one side right to the collector and the other side to the 470/10n junction). Also check out if you used the right trimmer legs and measure the trimmer. Measure anything you wanna solder up - that is my general advice.
Or maybe send a picture of the solder side.

yeeshkul · February 10, 2009, 02:20:52 AM

ah i see what you mean, i checked out the picture way above here. The another - "bias" - 470R is not necessary unless you wanna some sort of a permanent bias pot on your stompbox.

yeeshkul · February 10, 2009, 02:49:30 AM

one more thing - make sure you measure the C3 voltage right on the Q3C leg and not on the bias trim/470/10n output junction - this spot is always high(!).

Nitefly182 · February 10, 2009, 04:10:47 AM

I was measuring the bias at the Q3C solder joint. Ill take measurements and reflow every joint and take a solder side photo in the morning. Thanks for the help guys.

Nitefly182 · February 10, 2009, 01:36:22 PM

OK. I plugged it in today to take measurements and it miraculously was able to bias up to 4.5v on Q3C. There is almost zero output volume though. Could the low q2 voltage be causing the volume issue?

Q1C - -8v
Q2C - -229mv
Q3C - -4.5v

Electric Warrior · February 10, 2009, 02:38:09 PM

did you use a 1k (or is it 10k? hard to tell) resistor instead of the 470R on purpose?

Nitefly182 · February 10, 2009, 03:05:22 PM

Quote from: Electric Warrior on February 10, 2009, 02:38:09 PM
did you use a 1k (or is it 10k? hard to tell) resistor instead of the 470R on purpose?

Thats what was on my schem from small bear. If anything I've heard that should increase the overall volume of the pedal.

Electric Warrior · February 10, 2009, 04:04:33 PM

otherwise it looks great. have you checked for solder bridges?

here's a new version of the layout with switch and pots. hope it works, any input appreciated.

yeeshkul · February 10, 2009, 04:36:40 PM

"here's a new version of the layout with switch and pots. hope it works, any input appreciated."
nice job man

As for the 1k - yes it helps with volume boost. It is a collector resistor so the bigger it is the more volume you get (U=R*I). The other collector resistor(bias) is pushing on the output voltage from the other side, that's why is this unit normally so quiet - you can hear how the volume changes when you tweak the bias trimmer. I am using 1k5 in my units. The impact on the tone is about the same as swapping that 100k res to 47k = nothing. On the other hand, very remarkable impact on the tone has the Q1B resistor. If it is too small (10k) then the first tranny doesn't get enough bias voltage and the fuzz is weak (about like Fuzz Face). If you use 100k you will get insanely wild fuzz. That's why they went for 100k in later releases.

I tested everything i say here by ear on my test board this morning. So no funny stuff

Can you please tell me what voltage range you get now on the Q3 collector after changing Q2C res to 47k?

Electric Warrior · February 10, 2009, 05:00:48 PM

I think the 100k is a OC81D version thing. The late pcb Supa Fuzzes still have a 10k.

yeeshkul · February 10, 2009, 05:21:44 PM

sorry, yes you are right

- basically the leakier tranny you use for Q1 the smaller the resistor can be.

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Tone Bender MKII - Original Layout - What do you think?