Seymour Duncan Tweak Fuzz

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Seymour Duncan Tweak Fuzz

Postby TDR1138 » 18 Jan 2012, 19:15

Ok, so let me start by saying that I’m still relatively green with my comprehension of circuits, so forgive any ignorance… I picked up a SD Tweak Fuzz about 6 months ago in trade. I haven’t totally fallen in love with it, plus GC did their whole “let’s sell them all for $40” deal that pretty much devalued the pedal for me for any future trades, so why not have some fun with it…

analogguru posted a schematic here a while ago:
viewtopic.php?f=1&t=12#p17

First, my issues with the pedal:
Stock volume was lacking. I have addressed this with SD’s mod, but I have questions about that (see below).
Pedal tends to sound a little nasally in “tweak” positions 2-5, is too bassy in position 6 for guitar but needs a little more for bass, and position 1 is worthless (IMO).
Fuzz is a little raspy/harsh. I know it’s a fuzz, but I’d like to smooth things out a bit.

SD had a mod posted on their site to increase the volume of the pedal by removing/jumpering R5 and replacing R4 with the 8k2 resistor from R5 (or one of similar value). I’ve found that the “Roger Mayer” mods for this actually replace the 470 ohm R4 with a 1k resistor, and replacing the 8k2 R5 with 18k. Can someone tell me the point of these two resistors, and what the differences in the mods would be?

C1 on the main circuit is a cap across the base/collector of Q1. My understanding of this is to “soften” the clipping and give the Si transistor more of a Ge feel. Is that correct? (note: the Alex Saraceno Afro Fuzz version that this was based on uses a Ge tranny for Q1.) Could this be having the side-effect of making the pedal sound nasally, though?

Next, I was thinking of shifting around the caps on the rotary switch, removing #1 and making #2 - #6 the new #1 - #5, respectively, then adding an even bigger cap to use with a bass. For better response with a bass, would it be worth adding a larger output cap on a mini toggle to switch to? Also, looking at the rotary board, there is a 100k resistor grounded before the cap for each selection. What’s the point of these? I don’t see them on the “classic” FF circuits…

Also, I was thinking of doing one of the “Fuller” mods (I guess what Mike Fuller does on his Fulltone ’69 pedal) wherein he adds a pot in series with the input of the circuit, before the input cap. I’ve seen both recommendations for 50k and 100k. Has anyone tried this, and if so, what are your thoughts?

Finally the magic question… I want to stick with NPN Si transistors. Any thoughts for ones to try?

Thanks!
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Re: Seymour Duncan Tweak Fuzz

Postby allesz » 20 Jan 2012, 09:37

Hallo, I always liked the tweak fuzz (but never had one) since I read your review I am not shure.
I am not a super expert but I think that your idea to change the input caps on the selector is good, but before try to change the output cap, because it seems quite small to me (100nF would be better). After this maybe you can rethink about the input caps (that affects the tone but the level of dirt too).

TDR1138 wrote:SD had a mod posted on their site to increase the volume of the pedal by removing/jumpering R5 and replacing R4 with the 8k2 resistor from R5 (or one of similar value).


This mod will give you more volume and a brighter sound; you can simply disconnect the output cap from the junction between r4 and r5 and connect it between q2 collector and r5.

TDR1138 wrote:I’ve found that the “Roger Mayer” mods for this actually replace the 470 ohm R4 with a 1k resistor, and replacing the 8k2 R5 with 18k. Can someone tell me the point of these two resistors, and what the differences in the mods would be?


doubling the value of r4 will give you some more volume. I am not a "doctor" about biasing transistors, but changing from 8,2 k to 18 k can probably influence the biasing of q2 quite a lot and the pedal sound (doubling the resistance between q2 collector and the output cap) will get darker.

Try putting a 1k resistor in place of r4 and increase the output cap value to 100n, they seem the easier mods and they will increase bass content and oputput volume.
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Re: Seymour Duncan Tweak Fuzz

Postby TDR1138 » 24 Jan 2012, 19:47

Thanks... not trying to steer you away from the pedal - I think it's got a bit of potential (well, as much as any FF can), and I like the idea of the selectable input caps. I'll try messing with R4 and R5, see how that turns out. Also the output cap.

Anyone have thoughts about C1 across Q1, and about the resistors in the "tweak" circuit? Still wondering about those.
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Re: Seymour Duncan Tweak Fuzz

Postby snyder80 » 25 Jan 2012, 00:41

Hi!

I got the tweak fuzz, too.
First of all i dont recommend to tweak the in/out caps. The Tweak Knob already offers a lot different and common values. The outputcap is standard @ 10n.
Also i think the tweak fuzz volume-mod floating around is not quite smart, because it changes the bias of the two transistors .

First: you need to understand the fuzzface circuit. there is a technical article on geofex and fuzzcentral explains a lot about waht to tweak in the axis face silicon description.

Second: Measure your Supply-Voltage(~9.0 V). You should bias the Collector Q2 around 1/2 Supply V(~4.5V). Therefore i had to change the 8.2k to 12k-13k.

Greetings,
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Re: Seymour Duncan Tweak Fuzz

Postby allesz » 25 Jan 2012, 16:04

C1 is a small capacitor that filters out some high frequencies, hiss and noise... it should be a small value and I would leave it there.

I reckon that 10n is the standard fuzz face value as an output cap, but if you plan to use the pedal with guitar and bass the sound will probably be always to thin with bass: you can put 10uF as input cap... but the output one, being so small, will always filter out a lot of bass frequencies.

The resistors on the tweak knob looks like pull down resistors, and they should avoid pop noises when you turn the effect on or off, or you tweak the input cap; the value is small (100k right?) and this should also have an effect (don't now if good or bad) on the input impedance. I would live them where they are.

snyder80 wrote:Therefore i had to change the 8.2k to 12k-13k.
The direct experience of snyder80 can not be denied. Just to make it easy you could swap r4 with a 2,2K, the jump up in volume should be dramatic; for the sound I don't know, because the bias change will probably affect the tone too (but maybe in a good way as reported.
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Re: Seymour Duncan Tweak Fuzz

Postby TDR1138 » 26 Jan 2012, 16:31

I've read a few FF articles, which is why I was questioning the SD mod in the first place. But I'm still learning... :)

I swapped out for a 12k on R5 and 1k on R4, and it sounds much better now. I still might want to up the volume, though. Would taking R4 to 2k2 give me more volume without affecting the tone, or will it throw the bias off?

snyder - what's your objection to changing the output cap (at least on a switch)? or what would you suggest to get more low end to use with a bass?
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Re: Seymour Duncan Tweak Fuzz

Postby allesz » 26 Jan 2012, 18:58

Great result.

A bigger r4 should increase the volume even further.... but of course the bias will be altered.... you wil have to discover it by yourself.
Even if does not correspond to the original ff circuit I would try increasing the output cap; if you just want to give it a try you don't need to desolder your actual output cap and put a new one: just flip the board and solder a 100nf cap directly on the solder joints of the original output cap on the board (they will be in parallel and you will have a 110nF output cap).
This way, if you don't like the sound, you have only to desolder (or just cut the legs of) the new cap and go back to stock.
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Re: Seymour Duncan Tweak Fuzz

Postby B3ar » 04 Feb 2012, 05:28

Is R2 just working like a fixed-value version of the Fuller/Fuzzcentral input pot? (As in jumper it for moar fuzz?)
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Re: Seymour Duncan Tweak Fuzz

Postby allesz » 08 Feb 2012, 14:35

I guess that R2 and the other resistors like r2 are pulldown resistors in order avoid pop noises when you turn the effect on and off and when you switch between input caps.
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Re: Seymour Duncan Tweak Fuzz

Postby azrael » 08 Feb 2012, 19:12

B3ar wrote:Is R2 just working like a fixed-value version of the Fuller/Fuzzcentral input pot? (As in jumper it for moar fuzz?)

I doubt you'd notice much of a difference by jumpering R2, it limits signal, but only a bit. Not a pull down.

If P2 is only a 1K, try a 2K there for more fuzz.
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Re: Seymour Duncan Tweak Fuzz

Postby B3ar » 09 Feb 2012, 05:59

Btw, my stock voltages are 6.45v on Q2, .60v on Q1. (The pcb reverses Q1 and Q2 designation relative to the the Analogguru schem and every FF -- I'm going with the rest of the world.)
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Re: Seymour Duncan Tweak Fuzz

Postby blue_lu » 04 Aug 2012, 10:53

So did anyone swap out the Q1 transistor for a germanium yet? Which one did you use?
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Re: Seymour Duncan Tweak Fuzz

Postby nbabmf » 12 Oct 2012, 00:11

I just replaced Q1 (aka Q2 on every other FF schematic) with an NPN germanium "FD-1029-KM" (hFE ~100), and I'm very happy with the result. I used a trim pot and biased it by ear to 4.68V. It sounds great!
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