Heathkit TA-28 Fuzz build - Transistor substitutions

[bnickell]

I am about to start building a Heathkit TA-28.  I got the schematic and info on this thread http://www.diystompboxes.com/smfforum/index.php?topic=90489.0

There is a lot of discussion on which PNP transistor to use for Q2.  I have a 2N3906 which has been used as  a good substitute according to the forum.

My problem is, I do not have a 2N3391 NPN for Q1.  I have 2n5099, 2n2222, 2n3904 and 2n4401.  All the other parts are "in stock" in my workshop and I really don't want to order just a .40 transformer if I can help it.  Would any of the NPN's I listed work in Q1?  If so, which do you recommend?

The schematic is at http://tinypic.com/r/fcnso/6  Thanks to all.

[Mark Hammer]

Use a socket and let your ears decide.

[LucifersTrip]

I tried a ton of different ones for both and there was little difference as long as you keep the hfe's around 250 - 350

The most important thing is subbing 10K's for the 1K's in the tone control and experimenting with the 10K before the tone control...since the volume is lacking.

original:


My final version:

[bnickell]

Thanks.  I think I'll try a 2n5088 in Q1 and see what happens. 

I noticed you changed your cap value on input to .033.  How does that affect the tone?

[LucifersTrip]

Thanks.  I think I'll try a 2n5088 in Q1 and see what happens.  

for me, it was better with a bit lower hfe. but remember, you have original voltages to compare to

I noticed you changed your cap value on input to .033.  How does that affect the tone?

more treble of course...but I mainly added it to smooth out the raspy/farty/sag when the fuzz was turned up

[bnickell]

Do you think a 2n2222, 2n3904 and 2n4401 would be preferable at Q1?  The range of hfe is a litte hard for me to understand.  Thanks.

[skrunk]

just going by Lucifer's Trip advice, the 2n4401 would probably be your best bet.
mine measure hfe 250.
the gains of 2n3904s can vary and the 2n2222 might be a bit low.

also, like Mark said, put a socket in if you're not sure.
might be time to get a breadboard also, if you plan on building more pedals.

[LucifersTrip]

the bottom line is it's really up to your ears only...when you start using hfe's over 200-300, the collector voltage will probably just slowly change.

the hfe's I used (see above on schematic) gave me almost exactly the voltages on that original schematic

[bnickell]

I just made it per Lucifer's schematic, except I used a 2n4401 at Q1 and a .047uf cap on the input.  It sounds great.   When I turn the 10k trim pot to about 8k I get just a little gain/volume over bypass.  Thanks to all for your assistance and advice.

[Electron Tornado]

I just made it per Lucifer's schematic, except I used a 2n4401 at Q1 and a .047uf cap on the input.  It sounds great.   When I turn the 10k trim pot to about 8k I get just a little gain/volume over bypass.  Thanks to all for your assistance and advice.

I left out the 10k resistor before the tone section. I added a volume control after the tone control. My schematic is here : http://www.diystompboxes.com/smfforum/index.php?topic=99037.msg871979#msg871979