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.
Use a socket and let your ears decide.
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:
(http://www.experimentalistsanonymous.com/diy/Schematics/Fuzz%20and%20Fuzzy%20Noisemakers/Heathkit%20TA-28.gif)
My final version:
(http://www.luciferstrip.com/fuzz/heathkit-fuzz-final.jpg)
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?
Quote from: bnickell on December 27, 2012, 03:06:43 PM
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
(http://www.luciferstrip.com/fuzz/heathta28-orig-schematic.jpg)
Quote
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
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.
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.
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
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.
Quote from: bnickell on January 01, 2013, 05:47:12 PM
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 (http://www.diystompboxes.com/smfforum/index.php?topic=99037.msg871979#msg871979)