heathkit ta 28 fuzz booster

[pinkjimiphoton]

hi guys,
was surfing around evilbay earlier, and spotted this:

http://www.ebay.com/itm/150894762099?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648



they were kind enough to provide this:



and a gutshot!



and even a schematic, too:



so i looked up the transistors, to see what would sub, and it came up mpsa18 for q1, and our old friend 2n3906 for q2. i decided to suggest germanium there, but pretty much anything should do i would imagine.

that said, i was bored, so i worked up a vero...



gonna build it at some point just for sh*ts and grins...

just thought i'd share...was mighty nice of them to provide enough info to not need to build the pedal.

if anyone whacks it together, please let me know!

happy fumes!

[Electron Tornado]

I have one of these, along with a copy of the manual. There are some schematics floating around the net, but that one is the schematic from the manual.

I wonder how they decided on those substitutions for the original transistors. When researching the X29A829 I came across some info on a ham radio forum that suggested these subs for it: 2n2907, 2n4403, or an NTE159. One caveat is that the application they were discussing was as a "relay driver" in a Heathkit HW-8.

I think Smallbear may have the 2n3391.

It would be interesting to do a side by side comparison of the specs of those transistors. Either way, you could also just take whatever garden variety transistors you have and see how they sound.

As for how the example I have sounds, it's a sort of fuzzy overdrive, but there is a volume cut with it engaged. It needs another amplifier stage at the end. Something to try is to see if it sounds better with a buffer on the front. Come to think of it, I wonder why it was designed to operate at 1.5vdc, and how it would sound at a higher supply voltage.

[pinkjimiphoton]

yah, you know i'm gonna try it with a 9volt. 

i did a search on appropriate subs for the q1 transistor, and almost all said mpsa18, alot said 2n3904...so i'm figuring it's not too crucial.

i have some matched pairs of ac127/128's i may try in it. thinking maybe try a diode clipper on the output to get it a little louder. i bet 9v will make a difference, tho it may need biasing to run that hot.

thanks for the info bro!

ii actually have a couple of most of the trannys you named, so i'll try some of them, too.

[Electron Tornado]

thinking maybe try a diode clipper on the output to get it a little louder.

If you mean adding some clipping diodes between signal and ground (like a Dist +), that will just cut the signal more, and you'll really need the extra booster stage on the end.

This pedal has been discussed elsewhere on here, so it might be helpful to check out those discussions.

[LucifersTrip]

hi guys,
was surfing around evilbay earlier, and spotted this...

hey jimi!

cool to see you're still looking out for the odd fuzzes.

I built that one a while ago from the same schematic:
http://www.muzique.com/schem/heathkit.gif

To my ears, it is most similar in sound to the Sam Ash Fuzzz Boxx/ Astrotone...but better. It's one of the few 1.5V fuzzes that are silicon. Still my favorite is the Sun Buzz...

so i looked up the transistors, to see what would sub, and it came up mpsa18 for q1, and our old friend 2n3906 for q2. i decided to suggest germanium there, but pretty much anything should do i would imagine.

I actually had some vintage 2N3391's laying around, which had hfe's ~ 350 -400. The MPSA18 is way higher, 800+.
You know how it is with cross references...they're many times ridiculous. Coincidentally, I did use a 2N3906 for Q2 with a gain of around 200 - 250. Note that my vintage ones are in the 100 - 150 hfe range.  I have no idea why you're thinking about a germanium there. I doubt it'll bias well.

according to the analogguru schematic, Q2 would be cool with BC309B, which has min hfe 250.
http://analogguru.an.ohost.de/193/schematics/Heathkit_TA-28.gif

I did try many different Q2's before deciding on the 2N3906.

gonna build it at some point just for sh*ts and grins...

just thought i'd share...was mighty nice of them to provide enough info to not need to build the pedal.

if anyone whacks it together, please let me know!

yah, you know i'm gonna try it with a 9volt.

There are a couple things that are unusual about that pedal...It uses an NPN / PNP combo and it's a 1.5V silicon...so it'd be sacrilege to change to 9V...the 1.5V is part of the fun!  just kidding...you should always try everything.

Electron Tornado:
As for how the example I have sounds, it's a sort of fuzzy overdrive, but there is a volume cut with it engaged. It needs another amplifier stage at the end.

When tweaking, I noticed it was not loud enough and there was a simple fix. Just lower or remove the 10K before the tone control. I actually wound up putting a 10K pot there.

I also used a switch between the original input cap and a .033uF which smoothens out some of the raspiness when the drive (50K) is higher up.

Anyway, here's my final version with voltages & notes. If Electron Tornado could post voltages from the original, that'd be killer.

[pinkjimiphoton]

thinking maybe try a diode clipper on the output to get it a little louder.

If you mean adding some clipping diodes between signal and ground (like a Dist +), that will just cut the signal more, and you'll really need the extra booster stage on the end.

This pedal has been discussed elsewhere on here, so it might be helpful to check out those discussions.

it has been discussed? cool; i did a search but only got one or two hits.

i was thinking maybe an led clipper at the end of the circuit would boost it up some...thanks for the insite.

i love weird old fuzzes, is the volume drop that severe that it will need another stage ET?

thanks!

[pinkjimiphoton]

hi guys,
was surfing around evilbay earlier, and spotted this...

hey jimi!

cool to see you're still looking out for the odd fuzzes.

I built that one a while ago from the same schematic:
http://www.muzique.com/schem/heathkit.gif

To my ears, it is most similar in sound to the Sam Ash Fuzzz Boxx/ Astrotone...but better. It's one of the few 1.5V fuzzes that are silicon. Still my favorite is the Sun Buzz...

hi lu! cool, i had seen the schem in passing, but looking at it made me want it.... you know how THAT trip is!!

so i looked up the transistors, to see what would sub, and it came up mpsa18 for q1, and our old friend 2n3906 for q2. i decided to suggest germanium there, but pretty much anything should do i would imagine.

I actually had some vintage 2N3391's laying around, which had hfe's ~ 350 -400. The MPSA18 is way higher, 800+.
You know how it is with cross references...they're many times ridiculous. Coincidentally, I did use a 2N3906 for Q2 with a gain of around 200 - 250. Note that my vintage ones are in the 100 - 150 hfe range.  I have no idea why you're thinking about a germanium there. I doubt it'll bias well.

350 - 400 i can do...tons of silicon trannys in that range. i thought it seemed a little odd to reccomend the A18....IME they are way too hot for a lot of things.
i was thinking ge for q2 to try it,i often will try and put a germ in where i can cuz i just love the sound of them, so far, it seems to be more stable messing with q2 in a lot of circuits than q1.
thanks for the advice! i love hybrids lately...building a LOT of fuzzfaces like that. this thing was screaming harmonic percolator at me for some reason...tho i realize it's not related. i guess it was the way the input was wired. anyways...

according to the analogguru schematic, Q2 would be cool with BC309B, which has min hfe 250.
http://analogguru.an.ohost.de/193/schematics/Heathkit_TA-28.gif

I did try many different Q2's before deciding on the 2N3906.

that's why i was thinking GE...i have a bunch of lo hfe mp16b's still, and they often sound great instead of an 06...but good to know the 06 worked out for you.
that'll simplify things some when the time comes to build it!

gonna build it at some point just for sh*ts and grins...

just thought i'd share...was mighty nice of them to provide enough info to not need to build the pedal.

if anyone whacks it together, please let me know!

yah, you know i'm gonna try it with a 9volt.

There are a couple things that are unusual about that pedal...It uses an NPN / PNP combo and it's a 1.5V silicon...so it'd be sacrilege to change to 9V...the 1.5V is part of the fun!  just kidding...you should always try everything.

i liked the npn/pnp combo...these kind of fuzzes always have a "unique" sound to them... i WILL try it at 9 v, but i don't expect it to sound very good!!! figure i'd have to really mess with the biasing most likely. i'll report back if i do mess with it!
btw, remember one time i had said something about having to flip trannys 180 degrees? this was one of the kind of circuits i was talking about...if ya notice, q2 is opposite of q1's pinout. i guess i didn't know how to explain it that well back then!!

Electron Tornado:
As for how the example I have sounds, it's a sort of fuzzy overdrive, but there is a volume cut with it engaged. It needs another amplifier stage at the end.

When tweaking, I noticed it was not loud enough and there was a simple fix. Just lower or remove the 10K before the tone control. I actually wound up putting a 10K pot there.

I also used a switch between the original input cap and a .033uF which smoothens out some of the raspiness when the drive (50K) is higher up.

Anyway, here's my final version with voltages & notes. If Electron Tornado could post voltages from the original, that'd be killer.




[/quote]

that's awesome lu!! do you mind if i add that info on to the vero i did?

may try and hit this thing tonite...appreciate the info...

electron tornado, voltages would indeed be sweet!!

thanks guys!

[Gus]

EDIT

[petey twofinger]

thats excellent Jimi , good work bro .

i am just gonna throw this out there , i am guessing they designed it for a AA cell , was cost .

9 volt batts were more expensive , i am sure there are quite a few here that remember the radio shack battery club . did anyone ever get anyting BUT the free 9 volt ?  who would , lol .

i think i still have one of those floating round here , a green radio shack 9 volt battery ...

remember when realistic tagged the moog synth and they had one you could mess with in the showroom ?

or how about the trs-80 w/ speech synth module , you could type in " radio shack sucks " and make it loop with dos .

good times .

i know this is really off topic , but i just cant stop now , morning coffee is kicking in so i apologize in advance . here is a great one to do in best buy , if you have the balls .

go to the karoake machine isle , ( this works well with 2 or more offenders ) test all the machines to make sure the mics work , and turn the echo up all the way , shut them off . they should have at least a half dozen models from small to pretty large , make sure you utilize every single ione for it to work properly . now prop the mics up to the speaker grilles and crank all the volumes to max . synchronize your watches , and throw all the power switches simultaneously then walk away as gracefully as possible .

trust me , its freakin awesome , you WILL get asked to leave , but man is it worth it . extra bonus points are possible if you have enough people to activate ALL of the casio demos , at full volume of course , at the same time , or as an encore , if you get away with it the first time and really want to get caught .

[mac]

i am just gonna throw this out there , i am guessing they designed it for a AA cell , was cost .

9 volt batts were more expensive , i am sure there are quite a few here that remember the radio shack battery club . did anyone ever get anyting BUT the free 9 volt ?  who would , lol .

I built a 9v version without the tone control. Just for fun

mac

[Electron Tornado]

When tweaking, I noticed it was not loud enough and there was a simple fix. Just lower or remove the 10K before the tone control. I actually wound up putting a 10K pot there.

I also used a switch between the original input cap and a .033uF which smoothens out some of the raspiness when the drive (50K) is higher up.

Anyway, here's my final version with voltages & notes. If Electron Tornado could post voltages from the original, that'd be killer.

I can check the voltages on the actual pedal later this evening. There are voltages labelled on the Heathkit schematic in Jimi's first post above, if that helps. Q1 collector and Q2 base should be at the same voltage (1v), and Q2 emitter is 1.5 volts, in case it's not obvious.

I had this on the breadboard a while back and found it sounded better with a single transistor stage at the input. Off-hand, I don't recall whether I used a buffer or amplifier. It seemed to do a better job of playing well with others.

Here's something else I wanted to try with this. Take the notch filter circuit from the Univox Superfuzz and a DPDT switch to switch between the normal tone control and the notch. If I recall, my idea was to use a dual gang pot for the tone control, so you could also tweak the notch. I'm not sure just how tweakable the notch filter would be, however.

Come to think of it, I recently heard a pedal by Jetter that kind of reminded me of the TA-28.  I don't recall which one, though.

[pinkjimiphoton]

EDIT

hi gus, thank god i got the email with this post in it...

i like your idea, i'll try running it at 3v...maybe with a lithium coin cell!!

and sub out the 82k for a 100k trimmer, and see what happens.

probably not today, but soon..so stay tuned my friend!

[LucifersTrip]

350 - 400 i can do...tons of silicon trannys in that range. i thought it seemed a little odd to reccomend the A18....IME they are way too hot for a lot of things.
i was thinking ge for q2 to try it,i often will try and put a germ in where i can cuz i just love the sound of them, so far, it seems to be more stable messing with q2 in a lot of circuits than q1.
thanks for the advice! i love hybrids lately...building a LOT of fuzzfaces like that.

preaching to the germ choir!  I still build primarily ge stuff, but the odd silicon one catches my eye. I usually do try germs in si fuzzes that are harsh or very trebly and ones that look like the biasing scheme wouldn't have to be altered too much.

I thought this sounded pretty cool stock so I didn't screw around (except for the volume jack), but if I do build this again, I'll try 100% germanium.

that's awesome lu!! do you mind if i add that info on to the vero i did?

you can always do anything with any of the info I post anywhere...

may try and hit this thing tonite...appreciate the info...

like I always say...the more fuzzes, the better...

[mac]

I have an excel-based bias calculator for this if you want to experiment with vcc.

mac

[LucifersTrip]

I can check the voltages on the actual pedal later this evening. There are voltages labelled on the Heathkit schematic in Jimi's first post above, if that helps. Q1 collector and Q2 base should be at the same voltage (1v), and Q2 emitter is 1.5 volts, in case it's not obvious.

thanx & damn, I actually breezed over that since I already had the schematic...and damn again...It's looks like my fuzz ear is pretty good. I'm really close to the posted voltages.

() = on orig

Q1
.35 (.36)
.86 (.87)
.97  (1)

Q2
.97  (1)
1.20 (1.30)

your orig voltages would still be cool if you have the time...

[LucifersTrip]

i am just gonna throw this out there , i am guessing they designed it for a AA cell , was cost .

that could very well be...and whether the reason they give in the add is bull or not, who knows:
http://i605.photobucket.com/albums/tt137/pinkjimiphoton/Heathkit_Ta28_fuzzbooster.jpg

but one of the coolest things I've always loved about 1.5V fuzzes is not having to worry about the battery. I just checked the voltages for mine, which has had a battery in there for ~ 2 years and it measures 1.53V

edit:
speaking of 1.5V, I use these leds (they are not super bright, but work good enough) for my 1.5V fuzzes
http://www.futurlec.com/LED/LED2PINRpr.shtml
since they're the only ones (and the only color of those type) that I have found that can light at 1.5V without any "pump"

[mac]

I have no idea why you're thinking about a germanium there. I doubt it'll bias well.

Add a silicon diode after both emiters to simulate a silicon tranny voltage drop, and bypass them with a large cap. That and a little tweak of the original network will do it... if leakage is very low

mac

[artifus]

curious about that ad so i googled - $18 1970 dollars in todays money would be around $100 - does that make the heathkit a relative boutique? 

http://www.measuringworth.com/m/calculators/uscompare/

[pinkjimiphoton]

I have an excel-based bias calculator for this if you want to experiment with vcc.

mac

i sooooo don't have a clue how to use excel.

[artifus]

i sooooo don't have a clue how to use excel.

get that printed on a t-shirt and where it with pride.