NKT-275 in a Fuzz Face Clone - What's all the hype about?

[alex192]

Hi guys!

I'm currently looking for some components for my first pedal build - a Fuzz Face.

Now I don't want to come across as a newbie who has to have NKT-275s in order for it to be a true vintage pedal (btw I'm planning on building the FF to specs from late 60s, so Germanium trannies etc.). I pretty much have concluded that there is no way I am going to get some real NKT-275s, so I would like to ask what are the alternatives?

As long as the pedal sounds good, I don't care what trannies I am using. Could anyone give any good alternatives to transistors that sound as good as NKT-275s?

Also, reading around on these forums, it looks as though any low gain germanium transistor will give a classic FF tone, so I am looking at AC128s as alternatives. I know Banzai sells some AC128s, but there are a lot of NOS ones on ebay. If I went for some of these NOS AC128s, are the chances that they are genuine a lot higher than the chances of getting a genuine NKT275? I see a lot of auctions for NOS AC128s; are these real?

Cheers for all the help guys!!

[marlin]

Check out this shop:

http://www.smallbearelec.com/Categories.bok?category=Germanium+Transistors

Tested and ready to go! 4 pages of transistors.

Or you can go on ebay and buy 50 and sort out 1 of that lot that will do for FF build 

[alex192]

Cheers for the link. However, I can't seem to find any AC128s in that list. Could you recommend some trannies that will sound similar to these? Sorry, I'm new to transistors for FF circuits. Give me a page of 12AX7s and I'll happily sort through them!

I've heard about this site in Europe: http://www.banzaimusic.com/Fuzz-Face-medium-gain-transistor-set.html

Has anyone had experience with them?

Cheers!

[R.G.]

I pretty much have concluded that there is no way I am going to get some real NKT-275s, so I would like to ask what are the alternatives?

As long as the pedal sounds good, I don't care what trannies I am using. Could anyone give any good alternatives to transistors that sound as good as NKT-275s?

Even real devices from Newmarket stamped with "NKT 275" are not a sure bet. What matters is the device characteristics, and the part number stamped on the part is no guarantee that the characteristics will be good for a FF sound. This is partly because what went into a FF sound was not known even back in the day they were being made, and partly because the tolerances were so wide on the original devices.

Also, reading around on these forums, it looks as though any low gain germanium transistor will give a classic FF tone, so I am looking at AC128s as alternatives.

Actually, the gain needed is medium to high for germanium. Something around 100 works nicely. People will have other preferences, but between 75 and 150 about covers it. You're right, the actual part number stamped on the can is not important. Buying a pre-tested one from a reliable dealer is the best chance you have.

I know Banzai sells some AC128s, but there are a lot of NOS ones on ebay. If I went for some of these NOS AC128s, are the chances that they are genuine a lot higher than the chances of getting a genuine NKT275? I see a lot of auctions for NOS AC128s; are these real?

These days counterfeits are so common that I am suspicious of semiconductors I buy from real, bona-fide semiconductor distributors. I personally view buying any semiconductor from ebay as a gamble, nothing better.

"NOS" can be cynically viewed as "Not Old Stock"; the term is no guarantee. Even if it means what it says, what does "old" mean? There is - or was - current production of devices labeled "AC128" in some ex-Soviet Block countries. "Old" may mean "five years". And because of the FF mania, the world has been scoured for real old stock NKT275s. Chances of an amateur finding them are about nil.

Beyond that, real FFs were made with real AC128s back in the day, as well as NKT275. And it was common to have one good sounding (by today's standards) FF in a batch of ten or twenty.

Buy your transistors from a trustworthy pro. Banzai and Small Bear are two examples.

[tubelectron]

Hi alex192,

Yes, you can make a true-sounding vintage Fuzz Face without using the NKT275 Ge transistors...

I (and some of my friends - which are newbies) have hand-built several of them, sometimes using nice RI FF boxes as below :



In this FF above, I used AC128 cylindrical European made NOS transistors, home-selected in hfe and Iceo, acoording to R.G. Keen's web article "The Technology of the Fuzz Face" (to be read, indeed !).

As I remember I tested my transistors under 9Vdc, at Ib = 10µA and measured as follows : Q1 was hfe = 88 / Iceo = 100µA, Q2 was hfe = 110 / Iceo = 120µA.

This fuzz face was tested by several hi-level semi-pro guitarists friends (some of them old Hendrix fans) and they found that she has a "to-die-for" FF tone...

I have built another one using 2N527 NOS Ge transistors, with hfe around 90 and Iceo around 150-180µA, and it sounded great too.

I used japanese Ge Toshiba NOS 2SA/2SB trannies as well, with hfe around 120-150 and Iceo 180-220µA with success too.

Following my experience, if you find ANY lo-pwr Ge transistor following the recommendations of R.G. Keen, you will have the expected tone, no matter the reference of the transistor, and maybe no matter the polarity (PNP or NPN).

A+!

[alex192]

Thanks for all these great replies. In terms of the other components (resistors, capacitors, pots etc.), would I be safe just buying brand new, low tolerance parts and shoving them in, or do these also have a large effect on tone? I was under the allusion that the trannies made the biggest difference, and the other components didn't matter as much. Is this assumption correct?

Also, is it easy to mod the old FF circuit to be true bypass with LED (3pdt switch) and wire it up to a 9volt jack? I have done a few true bypass mods before, and I understand that the FF is positive ground.

Thanks!!!

[DougH]

Part #'s on Ge transistors are about as useful as tits on a boar these days. Even if you find the p/n you are looking for, chances are it won't meet your needs. Most if not all of the NOS Ge stock has already been picked over, sifted, and sorted for the ones that are not too leaky and with the gain characteristics that sound good. Chances are you will get a "bottom of the barrel" piece instead. As others have mentioned, in this game you want to concentrate on pieces with the right characteristics and forget the part #'s. Buy them pre-tested and don't be afraid of "unpopular part numbers". Of the Ge's I have, my favorites are some oddball NPNs that sound better than the fabled AC128's.

[tubelectron]

Hi again alex192

Thanks for all these great replies. In terms of the other components (resistors, capacitors, pots etc.), would I be safe just buying brand new, low tolerance parts and shoving them in, or do these also have a large effect on tone? I was under the allusion that the trannies made the biggest difference, and the other components didn't matter as much. Is this assumption correct?

This assumption is correct. A 5% tolerance is perfect for the other components (even 10% for the caps will do).


Also, is it easy to mod the old FF circuit to be true bypass with LED (3pdt switch) and wire it up to a 9volt jack? I have done a few true bypass mods before, and I understand that the FF is positive ground.

Yes. With PNP transistors (NKT275, AC128...) the battery is positive ground - so you need a specific separate wall-wart PSU. With NPN transistor (AC127...) the polarity is negative ground (classical) so the pedal is PSU compatible with others in the pedalboard.


Thanks!!!

A+!

[alex192]

Thanks again!

I think I will opt for the AC128s from Banzai (matched pair), as they look to be a safe bet. When I finish the pedal I might buy various Si and Ge trannies just to try them out, to find the best tone.

Another quick question. Can I wire a negative ground circuit into the power jack as centre negative, as long as it is isolated from all other postive ground circuits, or does the pin have to be centre postive?

[Michael Weidenauer]

There were different kinds of AC128s produced:    http://www.jacquesstompboxes.com/ac128.htm

My favourite FuzzFaces use OC44, OC71 and OC139(NPN ) - all of them in glass containers.

[tubelectron]

Another quick question. Can I wire a negative ground circuit into the power jack as centre negative, as long as it is isolated from all other postive ground circuits, or does the pin have to be centre postive?

Have a look to the ggg website about FF - I think they have the two wiring configuration shown, and even the NPN one.

Well, personally, I wouldn't use external PSU nor led and built my FF in an "at least used-cheap-dead" dunlop FF box. I had one on eBay for 20USD, it was a red dunlop, and it even was mint !!!! You must know that the current drawn from the battery is less than 1mA, so the battery will last a long time... No PSU nor annoying polarity problems required !

[marlin]

I have a bunch of old ones in my stash that I never bothered testing, always bought tested from shops for my FF builds. I guess these are pretty old but not sure:





Going to test them someday....

BTW the 2N1305 i bought from smallbear a while ago sounds excellent in my fuzzface! Not affiliated with Smallbear in anyway, just think they have excellent service.

[alex192]

OK, cheers for all this valuable help. The ggg article looks good, but the pcb is different to the original (I'm sure it is an improved one with bias etc.).

I'm looking to buy the pcb from here: http://cgi.ebay.co.uk/Vintage-Fuzz-Face-Circuit-Board-Clone-Kit-/140420049991?cmd=ViewItem&pt=UK_Guitar_Accessories&hash=item20b1afec47

I am assuming this is a replica of the original circuit, so would it be easy to adapt it to add in an LED and a 3pdt switch, along with posibly a 9v jack, or would you recommend using the other circuit? I would quite like to use the origina; circuit and component values, and perform my own 'mods' to add LED inidcation, true bypass etc.

[newfish]

OC45s work pretty well too - all depends on the Hfe and leakage.

Also helps having a trim-pot to help with biasing...

[tubelectron]

I have a bunch of old ones in my stash that I never bothered testing, always bought tested from shops for my FF builds. I guess these are pretty old but not sure:



Going to test them someday....

marlin,

That's exactly the AC128 I have, the european "cylindrical" ones, and these are New Old Stock, indeed. These have been made by PHILIPS, VALVO, TELEFUNKEN, SIEMENS, AEG, MULLARD, SESCOSEM...

But to test them you may have a reliable equipment - I mean which is ABLE to really measure a Ge transistor (Hfe, Iceo) under a defined Ib. I never found a satisfactory one, so here's my DIY GX-1814 Transistor measurment bench, testing an OC72 :



A+!

[marlin]

I have a bunch of old ones in my stash that I never bothered testing, always bought tested from shops for my FF builds. I guess these are pretty old but not sure:



Going to test them someday....

marlin,

That's exactly the AC128 I have, the european "cylindrical" ones, and these are New Old Stock, indeed. These have been made by PHILIPS, VALVO, TELEFUNKEN, SIEMENS, AEG, MULLARD, SESCOSEM...

But to test them you may have a reliable equipment - I mean which is ABLE to really measure a Ge transistor (Hfe, Iceo) under a defined Ib. I never found a satisfactory one, so here's my DIY GX-1814 Transistor measurment bench, testing an OC72 :



A+!

OMG!!

I was thinking more in testing for leakage with R.G's excellent article! hehe

After that  I'll do this:



Seriously, that's a great setup you have there. Ever tested the Avo Transistor Analyser Mk 2? Don't know anything about it except I've seen it for sale now and then. Would it be sufficient?

[tubelectron]

I was thinking more in testing for leakage with R.G's excellent article! hehe

This is a good start, anyway - therefore it is possible to do more consistent measurements, you guess it.

Seriously, that's a great setup you have there. Ever tested the Avo Transistor Analyser Mk 2? Don't know anything about it except I've seen it for sale now and then. Would it be sufficient?

Thanks marlin. To answer you, I just had a fast look to the Avo Transistor Analyser Mk 2 spec found at :

http://www.shopingathome.com/Avo%20Transister%20Analyser%20Mk%202.htm

It is able to measure the Iceo (the losses), but IMHO you won't usually need the rest of the features, and I think it is probably "collector item" and then expensive. Nonetheless, it won't have the accuracy of the Fluke 87 III and V DMMs... since Iceo is measured in µA DC. I should say : do not waste your money with a "gas-factory" meter, and have a look to a transistor book explaining the basics (Hfe, Iceo, VCE, etc...). There's often measurements diagrams in it, and I didn't do nothing more than use it and mix it to built my GX-1814. After, buy some affordable DMMs and that's done !

[smallbearelec]

Can I wire a negative ground circuit into the power jack as centre negative, as long as it is isolated from all other postive ground circuits, or does the pin have to be centre postive?

I suspect that you are asking if a FF using PNP devices can be wired to play with negative ground pedals on the same PS. It has been tried, it sometimes works and often doesn't, and previous threads on the subject will explain why it's not recommended. Use a battery, or a small, separate external PS. If you use a PS, make sure it has enough filtering or you'll wonder why the pedal sounds like trash. I have a design done for a suitable "Small Wart" and I'm waiting for a shipment of perfboards to clear Customs. Grrrr!

Regards
Steve Daniels

[alex192]

I understand that to avoid ground loops, you need to run positive ground and negative grounds on different loops. I was just asking whether or not you could wire it up as centre negative, but I kind of answered my own question.

In terms of the build, I have ordered all the parts, and chose the AC128 matched pair from Banzai. I will get the pedal working to start with, then maybe change the trannies for some sockets so I can experiment with various others, and possibly change some of the resistors out for bias pots.