These are quite cool and germanium tranny advice required

Gagaryn

These look quite cool, but not very pedal board friendly http://www.ebay.co.uk/itm/141336020781?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I quite fancy putting one of his Supa Fuzz boards in - http://pigeonfx.com/kits.html - but don't have much experience with germanium trannies - would OC75's be a good bet? Or any recommendations for a different kit that might be better? 

frankus

I love the authenticness of this stuff but I don't think OC75s are good for fuzz faces usually used in MK2 tonebenders IIRC - ideally you'd get some matched NTK275, which if you're prepared to pony up £30 for an enclosure should be a doddle from somewhere like mouser - somewere the ideal HFE and leakage are recorded on t'interweb

MattG

What the deals with those kits then?

Are they ready to go? (other than the pot,switch and enclosures) or would you need to buy extra parts?

octatonic

I thought this was going to be about German Trannies.

Don't google that.

jpfamps

OC75 were used in the original 60s Supa Fuzzes, and aren't that hard to find, although they are starting to get more expensive.

Germanium transistors are notorious for their inconsistency.

The Newmarket (NKT) brand are particularly poor quality, so I suspect that NKT275 I suspect was not chosen for the Fuzz Face due to it's sonic qualities but it's cheapness. In the mid 60s cost of the transistors used in pedal would have been significant.

OC75s were made by Mullard and are of much better consistency than NKT branded transistors, however they are still quite variable and so may need testing.

There is an excellent article on testing transistors for Fuzz Faces on RG Keen's Geofex website.

I've not seen any data on what transistor parameters work "best" in the Supa Fuzz circuit, so you may need to do some digging on the internet.

I recently helped a friend of mine make a Fuzz Face using AC107s (which is a high quality equivalent of the NKT275), with excellent results.

We did though make the circuit initially with transistor holders so we could "audition" various transistors before finally soldering them onto the board.

Remember no transistor was ever design to sound good in a Fuzz Pedal, so the "holy grail" may still be out there!

ecc83

Ah! AC107s, H! This forum keeps ripping me back to my teens!

Annoyingly, my boss when I was an apprtce'  (horrible bloke!) served his time at Pye Electronics so we had bucketfulls of NKT transistors of all shapes and sizes. Had I had the presence of mind to just fill an OxO tin (remember those?) I would be well setup now!

A point comes to me. We were always warned to use a heat shunt when soldering such transistors. I do not bother at all with modern components but it must be worth the slight trouble if they are 30quid a pop!

All you need is small, snipe nosed pliers and a lakkyband.

http://www.maplin.co.uk/p/heat-shunt-fr10l

Well bugger me! Maplin's search engine actually found what I was looking for!

Dave.

Gagaryn

Well, the trigger is pulled!

I've decided to put a Tonebender MKI circuit in the enclosure - PigeonFX did the enclosure and kit, pots and jacks (minus transistors) for £50. 

Kit below - 

And I'll use the D*A*M schematic - 

However 2G381 transistors seem to be extinct so I bought 3 tested OC75's and I already have a few AC128's so will have a fiddle and see if I can get it sounding good with some combination of those.

I don't know a lot about fuzz - I built a silicon fuzz face clone which sounds ok but the MKI Tonebender circuit has a bad reputation for being finicky! Any advice welcome.

ecc83

Gagaryn said:

Well, the trigger is pulled!

I've decided to put a Tonebender MKI circuit in the enclosure - PigeonFX did the enclosure and kit, pots and jacks (minus transistors) for £50. 

Kit below - 

And I'll use the D*A*M schematic - 

However 2G381 transistors seem to be extinct so I bought 3 tested OC75's and I already have a few AC128's so will have a fiddle and see if I can get it sounding good with some combination of those.

I don't know a lot about fuzz - I built a silicon fuzz face clone which sounds ok but the MKI Tonebender circuit has a bad reputation for being finicky! Any advice welcome.

Never built a fuzzbox but I would say the first 1meg bias resistor should go to -9V not +9/ground?

The last stage will presumably be signal biased?

Dave.

randomhandclaps

Apologies Dave if I've spotted the wrong one, but the 1M is part of the input filter and Q1 of a Tone Bender is indeed connected straight to the -9V rail.

@Gagaryn - two thing to watch out for, firstly if you can check an accurate gain for Q1 then be careful not to make it too high a gain or biasing the rest of the circuit becomes an arse pain.  The tranny can be pretty leaky but you really want something between 40 up to the very low 60s at most.  Secondly and more obviously solder a pot (or try different size resistors - marking results) in place of Q3 before settling on the final value.  I'm sure Pigeon will include it in the instructions but just in case you are looking for a reading around -6V (off 9V supply), not the half input voltage you might expect with a Fuzz Face. 

Gagaryn

@randomhandclaps I think that diagram is my instructions! Think I could have a problem though - the ac128's I have are all about 100 an the oc75's range between 70 and 120. Would I be better getting a lower gain for Q1. And to check my understanding, is it the 8k2 resistor that I should sub for a 10k trimpot to settle on the final value?

randomhandclaps

Gagaryn said:

And to check my understanding, is it the 8k2 resistor that I should sub for a 10k trimpot to settle on the final value?

Yes.

A transistor around 70 would be great for Q2.  For Q3 go for something between 90 and 105 (preferably right in the middle, but no biggie).  Whether you use OC75s or AC128s for any position really isn't going to make a vast amount of difference (if any audible) to your fuzz.  The only repeatable audible difference I have noticed in various models of germanium transistors is that the zero leakage Russian type tend to have a tighter sound when used in fuzz, which isn't my preference but some people love.

I think you would be better (or by the sounds of it will need to) finding a lower gain tranny for Q1.  You may just about get away with something in the mid 60s range.  The good news is you are looking for one in quite in undesirable range so they will no doubt be abundant and should be cheap.

Gagaryn

Excellent advice - you've saved me a lot of research time! I know now't about fuzz circuits. I've taken a belts and braces approach - asked the seller of the OC75s if he can supply the values you mentioned and also bought an AC128 with a gain of 50-55. Is their a way to measure these with a standard dmm?

randomhandclaps

There is but you need a couple of resistors.  A 2.2M and a 2.4K, obviously it doesn't make if you make up these value use a combination of resistors.

usedtobe

octatonic said:

I thought this was going to be about German Trannies.

Don't google that.

Too late..!

Gagaryn

randomhandclaps said:

There is but you need a couple of resistors.  A 2.2M and a 2.4K, obviously it doesn't make if you make up these value use a combination of resistors.

Cheers I will have a look.

Evilmags

German Trannies are quite expensive. Probably better off with Thai or brazillian in terms of bang for buck...

Gagaryn

We make our own here in Scotland. They are an acquired taste - I don't think they sound right.

Gagaryn

Well I finally got round to building this and I think I've been lucky, it sounds great! I tried it with a few different combinations of transistors and finally settled on 3 OC75's (pictures were before it was finalised). I bought a trio of these with gains of 50, 75 and 100 and I prefer the sound with the 50 in Q1, the 100 in Q2 and the 75 in Q3. I tried it with Q2 and Q3 values reversed but it was a bit too smooth and sustained for ever; it still sustains for ages before it starts to splutter out the way I have it now. The attack knob has little effect after about 11 o'clock but that seems to be correct for the Mk1. My voltages all seem good but the ears are a better test anyway - it seem's to be sounding in the ball park judging by this video - 

Min sounds most like the latest one in the video, maybe a tad smoother. I'm really surprised by the volume boost available - unity is at about 11 o'clock.

Here's a couple of pics -