DIYstompboxes.com

DIY Stompboxes => Building your own stompbox => Topic started by: pupina on May 24, 2006, 03:01:27 AM

Title: AC128..... incredible low "real" gain!!!
Post by: pupina on May 24, 2006, 03:01:27 AM
I just bought in E-bay a twenty AC128 NOS made by Tungsram, 20 pieces for 17 bucks ...I was very happy: enough tranny to get 2 or3 Fuzz to build at least!!!
Yesterday night i tested all this 20 trannys (and other 10 AC128 bought one year before...) and i found, (following the article of R.G. "Picking transistors for FF clones") that the MAXIMUN gain for Q2 in my hands was only  90 Hfe!!!!
Incredible! most of them had a normal leakage but a ridiculous gain : 38, 45, 61...only two pieces had 70/71 Hfe and other two had 90....no one was exceeding 90 of Hfe: in other words no 120 Hfe for the perfect Q2.....
Now I'm very sorry....maybe i don't understood the article (because the language...my English is not certainly perfect!!) or maybe I only have been unlucky...
what do you think about a 70 (Q1) - 91 (Q2) combination for a decent Fuzz Face?
May I use 3 "selected" stupid 63 Hfe transistors for a Tonebender Mark II?
Please tell me something that reassuring me.....over 20 Euro for 2 or 3 decent Q1......and Q2? where could I find one!?!

Thanks in advance; R.G. Keen, please, help me in some way!
Ciao
Title: Re: AC128..... incredible low "real" gain!!!
Post by: alderbody on May 24, 2006, 03:30:04 AM
Hey don't panic!

since the leakage is within spec, try some of your AC128's in a FF circuit and if you like the sound it's OK...

I have a low gain AC128 pair in the FF i currently use and i really like it.

If you want matched AC128's try banzai. (http://www.banzaieffects.com/home.php)

There are lots of them to be found there.
Olaf has 3 "gain levels" of matched FF transistors (low, mid, high) at 6.50 euro each. (inc. tax for inside EU)
I have one of each and they all sound great, yet slightly different. (i prefer the low gain set, while the normal FF would be the medium)

btw, if you haven't built your FF yet, get the reverse audio Fuzz pot (1k C taper) from Small Bear or banzai.
Much better control IMHO.

experiment!   :)
Title: Re: AC128..... incredible low "real" gain!!!
Post by: MartyMart on May 24, 2006, 04:00:46 AM
RG has gone over this many times, you will probably NOT get any decent NOS trannies from
Ebay .... or anywhere else apart from the specialists like Banzai and smallbear.
Buying "known/tested" gain range sets will always be a good idea .

I bought around 100 AC128's and 127's two years ago and got a handful of useable ones from
them, I just had to throw away 50/60% of them ( I dont need them for diodes!! )
Ebay trannies will have been picked through for all the best ones, at least once !

I've had Banzai "gain range" sets and also smallbear "matched" sets, both have been great.

The only ones I got lucky with were the CV7112 (OC140's) off ebay which are millitary spec
Ge NPN.
90% of these were good to go :D

MM.
Title: Re: AC128..... incredible low "real" gain!!!
Post by: zjokka on May 24, 2006, 07:29:58 AM
btw, if you haven't built your FF yet, get the reverse audio Fuzz pot (1k C taper) from Small Bear or banzai.
Much better control IMHO.

I got a cue here, was building my fuzz last week and all worked out fine. Except: first i had the gain pot (5k linear) wired in the wrong way. then the gain was very controllable. when I changed that, real gain only started kicking it at 8 or even higher.

What is this 1k C (?) taper for?
------

On topic: indeed no one says the trannys have to be one high one low. Same gain levels work also..

ZJ
Title: Re: AC128..... incredible low "real" gain!!!
Post by: MartyMart on May 24, 2006, 08:19:33 AM
should sound better with Q1 lower than Q2
In the three tranny tonebender, it's Q2/Q3 same deal.

MM
Title: Re: AC128..... incredible low "real" gain!!!
Post by: alderbody on May 24, 2006, 08:20:24 AM
What is this 1k C (?) taper for?

It (really) helps you gain better control over Fuzz.

"C taper" is the reverse log.

You can find it here:
http://www.smallbearelec.com/Categories.bok?category=Potentiometers+and+Trimpots  

at the bottom of the page, or here:

http://www.banzaieffects.com/product.php?productid=17320&cat=400&page=1


Really works!
Title: Re: AC128..... incredible low "real" gain!!!
Post by: pupina on May 24, 2006, 10:53:17 AM
Ok guys, thanks to all....but my last question is : can I have a good sounding FuzzFace with a couple of AC128 transistors having
Q1=71 Hfe and Q2 =92 Hfe?
Title: Re: AC128..... incredible low "real" gain!!!
Post by: petemoore on May 24, 2006, 11:54:08 AM
  Yes.
  If you socket the Q's, and trimpot Q2,  you can directly hear the differences different gain Q's make to the circuit.
  Also an added '1rst transistor' can be put into service...[for 3 total, and will give more of a Tonebender type tone], 're'-biasing the first transistor may be necessary.
Title: Re: AC128..... incredible low "real" gain!!!
Post by: analogmike on May 24, 2006, 12:54:51 PM
Ok guys, thanks to all....but my last question is : can I have a good sounding FuzzFace with a couple of transistors having
Q1=71 Hfe and Q2 =92 Hfe?

Yes! :)

Quote
AC128

No :(

(imho)

The only fuzzface to ever use an AC128 is the terrible grey UK made reissue, and of those about 30% had at least one transistor installed upside down. Including the one pictured in the manual/sales flyer! But the sound was so bad it made little difference which way the trans were installed so they were not caught by the builder.

You will get much better tone with the small bear generics than any AC128 that I have ever tested.

Have fun!

Title: Re: AC128..... incredible low "real" gain!!!
Post by: brett on May 24, 2006, 10:46:44 PM
Hi.
I respect Mike's huge experience, but I've used a fair range of GE transistors in fuzzfaces, and my current setup uses a pair of AC128s with DC gain (Hfe) of 90 and 150.  It is a little bit of a high-gainer when fully cranked, but in general it's excellent.

IMO the main problem with finding good AC128s is that they are getting rare, not that they they never existed.  Mine have come from a large pool (about 90 if you count 60 from e-bay that were ALL faulty or leaky).

I feel that the AC188 may be overlooked.  A good proportion (about half) of the 20 or so that I've tested have low leakage (<200uA) and gains between 50 and 180.  They also sound good IMO.
cheers
Title: Re: AC128..... incredible low "real" gain!!!
Post by: petemoore on May 24, 2006, 11:08:14 PM
  AC128's I got a few weeks ago and tried out are noisy, raw sounding, and flabby on the low notes.
  I put in a nice 'ol standby with gain of 87 in Q1, and an NTE158 in Q2, hfe 142.
  Anymore I just test 'em in the DMM's hfe checker, and can stick 'em in right after to tell how much I like them, with more focused sound and less noise seemingly related [comments?]...when a 'right' gain for the other's gain is used, the sound perks up [IMO], and it becomes pretty obvious when a great FF pair is in it.
  I try not to buy leaky Ge's, preferring to buy from SB or BYOSB, finding it is easier to get decent results when none of the transistors interviewed have leakage problems...other than that it's pretty easy to get fine FF tones, using a buncha transistor gains to find the sound that clicks...I've been remembering well now that I use rolloff and to test the circuit using the rolloff...basic hard fuzz seems pretty easy to get...high gain transistors'll do it every time...perfect sound of pick attack, and cleanup @ guitar volume that still sounds cool demands a bit more attention to every detail...cap values...transistors...bias adjust.
Title: Re: AC128..... incredible low "real" gain!!!
Post by: pupina on May 25, 2006, 06:38:09 AM
OK guys, according to ours advices i just made an order from Small Bear about a double set of trannyes: a couple of selected ones for Fuzz Face and a trio of selected transistors just  right to build a Tone MK II....i hope i do the right thing!
last question: Small bear ships in Italy???? because i pay w Paypal but i no one ask me to insert my physical address in Italy....I'm a bit confused
Thanks to all that replyed to my post
Title: Re: AC128..... incredible low "real" gain!!!
Post by: alderbody on May 25, 2006, 06:56:33 AM
last question: Small bear ships in Italy???? because i pay w Paypal but i no one ask me to insert my physical address in Italy....I'm a bit confused
Thanks to all that replyed to my post

I bet he does. I live in Greece and i ordered quite a lot of times from Steve and i never had any problems.

If you have a paypal account then your address is registered in there so the seller will know where to ship. Don't worry!  ;)
Title: Re: AC128..... incredible low "real" gain!!!
Post by: alderbody on May 25, 2006, 07:04:49 AM
Besides, if Steve finds out that he doesn't have enough shipping data he'll contact you.  8)
Title: Re: AC128..... incredible low "real" gain!!!
Post by: pupina on May 25, 2006, 07:52:36 AM
great! thanks alderbody!!
Title: Re: AC128..... incredible low "real" gain!!!
Post by: amz-fx on May 25, 2006, 08:39:38 AM
The AC128s that I sell come from a sealed Tungsram bag that I opened. They have not been sorted or picked through...

I will mail them to anywhere in the world!  :icon_mrgreen:

regards, Jack
Title: Re: AC128..... incredible low "real" gain!!!
Post by: JimRayden on May 25, 2006, 08:52:35 AM
I'd appreciate if anyone would drop a few words about 125's too.

----------
Jimbo
Title: Re: AC128..... incredible low "real" gain!!!
Post by: mac on May 25, 2006, 10:20:37 AM
Recently I posted my experiences with Texas Inst 2N388, because gain was below specs. Includes RG comments.
http://www.diystompboxes.com/smfforum/index.php?topic=45433.0
then added a somehow related post,
http://www.diystompboxes.com/smfforum/index.php?topic=45481.0

I built TB MKII that sounds great even though gain is below the reccomended range. I also tried hfe:50, 61 FF and it sounds fantastic. You could not tell the difference between this and (70-90,90-120) magic pair.

I'd appreciate if anyone would drop a few words about 125's too.

----------
Jimbo

I guess it is a matter of personal taste. It will probably sound almost identical to an AC128. Anyway, if you saw them on ebay be careful.

Different transistors have different tonal response. I don't care if it is an AC128, 2N388 or NKT275. They all have a beautiful side. I only care about too much leakage and defective devices.
My personal choice for TB, FF and RM is the 2SA102/103 CA or DA (matsushita). I doubt many people here would even consider using this transistor, or heard about it.

mac
Title: Re: AC128..... incredible low "real" gain!!!
Post by: analogmike on May 25, 2006, 10:47:06 AM
maybe I was a little tough on AC128s for 2 reasons:

1) the misunderstanding that they were often used in the original pedals in the 60s (so far zero out of a few hundred germanium fuzzfaces I and my friends have seen have had AC128s)

2) all the AC128s I bought from several ebay and non ebay sources, and all the ones I pulled from over one hundred reissue UK made arbiter england fuzzfaces sound terrible and have poor specs. I lost a lot of money buying these. And I thought IF there were any good ones available in the UK, then the company making the the reissue fuzzfaces in the UK would be using the good ones.

have fun and be fuzzy!!!
Title: Re: AC128..... incredible low "real" gain!!!
Post by: petemoore on May 25, 2006, 11:24:54 AM
2SA102/103 CA or DA
  >>Iv'e never heard mention of these device #'s.
  >>Any/All...as long as they sound great.
  I've sort of developed the ability to just plug a transistor into the DMM's hfe reader, and then into a FF or RM transistor socket and tell right away if it's a device I'm going to like working with...and prefer starting with 'decent' candidates [from BYOSB, SB, AMZ, even NTE].
  A decent FF with Thick Saturated Fuzz can be made pretty easily, may be noisy...
  But one with excellent guitar volume gain rolloff, Thick Saturated Fuzz, and low-ish noise would be the next level, just a little more fiddling than yer basic slapped together [with 'whatcha got available' FF...that extra diddling is what it takes to 'FF the light fantastic'...
Title: Re: AC128..... incredible low "real" gain!!!
Post by: amz-fx on May 25, 2006, 08:49:42 PM
Custom pedalmaker Jacques has this to say about the AC128 (which he uses in his Mercer Box):

http://www.geocities.com/stompbox2001/ac128.htm

-Jack
Title: Re: AC128..... incredible low "real" gain!!!
Post by: Fret Wire on May 26, 2006, 12:22:05 AM
maybe I was a little tough on AC128s for 2 reasons:

1) the misunderstanding that they were often used in the original pedals in the 60s (so far zero out of a few hundred germanium fuzzfaces I and my friends have seen have had AC128s)

2) all the AC128s I bought from several ebay and non ebay sources, and all the ones I pulled from over one hundred reissue UK made arbiter england fuzzfaces sound terrible and have poor specs. I lost a lot of money buying these. And I thought IF there were any good ones available in the UK, then the company making the the reissue fuzzfaces in the UK would be using the good ones.

have fun and be fuzzy!!!

Mike, I haven't tested as many as you've gone through, but enough to see a pattern emerge.

What I've found with a lot of AC's is that they are unstable now. They will show low leakage and proper gain, yet are internally (electronically) unstable. They'll bias up odd too. You can get Q2's collector at 4.5v, and Q1's emitter at zero, but the other voltages are slightly off from the ideal proportions. And they sound like ass: flabby, unresponsive, and too grainy. Don't clean up as well with the volume knob either.

Maybe RG can chime in with the proper electronic term for this internal breakdown. It's like the transistor is in a transitional stage where it still shows low leakage and good gain, but it is actually dying in front of you. It's like the stage the transistor goes through just before it opens up and goes high leakage.

You'll recognize this when you test them. Any type, not just AC's. A good stable Ge, when tested, will within seconds, indicate to a low leakage and it's gain of x. It will then hold on those gain and leakage numbers with almost no fluctuation on the DMM for a decent length of time. I've had good ones hold the same number for over a minute. These are the trannys that sound real good, bias up easy to nice proportionate voltages, clean up good with the volume knob, and hold their bias voltages (don't require re-tweaking every other month).

An unstable Ge will start to settle around a leakage number which may be low, and a particular gain (x), but never actually settle to any one reading. Your meter will never sit still on any one reading. It will always be in a state of fluctuation. If you leave the device on the tester long enough, the leakage will then start to climb up. Not necessarily over the limit for a good fuzz, but it will start to climb nonetheless. These are the Ge's that always seem to bias a little off, don't ever sound right, and are super temp sensitive (worse than normal). And real noticeable in a rig that is not only overdriven, but pushes some air also.

I might as well state the obvious about the above testing scenarios. I'm not talking about the initial heat induced flucuations from handling the devices with your hands or testing them in front of a heating duct. Use tweezers, gloves, and a stable temp room to test and an unstable tranny will still show the same symptoms.

Judging from the descriptions and voltages of a lot of fuzz posts I've read on the forum, I get the feeling a lot of people have used these unstable types. You order trannies, build RG's tester, they test around the right gain and leakage numbers you read about, then you build it and bias it, but it just doesn't seem to sound right. Sound familiar?

Getting back to AC's, in my testing I've found more unstable Ge's with the AC and OC types than I have with some of the american types, especially TI's. But I've also found that any stable Ge of the right gain and leakage sounds good, regardless of the brand. I have one of the original Mayer FF's from the early eighties that still sounds good today. It has BEL AC 128's. It's gotten a little tired over the years: Q2's collector is down to 3.75v. This tells me that these were very stable devices to begin with, and have very slowly increased in leakage over the years. Wish they would all hold up that long.

I think that back in the sixties and seventies, the playing field was level with all the Ge's. Now, forty years later, it appears to me that due to differences in manufacturing methods, some brands of Ge's have survived time better than others. Some brands seem to have yeilded more devices that are still stable today compared to other brands.

I think that not recognizing unstable devices has lead to alot of the brand preferences you read about hear. In my experience, good stable Ge's are all so close in freq resp that they sound boringly alike when properly biased up.

As an example, when Joe Davisson and Pete Snowberg put up the Fuzz Calculator on Joe's site, I decided to test it against my own biasing. Needless to say, it works very well. Anyways, I used Ge's that I tested and knew to be stable. I used pairs ranging from 40/60 hfe to 225/250 hfe and all different brands. After biasing, I put them in my fuzz jig, played them, and they all sounded identical. Even though they ran from a 40/60 pair to a 225/250hfe pair, and were different brands, every pair had two things in common. They were stable, and they had identical biasing voltages. Obviously, the different pairs required different resistances for Q1 & Q2's collectors. They all had the same sound characteristics, clean-up ability, and pick response. You would have failed a blind test trying to pick out one gain range or brand.

When I read a post using all these descriptive timbre type differences between Ge brands, I figure the poster has either an unstable pair and doesn't realize it, or has not biased one pair correctly versus the other. 

As time goes on, we're going to find more Ge pairs that will test proper gain and leakage, but are unstable.

Ge's are like people, they start dying the day they were born. :icon_sad:

 
Title: Re: AC128..... incredible low "real" gain!!!
Post by: zjokka on May 26, 2006, 05:40:41 AM
finding good Ge transistor in Europe isn't easy. the other day at the electronics store the was a 17 year old guy in front of me, starting on his first fuzz box, asking for GE trannies, being laughed at by the guy behind the counter -- "your're asking for components 40 years old". In the end he did return with some AC188s or so which is sold at 1.5 EUR a piece.

This guy laughed at me about a year ago when I asked for the same item. They certainly didn't have it. By now I know better.

I did get lucky in one store and got two usable (as far as gain is concerned) AC128s (gains 85 and 135) which I've used in a PNP negative ground Fuzz breadboard this morning. I got great gain, but apparently much less volume than I got used to when experimenting with silicone NPNs in the runoffgroove multiface setup. I don't know whether it is because of the PNP config, the different schematic, or the nature of the GE transistors.

I bought a whole bunch of different GE trannies, which I am about to test. I bought a PEAK component tester of Ebay, and it was the great deal, at least one electronics store let me select the transistors before purchase.

zj
Title: Re: AC128..... incredible low "real" gain!!!
Post by: amz-fx on May 26, 2006, 07:24:34 AM
Quote
But I've also found that any stable Ge of the right gain and leakage sounds good, regardless of the brand.

That has been my experience as well...

regards, Jack
Title: Re: AC128..... incredible low "real" gain!!!
Post by: mac on May 26, 2006, 08:02:28 AM
FretWire, you have resumed my experiences with the ACxxx family very clearly. If I were looking for AC128s I will buy them from a good source.

I just want to add that fortunately there a lot of good 2S jap germaniums and some 2Ns in my country at a very good price, under a dollar.
So I have quite a collection of germaniums, most of them ( 99% ! ) stable and ready to rock. I'm talking of Toshibas, Matsushitas, Sanyos, Hitachi, some euros and americans if I dig deeper, etc., intended for different applications, ie, driver stages, IF, RF, power, etc., and with different maximun Ic & voltage and transistion frequency. Being stable they are easy to bias, and above all they sit at a fixed collector voltage next time you turn it on, in the abscence of a drastic weather change of course. And they all do the things one expect from a FF. But not all of them sound the same. For example, a couple of 2SB172 sound dark as the 2SD352, 2SD72k & 2SB77, a pair of 2SA49 or 2SA53/52, 2SB65 are more trebly, less farty and roll back differently, two 2SA101/102 or 2N388 have a wider freq response, and so on. And more, silicons do sound different. A pair of BD139, MPSA42 or 2N2219 have their own flavour.

Not being a "tone purist" (lucky me!) or whatever that means, I look for a focused fuzz, not for Jimi's fuzz in that particular song. In fact, of the 3 Ge examples I mentioned above I like them all, maybe the 2SA102 or 2N388 is my favourite, but if I were not so lazy and have more time I will build all of them to enjoy their different tonal characteristics.

As this is a very subjective matter my point is: Which is the best??? None. You like it? Cool! Use it! Who am I to judge your tone?


mac
Title: Re: AC128..... incredible low "real" gain!!!
Post by: Paul Perry (Frostwave) on May 26, 2006, 08:11:51 AM
I just want to add that fortunately there a lot of good 2S jap germaniums and some 2Ns in my country at a very good price, under a dollar.
mac

Bet I wasn't the only person to click on Mac's details to check his country :icon_wink:
Glad there are SOME components you can get in South America!