Author Topic: AC128..... incredible low "real" gain!!! (Read 12511 times)

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

alderbody · « **Reply #1 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!

MartyMart · « **Reply #2 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

MM.

zjokka · « **Reply #3 on:** May 24, 2006, 07:29:58 AM »

Quote from: alderbody on May 24, 2006, 03:30:04 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

MartyMart · « **Reply #4 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

alderbody · « **Reply #5 on:** May 24, 2006, 08:20:24 AM »

Quote from: zjokka on May 24, 2006, 07:29:58 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!

pupina · « **Reply #6 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?

petemoore · « **Reply #7 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.

analogmike · « **Reply #8 on:** May 24, 2006, 12:54:51 PM »

Quote from: 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 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!

brett · « **Reply #9 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

petemoore · « **Reply #10 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.

pupina · « **Reply #11 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

alderbody · « **Reply #12 on:** May 25, 2006, 06:56:33 AM »

Quote from: pupina on May 25, 2006, 06:38:09 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!

alderbody · « **Reply #13 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.

pupina · « **Reply #14 on:** May 25, 2006, 07:52:36 AM »

great! thanks alderbody!!

amz-fx · « **Reply #15 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!

regards, Jack

JimRayden · « **Reply #16 on:** May 25, 2006, 08:52:35 AM »

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

----------
Jimbo

mac · « **Reply #17 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.

Quote from: JimRayden on May 25, 2006, 08:52:35 AM

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

analogmike · « **Reply #18 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!!!

petemoore · « **Reply #19 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'...

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Author Topic: AC128..... incredible low "real" gain!!! (Read 12511 times)