bluebird

UTC O-12 compared to A-21
« on: September 29, 2004, 04:18:14 AM »
for reference:

http://www.waltzingbear.com/Schematics/UTC.html

the A-21 is 50-200-500 ohms primary AND secondary.
the O-12 is 50-200 ohms primary and 50-200-500 ohms secondary.

the O-12 is used in the 1176 backwards as input. 500 ohms to 200 ohms.

I installed an A-21 with the same configuration except I used it normaly with the primary being 500 and using the 200 ohm tap on the secondary. same thing 500:200 step down.

The Problem:

with T-attenuator installed I start getting distortion when going into medium compression. I can only get about -3 or -4 db reduction before distortion. this is feeding it with numourous types of sources.

So what gives? I would think the A-21 would be able to handle more than the smaller O-12?

should I filp the A-21 around and use the secondary as input? I don't see how that would make a difference though.

the good news is the distortion actually sounds really good... I just wouldn't want it on everything.

Ideas?


UTC O-12 compared to A-21
« Reply #1 on: September 29, 2004, 09:44:31 AM »
Bluebird,

I think I remember reading somewhere (ssltech?) that leaving the meter reading GR while compressing can cause some distortion and that you have to switch the meter to read OP. Could that be causing your distortion?
Seth

The definition of insanity: "Hey, this thing could be really cool - if I had the money to fix it up, which I don't, but if I did it could be really cool - if I had the time, which I don't, but

bluebird

UTC O-12 compared to A-21
« Reply #2 on: September 29, 2004, 03:19:44 PM »
Hmmm, I don't know I'll have to give it a try.

maybe, I have to recalibrate the fet now that the input impedance is different. I haven't set it since it was a solid state front end.

I noticed it playing a bass into the G9 then into th G1176...like I said the distortion is nice, especially on bass.

thanks Seth

CJ

UTC O-12 compared to A-21
« Reply #3 on: September 29, 2004, 06:08:40 PM »
Make sure you wire it like the manual says for the 200 ohm tap.
If you only use 1/2 the winding, you can unbalance the core.
This will show up as distortion on the lows.
There are two coils inside the A-21.
Yes it should handle more power, much bigger core.
cj
And stay off the bicycle!
 :razz:
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

bluebird

UTC O-12 compared to A-21
« Reply #4 on: September 29, 2004, 06:50:55 PM »
Thanks CJ,

I'm pretty sure I wired it correctly but I'll check again....

Oh, and I'll be sure to be carefull... :green:

soundguy

UTC O-12 compared to A-21
« Reply #5 on: September 30, 2004, 02:00:17 AM »
my non technical comments:

an a21 sounds ridiculously larger than an 0-12 which I think makes stuff sound more compressed and in your face in comparison.  I have many 0-12 and a-20/a-21's in a box, so Ive done that comparison quite a bit.  Its possible that the A21 is passing more low frequency than the 0-12 let into the circuit, so that could be the beginning of your problem.

Does the distortion remain constant as you change the release time?  I often use an 1176 as a fuzz box for bass with the fast release, is it possible that that distortion has always been there and this is the first time you've noticed it?  do you have an 0-12 you can A/B with?

I would recalibrate the unit and see where you are, my guess is that the wider frequency response is probably the first source.  Put an adjustable hipass on the bass before the 1176 and see if the distortion goes away if you cut off everything below 65 hz or so, I would think that might approximate what an 0-12 would do.  To my ears, an a-21 is way extended on the bottom, I dont know what the published specs are on those two transformers are though.

some help I am.

dave

chips are good with dip...

bluebird

UTC O-12 compared to A-21
« Reply #6 on: September 30, 2004, 03:43:18 AM »
I had an Altec 600:600 line transformer in there for a while and I don't think there was as much distortion. At least I didn't notice it. there is a 270 ohm termination resistor so it worked just fine. I just thought an A-21 was closer to the original circuit. what your saying makes sense though. maybe thats why 1176's tend to brighten things up or give things a little edge.

I don't have an O-12 to compare.
I'm going to try everything out tomorrow....low cut/calibration...

CJ

UTC O-12 compared to A-21
« Reply #7 on: September 30, 2004, 03:13:50 PM »
Do you have a scope?
If so, just scope it right after the input x-former and see if the distortion has reared it's ugly head. If no, then move it on down the line.
cj
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

bluebird

UTC O-12 compared to A-21
« Reply #8 on: September 30, 2004, 04:05:34 PM »
good Idea, I have a scope. I don't think the actual transformer is overloading. I think it has to do with the FET.

ap123

UTC O-12 compared to A-21
« Reply #9 on: March 27, 2007, 02:37:07 AM »
Is responding to a thread 2.5 years after the last post in bad form?

Did you end up getting the A-21 to work to your likings?


NewYorkDave

UTC O-12 compared to A-21
« Reply #10 on: March 27, 2007, 08:47:25 AM »
Bluebird hasn't been seen around here in a long time. In fact, I was psyched when I saw this thread pop up today... I thought he'd come back.

SSLtech

UTC O-12 compared to A-21
« Reply #11 on: March 27, 2007, 08:53:51 AM »
Quote from: "NewYorkDave"
In fact, I was psyched when I saw this thread pop up today... I thought he'd come back.

+1.

I was going to ask him how family life is... For relatively few posts he contributed A LOT!!!

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

NewYorkDave

UTC O-12 compared to A-21
« Reply #12 on: March 27, 2007, 08:56:04 AM »
I just checked... His last post was in Feb. of 2005, over two years ago.

Wherever he is, I hope he's having a good time.

kato

UTC O-12 compared to A-21
« Reply #13 on: March 29, 2007, 07:22:09 PM »
Quote from: "bluebird"
good Idea, I have a scope. I don't think the actual transformer is overloading. I think it has to do with the FET.


Magnetized core on the A21? Could also produce low end distortion.

It would be interesting to hear the solution if you wander around these parts again someday.


 

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