1176 output transformer

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Stoffe

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Joined
Sep 29, 2004
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4
Location
London
Does anyone have any good information on the (Bill Putnam) custom built output transformer used in the original 1176?

What was uniqe with it? Schematic?

As far as I know the output transformer in the reissue 1176 is another type, and not the original one. Why was it so hard to make an exact replica?

/Stoof

:cool:
 
If Winston O Boogie would come out of hibernation, he could definatly tell you a lot about this transfomer thing.
I lost his number, out of sub-concious respect i guess.
 
I imagine the older one with the tertiary (feedback) winding on the split secondary is the one hardest to replicate. The later xfrmr for the AB circuit was a more standard type, also used in their LA4, 1178, BLA-40, broadcast consoles, etc.

The UA reissue is supposed to be of the earlier class A output, which used the tertiary winding on the secondary.
 
I bought a pair of repro 1176 trafos a while back. I have not yet used them (lazy me!) but they are available in the US...at least they were then and the price was very reasonable. I don't know who actually wound these. I don't want to make this easy to discover for fear of making this company upset over a bunch of trafo requests, though they might not mind at all. I'll let you guess for now where this might be. PM me if you have a guess.

I am wanting to use these for 1108 mic pres though I cannot find out enough info about the input trafo.

HTH!
Charlie
 
[quote author="cjenrick"]If Winston O Boogie would come out of hibernation, he could definatly tell you a lot about this transfomer thing.
I lost his number, out of sub-concious respect i guess.[/quote]

He must be busy with the REDD project.
 
Thank you all! :razz:

Speaking about the 1178...how many different revisions of the 1178 were made? Which model of the 1176 is it based on?

I have used the 1178 a lot but never the 1176...and people say that they sound very different. Is this due to the transformers?

Peace!

/S
 
The 1178 is quite different in that most of the circuit is done with op amps rather than the descreet transistors that you get in the 1176. Maybe half of the 1176 revisions have an op amp input rather than a transformer input, but the rest of the circuit is traansistors
 
For the class-a-units:

Would there be a chance of using two trafos in parallel on the output? One for the audio-output and one for the feedback-loop. Could be easier to find two seperate trafos to fit here than the one special 1176-class-a type, right?

Chris
 
[quote author="chriss"]For the class-a-units:

Would there be a chance of using two trafos in parallel on the output? One for the audio-output and one for the feedback-loop. Could be easier to find two seperate trafos to fit here than the one special 1176-class-a type, right?

Chris[/quote]

no...this wont work well. since the o/p runs classA and dc coupled to the driver transistor it must be specified to eat some amount of dc current thru the primary winding (gapped core). also, besides saturating the transformer(s) with dc, there may be crazy phase things happen depending on what transformers are used and you might get positive feedback at high frequencies (oscillation).

steff
 
..also the WHOLE point of a tertiary winding is that it has to be wound on the same core so that loading effects in the core (influenced by the secondary load, which may well be reactive) should also affect the tertiary. Basically the tertiary 'listens' to the core which is modified by the secondary load. -Make it a seperate transformer and it can't tell what's going on; it can't 'listen' any more.

Keith
 
Whats the part number on that 1176 output? I thought I tore one of those up already.

:?: :?
 
the class A 1176 output transformer (also used in the 1108) is a complicated beast. there are two 600 ohm "input" windings that go to different points in the line amp circuit, and then two 150 ohm "output" windings that are generally tied together in series to form one 600 ohm output winding. so from that perspective, it is generally a 1:1 output. there is also the tertiary winding, which has a 25:1 ratio in relation to the other windings, and puts the transformer effectively inside the feedback loop of the line amp.

the whole thing is wound bifilar, on an iron core of EI75 lams. right now, the only way i know to get one is to buy a purple mc76 kit. if CJ has taken one apart, he could share that info, and i'm sure some friendly trafo manufacturer could make some up for the group.

ed
 
thanks ed,

that sounds like the class-ab-version is more realistic to reproduce.
where do you have these informations from? measurement?

regards

chris
 
I have a few of the original class AB output transformers, nothing special there, IMO not worth the trouble to back design. Just pick something from cinemag, it will be better...

dave
 
Cinemag do the Class A o/p for sure!
Email David, he is a very, very nice bloke and will do all he can to help.

In terms of his love for transformers he's kind of like the US version of Brian Sowter...

chef
 
[quote author="edanderson"]right now, the only way i know to get one is to buy a purple mc76 kit.[/quote]

I hope I don't cause a problem by saying I have bought just o/p trafos from Andrew before. They were very reasonable too...

HTH!
Charlie
 

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