Peavey VMP-2 Transformer Output Problem
garyvee
The corresponding unbalanced signal is fine. I tracked the problem
down to the output transformer by swapping channel 1 and 2
transformers. The transformer is marked with DB-348 and 70500348
number codes.
I tried searching the web for information on replacement transformers
but found little if any help. I sent an email to Peavey parts about
replacement but it seems unlikely they would carry parts for a long
discontinued product.
I did find a Jensen model JT-10K61-1M but it is "Not designed for
single ended Plate circuit operation" which may not be suitable for
the VMP-2. Here the link to the Jensen transformer:
http://www.jensen-transformers.com/datashts/10k611m.pdf
Any advise on replacement transformers or the Jensen would be much
appreciated.
Gary V
Mark
Does the VMP use a single ended output?
Is it DC coupled to the transformer such that the current that feeds
the tube passes through the transformer?
If yes to both questions then you need to find a tranformer that can
support that amount of DC current in the primary without saturating.
If the tube is fed though a plate resistor and the transformer is AC
coupled to the tube, then there will be no DC current through the
tranformer and any one with the appropriate turns ratio and power
rating will work.
If you can post a schmeatic for the VMP we could be more specific.
Mark
PStamler
If I recall correctly, the VMP2 has a push-pull output, not single-
ended, so the Jensen would probably work fine, and would be a major
improvement over the stock transformer.
When I reviewed the VMP2 I found that the unbalanced output was a
*lot* cleaner than the balanced. Perhaps the Jensen will fix that, but
if you can live with unbalanced output, it's the cleanest way to use
the VMP2 by a long shot.
Peace,
Paul
Richard Kuschel
You'd be surprised what Peavey carries for replacement parts. Call
them, have your credit card ready,
garyvee
I don't have the schematic. I bought the unit used which included an
Operating Guide and doesn't offer much technical information. Thanks
for the helpful input though. I think if I can measure the output for
DC. I intend to call Jensen to inquire about a replacement since they
are such a great resource of information and products.
garyvee
Paul, I saw your comment when I did my web search. I actually have
been using the unbalanced output for some time but decided to
investigate a fix for the balanced output. Based on you advice I am
leaning away from a stock replacement.
Sean Conolly
news:e46679e5-856b-4ed8...@u8g2000prd.googlegroups.com...
On Nov 23, 2:14 pm, Mark <makol...@yahoo.com> wrote:
> On Nov 23, 4:21 pm, garyvee <gary...@gmail.com> wrote:
>
>
>
>
>
> > I have a VMP-2 with a very low level on one of the XLR out connectors.
> > The corresponding unbalanced signal is fine. I tracked the problem
> > down to the output transformer by swapping channel 1 and 2
> > transformers. The transformer is marked with DB-348 and 70500348
> > number codes.
>
> > I tried searching the web for information on replacement transformers
> > but found little if any help. I sent an email to Peavey parts about
> > replacement but it seems unlikely they would carry parts for a long
> > discontinued product.
They may have a transformer - they will certainly have a schematic
available. Everytime I've asked for a schematic they sent it free, including
postage. They may not have a rep for top shelf gear, but their support has
always been excellent for me.
Sean
Arny Krueger
news:bdc84675-44b0-4e19...@o9g2000vbj.googlegroups.com
> Does the VMP use a single ended output?
There's a block diagram in a service manual online that seems to suggest p-p
output. I can't find a complete detailed schematic.
Scott Dorsey
>I have a VMP-2 with a very low level on one of the XLR out connectors.
>The corresponding unbalanced signal is fine. I tracked the problem
>down to the output transformer by swapping channel 1 and 2
>transformers. The transformer is marked with DB-348 and 70500348
>number codes.
>
>I tried searching the web for information on replacement transformers
>but found little if any help. I sent an email to Peavey parts about
>replacement but it seems unlikely they would carry parts for a long
>discontinued product.
Peavey has parts for all of this stuff, and they have parts for stuff they
discontinued back in the seventies. They are really good about supporting
their products. However, they are very bad about email; call them on the
telephone.
>I did find a Jensen model JT-10K61-1M but it is "Not designed for
>single ended Plate circuit operation" which may not be suitable for
>the VMP-2. Here the link to the Jensen transformer:
>
>http://www.jensen-transformers.com/datashts/10k611m.pdf
I don't remember what the output stage is like, but I am pretty sure it is
not a step-down transformer in the plate circuit. Look at the schematic and
see; if the transformer comes off the cathode with a DC blocking cap, a 1:1
transformer like this will be fine. If it's a push-pull circuit with three
wires on the primary side, you will need a different Jensen or Lundahl product.
I don't have the schematic with me because I am very far away from my office.
However, a call to Peavey will get them to fax you a copy. They are very good
about this.
As always, if you put a different transformer in, it will change the sound, so
you want to change both channels.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
garyvee
I talked to a Peavey parts representative today and he told me they
don't stock this transformer anymore. He seemed a bit new and since
it's a holiday week, he may not have been the best contact since he
lamented how short of staff they were. He did however happily email a
schematic to me in pdf format.
I hesitate to put this up on the web because it is copyrighted and I
didn't find it in web searches so it certainly is not readily
available.
Interesting that the schematic doesn't show the output transformer but
rather only the to/from transformer connectors depicted by
'SPX2' (probably a designation for a 2 prong pin connector). The
output transformer is also not listed in the parts list for the VMP-2.
The schematic shows pin 3 and 8 on a 12AT7 are each fed though 1K
resisters to a 1.5A/1.5MF capacitor and then to a 2.7K resistor which
then connects to the transformer. The original transformer has 2 wires
in and out which appears to rule out the push-pull design you
mentioned.