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Old 9th November 2005, 08:33 AM   #1
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Default Pearl problems

Hi,

I just completed a pair of Pearls. Individually, they work great. However, when I connect both up together, I get a lot of distortion. I unhook the output of one channel, and then that channel works great. The voltages are pretty much bang on for both boards, and the grounds between the 2 boards are connected at the output jacks, as is the DC ground from the power supply. I am using one toroidal transformer, tied to 2 Promitheus power supply boards and then to the boards.

I'm thinking this must be something simple, as I said, both boards function individually.

-Warren
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Old 9th November 2005, 12:14 PM   #2
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Hi,

is it possible that you connect the two hot outputs with each other? Or have one hot/cold inversion?

William
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Old 10th November 2005, 01:49 AM   #3
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Default partially fixed-still not great though.

Hi,

Thanks for your help, I thought it must have been something simple like that. I had both inputs wired the same, so switching the polarity on one definitely improved matters. However, I'm still getting distortion in one channel, and it's quite a bit quieter than the other. So, now I'm thinking one or more transistors is potentially blown. Should I start at the output and work backwards, or the other way?

Any tips would be appreciated.

-Warren
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Old 10th November 2005, 07:41 AM   #4
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Hi,

if they work great individually then nothing should be wrong with transistors etc. It must be the way you connect or switch the outputs.
Im not shure what you mean by "both inputs wired the same"

William
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Old 10th November 2005, 11:16 AM   #5
Buhl is offline Buhl  Denmark
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Try to power both channels of just one supply, paralleling them on the supply - I had a similar problem when using a 30-0-30 volt trafo, two bridges and two caps - everything fine, until i plugged in the RCA-socket, and the two opposite voltage potentiales met, and then havoc !!!!

You have something to look forward to - the pearl is one fine sounding RIAA !!

Cheers !
Buhl
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Old 10th November 2005, 06:43 PM   #6
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Default Input wiring question

Thanks for your suggestion, I actually already have just one power supply board paralleling the two boards, just to take that out of the equation.

I'm using a toroidal transformer 15-0-15 with the secondary in series to get my 30VAC. I've checked all the voltages and they are as expected.

Here's possibly a silly question, do I connect both channels inputs the same, as in: Left side, pin to + input, shield to - input, Right side pin to +, shield to -? Or does one side have to be hooked up pin to -, shield to +? I'm confused as to why the inputs aren't just labelled + and ground, which is why it got me thinking.

I'm so excited to get this thing working, the one side that works great now sounds fantastic! If only I could be satisfied with mono, I'd be complete already!

Thanks again for your assistance.
-Warren
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Old 10th November 2005, 06:56 PM   #7
Buhl is offline Buhl  Denmark
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Im not sure I understand your question - but Ill try to straigthen this out - assuming there are two wires going from your turntable - each wire has a shield and a pin - We now say shield is minus (-) and pin is positive (+) - minus from turntable goes to ground(minus) on the PEARL board, positive goes to input in the pearlboard.

Alternativly you can use a starground, where all grounds meet at one place - try a search on star ground and you will find some excelent schematics......

Happy hunting !

Cheers !
Buhl
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Old 10th November 2005, 09:02 PM   #8
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Default Re: Input wiring question

Quote:
Originally posted by lumpylipton
Here's possibly a silly question, do I connect both channels inputs the same, as in: Left side, pin to + input, shield to - input, Right side pin to +, shield to -? Or does one side have to be hooked up pin to -, shield to +? I'm confused as to why the inputs aren't just labelled + and ground, which is why it got me thinking.

Thanks again for your assistance.
-Warren

This is what I meant. If you switch one output and use it alone you will have phase inversion but nothing else.
If you use both the positive output of one channel will be connected to the ground of the other wich happens to be his own ground. This would cause a lot of distortion.
- means ground in this amp.

William
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Old 11th November 2005, 09:09 AM   #9
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Hi there,

Are you using 1 tranformer for 2 power supplies?
If so you have a common ground there which mixes things up with another common ground somewhere.

An easy solution is to use one more transfomer of exactly the same type and do the wiring like in page 3 of the pdf file.
The 2 grounds from the 2 power supplies are separate there.

If you cant do this.
just connect + to +IN and the shield to -IN.
at the output connect + to +Out and the shield to GND.
Are your Input and output connectors isolated from the metal box you are using?
If not that could be a big problem.

I hope I could help you a little bit.

Greetings
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Old 12th November 2005, 08:07 AM   #10
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Default Still problems...more details

Hi guys,

Thanks for all your help thus far. I have tried all suggestions without success thus far. I have done some very careful checking, and I believe I've found a problem, but I don't understand it.

My voltages all look fine between the two boards, except at one spot, Q4. Here is what I get:

Board 1: Q4, C: 15.6 B: 14 E: 13.5
Board 2: Q4, C: 19.3 b: 14.9 E: 13.7

To me, the C of Board 1 is quite a bit off. So, I started checking R14/R17/R20. I literally removed each of them to verify the correct values, and they are all correct and very well matched between the boards. Also, there is 29volts at the + of C15 of both boards. That's the confusing part, the voltage is dropping differently across R14. I believe that this voltage difference, which looks correct to the passdiy schematic voltage reading for board 2, is what's causing my distortion problems.

Any suggestion?

Thanks again for all your help.

Warren
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