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
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
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
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
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
You have something to look forward to - the pearl is one fine sounding RIAA !!
Cheers !
Buhl
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
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
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
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
Re: Input wiring question
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
lumpylipton said:
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
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
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
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
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
Hi,
Since all the resistor values in that area are correct and very well matched between the boards, I'm thinking my 2SK289 is drawing too much current and must be defective. Is this a possibility, considering it does pass audio, albeit at a much lower level than the other board? I have it removed now (whew, what a difficult desoldering job that was!), is there a way to test it? I've tried to order another, but Newark only has delivery in Feb 06, and they seem to be the only North American supplier I've found thus far. I bought my original Q pack from Promitheus, I'm going to ask him if he'll sell me individual 389's. Otherwise, if someone knows another source in North America, I'd appreciate it.
Any other ideas would of course be welcome as well.
Warren
Since all the resistor values in that area are correct and very well matched between the boards, I'm thinking my 2SK289 is drawing too much current and must be defective. Is this a possibility, considering it does pass audio, albeit at a much lower level than the other board? I have it removed now (whew, what a difficult desoldering job that was!), is there a way to test it? I've tried to order another, but Newark only has delivery in Feb 06, and they seem to be the only North American supplier I've found thus far. I bought my original Q pack from Promitheus, I'm going to ask him if he'll sell me individual 389's. Otherwise, if someone knows another source in North America, I'd appreciate it.
Any other ideas would of course be welcome as well.
Warren
Hi folks,
I got my replacement sk389 today (thanks Promitheus), and while it does make the voltages much closer matched between the boards, I still have the distortion problems. Again, to recap, the boards work great individually, but hooked up together, distortion. The polarity of the inputs and outputs is correct, and all voltages are very close to the schematic.
William, you had asked what the voltage drops were across R24/R25. Both boards are identical, there is 0.11 V across R25 and absolutely no DC voltage across R24....is this correct?? It seems wrong...
Any assistance would be very much appreciated...I'm running out of good ideas!!
Thanks,
Warren
I got my replacement sk389 today (thanks Promitheus), and while it does make the voltages much closer matched between the boards, I still have the distortion problems. Again, to recap, the boards work great individually, but hooked up together, distortion. The polarity of the inputs and outputs is correct, and all voltages are very close to the schematic.
William, you had asked what the voltage drops were across R24/R25. Both boards are identical, there is 0.11 V across R25 and absolutely no DC voltage across R24....is this correct?? It seems wrong...
Any assistance would be very much appreciated...I'm running out of good ideas!!
Thanks,
Warren
Promitheus,
Here is my current grounding scheme.
I'm using a single power supply, paralleled to both boards, mainly for simplicity while I'm troubleshooting. It made no difference when I used a separate supply for each board. My transformer is not center tapped, so I'm NOT using +30 0 -30 or anything like that which I know from other posts can cause big problems.
The grounds on the individual boards are tied with a jumper (short wire) as shown on the board around C15.
The grounds of the two output RCA's are connected together by a short wire between them. I also tie DC ground from the power supply to this point (my star ground point). Currently I have no noise or hum issues.
The only thing I haven't done is tied AC ground to this star point, which I guess I'll try next.
Is there anything else I should try as far as grounding to get rid of this distortion?
Thanks,
Warren
Here is my current grounding scheme.
I'm using a single power supply, paralleled to both boards, mainly for simplicity while I'm troubleshooting. It made no difference when I used a separate supply for each board. My transformer is not center tapped, so I'm NOT using +30 0 -30 or anything like that which I know from other posts can cause big problems.
The grounds on the individual boards are tied with a jumper (short wire) as shown on the board around C15.
The grounds of the two output RCA's are connected together by a short wire between them. I also tie DC ground from the power supply to this point (my star ground point). Currently I have no noise or hum issues.
The only thing I haven't done is tied AC ground to this star point, which I guess I'll try next.
Is there anything else I should try as far as grounding to get rid of this distortion?
Thanks,
Warren
you have too many ground points.
you tie the 2 channels at too many points together.
Grounds from inputs and outputs should not be tied together but should go directly to the boards and should be isolated from the chassis. This is very important.
Each connector should only be in contact with the PCB.
Second part.
Make a star point on the chassis somewhere.
Tie the ground from the AC Power supply there and the ground from the mains power.
You should have no problems like this.
you tie the 2 channels at too many points together.
Grounds from inputs and outputs should not be tied together but should go directly to the boards and should be isolated from the chassis. This is very important.
Each connector should only be in contact with the PCB.
Second part.
Make a star point on the chassis somewhere.
Tie the ground from the AC Power supply there and the ground from the mains power.
You should have no problems like this.
Hi Promitheus,
Thanks a lot for your responses, let me clarify my grounding explanation...
I don't have the RCA input grounds tied together, and all RCA's are isolated from the chassis (in fact, there is no chassis yet, the boards are loose still, mounted on plastic standoffs while I troubleshoot.
The only point I connect the 2 boards together is at the output RCA jack grounds, to my "star point".
The AC mains ground is currently floating, but I will tie it to my star point along with the DC power ground.
I'll let you know how I make out.
Thanks,
Warren
Thanks a lot for your responses, let me clarify my grounding explanation...
I don't have the RCA input grounds tied together, and all RCA's are isolated from the chassis (in fact, there is no chassis yet, the boards are loose still, mounted on plastic standoffs while I troubleshoot.
The only point I connect the 2 boards together is at the output RCA jack grounds, to my "star point".
The AC mains ground is currently floating, but I will tie it to my star point along with the DC power ground.
I'll let you know how I make out.
Thanks,
Warren
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