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Old 19th August 2011, 05:11 PM   #1
tony Ma is offline tony Ma  United States
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Default not balance sound on tube pre-amp

Dear all,

Can any one tell me why I don't get even balance sound on DIY Jadis JP200?

Seems that one side is much louder than the other
I tested the AMP, CD and DAC and there is nothing wrong with it
So I am pretty sure the Pre-amp
here is the schematic

http://analogmetric.com/download/JP2...0Schematic.pdf

been asking their tech support but no reply

tks
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Old 19th August 2011, 10:01 PM   #2
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Have you tried swapping your audio input interconnect cables left to right?
Have you tried swapping your audio output interconnect cables left to right?
Have you tried swapping your tubes left to right?
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Old 19th August 2011, 10:32 PM   #3
tony Ma is offline tony Ma  United States
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Quote:
Originally Posted by Speedskater View Post
Have you tried swapping your audio input interconnect cables left to right? YES I DID
Have you tried swapping your audio output interconnect cables left to right? YES I DID
Have you tried swapping your tubes left to right?
YES I DID

I am suspecting maybe the volume control???
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Old 19th August 2011, 10:37 PM   #4
tony Ma is offline tony Ma  United States
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What happens was, the Pre-amp making a torch sound (Exessive hiss) but still at the beginning the sound is UN-balance. Accidentally I touch ground output section from one channel with ground from PS. (is this will cause a problem? / I thought it will remove hiss but it is not)
So What I did I change resistor to Metal Oxide the excessive hiss is gone but the unbalance stay
Even I change from chinese tube 12ax7b to tungsol still the same. I did swap the tube also
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Old 20th August 2011, 12:17 PM   #5
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Sometimes you have to check everything. If you just built it, high resistance solder joint is a definite possibility. Swapping the volume control is probably the next step. after that, swapping every component starting with the plate resistors and coupling caps. In its fortieth year my PAS2 preamp developed an imbalance that tube swapping nor electrolytic cap replacement would correct. So I took the opportunity last year to upgrade from carbon comp to metal film resistors, and from paper caps to polyester film caps. The resistors cut the hiss but did not fix the imbalance. After the ninth cap, the imbalance was still there. The tenth cap had a solder iron burn through the wax on the bottom (hidden by the builder) and that one was the source of the imbalance. You, as the builder, will know if you burned anything, but high resistance joints are not so visible.
Looked at the schematic. Your output stage has a cathode resistor instead of a plate resistor. I wonder why they used three 12AX7 stages instead of two like the PAS2? The PAS 2 has plenty of gain, even with leaky (high idle current) forty to fifty year old tubes, to get from a magnetic phono cartridge to power a CS800s power amp to disco volume levels.
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Last edited by indianajo; 20th August 2011 at 12:36 PM.
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Old 15th December 2011, 02:02 AM   #6
tony Ma is offline tony Ma  United States
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Finally I can solve the problem.
I change all the Resistor to Kiwame Metal Film.
It's very quiet and nice now
Also it balance out the sound
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Old 15th December 2011, 03:49 AM   #7
badman is online now badman  United States
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Just fyi- it was most likely something soldered wrong or something, rather than the resistor. However, since swapping out all resistors is a brute force solution, good job!
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