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Old 16th January 2013, 08:14 PM   #21
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I'll do my homework and I'll be back
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Old 17th January 2013, 10:39 AM   #22
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On each Test Point (TP) voltage on left/right channel. Houston, we've got a problem.
Death has taken a Fet? And worst, it's sending DC to my cartridge :'(
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Old 17th January 2013, 12:26 PM   #23
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Bad news.
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Old 17th January 2013, 12:46 PM   #24
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You mean I have to order matched pair on fleabay again? It's fried?
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Old 17th January 2013, 01:08 PM   #25
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Take off & measure Idss to be sure.
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Old 18th January 2013, 07:47 PM   #26
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Unhappy No idea, close to supernatural here: I must work, it does not...

Hi Kevin & fellows, I've been told "don't buy a phono amp, for far less money and few time you can build a great amp!" Lies! DIY stands for "Dig In Yard", to bury yourself of course!
Well you seem more optimistic than I am, hope we will find...

Quote:
Originally Posted by kevinkr View Post
Check the tone arm wiring, and does the problem swap to the other channel when you swap the left and right inputs?
Nop, it's with the phono amp, changed TT and channel, still following the amp channel. Wich channel is ok I don't know, they're not the same...
TT is innocent.

Quote:
Left and right inputs both return to ground somewhere on your nicely built boards? (No opens)
I'll do pictures but : it's a source selector with amp included for the phono, both channel having a dedicated single coper wire linking the whole left and the whole right RCA's ground to the main grounding point (the outside point for the TT ground wire), the DC socket with it's gnd only connected to that gnd point, the gnd track of each phono channel going only to that "star" point. The pics will say it all.

Quote:
Measure dc voltages on fet drains and make sure channel to channel that they match to say within 5 - 10%, if they do not, try to match some fets as variations in transconductance, pinch off voltage, etc. may effect the channel to channel gain match. I would not expect the differences to be that large unless the fets were grossly different.
In my above message. I've found a lonely 2SK170 to replace the one under 1V. (in fact maybe it's the 11V one that is dead?! I have no idea how it should measure!) So with Fet out, over 20V there, with the spare Fet... 0.6V, the same :'(

Quote:
Even better would be to measure the signal levels directly in each stage, verifying that levels match after the first stage, after the passive eq, and finally the second stage.
I may do it a bit later, I'm not that familiar with the spectrum/network analyzer we have at work. And that non voltage matching should be fixed first I guess.

Quote:
Post a reasonably sized picture of each side of the PCB and let us have a look, perhaps something different between the two channels will stand out.
Finally have someone else take a look at your handiwork.
Second picture is the ps wires bent down for clear view. Last one is of usless stuff :'(''
I've shown it at work, no idea, they're not in such things anyway.

Merlin, I may build a little fet tester and check it out. If I can manage to make a working tester, 3 parts so complicated for me under curse!


Ok time to listen to CDs then...
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File Type: jpg pcb1.jpg (236.6 KB, 173 views)
File Type: jpg pcb2.jpg (146.4 KB, 160 views)
File Type: jpg top.jpg (301.7 KB, 154 views)
File Type: jpg IMG_0549.JPG (124.3 KB, 148 views)
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Last edited by Malefoda; 18th January 2013 at 08:00 PM.
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Old 18th January 2013, 08:24 PM   #27
osscar is offline osscar  Latvia
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I am soldering a number of pacific RIAA (p2p and pcb) - never had any problems (using both N and P channel JFET without gate stoppers) source resistors 47R and i use drain resistors - 4k7 - it will reduce gain slightly. maybe your Fets are fakes ?
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File Type: jpg DSC07335.jpg (287.4 KB, 85 views)
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Last edited by osscar; 18th January 2013 at 08:34 PM.
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Old 19th January 2013, 12:08 AM   #28
kevinkr is offline kevinkr  United States
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Yeah, based on the voltage measurements I'm thinking there is something fishy about those fets. I'd expect something like half supply on the drains ideally speaking, what Idss family do these parts come from?
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Old 19th January 2013, 09:14 AM   #29
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They're all fets bought on fleaBay, the seller states about these 2SK170BL:
"This is Original Toshiba FETs made in Japan.
The price is for 4(four) items - 2 very well matched pairs: I declare +/-2% to be on a safe side but really I select no more than +/- 1% (Vgs = 10V)."
I only needed 4 matched, so bought that
As for the spare one its is unknow...
Want me to measure something? Got these three-legged bugs out of pcb is quite tricky...
If any of you know where to find a matched pair for my first stage that'll be nice (or offer me a deal in MP )... I can exchange first stage fet for the second stage's one on the harsh left channel to check voltage again an see if it's Fet related.

Thanks!
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Last edited by Malefoda; 19th January 2013 at 09:17 AM.
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Old 19th January 2013, 09:29 AM   #30
osscar is offline osscar  Latvia
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there should be about about 7-10 V on drain (depending from PSU voltage 24-27V ) and about 170mV on source with 50r resistors for both jfets.

good luck!
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