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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 7th February 2019, 03:46 PM   #3561
domenico80 is offline domenico80  Italy
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Originally Posted by Salas View Post
3X is translated to near 10dB. Proved practical enough with most amps and headphones. 17dB to 20dB is usually too much with modern digital sources.
thank you
I agree for the 10 db, enough and advance with the digital
with a line like this I have no problem connecting the power final to a volume potentiometer
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Old 7th February 2019, 06:50 PM   #3562
IDM is offline IDM  United Kingdom
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I think I have found the fault. I measured voltage across the input to the bad channel and rather shockingly there is 8.6V. So I can only assume its the UPA68H that has failed or was bad when I put it in. Unfortunately I have no spares.

Looking on Ebay the chines ones are very cheap whereas the UK ones are pretty expensive. Can someone recommend a reliable source?

Thanks
Ian
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Old 7th February 2019, 08:43 PM   #3563
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Ask Tea to send you a surely adequate couple of spares. Its a lottery with so many fake semis or factory rejects out there.
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Old 7th February 2019, 08:49 PM   #3564
domenico80 is offline domenico80  Italy
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even retailers in the Far East falsify the transistor codes
When test circuits , fireworks happen
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Old 7th February 2019, 09:06 PM   #3565
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
P.S. Meanwhile better remove the suspect package to verify damage on the transistor tester. Three legs from its left are one JFET three legs from its right are the other JFET. Middle leg is tied to the silicon substrate (no connection in this circuit).
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Old 8th February 2019, 09:04 AM   #3566
RainfallSky is offline RainfallSky  Russian Federation
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Quote:
Originally Posted by IDM View Post
Looking on Ebay the chines ones are very cheap whereas the UK ones are pretty expensive. Can someone recommend a reliable source?

Thanks
Ian
That's not what you asked but avoid this sellers for any electronic components:
littlediode, utsource, polida
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Old 8th February 2019, 09:30 AM   #3567
IDM is offline IDM  United Kingdom
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Thanks for all the advise on suppliers etc.

My main worry now is how to desolder the UPA76H. Even with solder braid, I am worried on how to get a 7 legged dual transistor package out without frying it or the board.

Ian
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Old 8th February 2019, 12:12 PM   #3568
vgeorge is offline vgeorge  Greece
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by IDM View Post
Thanks for all the advise on suppliers etc.

My main worry now is how to desolder the UPA76H. Even with solder braid, I am worried on how to get a 7 legged dual transistor package out without frying it or the board.

Ian
Better try with a desolder pump.
The braid is not good for this operation.
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"Without deviations from the norm, progress is not possible" - Frank Zappa
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Old 8th February 2019, 06:06 PM   #3569
IDM is offline IDM  United Kingdom
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After a great deal of fiddling I got the UPA68H out and then tested it to find that J1 was dead, though J2 was ok. So I finally get an answer to the problem :-)

I have a matched quad of 2sk170's (genuine) and its taking all my will power not to fit them! I will try and be patient and wait for the replacement UPA68H

Thank you for all the suggestions and help.
Ian
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Old 8th February 2019, 07:36 PM   #3570
transcendent is offline transcendent
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I have a matched quad of 2sk170's (genuine) and its taking all my will power not to fit them!

What's wrong with 2sk170's ?

Simon
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