new build - abdellah SE KT88 - Page 2

vince76 · 30th July 2009, 07:23 PM

grazie Piero Thank you Piero
I checked the grounding.
The fact is that the amp is dead quiet when no source is connected. I start thinking I have a bad source cable. Two bad cable actually.
V.

piero7 · 30th July 2009, 10:44 PM

chrish · 31st July 2009, 02:35 AM

Have you tied the grounds of the two inputs together and from there to ground?

Chris

vince76 · 31st July 2009, 05:48 AM

I have four input, two per source, and a selector.
I tied the four grounds together with the potentiometer ground and grounded all at preamp grounding point

V

vince76 · 31st July 2009, 04:12 PM

dear boys,
I'm in a dead point.
I need your advice.
My amp, when no source is connected is super silent.
if I connect one channel of the CD source to the amp using shielded or unshielded wire than the hum starts. The same happens with an Ipod. same if I connect both channels. Volume doesn't affect hum.
don't know what to search for since I don't understand where it comes from (50Hz hum, a loop....?)
thank you,
Vincenzo

Brit01 · 31st July 2009, 08:27 PM

Just one thing.

Did you put grid stoppers in? I don't see them in the schematics.

vince76 · 31st July 2009, 08:36 PM

I followed the schem... other builders report no hum problem.
Do you think grid stoppers would help? I think it's power related or ground loop.
Thank you
V

Brit01 · 31st July 2009, 08:41 PM

Probably not due to the absence of grid stoppers but I've always understood it's good practice to put in grid stoppers. Good quality resistors though.

Your RCA chassis connectors are isolated well yes (if you have a metal chassis)?

vince76 · 31st July 2009, 09:14 PM

rca connectors are well insulated (the hot is well insulated) checked today, the grounds go all to preamp ground point.

V.

porkchop61 · 31st July 2009, 10:07 PM

Quote:

Originally posted by Brit01
Just one thing.

Did you put grid stoppers in? I don't see them in the schematics.

It is good practice, I have 1k on mine.
I don't think this is the hum issue though (as previously mentioned)

31st July 2009, 04:12 PM	#15
vince76 diyAudio Member Join Date: Jul 2009	war to the hum dear boys, I'm in a dead point. I need your advice. My amp, when no source is connected is super silent. if I connect one channel of the CD source to the amp using shielded or unshielded wire than the hum starts. The same happens with an Ipod. same if I connect both channels. Volume doesn't affect hum. don't know what to search for since I don't understand where it comes from (50Hz hum, a loop....?) thank you, Vincenzo

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30th July 2009, 07:23 PM	#11
vince76 diyAudio Member Join Date: Jul 2009	grazie Piero Thank you Piero I checked the grounding. The fact is that the amp is dead quiet when no source is connected. I start thinking I have a bad source cable. Two bad cable actually. V.

30th July 2009, 10:44 PM	#12
piero7 diyAudio Member Join Date: Apr 2009 Location: Matera

31st July 2009, 02:35 AM	#13
chrish diyAudio Member Join Date: Oct 2003 Location: Sydney	Have you tied the grounds of the two inputs together and from there to ground? Chris

31st July 2009, 05:48 AM	#14
vince76 diyAudio Member Join Date: Jul 2009	I have four input, two per source, and a selector. I tied the four grounds together with the potentiometer ground and grounded all at preamp grounding point V

31st July 2009, 08:27 PM	#16
Brit01 diyAudio Member Join Date: Jul 2008	Just one thing. Did you put grid stoppers in? I don't see them in the schematics.

31st July 2009, 08:36 PM	#17
vince76 diyAudio Member Join Date: Jul 2009	I followed the schem... other builders report no hum problem. Do you think grid stoppers would help? I think it's power related or ground loop. Thank you V

31st July 2009, 08:41 PM	#18
Brit01 diyAudio Member Join Date: Jul 2008	Probably not due to the absence of grid stoppers but I've always understood it's good practice to put in grid stoppers. Good quality resistors though. Your RCA chassis connectors are isolated well yes (if you have a metal chassis)?

31st July 2009, 09:14 PM	#19
vince76 diyAudio Member Join Date: Jul 2009	rca connectors are well insulated (the hot is well insulated) checked today, the grounds go all to preamp ground point. V.

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