Gainclone HUM, THUMP problems - The solution - Page 8

chylld · 30th June 2008, 05:09 AM

one thing i've been curious about with my transformer box... there are 2 cables going from the transformer box to the main amp box, each one carries 25v ac. inside the amp box, this gets turned to V+/PG+ and V-/PG-.

so my question: what happens if i leave one of the cables unattached? (i.e. giving the chips only V+ or V-)

pacificblue · 30th June 2008, 06:36 AM

Simple answer. It won't work.

You must connect at least one of the PGs to have a ground reference for the amplifier.

chylld · 30th June 2008, 07:01 AM

Quote:

Originally posted by pacificblue
Simple answer. It won't work.

You must connect at least one of the PGs to have a ground reference for the amplifier.

what if i have V+ and PG+ connected, but V- and PG- not connected? (that's what would happen if one of the cables wasn't connected)

AndrewT · 30th June 2008, 08:05 AM

Quote:

Originally posted by pacificblue
Simple answer. It won't work.

again

chylld · 30th June 2008, 08:33 AM

Quote:

Originally posted by AndrewT
again

thanks for the clarification. reason i asked is because i was afraid it would blow my speakers up:

Quote:

Decibel Dungeon wrote:
When I reconnected the amp, I found that I had an offset of 34 volts! After assuming that I must have a faulty chip, and ordering some replacements, further investigating found that the negative supply rail measured 0 volts at the amp but -36 volts in the PSU. A wire had come loose in the umbilical from PSU to amp and reconnecting it solved the problem. It was lucky that I had decided to check the DC offset that morning of I would have destroyed a speaker.

AndrewT · 30th June 2008, 08:35 AM

Quote:

Originally posted by chylld

thanks for the clarification. reason i asked is because i was afraid it would blow my speakers up:

it might.
measure the output offsets with the various disconnections that you think are possible.

chylld · 30th June 2008, 10:02 AM

Quote:

Originally posted by AndrewT
it might.
measure the output offsets with the various disconnections that you think are possible.

ok these are the offsets i've measured (all in +/- volts):

both V+/V- connected: 0.002
only one connected: 1.94
only the other one connected: 0.49

so max of about 2V. i assume that's not a harmful voltage given that the AA (1.5V) battery polarity test is quite common and harmless?

gainphile · 30th June 2008, 10:06 AM

Never ever test using your 'real' speaker

... buy a $5 fullranger

AndriyOL · 1st August 2008, 01:30 AM

I have build a parallel configuration amp, based on LM4780 chips but have some nasty hiss at low frequency response, but the bass is not gone at all.
My unconventional solution is a use of non-polarized 47uF Ci cap in parallel to 100nF MKT cap.
Gould it be from improper grounding?

Thanks in advance for answers.

AndrewT · 1st August 2008, 05:41 PM

Quote:

Originally posted by AndriyOL
I have build a parallel configuration amp, based on LM4780 chips

post your schematic

30th June 2008, 10:06 AM	#78
gainphile diyAudio Member Join Date: Dec 2007 Location: Melbourne the sunny city!	Never ever test using your 'real' speaker ... buy a $5 fullranger __________________ http://gainphile.blogspot.com

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30th June 2008, 05:09 AM	#71
chylld diyAudio Member Join Date: Jun 2005 Location: Sydney, Australia	one thing i've been curious about with my transformer box... there are 2 cables going from the transformer box to the main amp box, each one carries 25v ac. inside the amp box, this gets turned to V+/PG+ and V-/PG-. so my question: what happens if i leave one of the cables unattached? (i.e. giving the chips only V+ or V-)

30th June 2008, 06:36 AM	#72
pacificblue diyAudio Member Join Date: May 2008	Simple answer. It won't work. You must connect at least one of the PGs to have a ground reference for the amplifier.

1st August 2008, 01:30 AM	#79
AndriyOL diyAudio Member Join Date: Jul 2008 Location: Lviv	I have build a parallel configuration amp, based on LM4780 chips but have some nasty hiss at low frequency response, but the bass is not gone at all. My unconventional solution is a use of non-polarized 47uF Ci cap in parallel to 100nF MKT cap. Gould it be from improper grounding? Thanks in advance for answers.

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