weird 1875 problem

jarcher12 · 22nd July 2009, 11:39 AM

Hi I have built a few 1875 amps but the last two have exhibited a strange problem. On higher volumes i get a distortion/crackling from ONE of the channels - no its not the speaker, i swapped them and the same thing happens in the other one. it usually happens when the music hits a portion with a higher volume (what do you call that - crescendo ?? ) anyway any suggestions welcome.

lineup · 22nd July 2009, 11:42 AM

How about the volume potentiometer?

jarcher12 · 22nd July 2009, 11:45 AM

wow that was fast. no no volume pot, using ipod.

jeff mai · 22nd July 2009, 12:07 PM

Sounds like you're clipping.

AndrewT · 22nd July 2009, 12:27 PM

can you intercept the signal line into the power amp and measure the average signal when you "turn up" the volume?

What gain have you set the two power amp channels to?
Are they both the same? Check the resistors.

Stuey · 22nd July 2009, 01:02 PM

Are you using a pre-amp?

Given that the last two amps have done the same, maybe it's a fault with a channel in the pre-amp? Try a known good power amp if you haven't already.

Alternatively, is there any component you may have used in common in both amps (such as the volume pot mentioned above)?

Cheers

Stu

jarcher12 · 22nd July 2009, 02:16 PM

Hi was out for a while. Andrew will try measuring. Stuey no pre amp, just an ipod. I had a thought that it might be connected to the 3.5 jack , maybe its not connecting well enough inside the ipod ? does that make any sense ? Otherwise its back to rechecking all the groundings, that is something i have learned with these amps it is 90% of the time a ground fault . I just dont get why it is only at higher volumes this is happening, btw the gain is set at 22 : 1 for one of the amps (both channels of course) and 30:1 for the other.

jarcher12 · 22nd July 2009, 03:05 PM

Tomorrow i will try a different source and see. Thanks for all the quick input.

22nd July 2009, 11:39 AM	#1
jarcher12 diyAudio Member Join Date: Apr 2009	weird 1875 problem Hi I have built a few 1875 amps but the last two have exhibited a strange problem. On higher volumes i get a distortion/crackling from ONE of the channels - no its not the speaker, i swapped them and the same thing happens in the other one. it usually happens when the music hits a portion with a higher volume (what do you call that - crescendo ?? ) anyway any suggestions welcome.

22nd July 2009, 11:42 AM	#2
lineup diyAudio Member Join Date: Dec 2005 Location: the north	How about the volume potentiometer? __________________ lineup

22nd July 2009, 12:27 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	can you intercept the signal line into the power amp and measure the average signal when you "turn up" the volume? What gain have you set the two power amp channels to? Are they both the same? Check the resistors. __________________ regards Andrew T.

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22nd July 2009, 11:45 AM	#3
jarcher12 diyAudio Member Join Date: Apr 2009	wow that was fast. no no volume pot, using ipod.

22nd July 2009, 12:07 PM	#4
jeff mai diyAudio Member Join Date: Aug 2002 Location: Melbourne	Sounds like you're clipping.

22nd July 2009, 01:02 PM	#6
Stuey diyAudio Member Join Date: Mar 2006 Location: Perth, Western Australia	Are you using a pre-amp? Given that the last two amps have done the same, maybe it's a fault with a channel in the pre-amp? Try a known good power amp if you haven't already. Alternatively, is there any component you may have used in common in both amps (such as the volume pot mentioned above)? Cheers Stu

22nd July 2009, 02:16 PM	#7
jarcher12 diyAudio Member Join Date: Apr 2009	Hi was out for a while. Andrew will try measuring. Stuey no pre amp, just an ipod. I had a thought that it might be connected to the 3.5 jack , maybe its not connecting well enough inside the ipod ? does that make any sense ? Otherwise its back to rechecking all the groundings, that is something i have learned with these amps it is 90% of the time a ground fault . I just dont get why it is only at higher volumes this is happening, btw the gain is set at 22 : 1 for one of the amps (both channels of course) and 30:1 for the other.

22nd July 2009, 03:05 PM	#8
jarcher12 diyAudio Member Join Date: Apr 2009	Tomorrow i will try a different source and see. Thanks for all the quick input.

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