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Old 11th August 2010, 09:33 PM   #8601
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Originally Posted by AndrewT View Post
Hi Trip,
shorting the amp input reduces speaker hum to inaudible. Does the transformer noise change?
What is the measured noise coming from the terminals.

Adding a source brings back the speaker hum. This could be hum coming from the source or it could be induced by the connections between the units.
Have you tried connecting different sources?
You may find that only one or few sources cause the hum problem. Which?
Hi Andrew

I have tried connecting a different CDP and its the same, as is the sound of the transformer when I short the RCAs

I have just rebuilt my LDR attenuator, and I have grounded it in the same way as my last. When either attenuators were connected, the amp hummed. But the previous didn't when connected to a chipamp. The chipamp is no longer assembled.

'What is the measured noise coming from the terminals'

How would I achieve this?

I'm just going to post a grounding question in the Lightspeed thread...

Thanks
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Old 11th August 2010, 09:35 PM   #8602
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Originally Posted by prooptiki View Post
I had also a small buzz, my solution was a ground star plus grounding the shield of the rca cable (both sides,together with the one of the two inner cables, it was a balanced shielded cable)


http://www.diyaudio.com/forums/attac...-f5-inside.jpg
Thanks Prooptiki
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Old 11th August 2010, 09:37 PM   #8603
AndrewT is offline AndrewT  Scotland
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attach a dmm to the output terminals set to 1000Vac. take a measurement. If it's <<10% of full scale reading go down one range to 200Vac. take a measurement. etc till you reach the 200.0mVac scale and take a reading. Is it 0.1mVac or 1mVac or 10mVac or 0.0mVac?
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Old 11th August 2010, 09:59 PM   #8604
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Quote:
Originally Posted by AndrewT View Post
attach a dmm to the output terminals set to 1000Vac. take a measurement. If it's <<10% of full scale reading go down one range to 200Vac. take a measurement. etc till you reach the 200.0mVac scale and take a reading. Is it 0.1mVac or 1mVac or 10mVac or 0.0mVac?
Andrew

One meter only has two options, 750Vac and 200. The other two range from 250/200/20/2Vac

I did as you said. There is a reading for a split second and it quickly drops away to nothing.
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Old 12th August 2010, 09:56 AM   #8605
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Hi,
now that you know there is only undetectable AC on the output, switch to DC voltage and again starting at the highest voltage scale measure the output offset. If both of these show very low voltages then connect your source and measure again.

The increase is due to the source or due to the method of interconnecting.

At this stage I cannot tell if the method of interconnecting is the result of a grounding fault inside your power amplifier.
Some one else may be able to give you a series of tests to carry out that can identify the location of the problem.
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Old 12th August 2010, 10:18 AM   #8606
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Quote:
Originally Posted by Nelson Pass View Post
Less feedback makes the sound more relaxed to me, which
you may translate as open. I like it that way myself.

Since you are reducing the resistance on the Sources of the
Jfets, it's probably wise to stick with 6.8 mA Idss, which will
keep the temperature down on them.

Thanks Nelson

But as I told: the Mini F5 does not drive the tweeters as I wanted, because there must be a roll of in the higher frequencies.

I am waiting for delivery of the 2SK2013/2SJ313 to try.

I have finished moving my workshop and can (re-)start activities soon.

Franz
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Old 12th August 2010, 10:22 AM   #8607
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Quote:
Originally Posted by AndrewT View Post
Hi,
now that you know there is only undetectable AC on the output, switch to DC voltage and again starting at the highest voltage scale measure the output offset. If both of these show very low voltages then connect your source and measure again.

The increase is due to the source or due to the method of interconnecting.

At this stage I cannot tell if the method of interconnecting is the result of a grounding fault inside your power amplifier.
Some one else may be able to give you a series of tests to carry out that can identify the location of the problem.
Hi Andrew

When I completed the amp I checked the offset over a few days, and at different operating temperatures. It never really went above 10mV without a source. I'll check again with a source connected.

I have a ESP ground loop breaker I could use in the Lightspeed if you think this would help. The F5s power supply ground is connected to the safety earth terminal with a CL60 in series
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Old 12th August 2010, 10:32 AM   #8608
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Here how the 1kHz square wave looks like (on my old Heathkit OS2) with the actual, unsatisfiying version of my Mini F5

Click the image to open in full size.

Too restricted bandwith.

Franz
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Old 12th August 2010, 11:05 AM   #8609
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Quote:
Originally Posted by AndrewT View Post
Hi,
now that you know there is only undetectable AC on the output, switch to DC voltage and again starting at the highest voltage scale measure the output offset. If both of these show very low voltages then connect your source and measure again.

The increase is due to the source or due to the method of interconnecting.

At this stage I cannot tell if the method of interconnecting is the result of a grounding fault inside your power amplifier.
Some one else may be able to give you a series of tests to carry out that can identify the location of the problem.


These readings were taken when the amp is cold

No source connected

Right channel
Peaks at 60mV and drops down to 27mV over a couple of minutes


Left channel
drops down to 14.2mV


Lightspeed and CDP connected, volume set at lowest setting

The readings are slightly lower than before, but the offset was slowly decreasing on the amp, so I guess there is no change.

Interestingly...when I rotate the volume control the right channels offset decreases from 27 > 8mV and the left increases from 12 > 37mV
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Old 12th August 2010, 11:25 AM   #8610
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I can't tell if you are measuring AC or DC.
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