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Old 11th September 2012, 08:31 AM   #81
bcmbob is offline bcmbob  United States
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Thanks, I'll do all the readings but monoblocks sound most appealing. That idea has been an option for the final configuration all along so I'll change over later this morning.
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Old 11th September 2012, 09:13 PM   #82
bcmbob is offline bcmbob  United States
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Quote:
Originally Posted by AndrewT View Post
Measure the resistance between Left signal ground at the RCA to the Right signal ground at the RCA.

Since both channels must be connected to PE, there must be a resistance that is measurable.

The two RCA signal grounds must be connected to PE, if ClassI.
If the Source is ClassII, then neither signal ground have a PE to connect to.
All of this is avoided by building monoblock amplifiers.
Well it's close but no cookie

The JC-2 to FE hum persists. The Mini2496 DAC direct connection is still completely silent. I got a second DAC (Weiliang DAC-5) operational yesterday and it also produced a hum. That was reduced by 80 -90% after connecting it to the new monoblock build. That low level hum does not increase with higher volume levels and is almost completely masked with any volume increase.

But here is the kicker - the Mini2496 DAC to JC-2 to Hafler 120 is completely free of hum. Music plays cleanly and and not distorted.

So it appears the JC-2 to FE connection is still the issue. I'll investigate the ground paths on the Mini DAC to see how it differs from the JC-2 and the DAC-5.

***************

FE readings:
Left signal ground at the RCA to the Right signal ground at the RCA. = 0.5 - 0.7 Ohm

Mini2496 readings
Left signal ground at the RCA to the Right signal ground at the RCA. = 0.0 Ohm

Mini2496 to FE amp = 0.9 Ohm

JC-2 to FE amp = 2.6 Ohm

Mini2496 to JC-2 to Hafler 120 = NO Hum - music plays properly.

The mystery continues............
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Old 5th October 2012, 12:37 PM   #83
gig is online now gig  Italy
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Default Trimmers adjusment

Quote:
Originally Posted by bcmbob View Post
One channel is showing 9.1 mV and the other is 5.4 mV. That indicates I need to adjust the on-board trimmers again. The process is clearly explained in the documentation.
Hi, after spotting this thread I bought the same kit from another ebay supplier. Got the schematics but no instructions about trimmers adjustment. May I ask you to send me the documentation you have about it?
Thanks for your help
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Old 5th October 2012, 07:56 PM   #84
bcmbob is offline bcmbob  United States
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PM sent.
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Old 10th October 2012, 10:30 AM   #85
AndrewT is offline AndrewT  Scotland
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re post82
McBob,
does the zero ohms of the Mini give a clue?
Quote:
Mini2496 readings
Left signal ground at the RCA to the Right signal ground at the RCA. = 0.0 Ohm
Do your other Sources measure same/differently?


Quote:
Mini2496 to FE amp = 0.9 Ohm

JC-2 to FE amp = 2.6 Ohm
what does this mean? What are you measuring?
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Old 10th October 2012, 11:53 AM   #86
bcmbob is offline bcmbob  United States
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Thanks Mr. A.

I've been trying to clean up a couple other projects first, but plan to clear the desk and dig into it soon. One new discovery is when the mini is fed with optical there is no hum. When the BNC is used there is some noise. That seems to confirm the issue is related to grounding.

I'm also going to order duplicates of the surface mount items in case I find hidden solder bridges or damage from excessive heat. I'll report my progress.
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Old 4th April 2013, 03:13 AM   #87
kp93300 is offline kp93300  Malaysia
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Hi Bob
What is the outcome of the hum problem?
I am also interested in the kit.
What is the gain and is it possible to adjust it ?
Is there a switch on and switch off noise through ths speakers when you powered it up ?

thanks

kp93300
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Old 4th April 2013, 10:04 AM   #88
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by kp93300 View Post
........... What is the gain and is it possible to adjust it ?
Is there a switch on and switch off noise through ths speakers when you powered it up ?.......
The gain and the compensation are crotically tied together.
Yes, you can change the gain, but then you must accept that you need to skills to reselect all the compensation components to give the same stability, or better.
The output has relay isolation. This ensures no start up, nor shut down, noises from the speaker.

If you read the MyRef Threads you will find all the information there.
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Old 4th April 2013, 10:33 AM   #89
bcmbob is offline bcmbob  United States
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Sorry KP, I don't have any additional information. I decided to wait till the final build and see if the hum was unique to my RC build. Nobody else has reported the same issue with the Fremen Edition RC amps.

The Pre itself is top shelf in my opinion and provides more gain than I can use. It works beautifully with the beta FE and several other flavors of MyRef amps. I have no reservation about recommending the kit to potential builders as the sound it produces is super clean and sweet. The switching and volume control elements are determined by user choice. Both discrete and integrated configurations can be applied.

I'll report back after the FE FV is done.
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Old 4th April 2013, 10:38 AM   #90
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by kp93300 View Post
...... What is the gain and is it possible to adjust it ?
Is there a switch on and switch off noise through ths speakers when you powered it up ?............
The gain and the compensation are critically tied together.
Yes, you can change the gain, but then you must accept that you need to skills to reselect all the compensation components to give the same stability, or better.
The output has relay isolation. This ensures no start up, nor shut down, noises from the speaker.

If you read the MyRef Threads you will find all the information there.

repost to correct error in original post.
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