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Old 20th July 2010, 09:35 PM   #1181
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The offset does not vary by pot setting; but I put 4.7microF caps at input and I read somewhere that in this way offset does not change.

But now is late in the night in Italy, I'll try to connect speakers tomorrow,

thank you Peter

Renato
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Old 20th July 2010, 09:47 PM   #1182
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Yes, that's correct, with caps the offset will stay at its highest level all the time.

I had 47Labs Gaincard, that also uses input coupling caps, and offset was approx 80mV, so yours is not that much off

You may reduce input shunt resistor (R2) from 22k to 10k and that will lower the offset as well.
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Old 21st July 2010, 08:54 PM   #1183
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Hi,

despite the offset the amp works fine!

Renato
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Old 23rd July 2010, 06:38 PM   #1184
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Quote:
Originally Posted by Peter Daniel View Post
You may try adding small cap as described here: Commercial Gainclone kit- building instructions

If that won't help, try adding Zobel (Rz 2.7R and Cz 0.1uF on amp board).

If noting helps, you may be forced to add some shielding to amp circuit.

I have some amp running without any enclosure and in my listening environment it's not a problem, but with other setups it may be different.
Panic over. Wooden box is fine. No need for adhesive aluminium shielding. No need for a metal case. No need for zobels. Damned cordless house phone was the culprit. Chucking out the "throbbing" EMI. I've read they're the absolute worst for radiation harmful to humans too (ie worse than mobile (cell) phones or Wi-fi). A metre further away resolved it completely.

Many thanks to Peter and all who helped.
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Old 24th July 2010, 07:16 PM   #1185
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Thanks for reporting Lucas, nice news...

Just for fun : I'm able to continue a call after I place the base of my DECT phone inside a stainless steel pressure cooker... and with the top cover in place !!!

Seems now "Low Radiation cordless DECT phones" exist, they don't have to permanently communicate with their base...

Welcome to the Frontpage

Not so easy to buy however...
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Old 20th August 2010, 03:26 PM   #1186
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Steele Hammond Chassis with Walnut side Panels -> 7" x 5" x 2"

Hammond Mfg. - Steel Chassis & Bottom Plates with Walnut Side Panels (1441 CWW & 1431 Series)

This looks like a pretty good option for the shigaclone. I'm sure you can fit the assembly into it, and finish the top off with a sheet of frosted plexiglass.
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Old 24th August 2010, 05:02 PM   #1187
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I have accidentally burned two mur860 in one channel. Can these to replace with MUR890? I am building Peter's LM gainclones (monoblock). Also, the LED light in the other monoblock seems to be turning off very slowly. It took a minute for it to turn off. The rail is at 27v. transformer is 2 x 25vdc. DC offset is at 80mv. what is wrong?

In picture 011.jpg, the bottom two mur860 are the ones which burned and the ones above are the mur890. The LED is shown in 013.jpg. I used a 62k resistor at R3.
Attached Images
File Type: jpg 011.jpg (57.4 KB, 356 views)
File Type: jpg 013.jpg (56.7 KB, 349 views)

Last edited by pmchoong; 24th August 2010 at 05:05 PM. Reason: describe attachements
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Old 24th August 2010, 05:10 PM   #1188
udailey is offline udailey  United States
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LED turns off slow because you have capacitance that keeps it glowing until the capacitor is completely discharged. If you are using a regular LM3886 or LM3875 you do not need better than MUR860. How in the heck did you destroy one of those diodes?!
IF you have MUR890 laying around it will do the same job as the MUR860
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Last edited by udailey; 24th August 2010 at 05:12 PM.
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Old 24th August 2010, 05:17 PM   #1189
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Yes...but lights goes off in 1 minute???
Sigh..it was a stupid mistake...the v+ and the pg+ from the psu was suppose to connect to the v+ and pg+ of the main board....and i connect the pg+ of the psu to the 'chg' of the main board...and the v+ of the psu to the pg+ of the main board. Heard the transformer buzzz but I thought it was humm and then 'pop'..spark flew and i have two destroyed diode. i am using the LM3875. Can I sub the two mur860 with the mur890? I have the 890 but not the 860.

Last edited by pmchoong; 24th August 2010 at 05:19 PM.
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Old 24th August 2010, 05:21 PM   #1190
udailey is offline udailey  United States
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Yes, the huge capacitance can run a little LED for a very long time. Yes the 890 is fine. Lets hope the chip is okay.
Uriah
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