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Chip Amps Amplifiers based on integrated circuits

eBay mono LM1875 kit
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Old 11th November 2019, 02:28 PM   #301
FauxFrench is online now FauxFrench  France
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Hi Chris,
Sorry for the delayed reply. I was traveling for a couple of days.

The 100pF capacitor should be of the foil type for best linearity and minimum noise.

Good systematic work (as always) when measuring the frequency response. 0.3dB at 17KHz is no problem.
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Old 11th November 2019, 08:10 PM   #302
chermann is offline chermann  Austria
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Thanks FF


have to look -actually nothing with 100pF in my box...just ceramic
chris
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Old 11th November 2019, 09:03 PM   #303
FauxFrench is online now FauxFrench  France
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Quote:
Originally Posted by chermann View Post
Thanks FF
have to look -actually nothing with 100pF in my box...just ceramic
chris

The ceramic are fine for deciding the value. For your level of detailed listening, the type may be noticed.
I am not in my lab right now but as I recall, my storage is also ceramic.
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Old 12th November 2019, 07:10 PM   #304
chermann is offline chermann  Austria
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Hi FF


Thank you for your time and help. i try to get a foil type cap for this.
2nd i have to start up with the second amp for better SQ compare....
chris
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Old 13th November 2019, 01:32 AM   #305
rabbitz is offline rabbitz  Australia
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I've only seen ceramic NP0/C0G used in that location. Neurochrome used a TDK FG28C0Gxxx on one of their amps I have in that location and I've also used Murata C0G for similar use in op amp circuits. I don't know if silver mica would be suitable as I've used them on small pF applications as are said to be better.

This is only an observation as I'm only an amp builder.
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Old 13th November 2019, 06:14 PM   #306
chermann is offline chermann  Austria
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Thank you rabbitz for your observation to this topic.

your are not just an amp builder in my view
chris
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Old 17th November 2019, 08:43 PM   #307
chermann is offline chermann  Austria
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Hi



for testing the other amp kits i start with building a next mock up
cpas are 4 times each rail - 3900F by chemicon (europe chemicon) the are nearly the same as the panasonic FC but much cheaper!


chris
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File Type: jpg mock up_amp2_1.jpg (146.8 KB, 117 views)
File Type: jpg mock up_amp2_2.jpg (137.9 KB, 115 views)
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Old 18th November 2019, 07:07 PM   #308
chermann is offline chermann  Austria
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Default ...step by step...

Hi again


i did some work in the evening... the 2x 0,1F are filter caps by wima. fuse is a 2,5A T - slow... --> interesting is that at the trani there is recommended to use 2 x 4A T=slow fuses (pic 2)


i test first the trani + rectifier - 20,2VAC
then i tested with cap bank - everything is fine. 27,06V each rail without load...- - next step are the amp boards and the cabeling...
enough for this evening...yes is should clean my bench
chris
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File Type: jpg mock up_amp2_3.jpg (144.6 KB, 104 views)
File Type: jpg mock up_amp2_4.jpg (150.1 KB, 103 views)
File Type: jpg mock up_amp2_5.jpg (127.9 KB, 102 views)

Last edited by chermann; 18th November 2019 at 07:10 PM.
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Old 18th November 2019, 07:46 PM   #309
chermann is offline chermann  Austria
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sorry...about the trani
it is a 120VA 18-0-18 VAC transformer with 3,33 A rated. so its "rounded up to 4A slow" (T) ??
chris
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Old 18th November 2019, 07:56 PM   #310
fdenys is online now fdenys  Netherlands
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This thread has inspired me to (finally) replace my legacy 30 years old Marantz amplifier.
However i will take a different route as far as the power supply is concerned.
I bought a dedicated low noise Audio Powersuply (picture attached) for about 23 EUR from AliExpress.

This supply delivers +24V, -24V (about 6A) as well as 12V (1A) for auxillary devices. (adjustable within 10%)
Bit overkill maybe - but it should be able to get about 30W of clean power out of the LM1875t.

Supply is relatively compact and i expect building a decent amplifier with this supply should simplify matters considerably.
Output voltage of course is well regulated and remaining ripple less than typical 0.1V.

Hopefully will receive the PS in about two weeks, and first will try an unmodified LM1875t Ebay kit and do some measurements on PS and amplifier before building final system with original LM1875t and audio quality capacitors.
Will keep you informed ..
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Last edited by fdenys; 18th November 2019 at 08:13 PM. Reason: Attaching image
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