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Old 25th May 2011, 01:22 AM   #31
gootee is offline gootee  United States
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Quote:
Originally Posted by maillard View Post
Hello Gootee,

I have 100 F panasonic FC + 100nF MKP Wima. (values of the kit)
I can easily make a try with 100 F more of the same type.

For the RF filtering, you mean 220pf in parallel with the (100F + 100nF) ?

Thank You.
Actually, no. I meant that the 220pF (or whatever value is used) should be connected between the two audio signal input pins.
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Old 25th May 2011, 05:06 AM   #32
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maybe add a input cap will give you some bass.. values from 0.1uF to 0.47uF nonpolar.. or you can try other values that you feel good.
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Old 25th May 2011, 06:36 AM   #33
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An input cap could reduce the bass response and perhaps add some distortion, the goal is to protect the amp (and the speakers) against a direct voltage.

I will add a speaker protection as soon as possible.
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Old 25th May 2011, 08:29 AM   #34
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I totaly agree with Andrew here, the minimum I put on a LM3875 is one of those 10 x 10 x 5cm snowlflake sinks, that is one per chip, It might still be enough for l886 but even bigger is recommended.
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Old 26th May 2011, 12:26 AM   #35
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you can increase cs cap from 100uF to 1mF-2.2mF//0.1uF at the v+ and v- chips pins.. maybe that will help..
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Old 29th May 2011, 09:41 PM   #36
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Quote:
Originally Posted by gootee View Post
What size bypass caps do you have directly across the chipamps' power pins? You might try experimenting with the sizes and types of those, especially with some electrolytics. They act as a point-of-load power supply that doesn't have the inductance of the supply rail conductors to slow down the response to the chip's need for changes in the current drawn, and to generate rail voltage dips and spikes when a chip's current draw tries to change.

I see that you haven't twisted together the wire pairs. You might have all types of strange things going on, in that case. Twist every pair of wires tightly together. Also add some RF filtering (even just 220 pF directly across the + and - signal input pins of each chip).
Good news, I've made a try with 100F more on each bypass caps and the result is very good, especially I have now a very pleasant sound stage effect with some good recordings.
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Old 31st May 2011, 03:35 PM   #37
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that is good for you....
what about 100uF or 1000uF more?... if you try pls post back...
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Old 1st June 2011, 05:34 AM   #38
gootee is offline gootee  United States
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Or 2200 uF...
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Old 1st June 2011, 12:58 PM   #39
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that is what i mean, but you have pointed that out...but still....
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Old 15th February 2013, 03:08 PM   #40
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Default end of the story

Hi,

I dig out this thread at the point where I left it 2 years ago:

- I changed the 2x100 F Panasonic by a single 330 F "Black Gate", the result was more detailled mids and trebles, but bass had disappeared .....,
- so I tried 2x100F + 330F and I finally got the fine sound of the BG and the strong bass of the Panasonics.

I still was not completly satisfied, but the sound was good enough for I decide to build a box for that amplifier.

After the box was built, I stopped working on the amp for a long time.

Four months ago I decided to try other changes. I have made a new PSU, very simple P2P, with 2x15000 F on each rails.

After a few Hours (20) of operation, I just could not believe my ear: a fantastic overall upgrade ! Open sound, Mid, Bass, soundstage, everything was significantly better. I am discovering all my Cds...

The most important points of that built were (8 ohm speakers):
- double mono Brian GT kit with :
- 300 VA tranfo 2x24 V AC,
-2 x 15000 F / rail (first try with 10000 F /rail),
- 2x530 F / rail on board (first try with 100F / rail),
- 1/W heatsink.

Some photos are available here:

Chip Amp Photo Gallery

Bye.

Last edited by maillard; 15th February 2013 at 03:28 PM. Reason: Add link to photos.
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