F4 power amplifier

[Babowana]

Originally posted by Andrzej Sochon


I am back to the original NP schematics without any extra rail caps at the input. I found the sound was to sandy, grainy... so I pulled out additional caps on input. Sound is more clean now, acoustic scene still perfect, listening is very nice, but I have some troubles with loud pieces of many instruments and voices.
I will try to use better quality C1/C2 caps, like Nichicon bipolars.
What do you recommend regarding C3/C4, Nichicon ?
andrzej

Sandy and grainy? It's not for me . . .

I have believed that C3 and C4 is to make the output and input
signals the same (not exactly tho), having limited current flow.
(so, flat frequency response down to the rockbottom bass region)
And,
I have believed that there are also very limited current flow through
C1 and C2.

Anyhow, better quality of C1-4 might be helpful . . .

By the way, when you had the additional input caps, no bass
sound change? Just wondering . . .

[Andrzej Sochon]

Originally posted by Babowana

...when you had the additional input caps, no bass
sound change? Just wondering . . .

Hi,
I was not able to check having no preamp, I did not observe any change in bass.

By the way, look what I use to measure temperature: simple car-thermometers I bought at supermarket, price approx. 3 Euro each.
Precision is not laboratory perfect but is quite enough! Important is that supply battery is easy to buy everywhere: 1,5V AA size.
I hope you can see 48C.
Best Regards,
a.

[jacco vermeulen]

Originally posted by Andrzej Sochon
car-thermometers, 3 Euro each.

[steenoe]

Originally posted by Andrzej Sochon


Hi,
I was not able to check having no preamp, I did not observe any change in bass.

By the way, look what I use to measure temperature: simple car-thermometers I bought at supermarket, price approx. 3 Euro each.
Precision is not laboratory perfect but is quite enough! Important is that supply battery is easy to buy everywhere: 1,5V AA size.
I hope you can see 48C.
Best Regards,
a.

Looks like a manly pair of amps to me, allright
At 48C you can raise the bias a bit, if you wanted to

[Andrzej Sochon]

Originally posted by steenoe
Looks like a manly pair of amps to me, allright
At 48C you can raise the bias a bit, if you wanted to

Yes, I want to raise the bias.
At the moment I got 48C without top cover.
If you compare my thermometer-photo with my awatar, maybe you will see there are no woodden insulators now. Now all walls are thermally
united/connected. With wooden insulators Mosfets temperature was as high as 68C. Now its much better.

[carpenter]

Originally posted by Andrzej Sochon


... maybe you will see there are no wooden insulators now. Now all walls are thermally united/connected. With wooden insulators Mosfets temperature was as high as 68C. Now its much better.

Good catch, and something for us to learn. Thanks for sharing.

[Andrzej Sochon]

Originally posted by jacco vermeulen

Jacco, I like this critter very much, I must try to use it...
wow, does it work?

[Andrzej Sochon]

Originally posted by carpenter
[BGood catch, and something for us to learn. Thanks for sharing. [/B]

Hi Carpenter,
I wish I did not measure temperature of side walls before, as my beloved SOZ was inside. Big aluminum resistors ware mounted here, and after half an hour side walls ware so high that I could not touch them, it was 80C or more. Mosfets ware mounted on the front walls so wood insulation was necessary.
Where are amusing critters...aha, ...

wow!

[carpenter]

Originally posted by Andrzej Sochon

...Big aluminum resistors were mounted here, and after half an hour side walls were so hot that I could not touch them; it was 80C or more. Mosfets were mounted on the front walls so wood insulation was necessary...

Now that makes perfect sense! More useful information.

[Andrzej Sochon]

Nothing special, for novices maybe...

Last weekend I tried to clear cables and other things inside my f4. I exchanged C1/C2/C3/C4 to Nichicon, I also exchanged internal signal cables. Hearing tests – oops...there is no left side. Brumm test... one of boards in the left monoblock does not respond. The reason was simple: black “additional insulation” of signal cable was touching R1. It slightly conducts...See attached picture, for better view copper shielding is removed.