F4 power amplifier

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#2,022
José Humberto said:
...what does sound with the Nichicon?
Do you hear differences?
Click to expand...


Hi Jose,

Differences are difficult to explain.

Before:
Ambient scene was larger, easier to observe, sound was sharper and more aggressive in the treble, especially at >50C, like conventional capacitors added more grain at higher temperatures. Altogether – I was tired after one hour of listening.

Now:
C1/C2 = 220uF/50V “Bi-polarized Nichicon MUSE ES (green)” plus added in parallel 47nF/100V “VISHAY MKP”
C3/C4 = 220uF/50V “Nichicon MUSE KZ”

There is more air but at the same time ambient scene is not so large as before, I do not understand why. Now the sound is clearer. Less grain. Piano sounds much better, almost perfect. Altogether – listening is more comfortable.

Someday I hope to try 100uF “Black Gate N”, maybe with added in parallel 0.47uF “Black Gate NX”.

Best Regards,
a.
 
#2,024
Nichicons need to "run-in" for quite a few hours - at least 24 to 48, before they start to sound good - MKPs taken longer.
If you are patient with them, you should get a very clean sound overall with a heavier, more solid base.
Might find the 47nF may (note: MAY) benefit from a 0.1ohm in series.
 
#2,027
jameshillj said:
Nichicons need to "run-in" for quite a few hours - at least 24 to 48, before they start to sound good - MKPs taken longer.
If you are patient with them, you should get a very clean sound overall with a heavier, more solid base.
Might find the 47nF may (note: MAY) benefit from a 0.1ohm in series.
Click to expand...


JH,
Thank you very much for interesting advices.
Today I listened with pleasure a cappella choir singing ancient music. I discovered delicate natural hisses. And a choir breathe in at Vangelis 1492. Very nice impressions. When capacitors mature maybe it will start to disturb me someday, or not, I will know. My wrong hearing depends on if I am tired, a little bit drunk, or just have a cold...
Best Regards,
a
 
#2,028
Helloo there!
I have built a pair of F4's and they work just fine, but i have a little problem with one of the chanels. It has a very little buzz. It is so little that it is bearly hearable with the ear next to the speaker - but it is there and it is annoying. The othere 3 chanels are dead quiet.
Anyoane any ideea of what shoud be the problem????

PS: I do not have ground loops and all of the other chanels work in the same conditions.
 
#2,029
Here is a drawing of the 2 f4's and the buzz...
 

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#2,031
ahegyes said:
Here is a drawing of the 2 f4's and the buzz...
Click to expand...

Hi...you can try the following:

1. Check the resistors for correct values. If you have a faulty ground resistor (as I had with my A30) you will have exactly this problem.

2. Isolate the humming channel, so it is the only active channel. trace with a scope where the humm is comming from. Is is 50 or 100Hz? 50Hz could indicate humm pickup from mains; 100Hz pickup after rectification. 100Hz could indicate a bad cap or high bias current.

3. Compare the DC voltages on every node of the amp and compare them with the other channels. Try to find the origine of each deviation.

4. Use cold spray / solder iron to heat/chill the Jfets Junction problems can cause this as well.

5. Inspect the PCB for parasitic traces of solder.

6. Only use the amp with teh humming channel. Leave the other disconnected. Is the amp still humming? if not...are you sure about your grounding?

I hope this helps. This can be quite hard to find...
 
#2,032
ahegyes said:
Helloo there!
I have built a pair of F4's and they work just fine, but i have a little problem with one of the chanels. It has a very little buzz. It is so little that it is bearly hearable with the ear next to the speaker - but it is there and it is annoying. The othere 3 chanels are dead quiet.
Anyoane any ideea of what shoud be the problem????

PS: I do not have ground loops and all of the other chanels work in the same conditions.
Click to expand...

- try to move cables (left, up, right, down) connected to this channel
- move transformer or the buzzing board - maybe the distance is to short
 
#2,034
I've read the earlier part of the thread where early builders had problems trying to dial in enough bias current when adjusting P1. Some circumvented the problem by changing R9 to 6.8k instead of the original 10k.

But I wondered if it is because the earliest schematic had R8 at 22.1k instead of the latest schematic which had R8 at 27.4k.

So did any of the recent builders using the latest schematic had issues dialing in the bias current with R9 at 10k?

thanks

her shann
 
#2,040
jameshillj said:
Nichicons need to "run-in" for quite a few hours - at least 24 to 48, before they start to sound good - MKPs taken longer.
If you are patient with them, you should get a very clean sound overall with a heavier, more solid base....
Click to expand...

Hello JH,
I try to be patient, not easy. I see I have some problems with my ears,
a kind of slight infection. Normally I do not hear the differences but while listening my f4 I discover sometime better perception of trebles at the left, sometime at the right side. From few days I plug my ears with cotton wool when I am outdoor, it helps me to keep acoustic symmetry of audio perception later, at home. I am sensitive for a cold weather.

I also observe not so deep ambient acoustic scene as before Nichicons with MKP Vishay caps. Sound is perfectly clear now, maybe to much highest frequencies, maybe I will detach MKPs later.
Did you have similar phenomena?
Regards,
a.
:wave2s: :crackup:
 
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