Dried out electrolytics in an amp.

[peranders]

Beppe it's a good idea to have your email button enabled. Your email address won't get revealed unless you answer.

 

[beppe61]

Dear Mr. Peranders,

" Beppe it's a good idea to have your email button enabled.
Your email address won't get revealed unless you answer."

How can I do that ?
Thank you very much again.
Kind regards,

beppe

 

[peranders]

Push "USER CP" at the top

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Your has a flat response down to 3.39 Hz.

The feedback consists of (47 uF+ 1k) + 22 k => gain is 23 times

The smoothing is 2 x 10000 uF per channel but.... the transformer has no centertap still it has ground somewhere??? An error in the schematic?

Otherwise the design is pretty basic. No rocket science

 

[peranders]

Beppe, could you do some reverse engineering.

1 Does the transformer only have two wires from the secondary winding?

2 Is it true that the center of the big 10000 uF pair of caps are connected with only one wire between the channels?

3 Where does the speaker ground go to?

 

[beppe61]

Push "USER CP" at the top
then EDIT OPTIONS choose "Hide Email Address?" check NO

- Thank you Mr. Peranders. Done !

> Your has a flat response down to 3.39 Hz.
- So the weak bass response is not depending on the design.

> The feedback consists of (47 uF+ 1k) + 22 k => gain is 23 times
The smoothing is 2 x 10000 uF per channel
- I confirm this. Some not well identified "custom made" caps.
I do not know anything on their quality.

> but.... the transformer has no centertap still it has ground somewhere???
An error in the schematic?
- Dear Mr. Peranders, I checked and actually the transfo has two windings that go to two diodes bridges and centertap.
So there is an error in the schematic.

> Otherwise the design is pretty basic. No rocket science
- I am all but an expert but it seemed the same to me.
But this is a mine field.
I remember a test of a british solid state amp where the reviewer said that the design was "obsolete".
It became his reference amp for the quality of sound.
But in this case I ma not talking about shadings.
I miss the low bass! the sound is very thin indeed.
I am afraid that the quality of the transformer is not that great.
My opinion is that of a basic but linear design undermined by bad components, firstly the transformer.
But I am gambling here.
What is your opinion?

Thank you so much.
Kind regards,

beppe

 

[beppe61]

Beppe, could you do some reverse engineering.

1 Does the transformer only have two wires from the secondary winding?
- There are 2 wires for each secondary (i.e. 4 wires) that come out from the transfo and go to two separated diodes bridges (one for each channel).

2 Is it true that the center of the big 10000 uF pair of caps are connected with only one wire between the channels?
3 Where does the speaker ground go to?

- The grounds of the two pairs of filter caps are connected together and go to a single screw where is connected the speakers ground as well.
I do not hear any particular noise or hum etc.
I am more and more convinced that this lack of energy in the bass could be related with a bad execution of the transfo (i.e. low regulation factor or high impedance secondaries).
As I said a nice simple even basic design let down by a cheap transformer.
In my experience all great power amps begin with a huge and high performance transformer.
I am even thinking to buy two separate 500 VA toroids, just to try a rescue.
I saw some nice ones from Talema (7% of regulation factor).
What is your opinion?
Thank you sincerely.
Have a nice weekend.

beppe

 

[peranders]

If you say the transformer has 4 wires, then the schematic has some errors, don't agree? So if you have two secondary windings you have proabaly a DC connected speaker output and this means flat response down to 3 Hz but not at full power of course.

If those 47 uF is a bit dry then you will have a reduced bass. If you want to test, just solder in a 47 or 100 uF in parallel. It can't harm to test.

Have you located the caps? Near the input, I think it says C609, in series with 1 k.

 

[beppe61]

If you say the transformer has 4 wires, then the schematic has some errors, don't agree?

- Definitely Mr. Peranders.

> So if you have two secondary windings
- Yes this is the case
> you have proabaly a DC connected speaker output and this means flat response down to 3 Hz but not at full power of course.
If those 47 uF is a bit dry then you will have a reduced bass.
- that is the reason of my original question: if a dried out cap in the feedback loop can give reduced bass response.
Thank you so much for this very interesting advice.
> If you want to test, just solder in a 47 or 100 uF in parallel. It can't harm to test.
Have you located the caps?
Near the input, I think it says C609, in series with 1 k.
- I will do it in the next days.

I swear Mr. Peranders, just a one last question.
I see 4A fuses (marked F601 and F603 on both channel) in series with the voltage rails after the filter caps.
Could they be some sort of bottle-neck for the supply?
May I bypass them with a piece of wire ?
I really do not like to see fuses between the power supply and the amplification circuit.
It seems quite strange to me.
What is your opinion?

Thank you sincerely again.
Kind regards,

beppe

 

[peranders]

I see 4A fuses (marked F601 and F603 on both channel) in series with the voltage rails after the filter caps.
Could they be some sort of bottle-neck for the supply?
May I bypass them with a piece of wire ?
I really do not like to see fuses between the power supply and the amplification circuit.
It seems quite strange to me.
What is your opinion?

Don't do anything with the fuses. Just check that the conact pressure is enough and the metallic surface of the fuses seems OK, meaning good contact. Sometimes it's enough only to roll them or take out and put themn back again.

 

[beppe61]

Don't do anything with the fuses.
Just check that the conact ...

Thank you Mr. Peranders.
I asked you because I found a thread about fuse impact on sound (i.e. someone state the ceramic ones are better than glass ones) so I wondered ...

Anyway thank you very much again.
Kind regards,

beppe