Upgrading PSU in old audio amplifier...

Hi,

I am about to upgrade an old (1982) 45W Class AB amplifier, and I have both new rectifier diodes (UG10DCT)and new ELNA capacitors (12.000uF/63V).

My original idea was just replacement of the old parts, but having played on the amplifier for some weeks, and it works well, I am considering other options also:

1:
Original idea, changing rectifier diodes and filter caps (8200uF/50V)

2:
Changing rectifier diodes but keeping filter caps. Then add R-C filters after with 0.22R and new 12000uF caps.

3: As in 2, but using the new 12000uF as first caps and using the old as second (part of R-C filter)

What would you do? :)
 

Eldam

Banned
2012-09-13 12:25 am
France
Hi Skorpio,

"3: As in 2, but using the new 12000uF as first caps and using the old as second (part of R-C filter)"


You have to do the opposite in a C-R-C: the lower value and the bigger ESR first (your old part is good enough for that or a resistant cap like 105°, then the big Resistor (10 W, 2 homs?? (or self)), then a 1,5 to 2 x value of the first cap but with very low ESR.

In the relation to the original value, a bigger value is maybe a risk to have a boomy bass (for example I have an old pionner with an unique PSU 70s' cap (ELNA) of 3300 and bass are very solid for this 15 watts amplifier even with 4 homs speakers !

My recette de cuisine with an old NAD Poweramp 2100 than I love with a lazy mod: replace the old good ELNA 10 000 uf caps (check at 8 000 uf after 10 years) with a basic Jamaicon 10 000 uf (50V/105°) : because the first cap behind the diodes is the one which suffer the more in an amplifier, but no RC after (I was in lazy mod) but just Panasonic FM 1500 uf (50V/105°), which has a very low ESR... I know it's the opposite than I write with the C-R-C, but in practice it works for me.
Very punchy, fast without hardness : very more better than the Elnas'.
You can use too the Elna Tonorex in second position, maybe in first (try): they sound natural, if this word has a sens in audio... My ref amp is a Chord 1100 B for benchmark my mods...

I would beginn with the caps and only compare with new diodes after...

My 2-R-1 cents...
 
skip the old capacitors

adding this much of capacitance for a 45 W pc of class AB amplifier will not change much ...

Though there plenty of other things that can be done to improve the other than that unknown amplifier .

Provide more data and then i may be able to share an opinion

Kind regards
Sakis

The amplifier itself is modded close to AKSA style, and performing very well...
 
Hi Skorpio,

"3: As in 2, but using the new 12000uF as first caps and using the old as second (part of R-C filter)"


You have to do the opposite in a C-R-C: the lower value and the bigger ESR first (your old part is good enough for that or a resistant cap like 105°, then the big Resistor (10 W, 2 homs?? (or self)), then a 1,5 to 2 x value of the first cap but with very low ESR.


My 2-R-1 cents...

As I read you, your recommend 2, but not changing the diodes first?

C1-R-C2, where C1 is original caps and C2 is new 50% bigger cap with low esr?
 

Eldam

Banned
2012-09-13 12:25 am
France
As I read you, your recommend 2, but not changing the diodes first?

C1-R-C2, where C1 is original caps and C2 is new 50% bigger cap with low esr?

Yes and Yes. In theory The CLC is the best, and the CRC in second. But we don't know anything about your amplifier. It's right you have to give the shematic or the ref for safety. I just talk for a transistors amp and never try tubes with high voltage.

With the datas you gave, I would do like that :

I always mod with the sames hifi systems to have a ref and with the same CD or LP discs to hears. I never change more than one thing before listing. I resetr the conf to benchmark two mods. I wait for tomorrow to listen again and go for anaother change or reset conf. It's a long empirical method but It's safer.

So here :
1: just add 10 to 20% value with a low esr cap (for example a panasonic FM, 1500 uF, cheap) in // with the old and listen. Is it better or bader, different ?
2 : Reset thye conf, listen, then if it's not difficult use the C1-R-C2, C1 is the original cap suposed to have a high ESR wich is better in this case, C2 is a newer cap with low ESR but the value 1,5 to 2 time bigger. Choose a strong R (10 W) because we don't know about the shematic, 1 to 2 homs mini with the hope than Voltage is sufisant after the drop. Then listen.
3: if 2 is difficult to do in your amp try this before : reset the conf, look at the spec of the original diodes and change with fast soft recovery diodes with the same spec (or better) in curent and reverse and voltage. (old cap in place). are there film caps // to the diodes, leave them if you put the soft fast recovery diodes...)

Which conf sound the best ? I you prefer 1 or 2, then after try 1+3 or/and 2+3. You can play too with C2 to mod the sound signature, but C1 has always to have a higher ESR (slower) and resistance (105°) and C2 better ESR, and 1,5 to 2 time the size.
The conf 3 is a half way between 1 and 2, maybe because fast recovry diodes play better than the old ones in theory. In practice you can damage the sound of a good design with these better parts. You have to try and reset if it's worse than before.
Step by step, it's long like my speach, but It's the better game I know after the lego when I was child !