Electro. tantalum caps ok for A-40?

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Hi everybody!

This is my first thread at DIYAudio.com Now see if it works like it seems... :)

I built a couple years ago an A-40 using Sprague capacitors for the 220µF 10V ones. They seems to be "CSR13" type as they bear the "M39003-01" code on them (vishay website http://www.vishay.com/document/40018/40018.pdf ). I buyed them as surplus and they seems pretty big as they don't fit the original PCB placement.

The point is I am having an excessive noise problem (can hear it from my listening posision) with the amp. I hear a 60 Hz hum and kind of harmonics buzzes. Now the amp is under a "two monoblocks" form factor. I mean completely seperated, as in two chassis. I thought of a grounding problem first (and this may still be the case), but I tried to ground lift one of the two amps: no better... I also tried some ohms (actually 20) (as Mr. Pass have suggested) at the ground interconnect end to eliminate any ground loop from my pre or the other amp: no improvements. Only my power amps are grounded. I begin to suspect the tantalum caps as they are pretty fragile (10V rated). If this can help, I also have a little DC offset at the input of the amp.

If anyone can help...

Thanks in advance

Nicholas Paquet aka Zappa
1st of all please do not use tantalum caps in analogue audio equipment unless absolutely required to. They simply sound horrid in most cases. Film caps are generally well favoured.

2nd, the noise you hear is almost certainly power supply noise ... you could try adding a nice big phat pi filter (20,000uf caps + 2mH choke + Lots more caps.) Also do the monoblocks have their own power supplies or are they running off the same power supply?
Joined 2002
I agree with AudioFreak that it sounds like the power supply, but you can't use a PI filter unless you change the transformer. The A40 is designed for +-32V rails and with a PI filter you'll have something closer to +-20V rails.

If the amp has seen a lot of use, or if you used surplus caps, you might want to check your power supply caps. One or more may be going bad.

Have you had the same noise problems from the start?:confused:

Is the noise the same from both mono-blocks?:confused:

I also agree with AudioFreak that you should get rid of the tantalums. Just replace them with some electrolytics. There are some recent threads that discuss audio quality electrolytics so I won't venture an opinion on brand. I have a bunch of 220uf Panasonics I bought many years ago just for the A40. If your interested, send me an email and I'll get some to you for postage.

Rodd Yamashita
Really, you're a kind person Rodd, :)

I must thank you but I think I have not-so-bad 220µF electrolytics at hand. I will try them.

For the noise, yes I get the same on both monoblocks (yes, each of them have his own seperated PSU), and I bought new computer grade 20kµF ones, as presicribed...

Unfortunately, the idea to get with 20V rails make my hair straight up :eek: , so no PI this time...

Anyway, I plan to build an Aleph 5 from the parts (mostly PSU) of my present A-40 if I can't get rid of this noise...
The one and only
Joined 2001
Paid Member
A couple of comments:

Don't use Tantalums in the signal path; they are indeed
a bad choice. They are fine, however, for supply bypassing,
and on the bias network.

A lot of people who build the A40 got JFETs with the pins
reversed as shown in the article. If this is the case, the
JFET does not function as a constant current source and
also too much current runs through the diodes which bias
up the bipolar constant current sources. This can be the
source of a lot of noise.
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