Preamp losing low end. Cap time?

[LowEZ]

I have a 25-year old solid-state Peavey preamp that over the last several years has been losing definition and authority in the low end. Peavey used electrolytics for almost everything - there's about 35 electrolytic caps in there other than power supply filtering. Do you think a cap job would help restore the low end? Even though it would only cost me about $20 in caps, that's still $20 more than I'd like to put into an $89 preamp before consulting others.

Thanks all.

[nashvillebill]

Entirely possible, I've found electrolytics in Peavey preamp circuits that had gone south.

Caps are cheap at Mouser or Digikey, once that preamp is re-capped it should hold its own compared to newer preamps. I'd recap it.

[LowEZ]

Thanks Bill, "entirely possible" is worth $20 to me. I'll give it a go.

Appreciated.

[B-string]

Just stay away from Panasonic caps!

[JGR]

It's worth changing the filtering in the power supply - that can certainly restore punch, clarity, and dynamics. I wouldn't bother with the regular signal caps, at least not initially.

[WingKL]

Small value low voltage capacitors are pretty cheap. Get an ESR meter ( a good investment if you plan on fixing more electronics with bad capacitors, especially those made between 1999 and 2010 ) and find out which caps have gone bad and replace those.

@B-string, what's wrong with Panasonic caps?

[bgavin]

I am not an amp tech, nor do I play one on TV.
However, as a computer tech, I have a load of experience re-capping system boards.

Electrolytics do indeed dry out and go South permanently.
Visually, you can look for leakage and bulged tops.
The ESR meter will confirm you have a bad cap, but often you have to remove it to check out of circuit.
At that point, it gets replaced anyway.

The caps most subject to damage are those that run the hottest.
Higher voltage, or caps subject to lots of ripple filtering are high on the list.

To do a decent job, you will require a soldering station with an adjustable range up to 450C.
You want to heat the local area quickly without heating up the surrounding area.
A desoldering station, with vacuum assist makes for the cleanest job.
There is a learning curve as you come up to speed.

These are not investments one makes for a one-off repair.
If you can find somebody competent at recapping, it is probably more cost effective to hire them.

I use Panasonic when I cannot get Rubycon.
A domestic supplier for Rubycon and other premium caps is The Cap King

[LowEZ]

Thanks Mr. Gavin. I'm not a tech, but I am a tinkerer. I should have pointed out that I am no stranger to this having recapped many amps over the last 30 years. This particular unit will be easy - thick PCB, thick traces and access panels top and bottom precluding the need to pull the board. There's no high voltage in this unit (+/-22Vdc supply) which is why I asked if 25-year old caps are still suspect.

Still wondering about B-string's aversion to Panasonic caps though...

[B-string]

I have found Panasonic caps to be more on the low side of the tolerance range at a high percentage. My second to last test final test will be at over-voltage (130VAC in USA) 1 in 4 high voltage Panasonic caps will blow under that test. Panasonic are my last resort and I will over-buy to weed out and replace those that fail before leaving my care. My experiences.

[beans-on-toast]

Interesting comment about your Panasonic cap experiences.

I've found that there are Panasonic caps, and then there are Panasonic caps. When it comes to that make, I've used Panasonic industrial HD, ED, and HC series snap in type caps in a lot of applications and have been pleased with the results. You see this type in amp power supplies. Maybe these caps are built better than the type that you've been using.

I like the ED series because of the high ripple current capacity. This lends itself well to amp power supplies. Trying to find this spec from a lot of manufacturers is next to impossible. Often you'll get a capacitance, tolerance, and temperature spec, sometimes an ESR but little else. Ripple capacity is an important consideration.

Worth checking them out if you haven't tried them. The only drawback is that they are best mounted in a circuit board designed for their leads although I've used them by wrapping and soldering wires onto the leads. I tend to buy boards to mount the caps on and customize them to fit the application.


David

[B-string]

ED series look interesting. My purchases are repairs so generally radial leads are the call. I do add vibration control so maybe wrapping to lead them would not be an issue for added failure point?

[beans-on-toast]

Yes, I know what you mean about applications requiring radial caps. In a lot of amps it is the best way to go.

With the snap-in type, you need to tie down or glue the cap to prevent it from moving if you aren't soldering them in place on a board. Even then manufacturers use glue as a supplement. Wrapping a wire and soldering, then covering with heat shrink tubing works but is not ideal.

I use these caps mostly in new builds, in prototyping, and sometimes if I want to modify an existing design. This is one of the boards that I use with these caps, SDS Labs Mk3 Capacitor board. I use it as is or trim it down to fit whatever footprint is needed. It can get very expensive but it works out a bit less than having custom boards manufactured. So it is good for one-offs.

[B-string]

Sweet idea. I might be in the position soon to do some of my own designing again. I bookmarked those links.

[grendle]

yep recap the whole thing. Never any problems with panasonic caps either. we dont run them even close to their ratings though (you shouldnt anyway).