Advice on recapping - Telefunken W690 faders

[flextone]

Hello,

recently one of my Telefunken W690 active faders started distorting. This happens when I turn up the fader to the point it becomes "active, i.e giving me some amplification of the signal. I got these second hand years ago and never recapped them. Since they are extremely old I guess it's time, although this is not my forte. I'm adding some pics, and the schematics are attached as pdf.

My instinct tells me these big electrolyte caps might be the culprit, especially the one that shows some discolouration. Maybe your eyes see some other problem? Would you try a full recap instead?

Also, can I use non-polarized caps to replace these? Any suggestions?

Thanks!

 

[MaxDM]

Regardless, you need to change those old electrolytic caps..

The other ones are probably ok

You need to post a sound file, to get a better response, though, because it might be something else

 

[Bo Deadly]

Honestly that doesn't sound like a capacitor failure mode. At least I've never heard of something like that.

However, those caps are probably ancient. I would have replaced them to start. But you'll probably have to order them from somewhere like Mouser because axial caps are much less common. Definitely don't need non-polarized. Using a fancy electrolytic in this case will do absolutely nothing. Just using a modern electrolytic will be an upgrade compared to what those were on their best day (but it still won't make a measurable difference in performance). Just get the right capacitance and voltage. Don't go higher or lower or try anything cute.

 

[rock soderstrom]

The white (yellow?) tantalum capacitors are the #1 suspects.

 

[mjrippe]

[snip] But you'll probably have to order them from somewhere like Mouser because axial caps are much less common. Definitely don't need non-polarized. Using a fancy electrolytic in this case will do absolutely nothing. Just using a modern electrolytic will be an upgrade compared to what those were on their best day (but it still won't make a measurable difference in performance). Just get the right capacitance and voltage. Don't go higher or lower or try anything cute.

No need to buy expensive axial caps, radial work exactly the same and modern caps are smaller so they will fit in the same space. At worst you might have to lay it on it's side. Those values (2200uf/16v and 1000uf/35v) are very common so yeah, no need to order something special.

 

[Bo Deadly]

No need to buy expensive axial caps, radial work exactly the same and modern caps are smaller so they will fit in the same space. At worst you might have to lay it on it's side. Those values (2200uf/16v and 1000uf/35v) are very common so yeah, no need to order something special.

But then you would have to have one lead going backward over the body of the cap and maybe even worse, tack on an extra bit of bus wire to make it work.

 

[flextone]

Alright thank you, so if I already have you guys here I'd like to diagnose this a bit before going further with locating the parts.

I'm attaching an audio file. These are two phrases, each recorded once with the fader around its middle point and once pulled all the way up. In the DAW, you can clearly see the difference in the waveform (DC offset?). See screenshot attached.


Thanks you guys so much.

 

[rock soderstrom]

My bet: One or more of the tantalum coupling capacitors are DC leaky, thus the operating point of the following stages is shifted.

I prefer the distorted phrases

 

[flextone]

My bet: One or more of the tantalum coupling capacitors are DC leaky, thus the operating point of the following stages is shifted.

I prefer the distorted phrases

Will measuring their capacitance help in this case, or is this just half of the story?

 

[Bo Deadly]

Will measuring their capacitance help in this case, or is this just half of the story?

No. It could be difficult to try to identify the particular capacitor at fault. If one is leaky it's likely that more are as well.

I would just remove all of the tantalums and replace with electrolytics of the same size / voltage rating or slightly larger / higher.

Just be careful desoldering that board as it could probably be damaged easily.

 

[dmp]

I re-capped a pair of Siemens W290V (similar) and racked them a few years ago. I only replaced the electrolytics - probably should have done the tantalums too These caps are all polarized, so pay attention as you take them out (taking pictures is a great way to reference back). I've got a w690 in a box here I need to recap and rack too.
These are really cool - they used a multi tapped transformer for the fader. Remove the old caps out using a desoldering gun like Hakko 808, if possible. You really don't want to tear a trace. And a desoldering gun is one of the best purchases I've ever made!

 

[flextone]

OK. 12 caps per fader without getting the polarization wrong on the tantalums. This should be fun...

Honestly I would just take it to a tech but this pair cost me 20€ on ebay and I just had a reverb unit repaired.

Looking at other faders from the era, it seems that this board is very heavily populated. Could it be that these have all the caps for a stereo version ready, but only half are being used? Then they could pop in the extra transformers and make a stereo version. Just a thought.

 

[dmp]

Nope - 12 for a mono channel is correct. Here's the schematic.
You got a pair of w690s for 20 euro? That's a steal! They are worth restoring. Where are you located?

 

[rock soderstrom]

I would just remove all of the tantalums and replace with electrolytics of the same size / voltage rating or slightly larger / higher

I would probably stick with Tantalum Caps, other types will work as well. You can test with the continuity tester of your multimeter, the completely defective ones show continuity, the half-dead ones are a bit more difficult to locate.

I would change them all, too. Shotgun mode.

 

[dmp]

I would change them all, too. Shotgun mode.

yes, but there are some tantalum that are just used in the power filtering and could be replaced with electrolytics.
The only polarized caps that are really in the audio path are #101 & #119 (15 uF). You might be able to hear a difference with those.

 

[rock soderstrom]

yes, but there are some tantalum that are just used in the power filtering and could be replaced with electrolytics.
The only polarized caps that are really in the audio path are #101 & #119 (15 uF). You might be able to hear a difference with those.

Yes, you can do it that way! But somehow the PSU caps are also part of the signal path. To stay close to the original I would probably choose the same types. Matter of taste.

 

[dmp]

I'm definitely not arguing with you! I would do it that way too. Just trying to contribute some helpful info to the OP.

 

[rock soderstrom]

Everything fine, we are on the same side. Thanks for your input

 

[flextone]

Nope - 12 for a mono channel is correct. Here's the schematic.
You got a pair of w690s for 20 euro? That's a steal! They are worth restoring. Where are you located?

I'm in Berlin! Yeah... they were sold as "untested" and I grabbed them. Racked, worked great for 6-7 years. Now I want more tbh, at least an extra stereo one. I also have two Filtek eq's and two Filtek comps, one of which doesn't work and I gave up on it.

Cool, I'll try to locate matching caps and see how it goes. I might need some help with the radial electrolytes substitutes, but we'll get there

 

[rock soderstrom]

Well, hop over to SEGOR and pick up some Tantal caps! Viel Spaß mit den Jungs dort!