Focusrite Red 6 Capacitor question.

[fazer]

I have a friends Red 6 in for repair.  It was having trouble with the mic preamp and eq High Mid Freq not working. 

I have a B&K 881 in circuit ESR tester.  I check the caps and find a bad cap in the in HMF eq section.  I replace it and the HMF comes back.  This thing has over 50 - 100uf/16v coupling caps and all of the caps show ESR of .9 to 2 ohms  ESR. 

The B&K tester says replace due to high ESR.    I have the unit working now and record some Acoustic guitar and it sounds good but this unit is 20 years old and I'm thinking about replacing all the caps in.   

My question is does the ESR really matter?  The unit is working well now.  and I'm sure that in time all of the  caps will fail.  I ordered a Hakko F300 to help with the desoldering.

Also I'm thinking of replacing with Panasonic low ESR type.  Kemet is what is currently used.  Any suggestions?

 

[fazer]

Picture to show layout.    51 of these 100uf /16volt caps used in this unit.  Most for coupling and a few used PWR supply filtering.

 

[jensenmann]

In my experience everything I ever recapped sounded better after recapping than before. I did record tracks through the gear before and after such efforts hence could compare what was going on audiowise. Recap completely and don´t look back.

 

[fazer]

quote from Jensenmann

In my experience everything I ever recapped sounded better after recapping than before

Well you were right.

I replaced all the coupling caps as they showed high ESR and were 20 years old.  I used - Nichicon KA 100uF/25vdc {3-KA-100025R0} there were about 53 .  I then replaced all power supply electrolytic caps  with new Nichicon as well, even though they checked out OK .     

The change in sound was very obvious.  It has almost a liquid like sound now in a very good way.  Very smooth, centered and linear.  I'm very happy with these Nichicon RA caps From Hand Made Electronics.  Also the Hakko F300 made the job much easier along with some other tips from the Forum.   

 

[jensenmann]

Thanks for the feedback!

 

[pucho812]

units that old should easily be recapped especially Neve designs as they tend to run hot which dries up caps over time.

Well done sir.

 

[Monte McGuire]

Not to dis' on your capacitor source, but Mouser, Digikey, Arrow, and others are authorized distributors who have new stock that will always be authentic, so I see no reason to buy from any third party. For a task like this, you just want fresh, authentic stock, and if you can figure out how to order from these dealers (it's easy) then you will have a simple and cost effective source of genuine components. For a recap, I don't want to do this often, just to limit rework stress on the PCBs and also to save the time. With known to be genuine parts, I know that I won't have to touch the box again for a decade or two, and that's nice.

Your earlier question - "is ESR important?" When using a tester, an indication of a worn out electrolytic is an increase in ESR, so in that context, ESR is important. For a power supply cap, low ESR will provide better filtering action, so almost all of the time, low ESR is better. The only time it is not better is when the capacitor is the load for an old linear regulator that was designed for a specific ESR capacitor, such as the LM337, and some other old regulators designed essentially for Tantalum caps. As long as you do a brief but thorough engineering of the circuit to see what it's doing, you can see if low ESR is a help or not. In general, it's almost always better, but again, some regulator circuits need to see a specific ESR, so you need to make sure what the case is.

A final concept is that sometimes low ESR, low impedance caps can have much higher leakage, which is usually not a problem with a power supply bypass, but it could be a problem for a coupling cap. Again, check the specs and the application circuit.

All the best!