Carver C4000 Recapp project

[cimix]

Hello, I decided to recap the preamp myself. I have a question, and I would be extremely grateful if someone could answer, please.

I am following the schematics that I downloaded, and I noticed that at least on the Tone and Bandpass boards, some of the installed capacitor values do not correspond to the ones in the schematics. The installed ones seem to be 10x lower. Ex 2.2 uF installed 22 on the schematics, 10 installed 100 on the schematics. What rule should I follow: replace the same values as the installed ones, or match the one on the schematic?

I purchased a kit from Ebay from Hi-Fi-Audio-rocks, and the capacitors match the schematics, not the mounted ones. His advice was: "I would stick to schematic! I would stick to schematic!It is common for assemblymen to make mistakes."

It seems too much of a coincidence. I recapped a Phase Linear amp last year, and I did not have the same issue.

Thank you so much!

 

[J!m]

Since it presumably worked after it left the factory, I always replace with the same value as on the board. Your friend is right- mistakes happen- but revisions also happen, that may be in a newer schematic or never documented.

Regardless, I always go up on voltage beyond both schematic and value of removed capacitors.

 

[mlucitt]

What rule should I follow: replace the same values as the installed ones, or match the one on the schematic?

Schematics are normally the rule. But many schematics were drawn by engineers before the unit went into production. Then changes were made (not always good) but mostly to improve the actual performance over the design performance.

For electrolytics in the Power and Ground circuits, mostly bypass and filtering, the values are not critical. It is typical to increase the voltage and capacitance by 50% if the same footprint can be found.
In the signal path, the Carver 4000 uses capacitors in high and low pass filters. Also, capacitors were used in timing circuits. Retain the same values in new capacitors as the installed capacitors to maintain the functionality of the unit. Often signal path electrolytics can be replaced by bipolar electrolytics. And, if the capacitance is small enough, Polypropylene Film capacitors can be used for reliability and consistency.

 

[cimix]

Agreed I will keep what is installed. Thanks.