ADR F760X-N/RS Capacitors

[John Mc Donnell]

i have some ADR F760X-N and a F760X-RS for recapping.
The F760X-N's have all original Phillips caps on board.
According to the schematic, the A board should have two 8/25v caps,
but I find 15/40's instead.

The F760N-RS has been partially recapped with 22/63v for all 15/40v and 8/25v's.
Also on both B boards output amplifiers, the 4K7 resistors from the outputs
have been cut.

Any wisdom on the above would be greatly appreciated.
JackMc

 

[Brian Roth]

Mods....this thread should be moved to The Lab, since the rules for this section are "Post Schematics Only, NO requests, NO comments". I might be able to assist this new member.

Bri

 

[John Mc Donnell]

Mods....this thread should be moved to The Lab, since the rules for this section are "Post Schematics Only, NO requests, NO comments". I might be able to assist this new member.

Bri

Any assistance you can offer will be great.
As you have noticed, I'm new to this.

JackMc

 

[abbey road d enfer]

Also on both B boards output amplifiers, the 4K7 resistors from the outputs
have been cut.

Very likely to increase gain by about 6dB.
These ADR moduules are known to have limited headroom. Previous owner may have found it lacked in this department.

i have some ADR F760X-N and a F760X-RS for recapping.
The F760X-N's have all original Phillips caps on board.
According to the schematic, the A board should have two 8/25v caps,
but I find 15/40's instead.

The F760N-RS has been partially recapped with 22/63v for all 15/40v and 8/25v's.

In many cases, recapping with higher nominal value results in improvement of preformance.
Modern capacitors have so much improved compared to those used in the 70's/80's that it would be silly not to benefit.
Take the opportunity to use a higher nominal value (for example these 15uF could be increased to 33).
Increasing nominal value decreases LF distortion.
The 40V rating does not really need to be increased, but the 25V could be increased to 35 at least.
And if possible use 105°C types, for reliability.

 

[John Mc Donnell]

Very likely to increase gain by about 6dB.
These ADR moduules are known to have limited headroom. Previous owner may have found it lacked in this department.

In many cases, recapping with higher nominal value results in improvement of preformance.
Modern capacitors have so much improved compared to those used in the 70's/80's that it would be silly not to benefit.
Take the opportunity to use a higher nominal value (for example these 15uF could be increased to 33).
Increasing nominal value decreases LF distortion.
The 40V rating does not really need to be increased, but the 25V could be increased to 35 at least.
And if possible use 105°C types, for reliability.

I find that with the resistors disconnected, the gain is 0.
When connected the gain is about +5db.

I notice the clone version of this unit has al the same capacitor values as the original,
apart from the 8/25v, which are 15/40v.

Still not sure what way to go here.
Any input would be greatly appreciated.
JackMc

 

[abbey road d enfer]

I find that with the resistors disconnected, the gain is 0.
When connected the gain is about +5db.

Then it must be other 4.7k resistors than the ones in the NFB loop.
Can you identify them on teh schemo?

I notice the clone version of this unit has al the same capacitor values as the original,
apart from the 8/25v, which are 15/40v.

Still not sure what way to go here.

About what? Capacitor values? I already gave an answer.