Upgrading Channel Cards to latest Revision?

[tlmaen]

Hi,
I am planning to partly recap the Channels of my 4KE.
I compared the VCA Card with the Schematics of the E-Series Service Manual (probably a very late manual, its from 86).
A lot of the Capacitor and Resistor Values have been changed in later Revisions.
Is it advisable to use these newer values?
For example, my VCA Card is Rev 4, but has the VR3 already fitted, wich was introduced at Rev 5.
The capacitor values are from the original Rev 4.

Good idea?

Thanks,
tlmaen

[amillar]

Hi,

Here's my thoughts on the changes, I probably designed (or at least advised) all these changes but as usual since it was nearly 40 years ago these are best guesses from distant memories and looking at the circuit.

• R35: If you are modding ALL your 13 cards then worth changing this. It stops you losing a bit of potential gain on your fader.
• VR3: I think we had a batch of DBX's that would not set up properly, after they changed from the gold can to the "bare PCB" type, so we added this. Only needed if there is a problem with the VCA setup
• C8: I will come back that after this list...
• C13, C14, C21, C22: Again I think problems came with the "bare PCB" 202X's, yes I would suggest making these modifications to improve the power supply smoothing. I can't quite remember what they were for, I think it was to stop signal appearing on the VCA control line and so reduce distortion.
• R60: again, for the "bare PCB" 202X's to improve setup (distortion trim), yes I would suggest making this modification, but you will need to setup the distortion trim afterwards.

For C8, definitely make it 100uF, it will improve the low end. I pulled this out separately because there is an important point here: generally when re-capping a 4000 I would suggest looking at increasing the values of all the coupling capacitors. Remember that when these were built electrolytics were physically bigger than they are today, so their value often had to be smaller than it ideally would be, which is why the bottom end of a 4000 is not very good (particularly the E series). Nowadays you should be able to fit higher value capacitors in the same space.

One day that would make a nice project for this forum - recommending re-capping values to improve the bottom end!

Thanks,

Andy

[Clip6]

Thanks Andy. So glad your here.

[horizonsound]

The 82E13 card went through a number of revisions (9 in total i believe).
Quite a few of these revisions were around the changes to the DBX module as Andy mentioned. 202X, 202C
Input and output resistors changed to suit, to improve gain, at the expense of THD. (Rev 7 onwards)
There were a few other mods on the board being :-
Addition of D30, D31 zener diodes to limit DBX control voltage input.
VR3 offset trimmer
Upgrade of filter caps to 220uF.

Anthony.

[horizonsound]

FYI regarding resistor changes.

[tlmaen]

Hi,

Here's my thoughts on the changes, I probably designed (or at least advised) all these changes but as usual since it was nearly 40 years ago these are best guesses from distant memories and looking at the circuit.

• R35: If you are modding ALL your 13 cards then worth changing this. It stops you losing a bit of potential gain on your fader.
• VR3: I think we had a batch of DBX's that would not set up properly, after they changed from the gold can to the "bare PCB" type, so we added this. Only needed if there is a problem with the VCA setup
• C8: I will come back that after this list...
• C13, C14, C21, C22: Again I think problems came with the "bare PCB" 202X's, yes I would suggest making these modifications to improve the power supply smoothing. I can't quite remember what they were for, I think it was to stop signal appearing on the VCA control line and so reduce distortion.
• R60: again, for the "bare PCB" 202X's to improve setup (distortion trim), yes I would suggest making this modification, but you will need to setup the distortion trim afterwards.

For C8, definitely make it 100uF, it will improve the low end. I pulled this out separately because there is an important point here: generally when re-capping a 4000 I would suggest looking at increasing the values of all the coupling capacitors. Remember that when these were built electrolytics were physically bigger than they are today, so their value often had to be smaller than it ideally would be, which is why the bottom end of a 4000 is not very good (particularly the E series). Nowadays you should be able to fit higher value capacitors in the same space.

One day that would make a nice project for this forum - recommending re-capping values to improve the bottom end!

Thanks,

Andy

Thanks Andy!
I noticed that none of my Schematics matches the revisions of my cards (My Cards are roughly between Rev 3 and Rev 7)
On top of that, my VCA Cards have different kinds of VCAs fitted. I have to check all of the channels.
Are you sure with C8? Isn't it C9?

I identified all of the filter Capacitors for the voltage Supply, they will be replaced by Elkos. They are all 10uf.
Is it recommended to increase these values to 100uf or even 220uf?
What about the increased load with higher Capacitors values when you switch on the Console?

It would be indeed a very useful project identifying all of the coupling Capacitors.
(can you say its generally advisable to replace all of the 35v rated C's with higher values)?

If someone has Schematics for the Channel Cards of a 80's E series, that would be great!

Thanks,
Tlmaen

[tlmaen]

FYI regarding resistor changes.

Great, thanks!