Request: Copland CSA-8 Schematic

[gianxdiy]

Hi everybody,
I have a Copland CSA-8 with some problems in the final stage.
Is there anybody so kind to provide a service manual or a schematic?
I searched the web and here on DIY, but it seems nobody cares about this model.
Many thanks in advance.
Regards,
Gianni

[john65b]

Ciao Gianni,

I had a CSA-8 a while back but sold it. Output was a single pair of 2SA1943/2SC5200 per channel. Front end was 2SK170/2SL74 JFETs (I think). The CSA-8 was a JFET version of the CSA-14 Tubed (6922?) front end. You can still see the noval tube silkscreen on the PCB marked CSA-14.

Can't help with a schematic, but you can check the rails and bias settings. Power supply caps too.

The only thing I did to mine was check the bias across the emitter resistors of output devices - there is a pot right there by the emitter resistor. I set mine for 20 - 25mv. I got that 20 - 25mv from a recommendation from a thread here - optimum bias setting for class A/B by John Curl. It was around 8 or 10mv initially. The sinks were fine with it...

This is interesting - I grew up near you in San Benedetto Del Tronto. Interesting, no??

[gianxdiy]

Interesting? We have also the same name and simiar age (1967)!
Back to the baby: I read your post here when you sold it.
Very useful information, thanks!!!
I saw it inside and i know it'a 14 no-tube, but:
-It has Toshiba 3281 and 1302 as output bjt's and rails a bit lower than that of the 14.
-Bias is 9mV (one channel, the other goes up and down).
The question about bias level is strange, class A/B tipically shows its minimum distortion around 45-60mA, and when we talk in mV we have to refer to the value of the emitter resistor. 20-25mV is for 100mA for a .5 ohm, a bit high i think.
I will check everything and than i will proceed.

Are you italian or not? i didn't understand this.

[john65b]

Si sono italiano. Nato 1964 in Chicago, venuto a San Benedetto 2 mesi eta, poi returnato a Chicago a 6 anni...mi parenti di San Benedetto e Rimini.

Sorry, my Italian sucks.

I think the 2SC5200/2SA1943 and your 3281/1302 BJT were similar (fast at 25 or 30mhz?). Is the channel with stable bias sounding OK? Just the channel that has unstable bias sounds bad?

I am recalling this from memory - maybe it was 20 - 25ma instead of mv...as you indicate, mv would depend on the emitter resistor value...

[john65b]

I managed to find a pic of my amp - I had R22 emitter resistors...sorry for the huge pic...

I remember my originally set bias was around 9 - 10mv with R22 emitters before I ramped it up to 20mv. You have 9mv on .5 ohm emitters...I wonder if this is because of the different output devices?

Both emitters show stable on same channel, while both emitters are unstable on the other channel?

[gianxdiy]

you lived in italy for 6 years, your italian is good!
So, for .22ohm, 20-25mV range would be perfect, 44-55mA, as John Curl recommended
Yes, i think 0.5 is for the different devices, less powerful, more local feedback and protection. The other channel sound dull, i'm checking now...