Upgrading a Creek CAS4040s1

[Mario Pankov]

Bought this little amp yesterday to replace a Denon PMA-860, it should arrive sometime tomorrow.
I have read very good reviews on this little amp, however the one I`m getting is the s1 version and is over 25 years old.
I would like to service it and upgrade whatever is possible to. What I plan to do is:
- replace ps caps, I think they are 6800uF 35V. I can get Epcos and Panasonic here, which one would be better? Should I add 0.1uF or 0.01uF bypass caps and if yes, of what type?
- Replace all other caps with teflon or polystyrene caps
- Remove and isolate the tone controls, I do not need them
- Possibly change the rectifier bridge diodes with ultra fast shotky diodes

I will need the schematics of this amp, is anyone able to post it here? I am not much into amps design and I would appreciate some help with the tone controls removal. What else should i change/upgrade and is there a reason to change the driver/output transistors ( if there are substitutes with better specs )?

[QSerraTico_Tico]

Contact Creek for schematic. They were generous to a friend of mine.

[Mario Pankov]

Ok, so I have asked Creek for the schematics, I have heard they are very supportive and I hope to get it soon.
The amp arrived today, it is in excellent cosmetic condition, like new which I didn`t expect. It is the one with the HP Filter instead of Mute. Now the interesting stuff:
On the manual it says that only DIn connectors are available, however this one has been fitted with RCA jacks on the Disc input. I looked carefully at them, they look like a factory instalment. Transformer is not toroidal but an R-core, I suspect it has been replaced. I`ll do some measurements tomorrow, following the manual, it should give 44V. Inside I see a pair of Rybicon 3300uF caps and a big cap connected to the mains transformer with the size of 4700uF. I noticed that the amp plays for a few more seconds after being turned off, perhaps this cap has something to do with this. I thought it has been added by someone and then suddenly I found this discussion on a italian forum where the amp looks like mine but this one has Mute and CD/Aux and I think has a repaired output stage.

Videohifi Forum

I will try to restore this amp to its original shape, won`t cut the bass/treble controls as it looks like a good machine and deserves it Some new caps won`t hurt it though but isn`t 3300uF too small for a 30W amp? I know the later s2 and s3 have 6800uF caps for the same power.

Just as I was writing this, I received the schematics, Creek replied on the next day following my request, excellent! The 4700uF cap appears to be factory fitted, the other two are 3300uF as in the amp. Disc appears to be an input with RIAA circuit.

Questions:
1. Is there a benefit if I replace the diode rectifier bridge with ultra fast diodes or shottky?
2. Is there any difference in the performance of Epcos and Panasonic FC caps?

If anybody wants to take a look at the schematics, let me know.

[aparatusonitus]

Originally Posted by Mario Pankov

Questions:
1. Is there a benefit if I replace the diode rectifier bridge with ultra fast diodes or shottky?
2. Is there any difference in the performance of Epcos and Panasonic FC caps?

If anybody wants to take a look at the schematics, let me know.

1. Yes, but try to find fast, soft recovery type.
2. Probably, smoothing caps are directly on output signal path

Also, I would like to to take a look at the schematic...especialy if it comes from Alex Nikitin so please send it to aparatusonitus(at)gmail(dot)com

[Mario Pankov]

I`ll revive this one. I got the amp and the schematics, a pretty simple circuit. I replaced the main power supply cap ( it is one and two smoothing caps on the signal lines ), result is that the hum that the AC hum that was coming from the right channel did not disappear and today while I was listening at some low level, the hum suddenly started to increase. I shut off the amp and disconnected the speakers in time I hope. What would be the problem? Should I look at the output smoothing caps ( I suspect them as only one channel exibits this ) or could it be a ps problem - diode bridge/main cap?

[Mario Pankov]

Today I opened the amp, replaced the smoothing ( Rubycon ) and ps caps ( Panasonic ) and did one more modification to get RCA instead of 5-din. Cleaned up all potentiometers with contact spray and assembled the amp. Buzz in the one channel was still there, like a sine wave at 90-100hz and quite strong. However the test speaker played with this hum with no problems. Now I suspect a grounding reistor...This was present on one channel but very low in sound level, suddenly it increased when I unpluged my main speakers.
I recaped the amp, replaced a pair of BJEts that had a faulty emitter ( one of them ) and buzz was still there. Amp worked or some 5-6 minutes and after i shut it off, it never powered again.
Should I look for the resistors connecting to ground or is it possible to be a faulty transformer? Sound was pretty much like a buzzing transformer.