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CA-1000 hiss in both channels

M

MonkeyRelish

Active Member
Hi all,

I am refurbishing a CA-1000.
I have replaced the main filter caps, relay, snap switches and have desoldered and polished the contacts of the coupling and phono selector switches.
I have also replaced the amp board trimmer resistors with Bourns multiturn, and cleaned and reapplied heat sink compound to the output transistors.
Now I am recapping the electrolytics on each board, testing after each one.
I have so far done both amp boards, the power board and the tone board.

From new (to me), the amp has what I consider a lot of hiss, equally from both speakers.
Very noticeable When the volume is above 3.
I also have a CA-610, which has no hiss unless almost turned up full.

The hiss is for all inputs, which discounts the function board, as the board us effectively bypassed when the aux input is selected. Also, when the mute switch is enabled, the hiss is gone, even when the volume is turned right up. So I think that this discounts the amplifier sections.

So, that leaves the tone and filter boards. Could noisy transistors or caps cause hiss on both channels equally ? I have yet to recap the electros on the filter board.

Maybe replacing all the 2SC1345’s with KSC1845’s ?
Anything else I have overlooked that could cause hiss ?

Mr Relish
 
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MonkeyRelish said:
So, that leaves the tone and filter boards. Could noisy transistors or caps cause hiss on both channels equally ? I have yet to recap the electros on the filter board.

Maybe replacing all the 2SC1345’s with KSC1845’s ?
Anything else I have overlooked that could cause hiss ?
Click to expand...
Yeah, I think you are on the money with 2SC1345's. Quites a few polar tantalums on the tone & filter boards
however these tend to go 'windy". Are you replacing the tantalums?

Remember to check/measure the fusible resistors, could be a power supply issue (maybe) since both channels affected

Do you have an oscilloscope? Probe the L&R wires on the tone board to/from volume & function board should indicate where
hiss is introduced.
 
I wasn’t planning on replacing the tantalums, but if the transistors don’t do the trick, that may be the next step.
The hiss is a constant white noise type of hiss, definitely nor windy.

I’ve been checking the fusible resistors as I go. Only had to replace one so far.

I haven’t discounted the supply board, as it is common to both channels as you say.

Yes, I have an oscilloscope, and will give it a try.

Mr Relish
 
Is the hiss present with the coupler switch decoupled?
 
avionic said:
I just completed one of these boards.2SC1345 ----> KSC945C (Better match than a KSC1845)..
2SC734Y ----> KSC1815
I wouldn't think so..
I would think you have a power supply issue that powers those two PCB's
Click to expand...

Yes, a noisy power supply board would make sense.
And thanks for the transistor sub for the 1345’s. Of course I have none of those, and 20 1845’s.
Hello Digikey, here I come.

Mr Relish
 
Yessssssss, the snake is gone.

The hiss was not present with the coupler switch decoupled.
Replaced all the electro’s on the filter board. No difference.
Replaced all electro’s on the tone board except the 220uF 50v between +B and E (ran out).
Still no difference.
Replaced all 2SC1345’s with KSC945C’s on the filter board. No difference.
Replaced all 2SC1345’s with KSC945C’s on the tone board, as well as the 220uF 50v electro.
Success, the snake was gone. Nice quiet background. So, it was either noisy transistors or the electro.

A big thanks to @avionic, for his advice in this and countless other threads.
Also a big thanks to @mbz, for the same, and I suspect is who I bought the amplifier from in the first place.

Mr Relish
 
The CA-1000 is a nice amp, one of my favourites. The CA-1010 and CA-2010 are also interesting and an easier rebuild
than the CA-1000 (I hate that filter board....) I'm particularly liking the CA-1010 at the moment but generally moving into
separates. I drive past your way maybe every 10 days so, happy to drop something off if you want to compare...
 
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