• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Restored CA-1000 Hiss

Roger Gorke

Roger Gorke

Well-Known Member
Several years ago, I restored a Japanese model CA-1000. I predominantly listen to vinyl and the radio through a CT-600. Over the couple weeks, I have been frustrated with a poor center image and thought it was due to turntable set up issues. Yesterday, I turned on the amp and noticed a hiss coming out of the right channel. In addition, the right channel began cutting out. I went to the 'normal' culprit...a bad cable. I have done a bunch to basic testing such as switching the pre/main switch on and off, turning the volume up and all the way off, tired different speakers and speaker cables.

What I've learned...Please confirm my assumptions...
  • With the pre/main switch "off", the amp is dead quiet. This tells me that the main boards are not the issue.
  • Using different inputs: phono, aux, tuner, the issue stays the same. Probably not the function board. I previously replaced the usual culprits (2SC1345 transistors).
  • With the volume off and still getting hiss, the problem is most likely limited to the boards between the volume controls and the "pre out" coupler: tone control, loudness, and filter.
  • The 2SC1345 transistors on the tone control board, electrolytic caps, and the tantalum caps have been replaced. I used BC550C transistors and yes, I did pay attention to the different leg pinout.
  • I have replaced the volume/balance control with a stepped attenuator. The original 4-gang pot was causing channel imbalance and, for those that know, a replacement pot is unobtanium. I now have no balance control but I have lived with that.
  • The loudness pot has been transferred to a new PCB with new components.
  • Therefore, my working hypothesis is that the problem is on the filter board. I have cleaned the switches on the filter board (and everywhere else) but not the transistors or any other components.
Am I missing anything?
 
Register to hide this ad
avionic said:
By-pass the coupler switch with a RCA interconnect cable (pre-out to main-in).
Click to expand...
Will do when I get home. I did remove the switch and clean it back during the restoration...per your suggestion/demand...;)

Additionally, I run the CA 1000 with the coupler switch off, 99% of the time. I am running a set of KLH1 speakers that have the Analog Bass Control (ABC) that goes between the preamp and the power amp.
 
Last edited:
Yeah likely to be a noisy transistor. That filter board is a PITA to get to. Assume you don't have a scope or audio probe. Probing the pink wire(R) in yellow wrap from the volume board would confirm filter or coupler issue.
 
mbz said:
Probing the pink wire(R) in yellow wrap from the volume board would confirm filter or coupler issue.
Click to expand...
I'll try that...but considering that I never swapped out those transistors, it would probably be wise for me to replace them anyway.

I also plan to match the hfe of the transistors as closely as possible left to right. I don't want to have one channel with more gain than the other. Or does it not matter here?
 
Roger Gorke said:
… Or does it not matter here?
Click to expand...
In most cases if you replace with the correct hFE rank of the same transistor, it should be okay but if you use a different transistor (which you most likely will), better to match hFEs as closely as possible. Most of these stages are emitter follower stages, so the ac signal gain isn’t affected, but the DC bias of the stage will be if hFEs are wildly different.

I match every one of them as best as I can so I can sleep better at night.
 
Roger Gorke said:
I mean 501 with 502, 503 with 504, etc.
Click to expand...
:thumbsup: Good start.

I’d go further, when you take out Tr501 or any other, measure their hFE (if they’re still operational and just old) and try to match that. Often I have found that the NPN and PNP pairs are not matched and are of different ranking. If you measure enough of these you see the pattern (ex: NPN 840, PNP 320 … etc.). That’s why I buy transistors in larger quantities to be able to choose what I need. See below.

814FC50C-D5A7-4E1E-8759-3F9DF5101670.jpeg
 
Sparkplug said:
In most cases if you replace with the correct hFE rank of the same transistor, it should be okay but if you use a different transistor (which you most likely will), better to match hFEs as closely as possible. Most of these stages are emitter follower stages, so the ac signal gain isn’t affected, but the DC bias of the stage will be if hFEs are wildly different.

I match every one of them as best as I can so I can sleep better at night.
Click to expand...
The transistors that I pulled are 2SC134D and measured:

TR501 - 297
TR502 - 321
TR503 - 320
TR504 - 356

All of my BC550c transistors measure 550-560 hFE. I suppose that’s too much of a difference…and I want to sleep ok…

What is the impact on the DC bias if the hFE is higher?
 
Last edited:
Roger Gorke said:
The transistors that I pulled are 2SC134D and measured:

TR501 - 297
TR502 - 321
TR503 - 320
TR504 - 356

All of my BC550c transistors measure 550-560 hFE.
Click to expand...
I think you mean 2sc1345D, there is no 2sc134.

As such, measure all your bc550c transistors you have and use 4 with lowest hFEs. I think you’ll be alright. Alternatively, order a bunch of BC550b’s and try them if you can find them. They are the lower rank in hFE for bc550.

In general, higher hFE means higher collector current for the same base current (Ic = β x Ib) where β can be taken to be practically equal to hFE. β is usually used for large signal and biasing whereas hFE is for ac small signal. I really don’t think you’ll be hurt or even notice any difference unless doing lab measurements. Try it out and provide feedback please.

Have a nice sleep.

EDIT: Read the post below. You’re fine as is.
 
Last edited:
Sparkplug said:
Tr501 ~ Tr504 are 2SC1345 D or E. E ranking is the same as BC550C that you already have. You’re covered. Go ahead and make the change.
Click to expand...
Thanks!!! I have a local electronic place that has the BC550B at $0.15 each. I am going to go fetch 100 this afternoon.

Sparkplug said:
I think you mean 2sc1345D, there is no 2sc134.
Click to expand...
And yes, that was a typo. I was fighting my phone trying to get the "D" bolded and of course messed it up!

mbz said:
Probing the pink wire(R) in yellow wrap from the volume board would confirm filter or coupler issue.
Click to expand...
Of course I forgot to do that prior to firing up the soldering iron. After I got the filter board out and started the solder sucking process, the pink wire in the yellow jacket broke off from the board. So there's that too!

Seems like it might be a good idea to use some Molex connectors or similar to make it easier to remove the different boards and take some stress off of the wire solder joints. That being said, the wire solder joints have lasted 50+ years as is.
 
Roger Gorke said:
I have a local electronic place that has the BC550B at $0.15 each. I am going to go fetch 100 this afternoon.
Click to expand...
:thumbsup: BC550c would work but hey, anything for sleeping better (short of drinking whiskey! @avionic ).

I’d get some BC560 as well, the complimentary pair to BC550, if they have any. They’ll come in handy when time comes.

Additionally, I’d install one or a couple at a time and test to find out which transistor was bad and also as a general check to make sure a new problem wasn’t introduced.

Happy hFE measuring
 
FAILURE…then SUCCESS...then back in the quagmire!

It was NOT the transistors on the filter board. After spending and enormous amount ($15) on BC550Bs and spending time measuring all 100 of them. I installed 4 that were 361, 361, 362, 362, fired it up and the hiss was still there.

I then took out the 3 BC550Cs in the right channel of the tone board.

TR302-564
TR304-304
TR306-557

That 304 sure didn’t look right. I replaced all three with ones in the 560-570 range and Shazam, dead silence!!!!

BUT

After getting the amp ready for the case, I was listening, switched the Audio Muting switch and POP! Yikes, that's not good. Back apart it comes and I find ~7 vdc on the right channel. No DC on the left, just the right. Nothing coming onto the board from the yellow bundle.

I heard Avionic typing...did you clean the switch? Yes, I took it out and cleaned it up all nice. Now, I am only getting 0.45vdc on the right channel.

Ugh, could this be from the new transistors? I did switch out the 4-10uf caps on the board.

Thoughts? I suppose I could just never use that switch but that's not the way to go.

Update:

I replaced one of the 10uf caps I put in and viola…all better!!!

Whew!!!
 
Last edited:
Roger, the sm did say that both high and lower rankings were okay to use. You did this because you wanted to and found it exciting … LOL, good for you, why not.

The pop you heard and the new transistors have nothing to do with one another, two separate events.

What is the current status? Amp working or has issues? Please advise.
 
You must log in or register to reply here.
Back
Top Bottom