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Quick question for C33 owners

Robisme

Robisme

Sansui Enthusiast
Subscriber
I have a C33 here with a start up problem. The owner says one channel has a delay before there is audio.

Looking at the schematics, it appears to have a mute circuit, which I assume would delay output until it's stable.

So at this point, I'm thinking the channel that has audio right away is the problem.

This leads to my question. Is there a delay in audio output on both channels of your C33 upon power up?

I see the mute function has LDRs and FETs which I will start testing.

Thank you,
Rob
 
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There are some reed relays in the compandor circuitry but not in the regular audio path. I had a defective muting FET go bad in one of my previous C34V's. Terry Dewick fixed it. From memory the muting is controlled in a double circuit with a series LDR followed by a shunting FET. I do not remember if the control circuits for these two devices come from the same spot. I assume Mac did this to completely eliminate any leakage signal from getting through. Usually, the gate of the FET is operated by an RC charging circuit. Make sure the capacitors are in spec.

Good luck,
John
 
Robisme said:
I have a C33 here with a start up problem. The owner says one channel has a delay before there is audio.

Looking at the schematics, it appears to have a mute circuit, which I assume would delay output until it's stable.

So at this point, I'm thinking the channel that has audio right away is the problem.

This leads to my question. Is there a delay in audio output on both channels of your C33 upon power up?

I see the mute function has LDRs and FETs which I will start testing.

Thank you,
Rob
Click to expand...
I have a C33 paired with a 2155. There is a delay, simultaneously in both channels upon startup. I always assumed that it was a feature of the power amp. Give me a day, I'll dig out some headphones and listen to the preamp direct and report back.
 
seacliffe301 said:
I have a C33 paired with a 2155. There is a delay, simultaneously in both channels upon startup. I always assumed that it was a feature of the power amp. Give me a day, I'll dig out some headphones and listen to the preamp direct and report back.
Click to expand...

Thank you.

I'm thinking the preamp has a delay.

Rob
 
If you take a look at the block diagram there are delay blocks in a number of places. Sounds like a fun project.
 
Thank you. This C33 has about 10 seconds on one channel and 0 on the other.
Haven't had a chance to dig into it yet.

Rob
 
The push button on the front is not in, and the switch on the top is in the normal position.

Rob
 
Robisme said:
The push button on the front is not in, and the switch on the top is in the normal position.

Rob
Click to expand...
I'm talking about the concentric rotating switch just to the right of the power button. One of the knobs says, compress, off, expand. I only mention this as a means to make sure your problem is not in the compander circuitry.
 
jlovda said:
I'm talking about the concentric rotating switch just to the right of the power button. One of the knobs says, compress, off, expand. I only mention this as a means to make sure your problem is not in the compander circuitry.
Click to expand...

It was set to expand with the ratio at minimum.

I powered it up that way and the left channel was silent and the right was playing. Turned off the compandor and the left channel kicked in. I have to let it sit between tests or both channels work fine even with the compandor on.

Thanks,
Rob
 
So, when the compandor is on expand or compress there is a delay on the left channel. Turn it to off and the left channel kicks in.

Power off for a while and power it up with compander off and both channels work right away.

Rob
 
At least we are beginning to close in on the area. The push button on the front switches the compandor from the record mode to the listen mode. It doesn't turn it on or off. The compandor circuitry is a big mystery to me.
Robisme said:
I have to let it sit between tests
Click to expand...
How long do you have to wait between tests? Usually a time delay would be caused by a charging capacitor.

Maybe someone else can chime in.
 
The compander off/expand/compress switch drives relays which pass the signal through the compander circuit, or around it (when off). When on, it passes 18V thru the listen/record switch and then on to relays K501A/B and K503A/B at either end of the compander voltage controlled amp. If it's off the relays bypass the compander VCA, if on signals pass through. There is an RC circuit w/ 10uF caps on that relay control signal, but the one signal controls both channels. So any selection on the compander switch should affect both channels the same way and at the same time. So I'm thinking your control switch is working properly, and the control signal is getting out to the relays, but I'm thinking you have a sticky relay that is causing your delay. Sounds like maybe when de-energized the relays snap back to the compander bypass readily, which is why when you turn it off the channels goes live. But it sounds like when energized the one channel's relays take some time to switch. That also might explain why both channels work after power down if you don't wait a few seconds, the relays may still be stuck on the compander side. I'd start with the relays.

Good luck,

Bob the Tech
 
clinic-audio said:
Reed relays ?

I think they are NLA at the factory
Click to expand...

After much time troubleshooting this preamp, due to only having 10 second to chase the signal before it kicks in and having to wait 10 minutes between power ups, I found the issue.

It was a reed relay. One of the DPST reed relays. I happen to have a few NOS NEC 12v reed relays, so I dropped one in and it is working.

Just for kicks and giggles, I messaged McIntosh to see if they happen to have replacements.

Thanks,
Rob

relay.jpg
 
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