Distortion on RCA input

[Gadusmorhua]

I recently bought a CA A1 int amp for a bargain £40. I have a WiiM Pro Plus and a Chord Mojo which was fed, via line out on the Mojo, to the RCA sockets labelled Tape /MD.
Everything sounded great but yesterday I noticed a tiny bit of distortion had developed. By elimination I worked out it was that circuit, so changed to AUX/Phono and returned to clarity.
I am a total beginner and hope to replace the amp with something boasting digital inputs in the near future, but I'm curious as to what may have happened, and wonder if I run the risk of harming other inputs? I'm sure it is just a case of what do you expect with a thirty year old amp, or why did you plug it into Tape/MD you fool(!) Glad I started cheap anyhow.

 

[Al ears]

I recently bought a CA A1 int amp for a bargain £40. I have a WiiM Pro Plus and a Chord Mojo which was fed, via line out on the Mojo, to the RCA sockets labelled Tape /MD.
Everything sounded great but yesterday I noticed a tiny bit of distortion had developed. By elimination I worked out it was that circuit, so changed to AUX/Phono and returned to clarity.
I am a total beginner and hope to replace the amp with something boasting digital inputs in the near future, but I'm curious as to what may have happened, and wonder if I run the risk of harming other inputs? I'm sure it is just a case of what do you expect with a thirty year old amp, or why did you plug it into Tape/MD you fool(!) Glad I started cheap anyhow.

Possibly something to do with the output voltage of the Mojo, I seem to recall it being switchable.
The amp inputs may not like anything above 2v.
You should be able to plug in to any phono sockets but I would avoid AUX/Phono unless it is switched to AUX.
Try Tuner or CD or whatever else you have there.

 

[Gray]

....changed to AUX/Phono and returned to clarity.

Those aux sockets go to the same place within the amp as the Tape / MD sockets do.

The input selector switch determines which sockets 'get through'.

And that is where your problem (almost certainly) is. Contamination of the switch contacts will be causing the distortion.

Look up a product called 'Servisol Super 10'
That is more than likely to be your solution.

Incidentally, if you were to have the amp 'serviced', you'd be getting little more than a few squirts of contact cleaner / lubricant.

 

[twinkletoes]

Possibly something to do with the output voltage of the Mojo, I seem to recall it being switchable.
The amp inputs may not like anything above 2v.
You should be able to plug in to any phono sockets but I would avoid AUX/Phono unless it is switched to AUX.
Try Tuner or CD or whatever else you have there.

This

 

[Gray]

This

But how would he have clarity on the aux input...that differs from Tape/ MD in name only (and is electrically identical)?

 

[Al ears]

But how would he have clarity on the aux input...that differs from Tape/ MD in name only (and is electrically identical)?

He had it working fine originally on the Tape socket.....
Sevisol always worth a try.

 

[Gray]

I am a total beginner and hope to replace the amp with something boasting digital inputs in the near future

With USB, coax and optical inputs on your Mojo, do you need a different amp?

 

[nopiano]

With USB, coax and optical inputs on your Mojo, do you need a different amp?

I was wondering that too! But the Mojo can definitely produce a hefty output, so always worth reining it in a bit.

 

[Al ears]

I was wondering that too! But the Mojo can definitely produce a hefty output, so always worth reining it in a bit.

If its set on a 3volt output this might cause issues.

 

[Gray]

If its set on a 3volt output this might cause issues.

Yes, standard CD level should be enough for most people (and still more than enough for old amps with the highest input sensitivities).

CA 200M DAC hits 4v doesn't it? 🤔

 

[Gadusmorhua]

But how would he have clarity on the aux input...that differs from Tape/ MD in name only (and is electrically identical)?

The Tape/MD input has a selector button, the other RCA inputs are on a switch, so could it be that?

 

[Gadusmorhua]

If its set on a 3volt output this might cause issues.

I have indeed been setting it to 3V output. Being a beginner I thought I had to press all three buttons just to select line out, rather than switch between voltages. The manual could be clearer in many aspects.

 

[Gadusmorhua]

Those aux sockets go to the same place within the amp as the Tape / MD sockets do.

The input selector switch determines which sockets 'get through'.

And that is where your problem (almost certainly) is. Contamination of the switch contacts will be causing the distortion.

Look up a product called 'Servisol Super 10'
That is more than likely to be your solution.

Incidentally, if you were to have the amp 'serviced', you'd be getting little more than a few squirts of contact cleaner / lubricant.

Thanks, I have some contact cleaner I use for my big diesel generator. I didn't think, after paying only £40, I would get much of a service, but it's nice it was opened, cleaned and checked. Better than buying blind, for sure. I should have added the Tape/MD socket is controlled by a button (the other inputs are on a switch), so I'll give it a clean/investigate.

With USB, coax and optical inputs on your Mojo, do you need a different amp?

I like being able to alter the balance on my speakers slightly if I can't be bothered swinging my sofa round to a 'serious listening' position, for one thing.
I bought vintage gear just to get started and I'm blown away with the sound I've got, but will join the 21st century when funds allow.

 

[Al ears]

Yes, standard CD level should be enough for most people (and still more than enough for old amps with the highest input sensitivities).

CA 200M DAC hits 4v doesn't it? 🤔

That's what I meant, older amps may be happier with 2volt

 

[Gadusmorhua]

That's what I meant, older amps may be happier with 2volt

I'm sure that's the case with my amp. Good job I'm learning with budget vintage gear. Haven't had any smoke yet though

 

[Gray]

I should have added the Tape/MD socket is controlled by a button (the other inputs are on a switch)

Yes, sounds like the old 'tape monitor' button.
Make sure you give its contacts and those of all other switches and rotary controls a spray and a few activation wipes.

Not sure, but you may have misunderstood me when I said, 'do you need a different amp?'
To be clear, what I meant was not that you should get another, but is it even necessary to buy another, when you're perfectly happy with what you have.
(Nothing wrong with a 30 year old amp....one that may well do another 30, after your 'repair') 👍

 

[Gadusmorhua]

Yes, sounds like the old 'tape monitor' button.
Make sure you give its contacts and those of all other switches and rotary controls a spray and a few activation wipes.

Not sure, but you may have misunderstood me when I said, 'do you need a different amp?'
To be clear, what I meant was not that you should get another, but is it even necessary to buy another, when you're perfectly happy with what you have.
(Nothing wrong with a 30 year old amp....one that may well do another 30, after your 'repair') 👍

I am indeed perfectly happy with my sounds right now, and in any case some better speakers ought to be the next thing, though I'm struggling to fault what I've got.
Thanks for the advice everyone, I'll warm up that aerosol.