Strange crackle in my Rega Mira

[mashley_nad]

Hoping someone can help with this ...

I have an old but much loved Rega Mira clamshell amp, used daily for years.

Yesterday I noticed that the volume seemed a bit weaker than usual, and there was a definite crackling, sometimes almost like a buzz in the right channel that seemed to coincide with peaks of volume.

I established it was not the speaker; then this morning, it appears in both channels. The sound is also slightly distorted as well.

I ran another power amp off the Rega's pre-amp out sockets, and that sounds fine, so the problem is with the Mira's power amps.

Anyone experienced something similar? Any clues as to what is wrong???

 

[vacuphile]

One or more elco's may be giving up the gost, I would first look at the PS. If the Rega's preamp has a regulated PS, it might not be affected, but the power stage would be.

 

[JonSnell Electronic]

Try cleaning or replacing the volume control.

 

[mashley_nad]

Thanks for the tips folks. Volume control operates smoothly and is before the pre-amp out, so that cannot be the problem; but the pre-amp and driver stages do have separate regulated power supply ... so I'll check power amp power supply first.

 

[eyoung]

Hola Y'all...

I'm afraid Mr. Vacuphile may be heading in the right direction more than likely weak electrolytic caps they get noisey when aged get a schematic and lets see whats in that bugger...

Regards, E

 

[mashley_nad]

circuit

Turns out my initial diagnosis was wrong. Only the left channel is a problem; and it is only the power amp.

Not a power supply issue: both power amps share the same power supply.

Have checked various voltages around the circuit to compare left with right; and no differences at all.

Any thoughts?

 

[fuerstfanta]

Same thing

Hi!

I have a problem with my mira that sounds extremely like the one described by you. I open the mira and touched the shaft of the alps input selector. This way I can reproduce the crackle on one channel. The other channel is ok.

Maybe it is the same for your circuit.
I sended the mira to rega several times for repair, but the didn't fix the problem. So I want to fix it myself. Does anyone know where to get the spareparts?

best regards,
Christoph

 

[tiefbassuebertr]

Shoot Noise (light crackling) and low Level at left Channel of MIRA 3

circuit

Turns out my initial diagnosis was wrong. Only the left channel is a problem; and it is only the power amp.

Not a power supply issue: both power amps share the same power supply.

Have checked various voltages around the circuit to compare left with right; and no differences at all.

Any thoughts?

Similar issue I observe at the Mira 3. If I use the Mira 3 as pre-amplifier, this problem don't occur. This means, the reason must be created in the power amp section, maybe in the LTP input stage.
Who can upload the whole schematic of the Mira 3 ?

 

[mashley_nad]

It was a very long time before I could look at the problem again.

I finally got the amp repaired professionally.

It turned out that driver and output transistors had blown.

I do not have Mira 3 circuit, but I can assure you it is almost identical to the Mira 2000.

I have attached the three diagrams I have for that.

I hope that helps!

 

[tiefbassuebertr]

It was a very long time before I could look at the problem again.

I finally got the amp repaired professionally.

It turned out that driver and output transistors had blown.

I do not have Mira 3 circuit, but I can assure you it is almost identical to the Mira 2000.

I have attached the three diagrams I have for that.

I hope that helps!

Yes, thank you very much.

Mira 2000 is here:
http://www.forum-audiophile.fr/amplis/crachottements-mira-2000-t16648.html
http://pstaudio.net/zeroboard/bbs/skin/ggambo7002_boardgallery/print.php?id=amp_gallery&no=98
The visual different to Mira 2000 is the absense of the Alps motor potentiometer - go to
http://www.audio-creative.nl/hifi/rega-mira-3-gentegreerde-versterker-en-apollo-cd-speler/

 

[fuerstfanta]

Hi!
Just want to inform you all, that I solved the problem by replacing the ALPS-motor-switch for switching the inputs. I got a new one from my german sales team and after replacing the mira is working fine now for 6 months already.

regards,
Christoph

 

[d0xdw8yai9zomt1]

Hi, fuerstfanta. It seems I have the same problem as you. After testing many configurations to isolate the problem (event thinking to some kind of ground loop problem), I finally opened the box and of course, manually shaking the alps thing make or stops the crackle noise. It seems it is one weak component of this nice amp.
Either I clean the contacts with some specific cleansing product, or I change it for a new one.
As there is no references on the component, could you tell me where you bought the ALPS and what reference should I look for ?
Thanks,