Mission Cyrus 2 balance control elimination

[Sandm0n]

Hi,


I have a Mission Cyrus 2 Integrated amplifier which I would like to remove it's balance control and install a better quality volume potentiometer to replace the original one.
As far as I see the pre amp stage in this amplifier is passive.



I attached a schematics and would like to know what parts do I need to remove/change after removing the original volume/balance potentiometer.
According to the amplifier's datasheet it's input senssitivity is 0.5mV (line) which is too low for "newer" 2V output sources, how can I modify the ampliifier's input section so it'll be a better match for 2V output sources?


Thanks in advance.

 

[bansuri]

The balance pot can be just removed
the volume pot needs to fit the enclosure and pcb


TKD 2CP-601/S Potentiometer | Hifi Collective
Alps "blue beauty" | Hifi Collective

 

[Pharos]

If completely removing the balance control, replicate the circuit conditions with resistors and put the wiper contact at what was the 'maximum' position.


If you want to replace the original balance control with two separate pots to provide individual volume controls, the connections will be the same, and your only problems will be mechanical, and physical accommodation of two pots instead of one with consequent aesthetics to consider.

 

[raul_77]

I did the same thing many years ago. Replace the balance potentiometer with a pair of resistors and a Bourns 91A for the volume potentiometer fits exactly into the PCB

 

[Sandm0n]

Thanks

 

[as_audio]

The resistor pair is not required and only drops some level.

 

[Sandm0n]

What resistor pair?

 

[as_audio]

Post 4

 

[Sandm0n]

Thank you.



There are 3 electrolityc Bipolar caps in each chanel, it seems that they are in the signal path and I would like to know if it would be better to change it to a non electrolytic caps?
Maybe just bypass it ???

Caps values are: 1uF, 2.2uF, 470uF


if it would be better so what do you suggest? what kind of caps?


Thanks

 

[raul_77]

There is no room for quality polypropylenes, if you replace them with normal metal film capacitors the sound gets much worse, I tried that at the time.
You can renew them with Nichicon Muse BP in case their characteristics have worsened over time.

 

[Sandm0n]

Thanks.


I just received the Muse BP capacitors, but only the 470uF and 1uF, couldn't find the 2.2uF so I bought 2.2uF Elna CE-BP instead, I hope that the Elna is good enough.
I'm also about to change all the electrolytics (non Bipolar) to Elna silmic II in the power amp stage and disconnect the phono stage as I'm not going to use it anyways and it gets power (and draw about 17W constantly) even when the amplifier is switched off.


Any more suggestions?

 

[raul_77]

Not much, you're on the right way.
It is convenient to change the insulators of the power transistors, with time they always have some degree of degradation, use the best ones you can find, a good evacuation of the heat is very important.
And the solders also are degrading with the time, remake them with solder with at least 2% of Silver. The one from RS goes well and has a reasonable price.

 

[JMFahey]

Hi,


I have a Mission Cyrus 2 Integrated amplifier which I would like to remove it's balance control and install a better quality volume potentiometer to replace the original one.

Wht´s the problem you are trying to solve?
Symptoms?

As far as I see the pre amp stage in this amplifier is passive.

Quite the contrary.
You have 3 active sections per channel, dedicated to Vinyl.
You also have an input selector switch, which in 1 position selects the active section.

According to the amplifier's datasheet it's input senssitivity is 0.5mV (line)

There is some mistake there, reread Manual

which is too low for "newer" 2V output sources, how can I modify the ampliifier's input section so it'll be a better match for 2V output sources?

If anything, itmight be too high.

I guess typical input Tape/CD/Tuner/etc. (any non Phono) sensitivity will be around 200mV, in principle send your Digital source there.

IF uncontrollably loud, consider using an input attenuator.

Do it only in a single input pair (say, Tuner ot Tape In) and label it accordingly.

 

[Sandm0n]

Wht´s the problem you are trying to solve?
Symptoms?

No problem in here, I just don't use the balance control and the volume potentiometer is "stepped" and I don't like.

Quite the contrary.
You have 3 active sections per channel, dedicated to Vinyl.
You also have an input selector switch, which in 1 position selects the active section.

Only the phono stage is active, all the rest passive.
The phono stage is always "powered", even when the amplifier is switched off.

There is some mistake there, reread Manual

You are right, it's 50mV for the line inputs.

 

[as_audio]

"Volume potentiometer is stepped and I don't want it" :
just remove the spring metal from the wheel

 

[Sandm0n]

That was just another excuse for me to "upgrade" it to ALPS blue velvet😉

 

[as_audio]

If you are at it the only necessary fix for any Cyrus is
careful disassembly and cleaning of the input selector.

 

[Mark Whitney]

To reduce the input, I build interconnect cables with two 4.7k resistors as a voltage divider.

If you are not using vinyl and want to disconnect it, lift one end of the diodes located before the regulators.

 

[jean-paul]

Caps values are: 1uF, 2.2uF, 470uF

Hi, Wima MKS2 in 5 mm are the caps for 1 and 2.2 µF. I would choose Nichicon MUSE bipolar for the 470 uF. When one can replace electrolytic caps for film one should do it. The MKS2 perform better than the average electrolytic cap. Please make sure to replace the 22 and 100 µF caps for Panasonic FC or the like. You can up the voltage rating a bit to have the same physical size as the old ones.

The balance potentiometer can be removed, I am not too sure an Alps blue is really an upgrade... A TKD would be.

The volume circuit has an input filter and the amplifier itself has it too. This is something some high end manufacturers may learn from. Even on diyaudio.com many recent designs lack an input filter which often leads to trouble with signal pickup.

Anyway, IF I would still have such an old device and I would like it a lot I would change the feedback resistors but this has some risks. 50 mV sensitivity is not compatible with normal sources. I did this with several classic circuits only to be able to use sources younger than 40 years. Over sensitive amplifiers may add a certain character (nervous 🙂) to the sound which may alter when the gain is reduced. In most cases it costs some time and is the reduction in gain rewarding. It is way better than any form of attenuating good 2Veff signals only to amplify them again....

To reduce the input, I build interconnect cables with two 4.7k resistors as a voltage divider.

If you are not using vinyl and want to disconnect it, lift one end of the zero ohm resistors located before the two small PSU capacitors.

Are you sure the impedance of the whole will not be too low for the average sources? I am pretty sure many sources will not like this and you'll experience loss of bass. The amplifier itself is already low ohmic. If one wants to keep it simple replacing R45 for a 15 kOhm is way simpler (I would however prefer the gain reduction method). C29 must be lower in value now (47 pF, make that a very good type). The plus of this simple mod is that the amplifier is also a lighter load for sources instead of being a heavier load.

 

[Mark Whitney]

Hi Jean-Paul,

Thanks for the info, I did consider most of your other options. Other resistor values can be chosen and I may have used two 10K resistors in the cables.

Sandm0n,

Its X24 and X25 to disconnect the power to the Phone PSU. On my amp some of the capacitors are starting to bulge and disconnecting power is an easy fix as I don't use the phono input.

WIMA 1uF and 2.2 uF fit and look good.
Also replaced C53-54-55-56 with Panasonic FC.