External volume control for MAC 1900

[Benz]

Greetings,

I just had my MAC 1900 recapped and faulty transistors replaced. After running it for about 100hrs it sounds great, better than it ever has so I'm thrilled with that. The volume control however is quite uneven (L/R) at lower volumes. I am not looking to replace the pot at this time, due to replacements being of purportedly low quality, and also because I don't want to send the receiver off again for repairs at this time.

I am looking at passive preamp options to allow me to control the volume separately. I've found a few options and am looking for thoughts on what's feasible without breaking the bank ($100 CAD maximum). I know impedance is important, but I'm no expert and unsure if any of the below would be appropriate to run through the AMP INPUT / PREAMP OUT as an external volume control. Options:

Nobsound Little Bear MC2 (20KOhms):
https://www.amazon.ca/gp/product/B07255VHZS/ref=ox_sc_act_title_1?smid=ADPE7GPX91ORE&psc=1

Nobsound / Solupeak Passive Preamp (50KOhm): https://www.amazon.ca/gp/product/B07GRLV7XG/ref=ewc_pr_img_2?smid=ADPE7GPX91ORE&psc=1 ; https://www.amazon.ca/gp/product/B07TT8VC1B/ref=ewc_pr_img_3?smid=A3A33Q2EAFDKWN&psc=1

Slightly different option:
Russound Table Top Volume Control TBL-75: https://www.russound.com/products/c...ntrols/indoor/tbl-75-table-top-volume-control

Anyt thoughts on the above or other viable, reasonably priced options would be very welcome!

 

[Benz]

Or this, perhaps?

Schiit SYS: https://www.schiit.com/products/sys

 

[62caddy]

Get a McIntosh CR7. Also has switched outlets sparing wear to the off/on switch.

Prior to the precision tracking volume control that first appeared in 1977 on the C32, practically all McIntosh volume controls had mistracking issues when they were new. There is no cure. They tend to track most evenly in the 11:00 to 1:00 range. With the CR7 connected, the receiver's volume control is set in that range and never needs to be touched again.

 

[Benz]

Interesting, thanks for the suggestion, this would be ideal. I'll keep an eye out for one. I suspect these may be well above my $100CAD max budget though.

Do you have any thoughts regarding the devices I listed in my OP (or similar passive preamps)? Would those work as volume control or would I run into issues? The main thing I'm unsure of is the ohm ratings, i.e. what's required to work with the Mac 1900 as a pre. Given the prevalence of the volume tracking issue with those early Macs, I would imagine I'm not the first to look into these options.

 

[TSmith8605]

1) Replace the preamp-to-amp jumpers with a fixed attenuator (resistor). Experiment with values and maybe start around 100K. This will lower the over all sound level so that you use the 1900's volume control at further rotated angles where it is not worn and tracks better.

You can also use a passive adjustable attenuator (per a couple of links in your OP) in this spot: in place of the preamp-to-amp jumper. You could either set this to a good level to act as a fixed attenuator, or just use it as your main volume control. No need for a complete other preamp.

2) Plug the 1900's AC power cord into a switchable power strip. Use the power strip switch to turn the 1900 on and off. This way you don't exercise the volume control through the lower angles causing even more wear every time you power on or off. This is what caused the excessive wear in the first place. Now you will only rotate the volume control when you change the volume.

This $15 solution has worked well for me for the last 15 years with no further damage to the volume pot.

 

[62caddy]

Interesting, thanks for the suggestion, this would be ideal. I'll keep an eye out for one. I suspect these may be well above my $100CAD max budget though.

Do you have any thoughts regarding the devices I listed in my OP (or similar passive preamps)? Would those work as volume control or would I run into issues? The main thing I'm unsure of is the ohm ratings, i.e. what's required to work with the Mac 1900 as a pre. Given the prevalence of the volume tracking issue with those early Macs, I would imagine I'm not the first to look into these options.

I don't know if a passive device will have any better channel tracking than the MAC. I can say there's a very high probability the issue will be eliminated with the CR7, along with the benefit of remote functions for volume, input selection and power switching for the entire system. CR7s in good working order usually change hands for around $200 - $300 last time I looked.

 

[TSmith8605]

Interesting, thanks for the suggestion, this would be ideal. I'll keep an eye out for one. I suspect these may be well above my $100CAD max budget though.

Do you have any thoughts regarding the devices I listed in my OP (or similar passive preamps)? Would those work as volume control or would I run into issues? The main thing I'm unsure of is the ohm ratings, i.e. what's required to work with the Mac 1900 as a pre. Given the prevalence of the volume tracking issue with those early Macs, I would imagine I'm not the first to look into these options.

You just need to insert another colume control in the pre-amp-to-amp loop and you don't need an entire preamp. So the first link is overkill.

The second 2 links are about what you want. Of these, the more expensive Nobsound High Precision Passive Preamp Volume Controller is an Alps which have a good reputation.

The last Russ Sound link is not a good idea at all, you don't need anything between the amp and the speakers.

 

[Benz]

1) Replace the preamp-to-amp jumpers with a fixed attenuator (resistor). Experiment with values and maybe start around 100K. This will lower the over all sound level so that you use the 1900's volume control at further rotated angles where it is not worn and tracks better.

You can also use a passive adjustable attenuator (per a couple of links in your OP) in this spot: in place of the preamp-to-amp jumper. You could either set this to a good level to act as a fixed attenuator, or just use it as your main volume control. No need for a complete other preamp.

2) Plug the 1900's AC power cord into a switchable power strip. Use the power strip switch to turn the 1900 on and off. This way you don't exercise the volume control through the lower angles causing even more wear every time you power on or off. This is what caused the excessive wear in the first place. Now you will only rotate the volume control when you change the volume.

This $15 solution has worked well for me for the last 15 years with no further damage to the volume pot.

1) ok, thanks for confirming, and for the fixed attenuator suggestion. I will also consider that solution as it would be cheaper
2) Yes, great tip, I have been using a strip for that very reason.

I don't know if a passive device will have any better channel tracking than the MAC. I can say there's a very high probability the issue will be eliminated with the CR7, along with the benefit of remote functions for volume, input selection and power switching for the entire system. CR7s in good working order usually change hands for around $200 - $300 last time I looked.

Very good point, I could experiment with the external attenuator at less than maximum, but where it tracks well which would cause the Mac's volume control to operate in a different spot. Something to consider.

You just need to insert another colume control in the pre-amp-to-amp loop and you don't need an entire preamp. So the first link is overkill.

The second 2 links are about what you want. Of these, the more expensive Nobsound High Precision Passive Preamp Volume Controller is an Alps which have a good reputation.

The last Russ Sound link is not a good idea at all, you don't need anything between the amp and the speakers.

Super, thanks for that!

 

[Benz]

So, I decided to give the Schiit SYS a try, it's supposed to be fairly transparent and the price fit my budget. Many reviews for the Nobsound indicate that the pot is quite asymmetrical and has balance issues, which is what I'm ultimately trying to fix. Will experiment with the Schiit and can always return it if I'm not happy with it.