I would like to add a balance control to a design that I'm working on, and have been able to find surprisingly little information on the proper way to incorporate one alongside a volume control. I have installed one, and it works, but I just want to make sure that there isn't something that I am not taking into account here. I have placed a 22k resistor in series with a 10k volume pot to limit gain. This amp uses 6GC5 beam pentodes for the output, and is driving headphones, so it is capable of delivering FAR more power than is generally necessary. That 22k resistor lets me max the volume out (and get hearing damage) without any clipping whatsoever. I placed an MN25K pot right after the volume pot to act as a balance control. My concern is that the resistances of the two pots in series is doing something that I am not considering. It sounds fine, but I want it to be done properly. I also tried a different technique that I found. That is, I used a linear pot with its two outer legs attached to each channel and the wiper grounded. With that, only the last ~20% or so of the pot actually changed the volume of either channel. IE, the middle 60% of the control did nothing at all. I tried everything from a 10k to 100k. Same effect, though the middle "dead zone" shrank with the smaller pot. Not completely though. Anyway, I'm feeding a 6DJ8 here.
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You can do it either way, depending on how much adjustment range you want.
Even in a worst case, the channel imbalance would be only a few dB before correction.
More imbalance than that would indicate a serious electronic or acoustical problem that
should be corrected first.
Even in a worst case, the channel imbalance would be only a few dB before correction.
More imbalance than that would indicate a serious electronic or acoustical problem that
should be corrected first.
Thanks guys. I'm not having any issues with one channel being louder than the other. I have some vintage headphones where one can is slightly louder than the other. I'd like to be able to compensate for stuff like that. It'd also be nice to be able to compensate if the channels become imbalanced due to age of the tubes. And I have to admit that I like switches, lights and knobs. 😀
There is a chapter here: Angelfire: Balance Controls
I looked a bit at balance controls and how they can be implemented when thinking about how to update an old integrated tube amp. The snag is that unless you have the special balance pots mentioned in the article, where only half the track is resistive, then there is a loss of gain without any benefit.
Could you find an old concentric volume pot with a single spindle, and adjust the left and right volume that way?
I looked a bit at balance controls and how they can be implemented when thinking about how to update an old integrated tube amp. The snag is that unless you have the special balance pots mentioned in the article, where only half the track is resistive, then there is a loss of gain without any benefit.
Could you find an old concentric volume pot with a single spindle, and adjust the left and right volume that way?
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From what I understand, that's how MN "Blend/Balance" pots are tapered. The one I have on the breadboard now seems to work fine, and they are readily available from electronics suppliers. They apparently use them on guitar amps a lot to blend two different sources together, but also work as balance controls. I don't know much about guitar amp stuff though. Mine also has a center detent so it's easy to tell when you have it centered.
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There's no necessity to have only one knob for the balance function.
You can use two independent single pots, one per channel. Just turn down the one in the louder channel.
You can use two independent single pots, one per channel. Just turn down the one in the louder channel.
Necessity no, convenience yes. I have two mono integrated amplifiers (Scott 99D) and they don’t see much use for that reason.
In the musicical instrument field there are some quite interesting, balanced and unbalanced dual concentric pots in both log and linear combos. I'll bet there is something there to interest you. As far as the "right way" to implement this type of balancing act - it's really down to the application and your specific requirements for maximum noise and distortion in use, since you probably don't need the ultimate in performance, right across the full range of adjustment.
To be honest, it depends upon how the pot is built...
You can use a single pot liner pot, but if the center isn't exactly half the total resistance measured across the pot, you can add a small value resistor to the "short" side, or simply mark the shaft where the exact middle is, and line the marking on the knob up with it.
There are also some single pots with a tap in the middle of the resistance element. Connect the tap to the wiper, and it'll bypass the resistive elements when centered.
There are also "MN" designated pots, like the ALPS "Blue Velvet" Balance pot. I think the part number is something like: RK27 - something -MN. They are dual-gang pots, and the resistance element is half resistive, half silver-plated brass. The wafers are identical, so the front half and back half are wired opposite. Connect the wiper tabs together
You can use a single pot liner pot, but if the center isn't exactly half the total resistance measured across the pot, you can add a small value resistor to the "short" side, or simply mark the shaft where the exact middle is, and line the marking on the knob up with it.
There are also some single pots with a tap in the middle of the resistance element. Connect the tap to the wiper, and it'll bypass the resistive elements when centered.
There are also "MN" designated pots, like the ALPS "Blue Velvet" Balance pot. I think the part number is something like: RK27 - something -MN. They are dual-gang pots, and the resistance element is half resistive, half silver-plated brass. The wafers are identical, so the front half and back half are wired opposite. Connect the wiper tabs together
This is supposed to be it, but the photo and the data sheet doesn't show it. It is a dual-gang pot, but the MN taper isn't on the data sheet. I've got one someplace, and it is indeed a balance pot, and has the "MN" taper marking. I remembered the action incorrectly though, the front and back wafers are opposites, one goes from 0 Ohms at center and stays at 0 Ohms clockwise, the other stays at 0 counterclockwise. The opposite direction on both is the resistive element. What I described before doesn't make sense!
https://www.mouser.com/ProductDetai...N104-RK271122004D?qs=oKW7zmyQiO5Fc1wniOb4yQ==
https://www.mouser.com/ProductDetai...N104-RK271122004D?qs=oKW7zmyQiO5Fc1wniOb4yQ==
Not ALPS, but these Bourns pots work nicely:
250K: https://www.mouser.com/ProductDetail/Bourns/PDB182-GTRB2-254MN?qs=MAZTpT1IVl9lP/ZA5KktUg==
500K: https://www.mouser.com/ProductDetail/Bourns/PDB182-GTRB2-504MN?qs=MAZTpT1IVl/Tcf8tEJvRPA==
They are also available at Antique Electronic Supply:
https://www.tubesandmore.com/products/potentiometers_0?filters=2341a2353c1902a1911c147a1902
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I use this style of balance control in my tube preamps.
I use 10k MN taper pots by Alpha. --> https://www.taydaelectronics.com/10...potentiometer-blend-balance-center-click.html
I use 10k MN taper pots by Alpha. --> https://www.taydaelectronics.com/10...potentiometer-blend-balance-center-click.html
Yes, that is nicer. It feels profligate to discard half the signal without using it.
I will replace a 500k one from an old amp with that style since I lose some gain in other changes. Any pointers for a spindle extender? The old one is 2 1/2" I'd say.
I will replace a 500k one from an old amp with that style since I lose some gain in other changes. Any pointers for a spindle extender? The old one is 2 1/2" I'd say.
One of these cut down?
https://www.goodcomponent.com/products/knobspotentiometers/potentiometers/1450.html
https://www.goodcomponent.com/products/knobspotentiometers/potentiometers/1450.html
what actually is the advantage, if I use this MN taper for balance in an integrated- or pre-amplifier instead usual and mostly to find style like those from attachment ? - found under
https://web.archive.org/web/2020020...s.com/cd_catalog/new_catalogs/Pots/tapers.htm
check out also this thread:
https://www.diyaudio.com/community/...usable-angle-of-rotation-what-benefit.397122/
P.S.: Harman's integrated amplifier HK-610 and HK-620 use balance pot equipped with MN taper
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