Tubelab SE, What Volume Pot/s?

[OneLiterPeter]

Hi all, Did some searching around and came up a bit empty handed so I figured I'd ask the experts.

OK So I'm building a Tubelab SE, 300B and I want to have one of two scenarios for the volume pot/s.

1. A left/right balance control and a volume control.

2. Two volume controls (one for left, one for right).

I'm also open to installing a remote operated volume if it's feasible.

The reason why I want this is that I have a pretty dominant left ear and a little extra adjustment really helps me a lot.

I'm also looking for the best pots I can reasonably obtain.

Thanks,

Pete

 

[boywonder]

here's one solution....

John Broskie (Tube CAD Journal) sells some cost effective and very interesting stepped attenuators that also allow balance control....They are somewhat unconventional but you get a stepped attenuator and balance adjustment for cheap, all in one package.

Attenuators and Signal Selecters

http://glass-ware.stores.yahoo.net/netcjstat.html

If you are interested in stepped attenuators, search for goldpoint and dact. Then there are really pricey ones like Shallco. Michael Percy audio sells these, and maybe a few others.

 

[VictoriaGuy]

Those Broskie attenuators are interesting- thanks for the link, BoyWonder.
The most interesting aspect for me is why people would find these appealing or useful- do many people want coarse/fine volume controls, or three or four or more volume controls to control two channels of audio? Obviously I need some 'edumucation' here, as there must be a market for these products.
Give me one volume control (with perhaps an added balance) any day. It's a pity that nobody is making ganged L-R volume controls that have a friction clutch in 50k or 100k sizes for tube amps. Those controls which are on some 'vintage' SS amps are excellent.

I didn't see any balance controls among the Broskie offerings, BTW.

And, the Broskie devices are kits, which may not be a problem for most of us.

 

[boywonder]

T

I didn't see any balance controls among the Broskie offerings, BTW.

And, the Broskie devices are kits, which may not be a problem for most of us.

The Broskie boards/kits are volume controls & balance controls as a unit....albeit a bit unconventional........as a bonus, they are stepped attenuators as well (no pots).

 

[VictoriaGuy]

All a matter of definition, I guess.
For me, a balance control is a single knob marked L & R - not two/3/4/6 volume controls.

 

[nic6paul]

I have used the Alps RK27 in one SSE and I have a Goldpoint in the other. The Goldpoint is very nice and the quality is top notch but I think my money could have been invested better else where.

 

[boywonder]

I have used the Alps RK27 in one SSE and I have a Goldpoint in the other. The Goldpoint is very nice and the quality is top notch but I think my money could have been invested better else where.

The Goldpoints are a bit pricey.....There are also lots of budget stepped attenuators on Ebay from China/Hong Kong.......although the OP is looking for "the best pots he can reasonably obtain"

 

[OneLiterPeter]

Hi all...

Thanks for the replies.

Boy Wonder...
I've used the Broskie attenuators before in a Glassware preamp. They are very high quality and the kit is very nicely organized. I've thought about using one in this amp but they're a bit large for the enclosure that I'm considering.

VictoriaGuy...
IMO, The reason why Broskie went with a series - ladder configuration is that all stepped attenuators suffer from the same limitation. They just don't have enough steps. With his design you have a master volume with 6 steps and a left and right with 6 steps. So for each step of the master you have 6 in between steps of the left and right. In total you end up with 36 steps for both the left and right channels. In theory it offers a lot of adjustment but in practice it's somewhat of a PITA.

I'm thinking of going this route... ESP - A Better Volume Control I'm wondering if anyone has tried something like this.

 

[OneLiterPeter]

All a matter of definition, I guess.
For me, a balance control is a single knob marked L & R - not two/3/4/6 volume controls.

Agreed.

I'd like to have one balance knob and one volume knob.

So the Alps pots are the best value for standard carbon pots?

 

[pieter t]

IMO, The reason why Broskie went with a series - ladder configuration is that all stepped attenuators suffer from the same limitation. They just don't have enough steps. With his design you have a master volume with 6 steps and a left and right with 6 steps. So for each step of the master you have 6 in between steps of the left and right. In total you end up with 36 steps for both the left and right channels. In theory it offers a lot of adjustment but in practice it's somewhat of a PITA.

36 steps not enough?
24 steps with the good quality Elma switch is plenty enough when your socalled "gain structure" is right.
When you control volume between 8 and 10 o'clock with the pot (difference between soft and loud), yes you might be short of steps but in that case you should question gain structure of your set up.

 

[OneLiterPeter]

36 steps not enough?
24 steps with the good quality Elma switch is plenty enough when your socalled "gain structure" is right.
When you control volume between 8 and 10 o'clock with the pot (difference between soft and loud), yes you might be short of steps but in that case you should question gain structure of your set up.

With regard to overall volume, I agree, 36 steps is plenty, the problem that occurs with the Broskie setup is when you increase (or decrease) one side from the other in order to adjust the balance. I've already run into a scenario where the difference in volume from one step to the next is too much.

Maybe my gain structure was off but I used it with a Broskie Aikido Line Stage so one would think that they would be mated to each other.

 

[pieter t]

Maybe my gain structure was off but I used it with a Broskie Aikido Line Stage so one would think that they would be mated to each other.

Not necessarily so.
You should look at the complete reproduction chain:
loudspeakers (how much power do they need?also take into account your listening habits);
amplifier (how much power? input sensitivity?)
preamp/source: how much signal available?
In my experience very often there is somewhere too much gain with the consequence that volume is controlled within a small range of the pot.

 

[OneLiterPeter]

Pieter...

Agreed, and I will take that into account with this amp build. Bear in mind that this amp my see different sets of speakers, preamp/sources and a variety of listening conditions.

That's why I've chosen to go the pot route. I may give up a little sonically but I will be able to experiment more and get in between the cracks.

 

[pieter t]

Broskie's Aikido Line Stage is a flexible unit.
The first tube does the voltage gain, and it is not difficult to change tubes to optimize the gain structure.
Just an idea.

 

[OneLiterPeter]

Broskie's Aikido Line Stage is a flexible unit.
The first tube does the voltage gain, and it is not difficult to change tubes to optimize the gain structure.
Just an idea.

Yeah... My Aikido has been sitting around collecting dust for a while. Mine is the Aikido All in one LSA/HPA and I'm currently using 4 6CG7 tubes. I think I'll turn this one into a headphone amp as I already have 3 tube preamps. For the TSE though I'm going to do some benchtop experimentation with pots and if they work well that will be the way I'll go.

BTW... Thanks for reminding me about the Aikido. It would be nice to have an HPA in the mix and I'm pretty sure it won't take much to convert it.

 

[boywonder]

Adding a volume control to the TubeLab SE

FWIW, of all of the amps I've built (all three! ), the Tubelab SE has the lowest input sensitivity............I run everything with an powered preamp. I switch between an Anthem Pre-1 and an Aikido.

 

[OneLiterPeter]

Which aikido do you have?

 

[hartze11]

Does anyone know of an active "volume stage" that is low cost (yet decent performance) that doesn't involve a linear/log pot in the audio path? E.g. an active variable gain stage?

I'm building a Pass B-1 buffer stage, but it too calls for a pot (or stepper) in the audio path...

Dave