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Effect of replacing 50K Pot with 10K

eastone

eastone

pfm Member
I'm thinking about picking up LordSummit's TKD pot currently for sale, but it is 10K as opposed to the 50K ALPS blue it would replace.

The reason for wanting to change is that the ALPS doesn't sound fully open and dynamic in the lowest part of its range, which is where I'm stuck for most recordings. The competent DIYer who sold me the pre had used a TKD in the past and thought it similar sounding but far better in that respect.

My only concern really is that I'd end up with less travel which obviously would defeat the point of the exercise.
 
You don't make clear if this is a volume pot, etc. if a volume pot on the input of an amp, two points:

1) Lower pot resistance means a more demanding load for the source. Check your sources can drive 10k OK.

2) If there is an input series cap as a dc break before the pot, this may need to be bigger to maintain the LF response.

if the pot is for something else, you'd have to say what.
 
Thanks Jim, it is indeed a volume pot, on a valve preamplifier. I have a single source - a Ciunas USB DAC. Will be simple enough to ask John if it will drive 10K.

Whether there's a cap in the preamp doing the job you describe, I would have to look into further.
 
OK, I can't see any input caps. But I have no detailed knowledge of the circuit. Just looking at the picture and not spotting any! Do the two red wires from the volume pot go to a 'balance' pot? If so, I'm wondering how that would interact with a change in value.


Add to that: I'd like to see the circuit diagram if possible. I'm wondering from looking at the photo if the balance pot is operating by using its wiper on real ground and using its ends as 'fake grounds' for the two sides of the volume pot. If so, Changing the value of the volume pot will alter the behaviour when you adjust the balance and change the min volume level.

Some similar effects apply if the balance is pulling down the volume wipers. And may mean with the volume set high the input impedance will be below 10k with a 10k pot.

Am I misreading the photo?

If it as as the above, not liking the results at low volume settings might be more a matter of the *balance* pot than the volume one.

But that is one surmise based on another... :)
 
A Concordant... Without a circuit diagram it's very difficult to say. Odd looking thing... doesn't seem to be enough passive components for the valves... unless there are others underneath...
If it has a phono stage then I doubt the 10K pot will be OK as it will be far to heavy a load for the phono stage.
The only schematic I can find on line is for a completely different Concordant pre which does have a phono stage and this one has a 250K pot to avoid too heavy a load for the phono section.... I hope the present 50K was not just thrown in cos it would fit?
 
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Jez I believe the 50K ALPS is original. It's a line stage only.

Definitely no schematics out there for these, I've trawled a number of times.

Jim, that is a balance pot, you're right. I'm not technical enough to say if it's operating in the manner you speculate, unfortunately.

Starting to sound as if I'd be better off buying a new 50K pot!
 
eastone said:
Jez I believe the 50K ALPS is original. It's a line stage only.

Definitely no schematics out there for these, I've trawled a number of times.

Jim, that is a balance pot, you're right. I'm not technical enough to say if it's operating in the manner you speculate, unfortunately.

Starting to sound as if I'd be better off buying a new 50K pot!
Click to expand...

Makes sense that its a line stage as there just aren't enough parts for anything else! Rather too many valves unless the dual triodes are in parallel too!
A 50K stepped attenuator would be the ultimate for it;)
 
I did briefly try an, admittedly cheapish, stepped attenuator but didn't get on with it at all. Very lean sounding.

I don't really want to get too bogged down in 'upgrading' parts as I'm happy with the overall balance of the sound. Also, I believe Doug tuned these units around inexpensive and readily available materials, and I'm told the TDK pots are sonically very close to the ALPS. I'll be putting back the original output caps soon too...
 
If going to a stepped attenuator a cheap way to see what works (before buying an expensive one) is to solder up a simple potential divider with two resistors. You cant change the volume but chosing the right values will give you a not too quiet and not too loud volume. Once you have found the values that work best you can then try different brands of resistor (bulk foil's anybody ?) and then buy a good switch and the resistors you like the best.
 
eastone said:
Jez I believe the 50K ALPS is original. It's a line stage only.

Definitely no schematics out there for these, I've trawled a number of times.

Jim, that is a balance pot, you're right. I'm not technical enough to say if it's operating in the manner you speculate, unfortunately.
Click to expand...

The photo seems to show a balance pot that only has three tags on a single pot. That tends to imply it has to be what I described. A more conventional stereo balance pot would have six tags.

But it hard to say more because I can't see the photo clearly enough, nor know what might be out of sight.

However the 'grounded wiper' balance pot raises a 'pathalogical' flaw. If you wind up the volume to max and then turn the balance fully to one channel you essentially connect the input on the other channel directly to ground. i.e. make the input resistance of the amp *zero* for that channel. Not nice for the signal source...

In real use, you're not likely to do the above. But it means that with a high volume setting the input impedance will fall on one channel as you offset the balance control from its central location, and may fall well below the stated values on the pots.

So it is an arrangement I personally avoid unless I know the situation is OK.
 
In my case the volume is unlikely ever to be high as I'm not even hitting 9 on the dial. But the 10K pot will make this more of an issue right?
 
eastone said:
In my case the volume is unlikely ever to be high as I'm not even hitting 9 on the dial. But the 10K pot will make this more of an issue right?
Click to expand...

Well, I don't know where '9 on the dial' sits on the resistance travel of the volume pot. Erm... is your '9' on a 'linear Spinal Tap' scale?... :)

But, ignoring that, yes, if you keep the volume wound down you won't reach the 'pathalogical' case. However the resistance seen by the source will be that of the volume and balance pots combined.

The problems will be less severe if the balance pot is connected to the 'ground end' of the volume pot rather than the wipers. That avoids the above pathology, and increases the resistance the source will see. But that arrangement means the balance pot then won't alter the actual balance if you wind up the volume pot.

To know more, we'd need to determine the actual wiring, etc. But it is safe to assume the load seen by the source will be less than the volume pot's rated resistance.

If you have a DVM you can try measuring the resistance at the input sockets *with the amp switched off*. The DVM's voltage probably won't bother valves that are cold and unpowered.
 
Well, I'd be happy to send a bottle of something nice your way, if it did show up :)

I find it a terrific amp, and it has bettered some highly rated kit in my system. I'd be very interested to know what's going on in that simple-looking circuit.

What did you think of the amps at the time?
 
eastone said:
Well, I'd be happy to send a bottle of something nice your way, if it did show up :)

I find it a terrific amp, and it has bettered some highly rated kit in my system. I'd be very interested to know what's going on in that simple-looking circuit.

What did you think of the amps at the time?
Click to expand...

Very average, but then I was working on ARC, Conrad Johnson, Krell, EAR, Beard etc at the time. I seem to recall it had quite a punchy sound but lacked refinement and resolution compared to others mentioned earlier. The power supply was quite crude. Doug used to work for Harold Leak so a lot of his circuits were "his" take on an old Leak design.
 
G T Audio said:
Very average, but then I was working on ARC, Conrad Johnson, Krell, EAR, Beard etc at the time. I seem to recall it had quite a punchy sound but lacked refinement and resolution compared to others mentioned earlier. The power supply was quite crude. Doug used to work for Harold Leak so a lot of his circuits were "his" take on an old Leak design.
Click to expand...

Interesting. I've had it up against current valve units at around the £2K mark and haven't found anything to beat it yet.
 
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