Variations on the Shunt Pot Mod

[david]

Hi Richard, All,
Killing a bit of time in a Greek Port while our friends run a mercy mission in their car to recover my passport which the apartment manager held onto by mistake........

Firstly, the shunt pot wiring I used was the tweaks version. I tried the other way round and it seemed to improve things, but I didn't do any measurements.

All the action in my TKD pot happens between 7 (0) and 9 o'clock. So probably on Monday I will measure the resistance at these points in two modes:

-as if the pot were connected conventionally
-with the pot connected in shunt mode as per tweaks

My theory is the former will be a normal log progression, the latter may still be log but will be a strange shape.......

I can't explain Bearded Fiddlers measurements as you say with two separate tracks, but it suggests an earthing problem where the earths are commoned. My guess is his earth connection here is faulty, which may exacerbate hos on /off sensation.

I need a motorpot and have previously been very happy with Panasonics as an upgrade from Alps, but Panas are now hugely expensive in log form and the conventional earth connection is commoned, ruling out the Tweaks version of shunt wiring.

The TKD is great, but this short usable volume range is annoying. I am about to try a Tocos, which I will motorise myself.

The motorpot no is CP2500.

My DAC outputs a bit over 2v rms. With 100k shunt into 20k pot this gives max 400mv out which works fine into the Alps wired exactly the same way.
Sensitivity of the 300b push pull clone is 300mv and my speakers are 89db sensitive.

The Alps volume range is still limited but the channel balance goes right to the end of the track whereas the TKD exhibits this measurement of 600ohms /300ohms right to left at the point where I am listening to quiet music.

David

[John Caswell]

Hi all,
If that is the way David's pot is wired then I am sorry it is not a very nice way if doing it, and I suspect is the main source of the problems. (there are only two ways of doing things - the wrong way and my way, at least this is what I told all my trainees as I proceeded to knock the corners off of them!!!!))
The input via the 47K should be connected to 3 and then go straight out again. There should be no other connections to 3 apart from the two mentioned above
1 and 2 are connected together and go to earth as per my previous drawing.
I suggest that you ignore the numbers 1, 2 and 3 (as mfrs have different nomenclature) and look at my lower physical drawing of the shunt wired pot. This is the correct way to wire it.
Richard's drawings and photos also make it very clear
If the pot is labelled somewhere in its part number with an "A" it is most certainly a log pot, if it has a"B" somewhere then it is linear and nor really suitable for a volume control but could be used as a balance control.

John

[A Stuart]

Spent this afternoon trying to learn how to draw graphs on OpenOffice - unsuccessfully!
Here for reference, but without graph, are figures from Alps 250k (541N 250KAX2) as supplied with KLPP1 a year or several ago.
Rounded to 2 signif figures.

[david]

John,
I'm afraid your post bears no relation to the thread. I have stated many times now that my pot is wired as per tweaks and this is not a connection issue.

I have said in my most recent post that I will take two sets of measurements, of the resistance 'seen' by the signal to see whether we get a log function when connected in shunt mode. Please keep your comments to this part of the discussion and not something covered a long time ago.
David

[Richard]

Hi David,

I think you're being a bit unfair there. You said this thread details a different way of wiring to the shunt pot in Tweaks.

I drew the diagram of what you described and you haven't said that is not the one you are using.

Then you referred to "conventionally wired" which most folk would read as being not shunt and certainly not your shunt description.

Now you say your pot is wired as per Tweaks shunt.

Really this is all going around in circles. It's not fair to expect folk to separate completely this thread from your other also running at the moment where you complain about the vol control and say you have 1M shunt resistors, http://www.world-designs.co.uk/forum...ead.php?t=6858

It's not at all clear what you've done and the results you post really don't make a lot of sense.

[A Stuart]

Originally Posted by david

All the action in my TKD pot happens between 7 (0) and 9 o'clock.

Hmmm. Just what you would expect with a linear pot . Reaches within 20dB of maximum in first tenth of rotation, much less happens thereafter, causing you to think this wiring does not utilise the "gentle end" of the pot at low volumes.
And, the effect would be more noticeable altering the variable against a fixed shunt resistance in "Shunt Mode", as opposed to the variable against a variable reducing shunt in standard mode.

Bags the chocolate Noddy, if no-one has eaten it yet.

Alastair
I could be wrong , of course.

[bob orbell]

Hi all, I agree with Richard, this post is going round in never decreasing circles, maybe it should be closed and start again. BOB

[david]

The post is going round in circles. I have stated many times now that I have the TKD pot wired as per the Tweaks section and yet folk keep coming back to connections, which is irrelevant. My old post about 1 meg shunt resistors is also irrelevant as that was with Pre 3 which had x 5 gain. I have since changed my Pre to firstly a CF pre, and now an Aikido Pre.

Alastair has been able to follow the plot, so I don't think the intellectual challenge was impossible

The TKD pot is behaving strangely for both Jan (Bearded Fiddler and I) and I will try and get to the bottom of it.

For anyone interested, do send your suggestions to a new thread and we'll consider this one closed.

I had a chance to measure the resistance at various volume positions between Pins 1 and 2 per Richard's diagram Post 14 this thread as follows:

L R

8 o'clock 6.03 4

9 o'clock 7.03 7.67

10 o'clock 6.42 7.4

11 o'clock 6.65 7.16

12 o'clock 7.11 8.02

There is nothing remotely logical, or logorithmical, about these readings.Readings were taken in circuit on the Aikido which means there is a 1 meg shunt to earth before the input cap.

So, any suggestions on a new thread please.
David

[Richard]

Hi David, all,

We'll keep it all in this thread please and move it to Problems as all the information so far gleaned and likely to be referred to will be here