Salas hotrodded blue DCB1 build

Davym - I guess you have the resistors in series with the input to the potentiometer, thus raising the input impedance, and practically halving the volume?

Correct, previously I had the problem where I reached close on full volume within the first third of the pots rotation which also seemed to reduce the bass weight at normal listening levels. Now I need to use the full rotation to reach maximum volume.

I realise this is not strictly pukka practice but it works very well indeed in my system. My power amps are mono block My-Ref FE's and this current configuration gives me the best sound I've had to date from them.
 
Thanks Salas!

Davym, I am very curious how the 50K Tocos will do in your system! I bought the 10K from the same seller, and he is very fast indeed!
The low price might have something to do with the quality, the taper closest to the shaft measures 600Ohm higher than the back one. Tracking is ok after soldering a 600R resistor in series with the back taper. Could you measure your 50K pot before mounting it?

Ok first I measured the first 20K stereo Tocos pot I bought which I got from hifi collective (they didn't want it back after refunding me for it) with the pot set at 50% rotation I get the following readings -

Inside pot (nearest the shaft) measured between lugs 1 & 2 = 2.68K. Between lugs 2 & 3 = 17.30K

Outside pot measured between lugs 1 & 2 = 2.78K.
Between lugs 2 & 3 = 17.29K

Now for the 50K Tocos pot again set at half rotation.

Inside pot between lugs 1 & 2 = 8.42K.
Between lugs 2 & 3 = 40.6K.

Outside pot between lugs 1& 2 = 8.78K.
Between lugs 2 & 3 = 39.6K

:spin: Not sure if this is the best method to use when measuring a stereo pot but it does show the inconsistency between channels. I started a thread last year about using a fixed resistor to balance the channels but got a lukewarm response which is why your post engaged my limited attention span :D

I'm kind of busy over the next few days but hope to fit the 50K Tocos to my DCB1 at some point over the weekend. I'll post my impression of it soon after.

Edit - just to add some info, my source (DAC) was measured by Stereophile as having a max output of 2.08V and an output impedance of 42 ohms at high and mid frequency's rising slightly to 78 ohms in the low bass region. Dario tells me that his version of the My-Ref has an input impedance of 100K.
 
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Your measurements actually look pretty decent!

Just came back from listening to the 10K with 30K in series ( coming from 20K ). Tuning the sound like this is like the Low / High one potentiometer thing on old radio's. With the 30K in series the bass was like I remembered from the Alps 50K, but the mids and highs began to suffer. It seems I cannot have both, but will try 25K in series to see if that works out.

My pot is also cutting out the right channel sooner than the left. That does not bother me too much because it is such a low level that I never use that. Would be bad if I wanted to sell the thing though, but then I would need a nicer case too :)

Any ideas welcome!!
 
Just wondering what kind of resistors you used and if paralleling them made very much difference in mine (doubtful) I only paralleled them because I did not have any 20K metal film ones left.

It might well be worth trying 25K in series with the pot. I also wonder what if any difference could be found by paralleling a decent quality carbon resistor with a metal film type of the same value. I might try that at some point just out of curiosity.
 
I have been toying with the idea of building a preamp which would be the DCB1 with a tortuga audio ldr3 for attenuation in front of the DCB1.

This would be the ldr3:

LDR3x.V2 Passive Preamp Controller | Tortuga Audio

diy LDR attenuators are quite popular on here as a search will show, you might even be able to take advantage of a group buy which could be worth looking into. Good luck with the build.
 
Davym, as we both have sources with very low output impedance, which should be able to drive the 10K pretty easy, it suddenly struck me: Can it be that my output cap of the squeezebox is too small? I used 10uF MKP output caps, paralleled with 0,33uF K42Y PIO's. Original caps were 10uF electrolytics.
Could enlarging the output caps have the desired effect?

Just looked it up on the v-cap calculator, and the 10uF in combination with 10K input impedance should do the job just fine. Theory vs practice??
 
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Theory vs practice is an area where I have had conflicting experiences before and probably will again.

My current form is to follow convention as far as I can go then carry out a few variations of my own to get closer to what I actually want to hear from my system.

imo fitting output caps may be the correct way of doing things but if no harmful level of DC exists in the output signal, blocking caps are not needed and they do nothing good sound quality wise either. If your power amp has blocking caps on it's signal inputs, there is no need for them to be fitted to the source as well. This may be part of your problem but there are better brains on here than mine. Could you try removing the blocking caps from your squeeze box then measure it's output for DC? If there is none or very little it could be beneficial to leave them out.
 
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Ok first I measured the first 20K stereo Tocos pot I bought which I got from hifi collective (they didn't want it back after refunding me for it) with the pot set at 50% rotation I get the following readings -

Inside pot (nearest the shaft) measured between lugs 1 & 2 = 2.68K. Between lugs 2 & 3 = 17.30K

Outside pot measured between lugs 1 & 2 = 2.78K.
Between lugs 2 & 3 = 17.29K

Now for the 50K Tocos pot again set at half rotation.

Inside pot between lugs 1 & 2 = 8.42K.
Between lugs 2 & 3 = 40.6K.

Outside pot between lugs 1& 2 = 8.78K.
Between lugs 2 & 3 = 39.6K

:spin: Not sure if this is the best method to use when measuring a stereo pot but it does show the inconsistency between channels. I started a thread last year about using a fixed resistor to balance the channels but got a lukewarm response which is why your post engaged my limited attention span :D

I'm kind of busy over the next few days but hope to fit the 50K Tocos to my DCB1 at some point over the weekend. I'll post my impression of it soon after.

Edit - just to add some info, my source (DAC) was measured by Stereophile as having a max output of 2.08V and an output impedance of 42 ohms at high and mid frequency's rising slightly to 78 ohms in the low bass region. Dario tells me that his version of the My-Ref has an input impedance of 100K.

Why estimating and not hitting the thing with signal to straightforwardly measure the level balance?

I got the following results from a 50K stereo Log Tocos when feeding its both sections from a 50 Ohm output signal generator 1kHz sinewave at 1.18 Vpp.
Turning down from max and stopping at arbitrary ref levels, front and back pot sections peak to peak readings were:

1.18V 1.18V
1.00V 1.02V
0.600V 0.608V
300mV 296mV
200mV 198mV
100mV 97mV
50mV 48mV
30mV 28.4mV
10mV 9.2mV

Those I copied from what the scope was displaying at its measurements section and double checked them with superimposition in more sensitive scale too. For the low mV area I run both average and hi-res boxcar method while the bandwidth limit was engaged in all cases just to avoid catching some fatter peak to peak due to interference on the open wiring in one or the other channel.
 

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I need output caps in my squeezebox, there is some ( believe 2.5V ) voltage on the output of the DAC. Now there is not much room left in there, after putting 10.000uF power input cap in, and adding all the output coupling caps. Could try an electrolytic just to test if I am on the right track. Salas, do you have any idea about this???

Salas, would your measurement give a better idea about the pot then putting 1,5VDC on it and simply measure the DC output? Just a question
 
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Never put enough DC across a pot, you may damage the wiper.

If we translate my AC measurements in dif dBV we have:

1.18V 1.18V 0dB
1.00V 1.02V 0.172dB
0.600V 0.608V 0.115dB
300mV 296mV -0.117dB
200mV 198mV -0.087dB
100mV 97mV -0.264dB
50mV 48mV -0.354dB
30mV 28.4mV -0.476dB
10mV 9.2mV -0.724dB
 
So you got a good one!

I took the chance and soldered a 220uF electrolytic ( Yageo low ESR ) cap parallel to the existing output caps in my Squeezebox to test, and I can report: the BASS is back, driving just the 10K pot so the clarity in mids and highs remained the same. After a while even the air came back into the sound, perhaps the burnin of the electrolytics doing its job.

Guess the Squeezebox is staying topless for the coming days to see how the caps are behaving themselves. Hope they don't get harsh sounding, the main reason to get rid of the Original coupling cap.

Will report back in a couple of days, right now I have to go listening again ( can you tell I am happy? )
 
OMG!!!

Well, 99% done...at last !!!!
(Will design the aluminum "volume gradation" ring to go around the knobs a little later)

I would like to take the opportunity to say a HUGE thank you to Salas, TeaBag, AndrewT (even if we sometimes had different points of vu, I respect what you bring to DIY community) and others who shared tips and all along the way.

You guys helped me more than I would have hoped.

My DCB1 has the test board in and is now playing. Really impressive, very well balanced sound even if music has been playing for about an hour only. Tonaly, it is almost scary good...

Can't wait for the "burning" to work its magic...

Anyway, thanks a lot again and again. Now moving to "DCB1 resistors tryouts" thread as I will begin testing soon (starting resistors kit: 220R Shinkoh tantalums, 1M Riken Ohms, 220K Allen-Bradley @ less than 5% after drift).


Here are a few pics.

Regards
Scorpion

The best I've seen... Thanks Scorpion - excellently built!

Regards
 
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So you got a good one!

I took the chance and soldered a 220uF electrolytic ( Yageo low ESR ) cap parallel to the existing output caps in my Squeezebox to test, and I can report: the BASS is back, driving just the 10K pot so the clarity in mids and highs remained the same. After a while even the air came back into the sound, perhaps the burnin of the electrolytics doing its job.

Guess the Squeezebox is staying topless for the coming days to see how the caps are behaving themselves. Hope they don't get harsh sounding, the main reason to get rid of the Original coupling cap.

Will report back in a couple of days, right now I have to go listening again ( can you tell I am happy? )

I got a long in the tooth Alps RK40 black beauty in a tube preamp that it may replace at a point. Does your 10K still cut out one channel first if you will jumper that extra 600R?
 
I got a long in the tooth Alps RK40 black beauty in a tube preamp that it may replace at a point. Does your 10K still cut out one channel first if you will jumper that extra 600R?

I have put the 600R in series with the input, and that only balances out the tracking between the front and the back pot.
The cut off point is not really a part of the resistance track, it is where the resistance track ends and the wiper is on solid copper or another conductor to make the zero ohms position. When this is not aligned properly between the two ends, the only thing you can do is open up the pot and bend the wiper, or replace the pot with a better one ( which is clearly the best solution )

It does not bother me in my use. The system is in a room only used for workout and listening, in both activities really low level listening is not applicable:D
 
Thanks Davym, now it would be great to understand what is happening here, as the math does not match the practice here. 220uF might be a little on the big side, and the Yageo cap might not be the best choice ( I never use electrolytics as coupling caps ). Also the bass does not seem quite right, it is a bit untidy, perhaps the 10uF MKP has to go, three caps in parallel is probably too much to get the timing right and avoid phase shifting. Will expiriment some more this evening...