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#702
Potentiometer sound quality?

I just built a B1 and broke one of the Bourns 25K linear audio potentiometers I purchased from Mouser during the assembly. I went to Radio Shack and got a 10K linear as a replacement. So I have a Bourns on one channel and a Radio Shack on the other.

The 25K Bourns sounds better. The Radio Shack 10K sounds tinny in comparison.

Is this because of the difference in resistance? Does the brand make a difference? I looked a the B1 output with a scope and a 5K sine wave and they both had the same output level when turned up all the way. I was going to order another Bourns pot to replace the radio Shack.

Should I spring for a better pair? I will end up paying a premium for buying just one part anyway.
 
#705
The choice of pots is one of the most influencial ones and most easy to notice a difference to as you have done. Except for the resistance values the resistance material and the wiper contact to that lane is cruical and the difference between low and high quality is huge. You will easily notice every change. And choose a log one as Andrew points out. Otherwise you will hardly notice the difference between half and full volume
 
#706
If one believes a linear potentiometer sounds better, some of the ebay-offered PCBs for the Alps RK27 etc provides for the resistor needed to make a linear potentiometer "logarithmic"
lin_to_log_pot.gif
 
#707
you can use a log faking resistor (LFR) to bring the control "shape" to closer to a log vol pot. The lin pot+LFR creates an "S" shaped control curve. The S can be moved around a bit by changing the ratio vol pot value: LFR value. LFR = 10% to 20% of lin vol pot value gets a useful range for the control of volume, but that useful range is only about 50% to 70% of the rotation. The other 30% or so moves even faster than the lin pot alone.
A second disadvantage of the LFR is that the input impedance is quite variable and may affect the Source. You need to check for this.
 
#709
Didnt Pass spec the 25K PEC linear pot? Maybe I am not remembering right, but I do believe that was the one. I used the parts he specified and it plays great. No boutique parts, just quality...not the most expensive but the result is wonderful, even the inexpensive PEC pots!

Check post #2
http://www.diyaudio.com/forums/pass-labs/124889-b1-buffer-preamp.html

Yup, they are linear Read down to where it discuss parts, including pots...
http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm

Russellc
 
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#711
At present I use a Bourns linear conductive plastic potentiometer. An Alps log RK27 is ready to be dropped in.
However, compared to the preamplifiers I used earlier, is auditory memory series me rigth, the B-1 is tremendously open and clear, with a fantastic soundstage, much improved and clean bass, well, everything. [Comparing to some oldies like the NS-10, the ML-1, but also Grace DAC/preamp 903.]
 
#713
Quality parts

slogger said:
I just built a B1 and broke one of the Bourns 25K linear audio potentiometers I purchased from Mouser during the assembly. I went to Radio Shack and got a 10K linear as a replacement. So I have a Bourns on one channel and a Radio Shack on the other.

The 25K Bourns sounds better. The Radio Shack 10K sounds tinny in comparison.
Click to expand...
After this I am rethinking always buying better quality parts, at least for the signal path. It's hard to tell from these forums what really makes a difference and what is consensus delusion. 🙂
 
#717
I broke my 18v wall power supply for B1, only other wall power supply I had @ home was a 12v 700mA, which I tried .... is working fine...don't even feel deterioration of sound....am I missing something here. This one is also absolutely quiet unlike the one I broke


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#718
18Vdc limits your maximum output to <6Vac
12Vdc limits your maximum output to <4Vac.
Since your peaks are likely to be <2Vac, you should not hear any difference. Your average levels may be around 100mV to 200mVac
Part of the reason for tolerating a low supply voltage is that the 2sk/lsk170 operate well at lower voltages than do low gm jFETs.
 
#720
bart_dood said:
Stock B1, used a 24v switcher power supply with a linear section to drop the voltage to 20.5v. Checked the PSU and audio outputs with a scope and found switcher noise in both so since these pics I added a larger inductor to drop it down. Its minimal now.

Sounds great and yes I built it in an upside down Ikea baking tray (stainless steel) with a plywood wooden bottom.

Can't decide whether or not to add the Pass DIY sticker or not (or where?).

Its feeding my penultimate zen amp and is fed by a ODAC DAC and an ESP battery powered phono stage from a Rega Planar TT.

Tip my hat to Mr Pass for making this all possible..

Chris
Click to expand...



You are a genious...baking tray is cool


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