[wushuliu]

Kingnubian , I have the digikey pot for my build but have not completed it yet so I can't coment on the sound....

Hi rtate, as I just said above the dual-gang PEC pots are not recommended. There have been serious issues reported w/ L/R volume matching in the past.

[wushuliu]

Huh?  The Gigawork 20K pot I ordered says clearly log type in the ad:
"Up for sale is one (1) piece Brand New 21-stepped attenuator 20K Type A (Log)  STEREO using SMT resistors.  Knurled shaft supplied with a nut and a star washer"

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120502791204&ssPageName=STRK:MEWAX:IT#ht_4201wt_907

That's what I thought too. I know they used to be linear, but mine sure operates like log...

EDIT: I see that I describe them as linear in the BOM. I'll change that.

[rtate]

wushuliu, thanks for the heads up I wish I would have known this before I spent the 32$ on it.
Where did you read about the unreliability??

[wushuliu]

wushuliu, thanks for the heads up I wish I would have known this before I spent the 32$ on it.
Where did you read about the unreliability??

It's come up several time on diyaudio.com. Doesn't mean yours won't be fine, but better safe than sorry. If you haven't used them yet, it's easy to do returns w/ digikey...

http://www.diyaudio.com/forums/chip-amps/40676-so-i-did-try-all-those-different-potentiometers-25.html#post807128

[wushuliu]

Here's a post from stereo.au that maybe of some help.

http://www.stereo.net.au/forums/showthread.php/21593-Dirt-cheap-stepped-attenuators-available?s=6d14852c87a8634f8b471a3a28111cba&p=326222&viewfull=1#post326222


Just to report my findings regarding these attenuators.

- Build quality is excellent. Nicely made gold plated spring brushes sliding over gold plated pads. I lubricated mine with Caig ProGold to start with. It is an open construction which may cause some dirt accumulation over time but it also makes cleaning a breeze.

- The log profile is more a dual-linear. I can post an graph to illustrate this - but essentially starts with almost a perfect linear transition with a slow slope from 0 to 10th step and then changes to a steeper linear curve from 10th to 21st step. I find this very useful because it gives more control at low levels.

- Precision is very good. Overall difference between channels is around 0.2% but never larger then 0.4%. To be accurate, on 4 attenuators (2x10K and 2x50K) that I bought I found only 3 steps on each of them to have larger channel difference then 0.1%.

- Physical size is also good because they are 1/3 smaller then standard Alps Blue and can be fitted anywhere in the case. Feeling when rotating the shaft is very smooth with very soft but distinct steps. Rotation resistance is just right to give a good control but also to allow a fast change.

- Listening test: the real benefit with steppers is always precision and control on low volume levels. This one is no different. When compared to Alps blue that it replaced - it brought more clarity as my first impression, on top of already anticipated (and achieved) improvements. In my case it was also the size that mattered since it allowed me to bring the pot closer to the selector relays at the back of the case (with an extension shaft) and shorten the signal path considerably.

- Bad things - none. Simply as that. That being said - yes they do have "only" 21 steps. I did not find that restrictive in any way simply because of the nicely designed pseudo-log curve. On top of that - standard steppers are all around 24steps and that is not a big difference. For more then that one has to go towards digitally controlled volume controllers like the one from Twisted Pear, but they do cost a lot and they need a PSU.

- The best thing - price! For $10 this is a steal. Who ever has Alps pots should think seriously about replacing them with these.

[rtate]

Thanks again wushuliu   
If I measue the pot with a couple of meters would I be able to see if the pec pot is ok??

[wushuliu]

Thanks again wushuliu   
If I measue the pot with a couple of meters would I be able to see if the pec pot is ok??

Dunno 'bout that. Maybe someone else can chime on the best way to assess matching accuracy.

[kingnubian]

That's what I thought too. I know they used to be linear, but mine sure operates like log...

EDIT: I see that I describe them as linear in the BOM. I'll change that.

I'm sold. I've sent in an order for the pots that you recommend.
Thanks as usual for the heads up.

[roymail]

wushuliu, thanks for the heads up I wish I would have known this before I spent the 32$ on it.

I'm not doubting wushuliu or the posts on other forums, but I got a chance to audition a passive shunt attenuator using a dual gang PEC and a Caddock 132 resistor on each channel.  I have to say it sounded awesome in my system, beautifully musical to my ears.

So as previously stated, yours may sound just fine.  Don't despair just yet. 

[kingnubian]

I'm not doubting wushuliu or the posts on other forums, but I got a chance to audition a passive shunt attenuator using a dual gang PEC and a Caddock 132 resistor on each channel.  I have to say it sounded awesome in my system, beautifully musical to my ears.

So as previously stated, yours may sound just fine.  Don't despair just yet. 

Good to hear as I also ordered the PEC for another upcoming project.

[Jon L]

Guess what came in the mail today  The lovely and expensive Vishay TX2575's.

[Jon L]

BEFORE



AND AFTER



I have my burn-in music going, but I couldn't resist so took a listen anyway.  So far, even before solder is dry, there's a feeling I went from tap water to a really good bottled water due to the gentle clarity.  A little bit of grit and grain I used to hear on certain vocal tracks are clean and clear. 

Will let'em burn for a gazillion years and report back. 

Too bad the SMT volume control is stuck at the post office.  I was home, but they must have rang the bell once and took off, with that pick-up notice stuck to my door 

[roymail]

Jon L, thanks for posting the pics.  What B1 board are you using?  Doesn't appear to be a standard Pass B1 board.  Did I miss something?

What's the benefit of using 330R value?

Thanks!

[Nick77]

  Guess what came in the mail today   The lovely and expensive Vishay TX2575's.

Nice work Jon, I have another pair of the Vishays on the way. How long did your order take?

[Jon L]

Well, the 20K SMT volume control is here from Hong Kong.  It sure is tiny compared to Alps it is replacing.  After only about half an hour, jury is still out on whether sound quality actually improved or just changed.

[Nick77]

I just installed a second pair of naked Vishays TX2575 in place of a pair of Rikens in the output position. I now have 2 pairs of the naked Vishays in the signal positions. The clairty has gone thru the roof, I lost a little bass and dynamics/volume, i think i have confused dynamics with noise created by using carbon/riken resistor. Anyway thru trial and error i can say if you can afford the Vishays you will be rewarded with awesome transparency and tight clean bass. This is using 330r Vishays and Sonicaps your results may vary depending on how revealing your system is. 

[roymail]

Well, the 20K SMT volume control is here from Hong Kong.  It sure is tiny compared to Alps it is replacing.  After only about half an hour, jury is still out on whether sound quality actually improved or just changed.

I would have thought that the SMT stepped attenuator would be noticeably superior to an Alps Blue pot.  Any thoughts as to what's going on with this? 

Please keep us updated.  Thanks!

[kingnubian]

I just installed a second pair of naked Vishays TX2575 in place of a pair of Rikens in the output position. I now have 2 pairs of the naked Vishays in the signal positions. The clairty has gone thru the roof, I lost a little bass and dynamics/volume, i think i have confused dynamics with noise created by using carbon/riken resistor. Anyway thru trial and error i can say if you can afford the Vishays you will be rewarded with awesome transparency and tight clean bass. This is using 330r Vishays and Sonicaps your results may vary depending on how revealing your system is. 

Thanks for the update. This is the exact route I will be taking.

I have one question though. I will be using my B1 build in front of a ClassDaudio SDS-254 diy build. Anyone with experience with this setup or driving another class D amp?

[Nick77]

Thanks for the update. This is the exact route I will be taking.

I have one question though. I will be using my B1 build in front of a ClassDaudio SDS-254 diy build. Anyone with experience with this setup or driving another class D amp?

Thats the exact setup i am running, the match up is impeccable. Highly reccomend!! 

[Jon L]

I would have thought that the SMT stepped attenuator would be noticeably superior to an Alps Blue pot.  Any thoughts as to what's going on with this? 

It probably is superior, but I had to adjust my system a bit.  SMT does sound more solid and resolute through mids to bass, but it seemed a tad too "controlled" AKA "darker" up top compared to Alps.  SMT may in fact be more accurate here and Alps injecting its own splash and "air" perhaps by making you notice the treble more due to less solid mids/bass possibly. 

Anyway, I changed out my Stereovox XV2 for a UPOCC solid silver digital cable and that seemed to have rebalanced things just right...

I do want to compare both volume controls to *no pot," meaning bypass the volume.  Do I just connect input wire to output wire (bypassing pot)? What do I do with the ground wire that goes to the vol pot?