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Old 10th November 2012, 01:47 AM   #1
Mihan is offline Mihan  New Zealand
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Default Valab Stepped Attenuators

Has anybody purchased any of the Valab 23 stepped attenuators?

I purchased a 20K log Stereo and a 20K log Mono and was surprised to find the stereo and mono attenuators measured differently despite being labeled as log.

The "Mono Log" version appears to be linear and the stereo version does seem to be log.

Here's how they measure.

20K Stereo Log: ............. 20K Mono "Log":

18.52K .......................... 19.78K
14.64K .......................... 19.63K
11.36K .......................... 19.58K
8.67K ............................ 19.53K
6.68K ............................ 19.47K
5.08K ............................ 19.38K
3.79K ............................ 19.28K
2.70K ............................ 19.15K
1.88K ............................ 19.00K
1.26K ............................ 18.78K
0.75K ............................ 18.53K
0.32K ............................ 18.21K
0.00 .............................. 17.78K
0.24K ............................ 17.27K
0.45K ............................ 16.65K
0.61K ............................ 15.84K
0.74K ............................ 14.74K
0.84K ............................ 13.44K
0.92K ............................ 11.85K
0.99K ............................ 9.86K
1.04K ............................ 7.17K
1.08K ............................ 3.88K
1.24K ............................ 0.00

Are my assumptions above correct, does the log version follow the correct curve and is the mono "log" really a linear attenuator?
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Old 10th November 2012, 03:10 AM   #2
ArtG is offline ArtG  United States
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I purchased a Valab stereo 100k item about a year ago. After some work, I'm now quite pleased with it, all things considered.
After I received it, during testing, I found that two of the resistors had their position transposed on one channel, so the curves didn't match exactly. I decided the easiest and most expedient thing to do was to correct the issue myself, by removing and reinstalling these two resistors in the correct position. My problem was that I was unsure which channel had the resistors in the correct order. Numerous attempts to contact the vendor for this information were futile, so I did some math, and a log plot to see if I could determine the correct order, which was difficult since the taper is “their own”, similar to a log taper but with some “twists” that makes it unique. Perhaps that’s the issue you are seeing. If I were you I'd try to contact them.
So I made the revision, installed it, still not being absolutely sure that the curve is exactly as designed, and I’m happy with it. It’s been used nearly every day since, without issues.
I have two criticisms: the curve could be better. A standard log curve would be better, IMHO, and I don’t think much of the idea that no leads are attached, requiring the installer to solder directly on a small tab that mounts an SMD resistor. This wasn’t an issue for me, but it could be for some.
I think it a good value, costing about 1/3 of the Switchcraft 23 position switch alone, and much easier to turn.
BTW, when the vendor replied, (after I posted negative feedback), he did offer to refund my money and send a replacement unit at no cost! I declined and noted that I’d review the item fairly. I’d recommend it, overall.
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Old 10th November 2012, 04:54 AM   #3
cotdt is offline cotdt  United States
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I have a 10k and 50k and they work great. I don't see the point in DACT and Goldpoint, which I've owned, as these work just as well.
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Old 10th November 2012, 12:18 PM   #4
Mihan is offline Mihan  New Zealand
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Thanks for your responses.

I originally bought the stereo attenuator to use in my B1 buffer build but then decided to do what Nelson Pass did in his design and use dual mono's.

The plan was to purchase a mono and use one section of the stereo attenuator for the other channel, thinking that they would be the same design. As Nelson specified linear taper these mono "logs" will probably be OK.

I will now order another mono and hope that it's the same as the one I have!
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Old 23rd July 2014, 10:30 PM   #5
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Ordered a log one, get a unique 464R resistors on it... not a very serious company seems. And yet no answer... Linear... a waste!
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Last edited by Malefoda; 23rd July 2014 at 10:37 PM.
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Old 24th July 2014, 02:17 AM   #6
Mihan is offline Mihan  New Zealand
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Update to my previous posts:

When I finally installed the two mono Valab attenuators they were open circuit and didn't work at all! As it was too late to send them back, I threw them away and installed 25K atttenuators from 8Audio.com. They work well and have a nice smooth operation.

Last edited by Mihan; 24th July 2014 at 02:20 AM.
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