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DACT stepped attenuator vs. Alps Blue Velvet: My observations

post #1 of 24
Thread Starter 
INTRODUCTION
I’ve owned the HeadAmp GS-1 headphone amp with the “standard” Alps Blue Velvet volume control (pot) for well over a year now. I am extremely satisfied with it powering my MS-Pros, as well as my K701s. In fact, I would say that the sound of my system is nearly faultless, to my ears. However, I started reading about and researched stepped attenuators and learned of its sonic benefits over standard volume pots (e.g. greater clarity, less noise, better channel balance). Inevitably, the upgrade bug bit me and I (impulsively) bought another GS-1, this time with the DACT stepped attenuator (http://www.dact.com/html/attenuators.html), which is a $175 option. I would like to share my impressions comparing the Alps volume pot with the DACT stepped attenuator with the GS-1. I used only my MS-Pros for the comparison to make things simpler.

ASSOCIATED EQUIPMENT
Headphones: Alessandro MS-Pro
CD transport: Music Hall CD25.2
D/A converter: Ack! dAck! v2.0
I'm hoping not to get too many of the ubiquitous "you need to upgrade your source" comments.
Cables: Kimber Silver Streak IC; power cords: VH Audio Flavor 1 (transport) and Zu Birth (amp); DiMarzio Big Red extension cord; Ack! Industries The Digital Connect digital cable

Can you guess which amp has which volume control?

METHODOLOGY:
I level matched the volume output of both amps to a fraction of a decibel using a Rat Shack SPL meter. I did my A/B/A comparisons by listening to a portion of a song over and over and over again until my ears got conditioned to the sonics of the recording. I would then rapidly move the interconnects, power cable, and headphone cable to the other amp and listen to the track again and note any differences.

I let the new DACT GS-1 burn-in for around 150 hrs before I did the comparison. Just to cover all posiblities, I swapped the removable amp modules between the Alps and DACT GS-1s and redid the comparison to make sure the differences I heard were not due to differences in burn-in time or some unforeseen design changes in the amp circuitry. It turns out my observations were still the same, confirming the differences that I was hearing were strictly due the different volume controls between the two amps.

IMPRESSIONS:
I never used a stepped attenuator before and did not expect the amount of “play” within each step. I (wrongly) assumed that there were crisp and distinct indentations at each step, so it felt quite sloppy at first but I got used to it. On some occasions, I could not find just the right volume (i.e. it was either a little too low or a little too high), as some people have noted. However, with the low and high gain switch, this becomes less of a problem.

OK, the sonic differences…
The most noticeable difference in the sound between the Alps and DACT is the treble. Using Steve Winwood’s Higher Love as the test track, the Alps is brighter, with more “sizzle.” The DACT is slightly duller. The percussion at the very beginning of the song is more crisp and has more “air” with the Alps. On certain other recordings, the “tape noise” is better heard with the Alps, which can be a good or bad thing depending on how you look at it. I would recommend the Alps pot for darker headphones (e.g. Sennheisers) if you had a choice when ordering a particular amp.

To test vocals, I used the Beatles’ Yesterday. With the Alps, Paul’s voice appears to have slightly more graininess and texture. The DACT seems “cleaner” and smoother. With the DACT, the solo acoustic guitar in the right channel has more decay and you can get a better feel for the body of the guitar than with the Alps.

The bass on the DACT is ever so slightly greater but is noticeably more articulate. My test track for bass articulation is The Police’s Tea in the Sahara. With the DACT, each bass note was easier to distinguish. With the Alps, it was slightly more slurred. With U2’s Bullet the Blue Sky, the kick drum sounds a little tighter with the DACT.

The Alps presents a slightly more forward soundstage compared to the DACT.

CONCLUSIONS

To me, it seems the DACT stepped attenuator is more neutral than the Alps volume pot. “Neutrality” is the word that keeps coming to my mind when listening to the DACT GS-1. I spent some time listening to the Grado HP-1 at a recent meet using my Alps GS-1. Based on memory, the DACT GS-1 makes my MS-Pros sound more like the neutral HP-1 than before. I think the Alps is coloring the sound slightly, which can be a good thing with regards to the treble and midrange...it makes for a livelier sound. The thing that bothers me most about the DACT is the slightly duller treble. This drawback is most noticeable when I use my DACT GS-1 as a preamp for my speaker system. I may have to change to a brighter IC between the GS-1 and speaker amp to compensate.

In the end, I am going to keep the DACT GS-1 and sell the Alps GS-1. I think the DACT’s benefits outweigh the slightly duller treble. However, I think after listening to it more and not doing anymore A/B comparisons, my brain will just adapt to the DACT's sound and everything will be "faultless" again as before.
post #2 of 24
Now you should compare the DACT stepped attenuator, which has many resistors in series, to a ladder type stepped attenuator, which has only two resistors in series.
post #3 of 24
thanks for the comparison, i'm a bit surprized you didnt immediately notice more transparany to the sound with better seperation and depth to the instruments, i never A/B tested between the GS-1 with Alps and DACT, but i had a GS-1 with Alps and upgraded to the GS-X with DACT. there was a fairly significant change in the presentation, its defininately smoother in the treble as you said but there are more tangible and obvious differences in the actual imaging and space. i assumed that these changes came mainly from the stepped attenuator but i guess i overestimated its effect.

i would really like to compare the GS-1 with DACT to the GS-X, that would expalin alot about each Dynalo design.

thansk again for a good review, i didnt read it before but i just saw the link in your for sale thread. so BUMP
post #4 of 24
Thanks for the great review. I am considering upgrading my amp with a DACT after reading your review. (I must resist.. )
post #5 of 24
Fantastic review that answers the question about high end volume pots in a scientific way.

As if we did not have enough variables regarding the quality of parts, now we must be wary of the conterfiet volume pots being used in chinese gear with the alps label.
post #6 of 24
Thank you.. This is what I was looking for..
post #7 of 24
This is a really interesting comparison. Great job! But isn't another benefit of a stepped attenuator more accurate and consistent tracking? With really bad potted attenuators, I can often hear some odd things (channel imbalances and "sound" or a better way to say it is I can hear the pot working) across the spectrum of the volume level, especially at low volumes.

I've never heard the blue velvet control, though. Maybe that pot has solved the issues.
post #8 of 24
the alps blue velvet has poor tracking, and only a quarter of them was able to pass my tracking tests. but alps black beauty is very good. there's very good pots that can match and surpass stepped attenuators. i heard that the penny and giles one is really good.
post #9 of 24
Great post and impressions. Thank you for taking the time and making the effort to do this, kontai.
post #10 of 24
Thread Starter 
Thanks for the feedback guys.

After over 2 months of use, here are my further impressions...

As I stated in another post, the slightly attenuated treble of the DACT is not bothersome to me anymore. Either I got used to it or could be due to further burn-in of the DACT itself or other amp component. I sold the Alps unit a while ago so I can't do any comparisons again.

One thing that bothered me about the Alps was that when the amp got warm (the GS-1 runs pretty hot), the resistance of the knob when turning becomes less "thick" and feels much looser compared to when the amp is cold. It's just a tactile issue, but got on my nerves for some reason. The feel of the DACT is the same hot or cold.

The transition between steps goes from 4db to the finer 2db increment at around the 10 o'clock position in my system. This is a problem with some CDs where I find the ideal volume is in or near this range. One step will be a tad loud, one step will be noticable too quiet. Luckily, the majority of my CDs are mastered at a lower volume where the ideal step is past 10o'clock, where the 2 dB increments are just fine.

Quote:
Originally Posted by cotdt View Post
the alps blue velvet has poor tracking, and only a quarter of them was able to pass my tracking tests.
I remember reading a post by Justin saying he does his own QC on the Alps to weed out the "bad" ones.
post #11 of 24
Quote:
Originally Posted by kontai69 View Post
The transition between steps goes from 4db to the finer 2db increment at around the 10 o'clock position in my system. This is a problem with some CDs where I find the ideal volume is in or near this range. One step will be a tad loud, one step will be noticable too quiet. Luckily, the majority of my CDs are mastered at a lower volume where the ideal step is past 10o'clock, where the 2 dB increments are just fine.
Hi kontai69,

Thanks for the review.

Regarding the volume increments, can I ask - is this with the gain on high or low? And what are your high/low settings at?

I am close to getting one of these....
post #12 of 24
I just received from Justin a GS-1 with stepped attenuator last week. It is replacing a CIA VHP-1/VAC-1 combo. I have Sennheiser HD650 with Equinox cable.
The CIA combo with the HD650 was a good match, fun to listen and very musical. I need to mention I was using an Audience PowerChord PC and a Revelation Audio Labs silver cryo treated umbilical cord between the VHP-1 and the VAC-1.

I didn’t even try to listen to the GS-1 until about 50 hours of burning-in (now it has over 150 hours). I am also using the same Audience PC and I replaced the internal fuse with a silver cryo treated fuse from HiFi-Tuning. Out of the bat I notice a change in the sound compared to the CIA combo but I was notable to pin point what. It just sounds strange to my ears. After some more listening and putting attention to details I realized the presentation of the sound was different to me because there was no noise!!

The background was so black and the separation of the instruments in the soundstage space was more defined. It was clear that the GS-1 is more critical of the recordings and the up-stream components in the system. You are able to hear every little thing in the recording. This can be good but also bad it all depends on your taste and software library.

One thing that was bothering me was that I was need to set the volume control to about 11 o’clock to reach an acceptable volume on my HD650 even with the gain control in High. I am used to it now and is not a problem.

I can summarize the GS-1 with DACT sound in 3 words. Clean, Accurate, Sweet.
post #13 of 24
Thread Starter 
Quote:
Originally Posted by kontai69 View Post

The transition between steps goes from 4db to the finer 2db increment at around the 10 o'clock position in my system. This is a problem with some CDs where I find the ideal volume is in or near this range. One step will be a tad loud, one step will be noticable too quiet. Luckily, the majority of my CDs are mastered at a lower volume where the ideal step is past 10o'clock, where the 2 dB increments are just fine.
Quote:
Originally Posted by mshimao View Post
Hi kontai69,

Thanks for the review.

Regarding the volume increments, can I ask - is this with the gain on high or low? And what are your high/low settings at?

I am close to getting one of these....
Gain is at "LOW" using my MS-Pro. With regards to the issue in my quote above, switching the gain to "HIGH" usually gives you more "choices" in volume levels. In other words, by swiching Low-to-High or High-to-Low O will often times find the right listening volume with any given headphone.
post #14 of 24
Quote:
Originally Posted by kontai69 View Post
Thanks for the feedback guys.

After over 2 months of use, here are my further impressions...

As I stated in another post, the slightly attenuated treble of the DACT is not bothersome to me anymore. Either I got used to it or could be due to further burn-in of the DACT itself or other amp component. I sold the Alps unit a while ago so I can't do any comparisons again.

One thing that bothered me about the Alps was that when the amp got warm (the GS-1 runs pretty hot), the resistance of the knob when turning becomes less "thick" and feels much looser compared to when the amp is cold. It's just a tactile issue, but got on my nerves for some reason. The feel of the DACT is the same hot or cold.

The transition between steps goes from 4db to the finer 2db increment at around the 10 o'clock position in my system. This is a problem with some CDs where I find the ideal volume is in or near this range. One step will be a tad loud, one step will be noticable too quiet. Luckily, the majority of my CDs are mastered at a lower volume where the ideal step is past 10o'clock, where the 2 dB increments are just fine.



I remember reading a post by Justin saying he does his own QC on the Alps to weed out the "bad" ones.
Hi Kontai69

Thank you for responding to my GS-1 thread btw ....

I'm not sure what you mean by the GS-1 runs hot....

I can't say mine even gets warm... sometimes I can just barely feel some warmth on the top of the case after listening to the HD650s or DT880s, hi gain, with the volume around 12, but I don't do that often.

My usual listening level is Hi gain 9 o'clock, internet radio (Radio Flemme, Dinner Jazz Excursion, MediaMerlin and Radio Paradise), and the stock GS-1 Justin sent me last week runs barely 1/2 a click north of dead cold even after being on for quite a while ..

USG
post #15 of 24
Quote:
Originally Posted by kontai69 View Post
As I stated in another post, the slightly attenuated treble of the DACT is not bothersome to me anymore. Either I got used to it or could be due to further burn-in of the DACT itself or other amp component. I sold the Alps unit a while ago so I can't do any comparisons again.
I would suggest the treble isn't attenuated on the DACT, but the treble is increased with the pot. Try comparing against some other amplifiers with equally good repute and I think you'll find it's where it should be.
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