[jonno41]

Is there any difference in sound quality between the DACT volume control and the Alps RK27 volume control.I find the steps on the DACT to sometimes be either too loud or not quite loud enough between steps.Looking at maybe changing my DACT to Alps.
Any information or advice appreciated.Thanks

 

[tomb]

The DACT will probably sound a little bit better, but it depends on the rest of the equipment in your audio string as to whether you'll hear that difference. There's also a bit of "Wow" factor with a stepped attenuator that may or may not translate into an actual sound quality difference.

The downside, as you've found out, if the gain range is not optimum - you'll probably find spots in volume level that you can't adjust to your liking, due to the fact that the steps are individual, non-adjustable, discrete resistor circuits.

The Alps RK27 is probably the best all-around stereo volume pot in existence. You'll find it in use on amplifiers that sell up to $5K or more, with no complaints. Be careful where you buy one, though. There are a lot of fakes out there and they are very, very difficult to spot. One tell-tale that's fairly easy is that the shaft on the genuine has no extras, save for a small slot on the end. If you see an "Alps RK27" with a knurled shaft or a flat for the volume knob, it's a fake.

Also, there's a catch with the Alps RK27: the optimum one for headphone amplifier use is 50K. Unfortunately, those are not a standard manufacture by Alps in Japan. You have to purchase a volume mfg order of a few hundred (Ask me how I know!). AMB labs still sells them at 50K and surprise(!) they're also available at Parts Express:
https://www.parts-express.com/ALPS-...KwnhlbU3lgAfyShi-3GF_iAF2K1YAKscaAiipEALw_wcB

Final caveat: Looks like the DACT is PC-pin based, but there's little chance the pins will line up with the Alps. You'll have to air-wire the Alps, which is not the most fun thing to do, since it uses PCB pins (6 of them). AMB sells a little breakout PCB, which might makes things easier: https://www.amb.org/shop/showpic.cgi?f=pics/a_xe27pcb.jpg&t=AMB+audio+shop&r=close&d=<a href="/audio/epsilon27/" target="_blank">&epsilon;27</a> volume pot mounting board for Alps RK27 stereo potentiometer
There may be other little breakout PCB boards available for the Alps, if you do some searching.

 

[jonno41]

Thanks very much for your very useful and concise explanation of the difference between the Alps and the DACT volume controls.I can live with the DACT and as I don`t have the skills to change the unit myself I think I will stick with the DACT.I can live with it.

 

[jonno41]

The DACT will probably sound a little bit better, but it depends on the rest of the equipment in your audio string as to whether you'll hear that difference. There's also a bit of "Wow" factor with a stepped attenuator that may or may not translate into an actual sound quality difference.

The downside, as you've found out, if the gain range is not optimum - you'll probably find spots in volume level that you can't adjust to your liking, due to the fact that the steps are individual, non-adjustable, discrete resistor circuits.

The Alps RK27 is probably the best all-around stereo volume pot in existence. You'll find it in use on amplifiers that sell up to $5K or more, with no complaints. Be careful where you buy one, though. There are a lot of fakes out there and they are very, very difficult to spot. One tell-tale that's fairly easy is that the shaft on the genuine has no extras, save for a small slot on the end. If you see an "Alps RK27" with a knurled shaft or a flat for the volume knob, it's a fake.

Also, there's a catch with the Alps RK27: the optimum one for headphone amplifier use is 50K. Unfortunately, those are not a standard manufacture by Alps in Japan. You have to purchase a volume mfg order of a few hundred (Ask me how I know!). AMB labs still sells them at 50K and surprise(!) they're also available at Parts Express:
https://www.parts-express.com/ALPS-...KwnhlbU3lgAfyShi-3GF_iAF2K1YAKscaAiipEALw_wcB

Final caveat: Looks like the DACT is PC-pin based, but there's little chance the pins will line up with the Alps. You'll have to air-wire the Alps, which is not the most fun thing to do, since it uses PCB pins (6 of them). AMB sells a little breakout PCB, which might makes things easier: https://www.amb.org/shop/showpic.cgi?f=pics/a_xe27pcb.jpg&t=AMB+audio+shop&r=close&d=<a href="/audio/epsilon27/" target="_blank">&epsilon;27</a> volume pot mounting board for Alps RK27 stereo potentiometer
There may be other little breakout PCB boards available for the Alps, if you do some searching.

I have found an Alps 50k available here in NZ on our local auction site.Attached a couple of pics of it.Does it look like the correct one and genuine.Thanks

 

[tomb]

I have found an Alps 50k available here in NZ on our local auction site.Attached a couple of pics of it.Does it look like the correct one and genuine.Thanks

EDIT: Warning - I checked the GSX-Mini and it is a balanced amp with a four-gang volume control, with choice for 4-gang Alps RK27 or 4-gang DACT stepped attenuator. None of this conversation (or what I typed below) is valid, except for some of the parts' number explanations and the discussion on impedance. You need to look for a four-gang RK27, which are quite expensive and somewhat rare. I actually suggest that you contact Headamp and see if you can send the amp to them to replace the volume control, especially since they originally sell the GSX-mini with the choice of volume control anyway.


Looks good to me and a bonus is that it appears to come with a break-out PCB! That should make the air-wiring much easier. Does it have the correct resistance curve?

The number is key. What you want is RK27112A-S25-C0-A503, although some of those numbers can vary, depending on what you want:
RK27 112A S25 C0 A 503

"RK27" is the Alps series, wit "27" the square width of the pot.
"112A" means single shaft, dual unit (stereo, two gangs)
"S25" means slotted shaft (S), 25mm long (they're easy to cut with a Dremel cutoff or even hacksaw).
"C0" means without detent.
"A" means logarithmic resistance taper (necessary for proper volume use).
"503" means 50K.

As for impedance differences, 10K is often used in portables (Alps RK097 is a favorite) and is quietest with best gain using low impedance, high efficiency phones. Depending on the configuration of the source, however, it can have bass response issues. 100K is noisier, but is often used in tube amplifiers because the noise of the tube(s) means the pot noise is insignificant anyway. Thus, the 50K was long ago chosen as the optimum for headphone use (even with tube amps).

 

[jonno41]

I am very grateful for all your help and advice and I will stick with the DACT control as there is no guarantee that I will get the correct Alps unit.Too expensive to send back to Headamp as they want $200 to replace the unit plus shipping both ways from New Zealand.Thanks

 

[tomb]

I am very grateful for all your help and advice and I will stick with the DACT control as there is no guarantee that I will get the correct Alps unit.Too expensive to send back to Headamp as they want $200 to replace the unit plus shipping both ways from New Zealand.Thanks

Actually, knowing what's involved and the cost of that amplifier, that's a reasonable price. I'd charge about the same. If you think that's too much, it's an indication that it's a mod not to be taken lightly. Depending on the amplifier design, you can burn a labor hour or two simply from disassembly and re-assembly. Then you have to count that the labor in removing the existing DACT attenuator is at least 3 times - perhaps 4 times - the amount of time it took to install it. You have to balance removing pins and solder from 12 PCB pads, while trying to pry the pins out. Then you have to clean up all the pads in preparation for soldering in the Alps. This is assuming that you weren't unlucky enough to destroy some of the PCB traces connecting to the pads, which frequently happens. All the while, you have the "risk" of working on a $2,000 amplifier and the responsibility of not tearing up.

Believe me, I've worked on many amplifiers that cost that much. Knowing you could potentially destroy a $2,000 amplifier if your repair/mod/upgrade goes sideways increases the stress level of the work exponentially. That increases labor costs alone.

Actually, if they stock both amplifiers, it might be simpler for them to simply replace your amp for one with the Alps already installed. Or, swap out the PCB - that would remove any issues with selling "new" if your casework has some "use" on it. That's probably the choice they will make, but it still involves a lot of labor outside of the production "line."

I just checked pot/attenuator prices and this should make you feel a bit better, despite your problems with obtaining the optimum volume level:
An Alps 4-channel RK27 runs about $25-$30. The DACT 4-channel attenuator is well over $300! The value/re-sell is much higher with your amplifier in the configuration that you now have it.

Finally, you could try to whip up some simple in-line resistor adapters for your headphones. That might help you reach an optimum volume level for a lot less work and risk. Use a jack and plug combination with resistors in line with the solder connections. If this is 4-pin XLR, there's plenty of room to work in those things and despite having to solder 4 resistors, it would still be easier/less risky/not value damaging compared to changing out the attenuator in the amp. Perhaps start with resistor values in the 10-20% range of the headphone's impedance, such as 3-5 ohms for a 32 ohm headphone or 30-50 ohms for a 300 ohm headphone. Just a suggestion ...

 

[jonno41]

Actually, knowing what's involved and the cost of that amplifier, that's a reasonable price. I'd charge about the same. If you think that's too much, it's an indication that it's a mod not to be taken lightly. Depending on the amplifier design, you can burn a labor hour or two simply from disassembly and re-assembly. Then you have to count that the labor in removing the existing DACT attenuator is at least 3 times - perhaps 4 times - the amount of time it took to install it. You have to balance removing pins and solder from 12 PCB pads, while trying to pry the pins out. Then you have to clean up all the pads in preparation for soldering in the Alps. This is assuming that you weren't unlucky enough to destroy some of the PCB traces connecting to the pads, which frequently happens. All the while, you have the "risk" of working on a $2,000 amplifier and the responsibility of not tearing up.

Believe me, I've worked on many amplifiers that cost that much. Knowing you could potentially destroy a $2,000 amplifier if your repair/mod/upgrade goes sideways increases the stress level of the work exponentially. That increases labor costs alone.

Actually, if they stock both amplifiers, it might be simpler for them to simply replace your amp for one with the Alps already installed. Or, swap out the PCB - that would remove any issues with selling "new" if your casework has some "use" on it. That's probably the choice they will make, but it still involves a lot of labor outside of the production "line."

I just checked pot/attenuator prices and this should make you feel a bit better, despite your problems with obtaining the optimum volume level:
An Alps 4-channel RK27 runs about $25-$30. The DACT 4-channel attenuator is well over $300! The value/re-sell is much higher with your amplifier in the configuration that you now have it.

Finally, you could try to whip up some simple in-line resistor adapters for your headphones. That might help you reach an optimum volume level for a lot less work and risk. Use a jack and plug combination with resistors in line with the solder connections. If this is 4-pin XLR, there's plenty of room to work in those things and despite having to solder 4 resistors, it would still be easier/less risky/not value damaging compared to changing out the attenuator in the amp. Perhaps start with resistor values in the 10-20% range of the headphone's impedance, such as 3-5 ohms for a 32 ohm headphone or 30-50 ohms for a 300 ohm headphone. Just a suggestion ...

The $200 asking price from Headamp is more than reasonable.I have no problem with that.It is the cost of shipping from here in NZ and back again.I didn`t realise just how complicated the job would be.I can live with the DACT and after taking in all your advice I will stick with the DACT unit.Thanks.