Budget passive preamp with stepped attenuator?

[solderdude]

What is this actually, an Alps RK27 Potentiometer or a Stepped Ladder-Type Attenuator?

RK27 is a potmeter. Also known as 'blue velvet' or more accurately RK271 series.
They exist in mutiple tapers (semi-log, semi-antilog, balance and linear), resistances (5k to 250k), can have multiple 'gangs' (1 for mono, 2 for stereo or 4 for balanced for instance) and exist in various shafts (to accomodate for various push-on knobs) and can even be motorized (for remote control) Also there are ones with 21, 31 or 41 'indents' or one in the center (gives a feel of steps) if needed.
These are affordable and good quality. The older ones appear to be of higher quality than the current ones.

stepped = basically a bunch of resistors similar to the track of a potmeter where a switch contact connects with only one joining of resistors. So basically a stepped potmeter where the 'taper' is determined by the used resistors and the number of steps determines the attenuation per step.

Then there is the relay attenuator that looks more like the output of an R2R DAC. With just a few relays (similar to bits) you can have more and smaller steps and switch instantly to a desired attenuation. Easy to remote control but requires power and you can hear relays 'click' when adjusting the volume.

 

[solderdude]

It would have channel imbalance at low volume levels, would it not?

Hardly, the tracks are large in size and of equal length and diameter.
With cheap potmeters the tracks may not be of equal length/diameter.
That said, there will always be some variances between L and R tracks, certainly fully CCW, and in that aspect stepped or ladder are 'better' in that aspect.
IME there is no practical imbalance issues with any of the RK27 pots I have/use.

 

[Deleted member 58865]

Hardly, the tracks are large in size and of equal length and diameter.
With cheap potmeters the tracks may not be of equal length/diameter.

But, any potentiometer would degrade over years, would it not?

 

[solderdude]

All mechancal contacts do, so do relay contacts and the contacts of stepped ladders.
I have a few RK27 pots in use for over 30 years and still feel mechanically as good as new, do not 'scratch' nor show imbalance.
The Ayima will not last as long nor won't the SMPS.

 

[Deleted member 58865]

You say RK27 and RK271 interchangeably. Which attenuator products do you recommend specifically for my use case?

 

[solderdude]

RK27 is an abbreviation of the RK271 series and refers to the 27mm width of the enclosure.

 

[Deleted member 58865]

Unless there is any recommended 10K-ohm RK271 passive volume control product, I'm going to buy a passive stepped attenuator.

 

[sonder]

• 10K Jenson https://www.ebay.com/itm/273591977617
• 50K ALPS 09 4 channel https://www.ebay.com/itm/253646372699
• 50K ALPS 27 https://www.ebay.com/itm/253818627052

from a day or so ago.. in that time I've had both the ALPS 09 delivered and the ALPS 27, the 27 will fit your needs just fine here.

also worth noting that the ALPS 27 is now 20k rather than 50k if you get a new one, they swapped the pot in it, confirmed via support yesterday.

so to be specific, the HIFI version of https://www.ebay.com/itm/253818627052 is a 20K ALPS 271, with good connectors, good build quality, and will out last your amp. I've opened it up, very happy with build quality, and confirmed correct pot.

 

[Deleted member 58865]

from a day or so ago.. in that time I've had both the ALPS 09 delivered and the ALPS 27, the 27 will fit your needs just fine here.

also worth noting that the ALPS 27 is now 20k rather than 50k if you get a new one, they swapped the pot in it, confirmed via support yesterday.

https://www.ebay.com/itm/273591977617 is too ugly.
https://www.ebay.com/itm/253818627052 is a 50k-ohm volume control.

Which impedance for RK271 do you recommend? I read 10K is ideal for most amps.

 

[sonder]

https://www.ebay.com/itm/253818627052 is a 50k-ohm volume control.

Which impedance for RK271 do you recommend? I read 10K is ideal for most amps.

also worth noting that the ALPS 27 is now 20k rather than 50k if you get a new one, they swapped the pot in it, confirmed via support yesterday.

so to be specific, the HIFI version of https://www.ebay.com/itm/253818627052 is a 20K ALPS 271, with good connectors, good build quality, and will out last your amp. I've opened it up, very happy with build quality, and confirmed correct pot.

 

[Deleted member 58865]

https://www.ebay.com/itm/253818627052 doesn't mention 20k. It only mentions 50k. If they don't bother to mention 20k, I don't want to buy from them.

I don't want to spend money and wait for a week or two to find out that it's actually 50k. If they don't mention 20k, they can pull the rug on me and send me 50k any time.

And, is 20k good for most amps?

 

[sonder]

Budget passive preamp with stepped attenuator?

The main thing I wondered is the step size. 256 .5 db steps is 128 db which is more than enough. Even .25 db steps for 64 db would work for almost anyone's system. I have made my own in several configurations. 1 db steps are as good as a continuous control. So smaller steps are only...

www.audiosciencereview.com

 

[Deleted member 58865]

I am not seeing a good 10K-ohm RK27 passive volume control, so I think I will buy a good 10K-ohm passive stepped attenuator.

While it's good to have finer control, 3dB steps aren't bad. I can use DAC volume for fine 1dB control.

If the input impedance is high, the output impedance is going to be high. If the output impedance is too high for the amp, low audio frequencies will be reduced.

 

[sonder]

Cheap amps will have cheap potmeters because... well... they are manufactured with cheap components.
The Ayima is a very cheap so that explains some of the things you ran into (leakage, enclosure connected to audio ground). You get what you paid for in essence. You can't sit front row for cheap in the world of electronics when it concerns quality. You can when it comes to more than decent technical performance but not for longevity and build quality. Something has got to give.

A solution could be to use an external volume control.
I think, when exploring this option, the best method is to go for 10k RK27 attenuator. It will outlive the Ayima and prevents possible costly errors that could occur when using a DAC and digital volume control.

Neither is 'better' but the external volume control is safer, has a better 'feel' when adjusting the volume and good adjustment range.

RK27 would be preferred over stepped as a volume control. Stepped would be preferred if you want to use the volume control on the Ayima.

RK27 is a potmeter. Also known as 'blue velvet' or more accurately RK271 series.
They exist in mutiple tapers (semi-log, semi-antilog, balance and linear), resistances (5k to 250k), can have multiple 'gangs' (1 for mono, 2 for stereo or 4 for balanced for instance) and exist in various shafts (to accomodate for various push-on knobs) and can even be motorized (for remote control) Also there are ones with 21, 31 or 41 'indents' or one in the center (gives a feel of steps) if needed.
These are affordable and good quality. The older ones appear to be of higher quality than the current ones.

stepped = basically a bunch of resistors similar to the track of a potmeter where a switch contact connects with only one joining of resistors. So basically a stepped potmeter where the 'taper' is determined by the used resistors and the number of steps determines the attenuation per step.

Then there is the relay attenuator that looks more like the output of an R2R DAC. With just a few relays (similar to bits) you can have more and smaller steps and switch instantly to a desired attenuation. Easy to remote control but requires power and you can hear relays 'click' when adjusting the volume.

For your budget, as solderdude has explained throughout, an RK27 would be preferred over a stepped here, unless you are using relay attenuator, but they are significantly more expensive.

again: Stepped would be preferred if you want to use the volume control on the Ayima. - which is the very thing you are trying not to do here.

not ayima volume = not stepped.

 

[Deleted member 58865]

For your budget, as solderdude has explained throughout, an RK27 would be preferred over a stepped here, unless you are using relay attenuator, but they are significantly more expensive.

again: Stepped would be preferred if you want to use the volume control on the Ayima. - which is the very thing you are trying not to do here.

If there is a good 10K-ohm passive RK27 attenuator, then I may consider it. I haven't found one, yet. So far, I found an ugly 10K-ohm attenuator which is not necessarily RK27.

I'm okay with using a stepped attenuator and then adjusting DAC volume. Most of the time, I will fiddle with application volume.

Set the maximum volume on the amp. Reduce the volume further on the attenuator. Adjust the volume further on DAC. Adjust application volume most of the time.

Most of the time, I won't touch the stepped attenuator or the DAC volume unless I need to massage the gain structure. If I need to massage the gain structure a little bit, I may adjust DAC volume. If I need to massage it a lot, I may fiddle with the stepped attenuator. I won't touch the amp volume pot.

The stepped attenuator just allows me to avoid sacrificing audio bit-depth by reducing DAC volume too much. Much of the massaging on gain structure will happen in DAC volume.

 

[sonder]

Most of the time, I won't touch the stepped attenuator or the DAC volume unless I need to massage the gain structure.

If you didn't have to massage it, line level attenuator pads as mentioned somewhere in these threads may be optimal, as an alternative.

Which country are you in for deliveries, I'll have a look too.

 

[Deleted member 58865]

If you didn't have to massage it, line level attenuator pads as mentioned somewhere in these threads may be optimal, as an alternative.

I don't know how much attenuation I want or need. Thus, I can benefit from a stepped attenuator which allows me to experiment with various gain levels.

But, my DAC volume is currently set to -20dB with the amp volume knob at 9'o clock. I will have to experiment with amp volume pot and DAC volume a lot to find the right attenuation level for in-line attenuators. Or, I can just buy a stepped attenuator.

 

[sonder]

I don't know how much attenuation I want or need. Thus, I can benefit from a stepped attenuator which allows me to experiment with various gain levels.

But, my DAC volume is currently set to -20dB. So, I think -16dB or -20dB attenuation is a good target as long as the input impedance is 10k.

It'll be max 10k as explained by others in the threads, often much lower which is better.

I've been involved in these threads as I wanted to achieve the same thing, firewall off a new hypex nc252mp (being built), to replace a topping pa3s I currently own, handling the same issues as you (assuring max vrms in is limited, safety, audio grounding, tactile experience etc etc) before later replacing my dac with a fully balanced one, I've ordered several devices, but the main one I'll likely keep is this https://www.ebay.com/itm/255455371503 - more details are available here and here and feedback from owners here.

For me, it's worth the additional cost as it'll work whilst I'm RCA, and when I move to fully balanced XLR, and at each stage in between, and likely work out cheaper than several different iterations of devices (though not for me, as I've bought all different kinds to test anyway!).

 

[Deleted member 58865]

Look, when I have more money and time, I will buy a new XLR audio stack and sell my current RCA audio stack or give it to someone for free.

Right now, I would be satisfied with a stepped attenuator. 3dB steps are fine enough for DAC to take over afterwards.

 

[sonder]

Right now, I would be satisfied with a stepped attenuator. 3dB steps are fine enough for DAC to take over afterwards.

One thing is for sure, you're making a very very informed decision, and every aspect has been covered thoroughly.

However, I can't help but notice that after more than 10 full pages of discussion and thorough coverage of every single aspect multiple times, from rather amazing forum members sharing over and above, you've just went to the option you found yourself on ebay 8 minutes after posting about 3 days ago.

For me at least, the threads have been invaluable, and I thank everybody involved.