Passive Volume Control

Active volume control/pre-amp offers more features/convenience but my focus here is sound quality only. Can passive volume control be used in higher-end setup without compromising overall sound quality? I'm talking about setups like Denafrips Terminator/Holo Audio May DAC + Benchmark AHB2. How do good PVC compare to active pre-amps like Benchmark LA4?

In Stereophile's review of Holo Audio May, Parasound Halo JC 1+ was used with an NHT PVC, a $160 unit released in 2007. I suppose the NHT PVC was able to keep up without bottlenecking the system. But it's discontinued - what are some othe good PVC? Goldpoint from what I read is pretty good, but they're fairly expensive.

I'm tempted by some Denafrips/Holo Audio DACs but they dont have volume control, and I haven't budged a good pre-amp. So I wonder if DAC + PVC + amp is a viable option before a good pre-amp is in place.

 

I use a Tortuga Audio passive and it has a nice remote and is very open and clean sounding.

 

I had a Luminous Audio Technology Axiom passive attenuator and it worked great when my system was comprised of a CD player + Axiom + Martin Logan Purity self powered hybrid electrostatics. Simple. No remote volume control.

 

I have a NVA passive.
It's excellent
I also built a passive using Tocos 20k
Audio taper pots.
I use 2 as I love dual mono.
Perfect balance.
This passive is as good as It gets.
I added an attenuator circuit courtesy
Of Goldpoint.
Cheap enough to try out for yourself.
You may not need to attenuate.
My poweramp only needs 125mv
For full power.

 

You need to try it in your own equipment and see, these units are not all the same, initially I thought it was a good thing but I discovered it made the sound dull. I might reuse it just for the computer but not serious listening. I suppose that if you don't have a volume control in your amp you will never be able to make comparisons with and without

 

It depends on the output impedance of the DAC and input impedance of the amp. The rule of thumb is that you want an output impedance that is about 1/10th of the input impedance. Since the passive attenuator is "passive", it's output impedance is going to be determined from a combination of it's passive elements in series/parallel with the output impedance of the DAC, but will ultimately always be higher than the DACs output impedance. The specific formula will depend on the type of passive attenuator.

If the amps input impedance is at least 20x or so times the output impedance of the DAC, you should be able to find a passive attenuator that will work ok. The input impedance of the AHB2 is spec'ed at 50K ohms, so a DAC with an output impedance lower than 2.5K ohms should work ok with the right attenuator.

The Holo May DAC has a balanced output impedance of 27;.5 ohms (and 13.7 ohm in single ended mode), so this would provide plenty of flexibility in choosing a passive attenuator that would work. The Denafrips Terminator output impedance is quite a bit higher at 1250 ohms, so this makes choosing a passive attenuator more challenging. It should be possible to make this work, but you'll need to be more careful choosing the right attenuator.

I have tried passive attenuators a couple of times in the past (most recently in my current system), and compared them against a good preamp and found I preferred the sound of an active preamp. In my current system, I am using a Denafrips Terminator Plus to drive a Khozmo attenuator followed by an active buffer stage to feed my amps. I built the preamp myself so was able to try using the attenuator by itself, and I preferred the sound with the buffer stage - it seemed to have more energy (dynamics) and was a bit more open sounding. I should note though, that I am using 25ft cables to the monoblock amps, so it's possible that shorter cables would be less of an issue.

 

Tortuga reviews...
6moons audio reviews: Tortuga Audio LDR6
Tortuga LDR3.V2 Passive Preamplifier - The Absolute Sound

 

In some ways it could be better, if you have enough output to drive the Benchmark AHB2 (I think the unbalanced input sensitivity is 2V so should be OK with a modern CD player or DAC, maybe not if you're adding a phono stage to the signal chain), and if the amp input impedance is high enough -- at 50K ohm unbalanced, maybe a little lower than ideal for a passive, depending on the maximum output impedance of the particular passive you're using. And if you use short enough low capacitance cabling from the passive to the amp. And depending on the maximum and minimum impedance input and output impedance of the particular passive. Then, maybe it'll be lower noise, lower distortion and less compromised.

 

I recently purchased a line selector from eBay seller EricYam, and am very impressed at it’s transparency. He also makes units with passive volume attenuators for $129, and a deluxe 33 step unit with separate left and right volume control and balance for $650.

I have a tube phonostage and tube CD player, so it was very important that the line selector not hurt the tube sound. I had been using a Niles unit, and that did the job, unlike a Schiit Sys, where The tube sound was lost. However, once I put the Eric Yam unit in place I was startled by how much more dynamic the sound was. The Niles was damping down the tonal range, the Eric Yam let it come through.

 

Some cheaper but very effective solutions discussed there: A little passive preamp help: Schiit vs Khozmo

 

Eric Yam - passive volume attenuators That is what I use too. The simple single ended only

 

I used the Schiit Freya+ in passive mode with my AHB2. It was good. My transformer-coupled Allnic 1500 is a wholly better pairing, especially regarding dynamics.

 

In my system the Khozmo has been the most transparent of the passives and other preamps I've tried. My Coda amp has a 50kohm input.

 

Yes. Best I've ever used. Now I'm choosing passive for my permanent setup. No more preamps.

 

The rest of the system needs to be a good match for a passive preamp. You need a good higher output source(since there is no other gain provided), plenty of juice from your power amp/speaker combo and short run low capacitance cables. If all is set up well, a passive preamp will be totally transparent for sure.

 

My Khozmo preamp is extremely transparent, I couldn’t see myself going back to an active gain line stage. My MC 60s have an extremely high input impedance but my Parasound amps have an input of only 33k.

 

Smart icOn4 AVC (autoformer) passive preamp with remote

 

Those are very nice with the Dave Slagle autoformers and remote microprocessor control, albeit a bit pricey. If a volume control is all you need, can't do too much better, I'm sure it would make most potentiometer passives sound broken, and probably competes with the only the best switched resistor passives, like high quality relay switches in a ladder configuration, with Vishay resistors or better. After all, it is really just a copper path.

Of course, can do it far cheaper without the remote, especially if you can DIY, transformers are available from Intact. I've been toying with the idea of building one using the Silk transformers from SAC Thailand, but too many projects in front of it right now. My CJ preamp uses relay-switched Vishay resistors followed by a monolithic triode and Teflon capacitor, so doesn't give up too much to a nice passive.

 

Thanks for the input guys. So passive volume control might be a viable option. Per this reviewer, the goldpoint sounds very clean.

 

LDR attenuators can sound very nice.
Better than most of the actives that I have used.
Stereo Coffee is a low volume locally made unit with exceptional audio qualities

 

Some of the very best pre-amps made are passive. If you can put up without the features, they are well worth considering. If one comes up at a good price I will probably bite.

 

Matching is key, as mentioned, but in the right chain they can sound stunning.

IME (had a Khozmo for a while) for better or worse it felt like more of the original recording coming through.

 

Just note that there are a few ways to implement a volume control, and some of the suggestions above use transformers or autoformers, which is quite different from the method used in the Goldpoint. It uses a string of 23 or 47 surface mount resistors in series to ground, and the switch selects which junction is used for the level of attenuation desired, but all those resistors are in the signal path. Still, often sounds much better than the standard carbon slurry on plastic potentiomer used in most preamps.

There are other types called ladder attenuators that are more costly to implement, but each attenuation setting only uses two resistors in the signal path, just a simple voltage divider. The latter method is what my Conrad Johnson preamp uses, though it uses relays to select the Vishay resistor values, and has a gain section following the attenuator so isn't a passive preamp.

I'm not saying which method is best, someone else above just mentioned the photoresistor method, which is another, but that's one thing that you should decide up front. With a resistor attenuator, you need to make sure the capacitance on your amp input is low and the cables are also low capacitance or it will roll off the high frequencies since it forms a low pass filter. And as others have already mentioned, you need to be careful with the source output impedance as well, since the passive preamp load will be in parallel with the amp input load and will lower the impedance the source "sees", which can be a problem if the source is AC coupled with a capacitor on the output, like most tube gear, you may rolloff the low frequencies.

There are a lot of tradeoffs involved, but if you can make them and stay in the "good zone" for a passive preamp, it can be very good sounding compared to most active preamps.