Passive Volume Control for DACs/Sources

From an era where the semiconductor industry was fun.

The Signetics Write-Only Memory is of the same spirit: http://repeater-builder.com/molotora/gontor/25120-bw.pdf

Tom

 

I died xD

 

After listening to a Schiit Sys, Saga, Tisbury Audio Mini passive preamplifier, The Truth active preamplifier and the Tortuga LDR3.V25 passive preamplifier I really recommend you first try a Schiit Saga (or Freya if you run balanced) if you need a preamplifier since they have the 15 day trial. Really, don't even bother with a Sys if you have a very resolving system (sorry Jason and Mike.) The Sys is a very good value at $49; the Tisbury has more features at $150 but in my system to my ears neither is as transparent as the Saga.

You will have to replace the stock tubes supplied with the Saga or Freya. No way around that. The tubes Schiit supplies are just OK but in the case of my Saga really held back the Saga in ability to resolve detail and give best imaging and natural timbre to instruments and vocals. There was a midrange warmth or bloom to vocals in active mode that was fixed by using a better NOS tube.

You can't fault Schiit for this: they are selling at a price point where they could not possibly justify using an $80 NOS tube nor probably even source enough old Sylvanias given their sales volume. For $349 you even get a (plastic) remote control. Just get the stock Russian 6NS8 tube and spend $18 extra for the nice metal remote that comes standard with the Freya rather than $25 extra for the Tung Sol 6SN7GTB. You are going to be buying a better tube anyway unless you just run Saga in passive mode.

Using the stock tube my Saga sounded best in passive mode. And it sounded way better than you would expect for a $349 preamp. Swapping in a 1951 NOS Sylvania 6SN7GT made active mode sound better in my system. And the Saga keeps scaling up with more expensive NOS tubes: I have tried the 5692 and settled on a 1940's vintage Tung Sol 6SN7GT (roundplates and blackglass.)

The Tortuga has reported high THD and IMD that should not exist in a preamp selling for $1195 which may have caused or contributed to the coloration I heard. The Tortuga had what I call an exciting, Technicolor sound that emerged from an inky black background which impressed at first but became fatiguing on extended listening.

The Truth preamp is not passive. It is a unity gain active buffered, photocell controlled volume control that looks like a science project but has gotten some rave reviews. In my system I did not care for it. The high end was rolled off and it lacked bass extension and definition. The active buffers should have eliminated any interaction between my DAC and amp but either the unit I received was faulty, did not match well in my system, or just plain did not sound good on its own merits so I returned it.

To their credit Tisbury, Tortuga Audio and Ed Schilling took back the preamps and promptly issued refunds to PayPal. I only lost some shipping charges and had the chance to compare a good handful of preamps last month which once again verified that Schiit is selling some very good gear at low prices. I hope my little experiment can save someone else the time and money. Hey, I had some fun though and my system is now sounding better than ever

 

You've mentioned the Mackie passive a couple times now... is this the Big Knob 2x2? I've only heard the active versions which were not so great, though in general I like Mackie's dedicated mixers (though for their usage I like them for their durability; PA work is not really somewhere you chase utmost sound quality from esoteric electronica).

 

Interesting on the Truth experience. I got mine used but Ed somehow caught wind and emailed me repeatedly wanting to make sure it was working OK. I don't know if it's common to have problems or not. But sonically it was fine, just that the drift issue isn't what he claims. Sound-wise, I don't have a bass extension issue with mine (nor treble). I had it around during a particular OTL phono demo as that unit was particularly wimpy even driving the light load of my TVC/amp. The Truth brought the bass out in that case, where an active preamp actually was needed and my TVC wasn't cutting it. Elsewhere, the Truth had equally deep and articulate bass vs the passive TVC that has bested many expensive preamps particularly in the articulation department. Just high overall clarity. I don't know enough about Saga in passive mode, e.g. what impedance it provides to the source, if it's constant, its output impedance, etc. I do know that I liked the Truth enough to breadboard a few different unity buffer arrangements similar to how the Truth is doing it, while replacing the stupid optocoupler with a shunt resistor attenuator. Jury is still out there...

 

Modern Chinese made Mackie sucks. Warning: Avoid all modern Mackie products. The old stuff from the 90s is often still a good deal if it works and is cheap.

Passive Big Knob has channel imbalance issues.
Active Big Knob has major noise issues.

I don’t know of a good, dirt cheap balanced pre. The JBL M-Patch2 has phase issues or something that distort stage across volume and broke quickly on me. Mackie sucks. Good opportunity for someone like @schiit to beat JBL here with a balanced version of sys.

The best solution is to just use a DAC or interface with volume control. If otherwise, go diy but really If you can afford a dac or interface that costs over a thousand dollars, you shouldn’t be scrounging for couch change for a pre.

I like the Drawmer stuff for cheap as it’s sturdy and the pot feels nice. Drawmer CMC2 is 300 bucks and uses NE5532. Yeah it is a tiny bit warming (it’s made in the UK so what do you expect but not full British sound) but it won’t kill treble like passive pot/resistor ladder pres or add transformer. The knob feels dope, features are adequate, and it’s what the Big Knob crap is trying to clone. The more expensive Drawmers keep the same sound just add more features.

 

Behringer made their name just ripping off other designs. Even though the quality of their stuff improved after they switched factories, I just can't support a company like that.

Mackie gear when it was made in Italy is highly sought after (though of age now where you probably want to recap). Their SRM line of powered monitors was their bread and butter. When Mackie moved their production to China, their quality (particularly the SRM v2's) tanked so badly it nearly killed the company. Coincidentally, the factory they moved into was Behringer's original one. Once they fixed things back up, it took their mixer linup to eventually bring the company back. They've since sorta redeemed themselves with the SRM v3's, but no one trusts the SRMs anymore.

Anyhow, I wound up on this tangent because I've heard good things about the SPL 2Control as a balanced active pre, but as all SPL offerings go, it ain't cheap. Of course, there's a Behringer knockoff in the Monitor2USB.

 

@Psalmanazar thanks for your thoughts. I wound up needing a preamp because my previous DAC actually did have a volume control but when I upgraded to Yggdrasil I lost the volume control and the 2V output of the Yggdrasil is too hot for my Kenzie amp, which does have a volume control I found I could no longer turn up past 8 AM. Hence the search for a preamp that worked well with both the Yggdrasil and Kenzie. I can appreciate why Schitt does not have volume controls on their DACs but if they did have that feature it could have saved me a lot of time and trouble. Schiit does make fine preamps for those who run into the same problem I did.

 

I had Big Knob passive with some channel imbalance. I was using it to switch between TV and cheap Roon endpoint going to LSR305. It was not an issue because when I turned the volume down on the monitors and cranked up the Big Knob pot , it was OK. But I exchanged it anyway, and the new one does sound like if it hasa channel imbalance.
Not when I am listening and I tried it on main setup. It does not change the stereo image, listening to various frequencies from left and right sounds the same, and I measured it from the listening position it was like 1dB difference. More sensitive ears may be offended but not mine.
Then I tried Palmer Monicon for $99, Made in Germany to control the volume of dual mono Nuforce HA200. I read a complain about channel imbalance on this one, and I repeated the whole procedure as above. It sounds OK it is a bit more transparent than Big Knob. But at least both are quiet, unlike a Nobsound that I tried before which was noisy like hell.
With those products the channel imbalance may be more the issue of QC than with the design or parts. For a cheap one I would try this one first. But any of them should be used with the pot at least on 12 rather than 9 or 10.

 

Let alone recording off of FM.

 

Also, we all knew how to program our VCRs.

 

Or plugging their radio alarm into the amp.

And yes, I did. TV too. Don't look for the soundstage: of course it was mono. Great hifi? Maybe not, but several million times better than not doing. Ahh... those were the days when the BBC did a whole series of Young Musician of the Year, not just the final and/or highlights.

Which reminds me, not that it is on topic, but: the year I was confident in my choice of winner, until this youngster started to play and I found myself on... the... edge... of... my... seat. Still brings a tear to my eye.

What's on topic is that that's the power of music. Big knob, small knob, whatever.

 

CanJam 2021:

 

I suppose in the grand scheme of things, the premade Khozmo stepped preamp isn't bad for the price:
https://khozmo.com/balanced_stereo.html

 

knobs big or small... but I confess to preferring a smooth knob.

And am I being audiophoolish to worry about wanting a setting between steps? I suffered this with electronic stepped controls, but I've never tried the physical resistor kind.

Anyway, my McCormack TLC1 is getting a bit of a makeover, even though I don't currently need a pre-amp right now.

 

I have a 47-step goldpoint and it seems like enough. Certainly the 64 steps on the saga are.

 

Hattor Audio in Poland makes some interesting remote controlled single ended and balanced passive preamps with your choice of resistors in the stereo attenuator, with the option of adding an active opamp buffer. Cost for basic passive with Vishay resistors runs from $660 for single ended to $810 for balanced. Thanks to @lcmusiclover for the tip, sold through Mockingbird Distribution in the US.



Hattors have two sets of outputs which many may need. The lower priced Goldpoints only show one set of outputs but by reconfiguring internal jumpers one set of inputs can be converted to a second main or tape output.

No remote control is available for the Goldpoint passives. If you don't need a remote you can save about $200 buying a Goldpoint rather than a Hattor but you do only have 47 steps on the attenuator compared to 64 (1 dB/step) for the Hattor. If I was aware of the Hattor when I was looking for a passive preamp I would have enjoyed comparing it to the Saga.