Passive Volume Control for DACs/Sources

I was preferring passive mostly, until I recently obtained a Sylvania VT-231, which I'm quite enjoying now. It's the first tube I've heard that doesn't actually add any negatives to the sound (as far as what I prefer)- just slightly more openness, soundstage expansion, layering, and a bit more sparkle on the top end, not to mention what seems like a slight amount of more tightness in the bass and more present vocals. All "colorations" I guess, but positive ones for me, and in the right dosage - like 5-10%.

I've read (dangerous I know) that AVCs and TVCs are more "dynamic" (less inhibited?) than traditional attenuators, so was just curious to hear one. However at the prices a commercial preamp based on those are going for (especially remote controlled ones), I'll likely stick to Saga for now, and maybe watch for a decent deal on the used market, so i can flip if I dont prefer it. I've also got Freya and comparing that as well, but with the VT-231 in Saga now, I think Freya may be beaten, we'll see. The only thing I lose is balanced inputs from Gungnir Multibit, but I'm not really sure I'm losing much there as far as what I'm hearing right now. Still more listening to do.

 

Not any longer my setup has changed, cable run is now reduced to 3 m (under ten ft) with capacitance at 42 pF/m, my observations above relate to the new setup

 

Classy as f**k, dude! Very nicely executed - Mr Mayer himself would approve! A fun looking project, too. And you now have a line stage that bests $20k jewelry-fi pieces without breaking a sweat.

 

Since I upgraded to a Yggdrasil A2 I found myself in serious need of a passive preamp before my Kenzie amp. I could only turn the volume control on the Kenzie up to about 8 AM before sound became too loud so I needed more range. I first tried a Sys which did sound OK but bought a Tisbury to try as they do have the 15 day trial. Well, the Tisbury is definitely a step up from the Sys. It is more transparent, images better and presents a less congested, clearer high end.

I became interested in passive preamps like the Lightspeed, Java and Tortuga which use resistive optocouplers. Not wanting to order the Lightspeed from Australia I have a Tortuga LDR3.V25 passive preamp coming in next week. Shipping is quick since they are also in Florida. As they offer a free trial period if the SQ is not a significant improvement over the Tisbury I can just return it.

 

Glad to hear you're liking the Tisbury. It's quite the bargain imho. I'll be interested to hear how much better (surely) a Tortuga is in comparison, and in what way. Please let us know!

 

You bet. The Tisbury is definitely a bargain at just under $200. At 6X the price the Tortuga needs to present a serious step up in SQ or it is going back. Should be able to comment late next week.

 

Attentuation between DAC and headphone amp is something that still keeps me busy. Most sources are way to hot for my taste. I've been using a Sys for a long time but find it colors the treble too much (seems to be the pot), it's also slightly soft but has a nicely holographic stage. I think it's fine until you get into top end territory. I've also tried the Rothwell Attentuators and they are soft (especially bass) and veiled on my system and collapse the soundstage.
I'm getting some Goldenjacks attentuators soon and just bought a Tisbury and hope these don't let me down. ;-)
The SPL Volume 2 seems to be interesting though it's active. SPL know analog audio very well though.

 

I've been real happy with the Saga, I don't like the way tube buffer sounds with NOS tube when I listen to speakers with vidar. Been contemplating trying a different tube or 2 but haven't because most of my listening has been headphones. Tube buffer is kind of useless with headphones for me, I just put the LSST in and forget it. As a passive pre amp though I cannot tell a difference at all with it in the loop with either of my headphone amps.

 

Both the Rothwell and Harrison in-line attenuators SQ is inferior to the Schiit Sys so don't even bother. If your budget is $200 suggest just try the Tisbury. You can send it back if it doesn't work for you in your system. As a Schiit fan I was going to buy a Saga but decided what the hell take one for the team and try out the Tortuga first

 

I picked up a used "The Truth" on the cheap just to compare to my copper Slagle AVC. This is a photo cell design, similar in concept to optocoupler based designs. It's pretty quriky. (1) the balance control is off center when channel balance is achieved within a measured +/- 0.01V, and apparently this is normal. (2) You're supposed to keep it powered up all the time, and there is no on/off switch. Fine. But when you do power off, balance will drift slightly at the next power on. (3) 3/4 of the attenuator range does nothing, then volume rises quickly within the last 1/4 of the range. (4) You can't power it up (are advised not to) without an input connected and selected. I did. I don't know why it would, but perhaps this caused the power on drift. (5) wide open, it has lower than unity gain.

Soundwise, I think it's slightly better than the copper Slagle. I think there's a touch less veil. But then again neither devices are veiled, both being highly transparent. I could live with either one, but slightly prefer The Truth. Due to it's lack of quirks, though, I'll continue to use the AVC.

 

What improvement does the optocoupler based devices offer that would offset the added odd order distortion?

 

I don’t know any objective reason but I think guys who believe different materials used in resistors affect sound say cadmium sounds very nice.

 

Amir loves the Neurochrome HP-1 and dismisses the Tortuga reason enough for me to try it out in my system.

 

Pretty sure that Amir also loves breathing air. Nelson Pass has also shown the high distortion of optocoupler attenuators, have you chosen what to like that he hates or vice versa?

 

Sorry if my tongue in cheek remark offended you. I don't much care for Amir or his forum. After forty years of critical listening my hearing is still just fine and I trust my own ears. I will try the Tortuga out and post my impressions. If I have any problem with the sound quality you will hear about it in this thread and I will send it back for a refund. Fair enough?

 

You're really asking about the Tortuaga design itself, which I've not heard. And I can't say how it compares sonically to the "Truth" design. Since you seem interested in the Tortuaga, maybe you'd like to read more about it. If you do, you'll find that it uses a software-driven closed loop measurement and auto-compensation circuit. This active circuit has to attach to the signal path, which then sort of negates the "passiveness" of the device. On the other hand, the Truth does not have any active compensation circuitry as this is performed manually with a "balance" control which is further claimed to not be in the signal path. Either way, it is a passive device. Some will prefer the convenience of auto calibration. I wanted to compare two passive devices, and had no interest in the Tortuaga for this listening experiment. I guess the Truth designer says he uses photo cells as opposed to optocouplers, also.... I'll amend my original post.

 

The output impedance also varies a lot if I'm not mistaken - they assure it doesn't make a difference in the 'real world' but it seems rather high.

Yup, rising to about 5kOhm at step 61 of 70 (0 = mute): https://www.tortugaaudio.com/documents/attenuation-and-impedance/

 

Coincidentally, this is also the peak output impedance [of the SYS]