2. amps-preamps
  3. 158111-3787

A world class volume control for pennies on the dollar

In my role as a reviewer I have had five different DACs in-house for the auditioning process in the last six months. Two of them have analog volume controls ( Bricasti Design M3 / Rockna Wavelight) that negate the need for a preamplifier because their performance using their internal volume devices is excellent. However, the other DACs have no internal volume control and have to be used with some type of preamplifier. In what I refer to as my big system, my go to preamplifier is the terrific Coda Technologies 07x. In my smaller system I had sold off the line-stage I used to a friend who really wanted it for his system. So, the search was on for a high quality truly balanced preamplifier for a very reasonable amount of money.

In my search I came across a rave review on Six Moons from 2010 about the SPL (Sound Performance Lab) Volume 2 active totally balanced in/out XLR based volume control from Germany. SPL mainly designs and builds very high quality devices for the professional recording industry. The only piece aimed at the audiophile market is the Volume 2. This is a "hair shirt" design, one XLR input-one XLR output, no remote volume control, a mute button, large volume knob, and a on/off switch on the back (recommended that you leave it on for ever). It either comes in sliver or black, and retails for $450.

The DAC that was going into this system, the Mhdt Balanced Pagoda, really only shines if it is driven balanced and uses its XLR analog outputs into a balanced preamplifier. In the past I have had some of the finest transformer and resistor based passives, two different Shitt Audio preamps, LED based buffered designs and excellent tube based line-stages. Well, I saw that on US Audio Market, someone was selling a pristine condition SPL Volume 2 for $200. Hell, when I used to go out for dinner to a new joint, before the damn virus, I would often spend about that amount on dinner/drinks. Often, the food was not that good, but you don’t know unless you try. I could afford the loss, if the Volume 2 turned out to be a bust or just OK.

The SPL Volume 2 turned out to be a "killer" linestage/volume control. It adds "nothing" to the signal that’s feed to it. It is a pure conduit at passing on the upstream gear’s tonality/colors, dynamics, and spatial qualities. It has a vanishing noise floor, that allows micro-details to pop out to be easily heard. The volume control is not stepped, so you can easily deal-in the "sweet" spot for each musical selection. I got all this for $200 bucks! With the beautiful, musical Mhdt Balanced Pagoda into the Volume 2 controlling the dB levels, the system had the timbres/tonality of the NOS Western Electric 396 tubes and an over all liquidity/ease that this DAC produces was passed on intact by the SPL piece.

The SPL Volume 2 is my new "reference" for someone looking for a truly balanced design for less then a thousand dollars. So, if you run a balanced DAC without an internal volume control, want to spend a very small amount of money, $450, and not be bothered about not having a remote volume control, this well designed, German built piece might be a wonderful addition to your system.


teajay
mitch2
3,972 posts
 
@dgarretson That is sort of like my Metrum Adagio where the pot controls the reference voltage.
@teajay I did go to the site and must have missed the 6moons review but I see it now.  They always have the best pictures.  I really like how they will not review something unless they can post pictures from under the hood.  I will have to take the time to read the review - I didn't realize this has been out there for 10 years!  Seems like maybe a good alternative to basic resistor volume controls like the Goldpoint and Endler attenuators I own.  I wonder if there are better op amps that could be used now.
kr4's avatar
kr4
3,680 posts
 
The SPL Volume2 (and Volume8) have balanced in/outs.  However, the input buffer converts to single-ended, the potentiometer is a single line per channel and the output buffer creates a balanced output.
https://www.audiosciencereview.com/forum/index.php?attachments/_32a6963_1004-jpg.38139/http:// 

dgarretson
2,598 posts
 
@Kr4 Not a bad idea, as achieving good CMRR would be difficult with a balanced pot due to variations in tracking across four sections.
Assuming that the buffers are well executed, I would swap out the ALPs pot for a Goldpoint stepped attenuator or DIY Lightspeed LDR.
auxinput
2,920 posts
 
yes, like kr4 said, this SPL Volume 2 is basically a preamp with only a single input/output. There are two monolothic op amps internally with a smallish normal linear power supply. Nothing special here in my opinion. It's likely good for the money. If you want a low cost active XLR preamp, it's probably a good deal. I'm not sure how you can do even a balanced preamp with only two op amps and a single-ended ALPS potentiometer. It's probably using one op amp as input buffer to convert to single ended, then routing through ALPS pot, then using the second opamp to just create an inverted signal from the potentiometer. I suppose it works, but you really want two opamps on the output for stereo balanced signals.

It's more expensive, but the Wyred 4 Sound STP-SE is supposed to be a passive/active design. It's supposed to work as a passive circuit until the signal needs active gain (i.e. depending on signal level and input impedance of the amp its driving).

A cheap solution would be to look for a used Rane MLM82a stereo line mixer. These are fully balance inputs, fully balanced outputs, and use a single-ended internal volume control. They are cheap at under $100 typically and still use a linear power supply. You'll need to get an XLR-to-TRS cable for the inputs, but it's cheap. Not sure how this compares to SPL Volume 2.

atmasphere's avatar
atmasphere
11,800 posts
 
Not a bad idea, as achieving good CMRR would be difficult with a balanced pot due to variations in tracking across four sections.
@dgarretson  Actually if you have a balanced control, even if it does not track perfectly, its a lot better than applying a single-ended signal if the input is balanced differential (as is the case with most opamps). It would have to be well off before you would notice the gain difference.


The reason the Volume2 does the conversion to single-ended is based entirely on price point.
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