Dave Slagle Monoblock Transformer Volume Control Build

[jdg123]

If I may, I'll jump in with some experience, my POV: I have built 5 preamps and 4 passives, every logical approach, in an effort to discover the best way to get signal to my amp (BOS 45) Dan designed. My DAC (California Audio Labs: Alpha) is set for 2.5V out (by the way, that DAC has a high Z of 2K and the TVC has no issues with it, plus I run dual outputs from the TVC, the second one to drive a sub woofer amp - still no issues!). The BOS 45 has only, maybe, 6dB of gain. The TVC from Slagle wins! Against everything I could throw at it. There was no deliberation at all. More music comes through, more information. It is just an obviously better way to control the strength of the input signal. I need no preamp at all.

I'll let loose one caveat: I tried to get my friend with a monster amp (a vintage Threshold) and the same DAC, to go TVC so we swapped in my TVC for his Conrad Johnson Premier 14. He lost the warmth he had come to love from his CJ and I think too he needed the drive for the Threshold to muscle his 83dB speakers into submission. We did not have the time to use my TVC for volume control ahead of his CJ. I will one day try to get him to run that experiment; he has a low tolerance for fussing with his stereo...all those wires to reconnect...

I too have retained a preamp for my TT. I have subverted that preamp's volume control (turned up/out the resistance volume control and use the TVC for that job). No regrets there at all, in fact a surprising improvement given this Supratek's reputation as a phono preamp! That Slagle TVC just sets a new standard for all volume control. You'll need a system so good that even the best resistive measures used to control volume are that system's choke point but you might just be surprised to find you are in that very position!

Cheers!

 

[rogerfederer]

 

[Joe Roberts]

I must concur with those who are discovering that the Slagleformer is possibly the best volume control. We use a custom silver wire version in TOTL Silbatone gear and we have tried everything, cost no object: several approaches to LDRs, $6k+ retail Silver/Amorphous transformers, etc. Our "bottom of the line" gear uses Tokyo Ko-on stepped attenuators and the improvement in immediacy and vividness with Dave's autoformers is remarkable. As far as I know, this is the end of the line for volume controls.

Where these really shine is as a input control on integrated amps, basically a passive TVC setup moved inside the box.

Disclaimer: Slagle is a friend of mine, but so far I have not received any kickbacks and Silbatone pays full retail for the Slagleformers. I'm just throwing my personal opinion in that if you are thinking about this approach, it is well worth it. Everybody I know who has tried it likes it.

 

[rogerfederer]

this looks like a nice build:
http://img.usaudiomart.com/uploads/...-slagle-autoformer-volume-control-modules.jpg

 

[SET12]

this looks like a nice build:
http://img.usaudiomart.com/uploads/...-slagle-autoformer-volume-control-modules.jpg

I must concur with those who are discovering that the Slagleformer is possibly the best volume control. We use a custom silver wire version in TOTL Silbatone gear and we have tried everything, cost no object: several approaches to LDRs, $6k+ retail Silver/Amorphous transformers, etc. Our "bottom of the line" gear uses Tokyo Ko-on stepped attenuators and the improvement in immediacy and vividness with Dave's autoformers is remarkable. As far as I know, this is the end of the line for volume controls.

Where these really shine is as a input control on integrated amps, basically a passive TVC setup moved inside the box.

Disclaimer: Slagle is a friend of mine, but so far I have not received any kickbacks and Silbatone pays full retail for the Slagleformers. I'm just throwing my personal opinion in that if you are thinking about this approach, it is well worth it. Everybody I know who has tried it likes it.

Joe,

Thanks much, It didn't take much for me to realize how special they were, I can't ever picture myself listening without them. Dave Slagle is Godsend for the DIYer like myself and others.

I especially would like to thank you for the "Sound Practices" issues that you published yrs ago. I was a subscriber to them. I and others learned so much from them. I sure do miss them. I know they are offered on a CD yet. The information in those issues is worth their weight in gold IMO.

So, Thanks Again!

SET12

this looks like a nice build:
http://img.usaudiomart.com/uploads/...-slagle-autoformer-volume-control-modules.jpg

Thanks rogerfederer, yes it does look nice. I would hope the box is anti magnetic. It looks like just the hots are being switched through a very high quality switch. I chose to use a DPDT on-none-on toggle so that I could switch my grounds as well for 2 sources.

I did a little research. And I found that a DPDT (on-on-on) switch can be wired for switching 3 inputs (Just the hot leads not grounds)). The diagram on the right shows the actual paths internally within the switch which enabled me to understand a little easier as to whats going on. As I like to say I learn something everyday!

If one uses a 4PDT on-on-on then one can use a toggle to switch 3 inputs with their grounds as well. I might add Mark Levinson Preamps do this for improved sonics.

SET12

 

[rogerfederer]

set12,

i'm pretty close to taking the plunge on this. appreciate your ideas re the input switch as that is a question mark for me. i can't see the images you posted. can you try again?

i've been messing around with passives for a while and built a Pass B1. this would not be a hard build.

thanks,
doug

 

[Gibsonian]

So total cost of a diy version of the OP's unit would run in the $800 and up range for parts? Do I have this about right?

 

[Joe Roberts]

So, Thanks Again!

Thanks for the affirmation!

Little did I realize at the time that, like Monica Lewinsky, I could live on my past glories decades into the future!

I believe Dave originally came up with the autoformer idea after using variacs for volume controls. Slagle was always an outside the box thinker. I don't think he ever realized there was a box.

 

[HypnoToad]

I am wondering if you could make the tapped transformers yourself, you would just need to work out how many windings and have 15 - 20 taps on the secondary's. A ferrite core could be good? Just a thought it would probably be a big job though.

 

[SET12]

set12,

i'm pretty close to taking the plunge on this. appreciate your ideas re the input switch as that is a question mark for me. i can't see the images you posted. can you try again?

i've been messing around with passives for a while and built a Pass B1. this would not be a hard build.

thanks,
doug

The above probably got lowered in resolution from a previous post that I used elsewhere but its fairly clear on my 23 in. monitor, but anyway here it is again, it looks the same to me, so what I would suggest is saving the photo to your computer and look at enlarged on your monitor. Otherwise let me know and I'll try and dig up the site that I got it from. Of course I take it your clicking on the image to open it up. I hope the above helps.

So total cost of a diy version of the OP's unit would run in the $800 and up range for parts? Do I have this about right?

The basic cost for Dave Slagle's pair of transformers is $350. Stick them in an ABS box a couple of knobs, switch or switches, jacks of your choice and I think it can be done under $400. One guy even put his in a cardboard box not that I agree with what he did but that's what he did.

Thanks for the affirmation!

Little did I realize at the time that, like Monica Lewinsky, I could live on my past glories decades into the future!

I believe Dave originally came up with the autoformer idea after using variacs for volume controls. Slagle was always an outside the box thinker. I don't think he ever realized there was a box.

Yes an outside of the box thinker, I like to tell people that if they want extraordinary sound they must do extraordinary things. The Siren Song Phono by J.C. Morrison that you published was one such project that inspired me to think outside the box. It resulted in an extraordinary phono that to this day that I have never heard exceeded. The phono is retired due to age. But it was a MC with 66db of gain no step up transformers. I was told an all tube MC phono could not be done as it would be too noisy. The one that I built was dead quite, when you look at the size of the supply one would think it would be ugly sounding but that's quite the contrary. It was extremely transparent and very explosive. I learned by accident how to make it transparent but my first goal was to make it explosive. As J.C.M. said, its not easy to design a phono. One of these days I hope I will design another one and maybe it will be even more explosive.
.

I am wondering if you could make the tapped transformers yourself, you would just need to work out how many windings and have 15 - 20 taps on the secondary's. A ferrite core could be good? Just a thought it would probably be a big job though.

You probably could but as you said it could be a real job not to mention the time that could be involved, but me I'm happy to pay the $350 for the years of voicing that Dave Slagle did and he did a very fine job of it too.

 

[rogerfederer]

thanks, set12
i can see them now
something like this? http://www.amazon.com/DiMarzio-3-Position-DPDT-Mini-Switch/dp/B000H1AKJ8

 

[Gibsonian]

The basic cost for Dave Slagle's pair of transformers is $350. Stick them in an ABS box a couple of knobs, switch or switches, jacks of your choice and I think it can be done under $400. One guy even put his in a cardboard box not that I agree with what he did but that's what he did.

Thanks for straightening me out as I thought each transformer/board assy was $350. A project for my future plans.

Maintaining balance between left and right channels is simply turning each of the volume knobs the same number of clicks up or down?

 

[SET12]

thanks, set12
i can see them now
something like this? http://www.amazon.com/DiMarzio-3-Position-DPDT-Mini-Switch/dp/B000H1AKJ8

That will work for 3 hots, all grounds would have to be common. Now if you got a 4 pole 3 position or I think that would be a 4PDT you could switch grounds as well.

One of my line stage preamps would have 50 VAC bleeding flux from its transformer to the chassis. If I reversed the power cord the VAC would "0" measured from the chassis to earth ground on the power receptacle. The whole idea about switching the grounds is to keep current from flowing from one source to another.

I suppose it would be a little tricky wiring it all but I find its worth it. But heck I'd rather see you with a TVC and just switching the hots then no TVC at all.

Hope you get one!

SET12

Thanks for straightening me out as I thought each transformer/board assy was $350. A project for my future plans.

Maintaining balance between left and right channels is simply turning each of the volume knobs the same number of clicks up or down?

Yes you are correct! And you will be surprised at how good the volume tracking is! especially at low levels. My Marantz is not particularly good. I have to use the balance control if I use its volume pot. Most pots are not the best.

 

[rogerfederer]

this one looks nice:
http://www.bestbassgear.com/4pdt-on-on-on-chrome-mini-switch.htm?gclid=CMTWkuKqk8sCFUQkhgod_x8G_Q

 

[SET12]

this one looks nice:
http://www.bestbassgear.com/4pdt-on-on-on-chrome-mini-switch.htm?gclid=CMTWkuKqk8sCFUQkhgod_x8G_Q

Yes, this will work and it looks to be a very high quality switch.

But as I think about it. Just one 4PDT on-on-on will switch 3 hot inputs for a stereo chassis.

It would require two of them (one/channel) if one wanted to switch grounds as well.

Since one has to turn controls for each channel anyway I don't see it as out of place to have two.

Also I have heard of cross-talk between channels when adjacent channel wiring is in close proximity to each other, so I like the idea of channel switching separated.

SET12

 

[rogerfederer]

i talked with a friend who had a slagle/TVC based preamp. he had a problem with his: he couldn't turn the volume all the way down. have any of you had this same problem?

 

[SET12]

i talked with a friend who had a slagle/TVC based preamp. he had a problem with his: he couldn't turn the volume all the way down. have any of you had this same problem?

No, the TVC has a short position of off if you need it.

I wonder how much gain your friends had? which would totally offset the maximum attenuation level no doubt. That first step would be up in volume

On the very first position I can hear the TVC with my Marantz Integrated Amplifier. But its not that loud and its source dependent.

If I want lower than that first step I just back off the Marantz's volume control a little bit. When its this low I'm not listening to anything serious. Its just background stuff

So the lowest it can go would be the first step of the coarse then the minus step of the fine.

Then the next step in levels would be the "0" position of the fine, then the plus of the fine.

Then the next step from above would be the second step up of the coarse of TVC and the fine to the minus step.

So from the site the specs are, 1.25dB steps that give a maximum attenuation of 41.25dB, Its not the range of a pot by any means, but you have the short position.

So there is no way I'm going to give up on this TVC because I might want a particular low volume level. The performance is to great for me.

Now some of the remote TVC models will give as many as 60-1db steps. The model from Bent Audio when it was being sold was $1600. And now I'm seeing people ask more than what they paid for there's when they sell them.

Also building input switching that switches grounds will help eleininate any adjacent input cross talk, Otherwise shutting a source not bing used off does the trick too. That's if its a problem.

This one does only 2db steps with 23 steps of its remote

Looks like $890 ready to use here http://store.diyhifisupply.com/index.php?route=product/product&path=237_228&product_id=1626

But as far as volume adjustment the manual Dave Slagle with 1.25 db steps will be more versatile for actaul volume levels IMO.

SET12

 

[rogerfederer]

OK, thanks
to be more accurate: his problem was he couldn't get the volume low enough for late at night listening (in apt building with neighbors).
i'll ask my friend what amp he was using this with. think it was a pass amp; not sure how powerful.

 

[mkane]

I'm ordering parts

 

[drtool]

Thanks Set 12, this is on my list, just getting into tube rebuilding Eico 20, 22's, in my spare time. Seti I love your box.