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Jeffrey D. Medwin

Autoformer Volume Control

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Dave Slagle, who runs Intact Audio in NYC, has been designing and offering  Autoformer Volume Controls for over a decade, which many picky folks tend to say, sounds very good.

 

A audio friend I assisted, sent me a pair of one of Dave's ( many different ) module types, and just yesterday, I found a budget enclosure for them ( fifty cents, on sale, reduced from a dollar, at our local Salvation Army Goodwill Store). 

 

I do not like these modules' thin PC board traces, so I augmented the PC board traces, between the two volume selector switches.   Carefully soldered Mil Spec M22759/11 18 AWG to board traces, where I could get to them.  M22759/11 is copper multi-stranded, silver plated, teflon sleeved wire, available surplus-priced at places like Apex Junior.

 

Connecting the boards and RCA jacks, I used the same wire - type, except heavier,  it was 16 AWG.   'Just stripped off all the teflon outer covering,  because this wire, bare,  sounds slightly better.  Used 7 1/16th inch lengths, a 1/8th divisor of Mr. Robert W. Fulton's 1970's  laboratory - ascertained 57 1/8th inch preferred audio wire length.  

 

All these bare non-insulated cables were carefully positioned, so they don't touch each other, and so their tiny fields do not interact, polarity - wise.   Just got it done, today.

 

After XMAS, it gets listened to.

 

I will try this out as an overall System Attenuator, between my Pioneer Elite BDP-09FD blu-ray player, and the new DIY /( 2019 built) KT88 SE DC amp.

 

If it stays permanently in the system, I will cut and glue a piece of nice looking wood into the top-most inset part, and maybe upgrade the RCA jacks.

 

Jeff

 

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Whoa,

Fascinating concept. Those look like quality autoformers. Nice wiring job! I like how you beefed up the traces on the board. I'm gonna have to try that! I must admit I know very little about a passive component of this type, but the autoformer aspect makes sense, I'm gonna have to look into it some. 

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On 12/19/2019 at 4:49 PM, MechEngVic said:

Whoa,

Fascinating concept. Those look like quality autoformers. Nice wiring job! I like how you beefed up the traces on the board. I'm gonna have to try that! I must admit I know very little about a passive component of this type, but the autoformer aspect makes sense, I'm gonna have to look into it some. 

 

 

Dave offers a whole series of Autoformer Volume Controls, both at Line and Speaker level, and he custom winds versions also.  He offers a LOVELY Speaker Autoformer, very compact, housed in nice brass frames and wound on high-quality cores.  Dave's winding design allows us to make speaker level adjustments to our tweeters in 1/2 dB. increments !!  There are three "ranges" of Intact Audio Speaker Level Autoformer Modules listed  : -3 to -12.5 dB , -9 to -18.5 dB, and " Custom Tapers ".   Compare Dave's useful level choices to the Klipsch and Crites' Autoformers, ........with 2 DB increments.  

 

 

                                   804007521_SpeakerAutoformers.thumb.JPG.7a6275c2d4348c552abde9ca663b85b4.JPG

 

Go to his Intact Audio website, and read the literature, and study the FORUM on his magnetic Attenuator products, which are all autoformers.  I recently spent several days, just reading and learning...was fascinating to me.

 

I have no financial affiliation, etc.,  with this company !    Here we are :

 

http://www.intactaudio.com/index.html

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  Good to see these. I am sure they are fine sounding. 
  Do not believe in the standardized wire length thought. I would use shortest possible to minimize wire loop area. Less of an antenna. 
  You being back posting will increase the activity here. 

  

 

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Much easier than taking the back panel off, fiddling around with contortions to get the quick connects to go where the documentation says, and tighten it all down again.  Then, listen and go, ah shucks I liked it the way it was BEFORE!  Nice job.

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On 12/19/2019 at 6:03 PM, babadono said:

Are the wires in the autoformers multiples of 57 1/8"?

 

 

No sir, not at all.  Its fixed, its a given.  We don't have any control over that. 

 

But sir,  that does not preclude one from optimizing, in any and every way possible, the wiring in and out of each and every magnetic component. 

 

I have been doing this routinely, augmenting magnetic's leads, for many years.   I find it is totally audible.  Once heard, experienced directly,  its truly  impossible to go back to conventional build methods.

 

As a good example, recall the 2019 KT88 build I posted here earlier this year??   'Was likely audio's "first-ever" directly coupled KT88 amplifier.

 

It used a single 8 AWG Mil Spec lead out, from the Power Transformer's high voltage winding's center tap, to become the amp's main ground buss.  See :

 

 

       689959192_P1010017Edited4.thumb.jpg.ccf5a8c031e00680e95ea197a197e488.jpg

        

 

 

 

Jeffrey Medwin

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Well,  I telephoned the audiophile, who gave me these Slagle Autoformers, and asked him " what are these RCA jacks you were using, and sent to me, are they anything special " ??

 

He tells me they are the cheapest RCAs he could source, from Radio Shack.  I see where they sell some, four in a package, for $2.99.

 

The $2,000 Passive Control he uses now, ( that " beat out " this Slagle module ), uses Vampire's  best RCAs, and fancy silver internal wiring and $$$$ silver switches.

 

CM2F/CB Vampire RCA jacks, Michael Percy sells for $33.95 a pair....directly gold plated over OFC. I will not ( because I can not ) use such expensive Vampire RCAs on this Autoformer.  However, there are two audio Manufacturers, who speak highly of the Neutrik RCA jacks at only about $2.00 or so, each.  As I recall, they are direct gold over brass.  Information is in the URL that follows.  Model number is NYS367- and its made by REAN, a division of Neutrik AG.     URL  is :                                                                                                 

 

                                                                      http://www.rean-connectors.com/en/products/phono/phono-jacks/nys367

 

 

Having ( in my fully unsubstantiated opinion )  too-thin PC board traces between the two switches on my specific / stock Slagle boards, and the use of these four Radio Shack RCAs,......... there is no telling what the difference in sonics there will be, when this is fully done. The pretty piece of ( walnut, zebra wood, you name it ) that gets put on the 50 cent box's top, is the LAST thing I am concerned with. 

 

This may be a lot of fun. 

 

I DO have another DIY passive Attenuator, built 4-2018 in a "cool looking" 1940s General Radio Decade Resistor Box chassis, with wire wound precision 3 turn pots, a 10K Ladder,  Cardas Polished Silver 19 AWG wire, that I will be able to A-B ................... against this new build. 

 

Interesting.

 

Jeffrey

 

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Please Note, I am NOT yet sure the Phase Inversion switching, shown above will work !!   One certainly CAN use the Grayhill switches to chose between multiple sources. It is a VERY transparent switch, according to two high end Manufacturers that were questioned.

 

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I was unable to find two precision wirewound 10K Pots I wanted to use, both mounted on a common shaft " dual ganged ".    I reverted to using this MXL belt drive, and the larger ( drive ) pulley adjusts the Volume Control knob's sensitivity to turning, which is desirable .  ( Wanted LESS than 3 turns, but certainly more than one turn. ) 

 

I truly enjoyed designing and building this.   Eliminates the Line Stage from my system.  Its the concept :  "less is more."

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Here is a compelling ( to me ) simulation, of an Autoformer and a 10K Pot, at Line level :

 

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Simulation done by Dave Slagle, at the Intact Audio website's Attenuator Forum .

 

Jeff Medwin

 

      

 

 

 

 

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14 minutes ago, Thaddeus Smith said:

The case is the wrong color for audio applications. White is literally the worst color plastic one could select.

HA HA HA !!! That is so funny because everybody knows that you're the smartest guy on this forum and you only use white! You crack me up.

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4 hours ago, MechEngVic said:

everybody knows that you're the smartest guy on this forum

 

I mean, you're not wrong. Thank you for the additional acknowledgment.

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On 12/19/2019 at 6:20 PM, MechEngVic said:

 

 

LOL, finally understood your answer.  It has ODD multiples of Mr. Fulton's 57 1/8th inches, not EVEN multiples !!!   I could not imagine you fibbing !!

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The autoformers that we use come from Universal Transformer. They’re good units. They are bifilar wound and will take quite a bit of power before saturation. The 3636 that Bob sells will do 1dB increments.

 

Slagle’s units are overpriced. I’m also curious how attenuation is achieved without moving the crossover point. 

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I see where Crites' 3636 units are $38.00 each.  That is very reasonable IMHO.  Thanks for pointing it out, and the 1 dB steps.

 

Slagle's units command a higher price, it seems, than those made by Universal Transformer Co..  I wonder why ?? 

 

As to the Intact Audio units being "overpriced", that is a horse of a different color, and is simply your opinion. 

 

I have not have full knowledge - nor have I A-Bed these two different products, so I have NO opinion to express. 

 

Bifilar winding is very nice, but then, so are Intact Audio's partial nickle cores, 1/2 dB increments, and brass frames very nice. 

 

I fully take your word, that Universal Transformer autoformers are "good units". Some may want the best available units, and are willing to pay extra for them.

 

Has anyone besides SET 12, years ago, done A-B comparisons?  His was VS: German Autoformers.  And on what type of audio playback system?? 

 

We should do our testing and determinations on our own, and decide on our own, based only upon what we hear .

 

The photographed Autoformer build was for a LINE attenuation.  I'll compare it to my resistive 10K LINE Attenuators in 2020, to these Autoformers,  and report what I hear.

 

Regards, 

 

Jeff Medwin

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4 hours ago, Deang said:

The autoformers that we use come from Universal Transformer. They’re good units. They are bifilar wound and will take quite a bit of power before saturation. The 3636 that Bob sells will do 1dB increments.

 

Slagle’s units are overpriced. I’m also curious how attenuation is achieved without moving the crossover point. 

 

Not sure I agree about overpriced. Is there anyone else out there offering these variations in autoformer volume controls. He can also custom wind anything you can think of.. Been using his solutions for years as passive preamps and attenuation controls in diy amplifiers. Dave builds incredible gear as well...

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7 minutes ago, seti said:

 

Not sure I agree about overpriced. Is there anyone else out there offering these variations in autoformer volume controls. He can also custom wind anything you can think of.. Been using his solutions for years as passive preamps and attenuation controls in diy amplifiers. Dave builds incredible gear as well...

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So Cool !!

 

Looks like you and I own the same Intact Audio double-switch modules

 

Have you ever A-Bed , say a Crites 3636 VS a Slagle , as, say, a Line Attenuator ?? 

 

Have you ever thought to augment the module's  PC traces, between the two switches ??

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Was talking about in the context of an autotransformer for a loudspeaker (in a filter). 

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35 minutes ago, Deang said:

Was talking about in the context of an autotransformer for a loudspeaker (in a filter). 

 

The Intact Audio Speaker Autoformer modules have a very handy multi-tap-switch to choose taps, and I think it has a provision for a shunt resistor, as part of the network, to address your comments about frequency shifting when applying different taps.  Dave spent considerable time, showing this on his Forum.

 

                                 http://www.intactaudio.com/forum/viewtopic.php?t=944

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