[Dracule1]

Hi John,

I'm intererested in going the TVC route for my line stage.  But I'm a little confused on all the transformer types used in this application.  I'm leaning toward your TVC as it as many features not found on other TVCs.  Anycase, could you explain the differences in these types of transformers?  You used to use the S&B, but I know hear you are using an autoformer in your new TVC.  Was the S&B a C-core? 

Thanks for unconfusing me.

[John Chapman]

Hello!

I don't know that 'unconfusing' is my specialty! I'll do my best.

There are two things you are mentioning - the type of windings used and the core type (material and design).

The two basic types of 'magnetic' volume control options are transformers and autoformers. Both can work well sonically and each has it's strengths and weaknesses. Here are a few notes on each:

Transformers:

cons:
- bit less 'direct' signal path than autoformers.
- bandwidth not as wide as autoformers (but still high enough if designed well).
- XLR mode not a true 3 wire ballanced connection - floating ballanced. Works well in practice though if designed for that.

Pros
- Can be used to break the input ground to output ground connection to break ground loops. Not often used but can be handy.
- Some (but not all or even most designs) can be used to mix RCA and XLR connections.

Autoformers:
Cons:
- Can't be used to break ground loops.
- Tricky to mix RCA and XLR signals (at least tricky to do it right).

Pros:
- More 'direct' signal path
- Wider Bandwidth
- XLR mode is a true 3 wire connection - but it takes essentially 2 autoformers per side to do it......

There will be more pop up I am sure but those are some basic functional differences. It is impossible to talk about sonics since other factors (winding geometries, core materials, etc) would tend to dominate sonic results.

If you need a certain 'function' that one or the other offers then that is the one for you.

Now for the core materials and types:

There are many different core types and geometries. I am not a specialist so here I am passing on what I have heard from various transformer designers.

There is no 'BEST' core material or core type. If there was the others would simply fall away and not be used.........

Basic core material found include Nickel, Steel (m4, M6, etc), and Amorphous types (using various base materials). In the testing I have done I keep comming back to the Nickel cores - the 80% Nickel version of that core material. It has a directness and clarity I miss when it is not there. It is the most expensive material appart from the exotics like cobalt. This has particularly been the case this past few years - just look up a chart for the nickel price!


The two common core type I have seen autoformers and TVC's made with are E-I type and C-core. When I started my new TVC search I did a lot of reading up and was thinking the C-cores would be the way to go. The winders I talked to all were for various reasons fans of the E-I over the C-core. Stacking possiblities and the fact the small residual gap being a bit more tolerant of small dc offsets from sources were reasons mentioned.

As I get time (not likely really......) I'd be happy to play with other material and core types but for now the two units I have played with most (S&B and Dave Slagles Autoformers) both had E-I lams and both used Nickel core material and both do nice things sonically.

I think it would be a BIG mistake to try and search the web to compile a list of the best features and combine them into the dream TVC. The devices are really the sum of the parts and need to be looked at as a working unit designed to give a certain result.

Good question - thanks for that!

Hope that helps a bit.....

Thanks!

John

[Dracule1]

Thanks!  Very helpful.  I guess the question is how does your new autoformer TVC compare with your old S&B TVC sonically.  Will you make a truly balanced version of your new autoformer TVC?

[John Chapman]

Hello!

In many ways I think how it compares to the S&B is of only academic interest - since the S&B is no longer readily availiable - or at least for most folks the price makes it not an option. I hear they have a new pre-amp with a motorized switch but I gather it is rather expensive - $16K someone said........ I no longer have any S&B TX102 based units here to compare with. I like it that way. 

I have a rule not to comment on how my stuff sounds compared to other gear - since I could be biased I suppose. I guess I can not escape at least a bit of a comment in this case though. I find the Slagleformer based units to have a bit more clarity and extension. In a system that is on the edge of biting your head off this would not be a good thing. The S&B is more forgiving in some ways so would likely suit an aggressive system better. I am absolutely sure that there would be some systems that would be a bit happier with one or the other but that in most systems either would do a fine job as a pre-amp.

I won't be elaborating any more on the comparision. I hope the new unit will be taken for what it is - good value for a decent pre-amp with lots of nice features! 

As to the balanced question - It is actually very easy to build a ballanced version. All that needs to be done is to double up on the modules and you have a truely ballanced attenuator c/w a center tap on both the input and output side.  The trick is when you go to mix RCA and XLR signals on both the input and the output. I want to take a bit of time to work out the very best way to handle every combination.  If anyone needs a unit with XLR in and XLR out only that can be made quite easily as soon as the RCA version ships.

The design is really done now - the first 2 'production beta' units are shipping tomorrow. I will need a bit more time to get inventory of module boards and a few other things before shipping more and I will be waiting until I have stock of all parts here before posting info on the web page. I want to be able to ship product as soon as it is all released.

Thanskj!

John

[ludimagis]

Hey John,
Do you have an idea of what the pricing will be for a 2 or 3 input (rca) Slagleformer based unit?
Thanks

[John Chapman]

Hello!

The new pre-amp will be built as a single input unit or a 6 input full featured unit - just like the TAP was. With the older pre-amps I made (based on kits I sold mostly) I used to config custom - after all basically I was just building the kit for the customer. The cost once you go to multiple inputs to just fully config the unit with 6 inputs is not all that much. Over the years I have had quite a few customers want to add one more input and the cost to do it (almost all shipping charges...) gets so high it is frustrating. What would have cost only a small amount if we'd done it up front would end up costing many many times more after the fact.

I am determined to keep the 6 input rca version at around the $2K price point.  This will include 6 inputs, a buffered and separately level controlled  sub output (to keep it entirely out of the passive signal path) and also a buffered tape output. 1db step size from -51dB to +7dB. Full remote control of all functions including volume, mute, source select, right/left balance, buffer on/off, and display on/off.  Two of these units now with customers and both are smiling!

I will work out pricing for the single input version but likely it'll be around $1500 or so. Using this version right now in my system.

The modules will be for sale to diy builders and OEM's as well. The Slagleformer module turned out really nice - super clean signal path in a neat little package.

All this new stuff (and a few more things too) will be at the VSAC show this May. I will have my web page fully updated before the show and will have all products in stock by then too.

Thanks!

John

[Joel D.]

Hello all,
I thought I'd chime in because I'm one of the two lucky owners of the "production beta" unit based on the autoformers that John mentioned above, which I received last week. It's really very very good (no, John isn't paying me to say that!); it works perfectly in my system. I suppose on of the main reasons to buy a passive in the first place is transparency, and I have to say that this new unit is as transparent as a direct connection--I've tried both. There are also a few additional clever ideas that make it very flexible to use; one I particularly like is the "level memory" control (I don't know if that has an official name) which allows one to store in memory a set volume level associated with a specific input.

To answer one of the above questions about how this new unit compares with the older one, I had the opportunity yesterday to compare it with an older Bent passive, the Flex unit (based on the Stevens & Billington TVC); a friend of mine brought it over and we tried both with a variety of music and both analog and digital sources. In all cases, the new model sounded more transparent and better tonally. In comparison, the Flex seemed a bit veiled and darker, with a little more emphasis on the lower part of the register. It was quite audible.
I hope that helps.
Cheers,
Joel

[Sonny]

Hello all,
I thought I'd chime in because I'm one of the two lucky owners of the "production beta" unit based on the autoformers that John mentioned above, which I received last week. It's really very very good (no, John isn't paying me to say that!); it works perfectly in my system. I suppose on of the main reasons to buy a passive in the first place is transparency, and I have to say that this new unit is as transparent as a direct connection--I've tried both. There are also a few additional clever ideas that make it very flexible to use; one I particularly like is the "level memory" control (I don't know if that has an official name) which allows one to store in memory a set volume level associated with a specific input.

To answer one of the above questions about how this new unit compares with the older one, I had the opportunity yesterday to compare it with an older Bent passive, the Flex unit (based on the Stevens & Billington TVC); a friend of mine brought it over and we tried both with a variety of music and both analog and digital sources. In all cases, the new model sounded more transparent and better tonally. In comparison, the Flex seemed a bit veiled and darker, with a little more emphasis on the lower part of the register. It was quite audible.
I hope that helps.
Cheers,
Joel

Joel, thanks for the comments on the new pre...
I am in line as well, hopefully John can get one out to me by the end of the month...we'll see.

Could you please let us know the associated equipment?  That will help...
Also, could you post some pictures? both front and back?
Thanks
Tuan

[Joel D.]

Tuan,
Sure; associated equipment:
Spectral D-3000 Reference CD transport
Audio Note 3.1x balanced DAC
Acoustic Solid Classic Wood tt with Acoustic Solid WBT211 arm and Zyx R1000 Airy 3 cart
Zyx CPP-1 headamp
Hagerman Trumpet phono stage
Bent Audio TAP-X preamp
Channel Islands Audio D-200 monoblocks
Quad 989s, with Velodyne DD-12 subwoofer and Tonian TL-R1 super-tweeters
ICs: from AN DAC to Bent preamp: Audio Note Sogon
      from Bent to CIAudio amps:  Coincident Speaker Technology CST-IC
Equi=Tech 1R Son of Q Jr balanced power conditioner


You can see a photo of the TAP-X on the Bent Audio website; it's pretty much the same box as the old TAP-X, front and back (I don't know if the RCAs in the back are Vampire or WBTs; John can tell that better than I); the insides of the beast are different from the old one because of the 2 autoformers. (I can post a photo of the inside if John is ok with that; John?)

Cheers,
Joel

[Sonny]

Thanks Joel...
I too have digital amps (switching amps) from EVS...I have the EVS 100 for the m/t and the EVS 500 for the bass...  I am currently using a tube preamp, but for the convenience, I wanted a passive to be in the loop so I can leave my equipment on all the time without violating the "Green" effect too much...

So, how's the midrange with the Channel amps?  I sometimes am a little hesitate to go Digital and passive...afraid of the brightness/harshness, but Ric's EVS amps are nothing like that...

So, it's good to hear that you find the Autotransformer pre to work with the channel island...
Ok, I can't wait for mine...

Tuan

btw, where are you located?  I am in SF bay area.

[Joel D.]

Tuan,
The CIAudio amps are quite good in the midrange; no harshness at all. These are very smooth amps.
However, I'm looking forward to receiving my new Altec/Tutay 1570Bs in the next few weeks (?); Tom is currently building them. I'll  be leaving the digital world for tubes, if all goes well.
I'm just up the coast from you, in Seattle.
Cheers,
Joel

[Sonny]

Ah...Seattle..."where I tell people I'm from" hometown...though I am really from Tacoma, via Hong Kong / Vietnam.

Well, I had all tubes not too long and miss them, but I just couldnot afford the power I needed to drive my speakers...I had the Cyber 800 monoblocks and love them, but at 78wpc, they can't compare to what I have now on the speakers, that' over 1100 wpc!!!

Hm...I am glad you like the new pre...So, you have enough gain than, as it appears to drive your amps?

T

[Joel D.]

No, no problem with gain, I'm not even close to unity (54) with any of my sources; the one with the least level is the SACD output of my Denon/ModWright-modified DVD 2900, but even there I don't need to go higher than 47. With the DAC, it's low 40s and with the phono stage, low to mid-30s.
The volume control is really nice, 1dB increments, very smooth.
But I don't want to make you more impatient than you must be already....
Joel

[Sonny]

No, no problem with gain, I'm not even close to unity (54) with any of my sources; the one with the least level is the SACD output of my Denon/ModWright-modified DVD 2900, but even there I don't need to go higher than 47. With the DAC, it's low 40s and with the phono stage, low to mid-30s.
The volume control is really nice, 1dB increments, very smooth.
But I don't want to make you more impatient than you must be already....
Joel

Thanks good to hear Joel...
I am patiently awaiting mine as you, Lucky guy, got one of the first two...
I will be driving it with the following:

VPI Scout with Shelter 501 mkii
Diva Audio Virtuoso phono (12ax7) with step up
Marantz SA11S2 digital source
EVS 100 (tweet/mids)
EVS 500 (Bass)
All cables are DIY by me...

Tuan