My new passive preamp: S&B TX-102 transformer volume control

I admire this apparatus, and certainly the quality of workmanship. But I seriously question the nomenclature.

Could it perhaps be called a volume control?

Passive Preamplifier seems a trifle oxymoronic....dontcha think....? :scratch2:

Maby they should now be called a Prefier. Probably a good idea for me with DIY, it exists before the fire....(Caused by my tom foolery)
Anyways, I think this may be an excellent thing for me to try. I have a Receiver and an intergrated AMP both with completely stuffed Preamps. Extreme simplicity that you can build without fully understanding what you are doing, that sounds like my style.:D
 
nice!

Nice work redboy! Yesterday i've received a pair of S&B tx-102 used trasformers and i'll have to do a TVC pre too so i need ideas:
a) what system have you used to fix the metal rings on the underside of the chassis?
b) have you used a special quality switch for the inputs ? I need only a pair of inputs for now

thanks, Roberto
 
Really never got the passive pre-amp thing, as it's really nothing more than an attenuator box that places larger impeadance load's on the power amp input section. Inserting extra isolation transformer based pot's in the low level stream, certainly can't be helping thing's. Curious how you're handling the TT's 5 mv output and RIAA equalization, with what's basically a passive switch box. Think I'll stick with my Adcom 565.
 
Very Nice Nate!! Love that Seiden switch and I too am a Big fan of TVC`s. :D
I think simple is great. I Love the clean and clear sound they give (but maybe thats just me)! :yes:
 
Nice work redboy! Yesterday i've received a pair of S&B tx-102 used trasformers and i'll have to do a TVC pre too so i need ideas:
a) what system have you used to fix the metal rings on the underside of the chassis?
b) have you used a special quality switch for the inputs ? I need only a pair of inputs for now

thanks, Roberto
Thanks for resurrecting this thread, Roberto. I didn't build this one. It was custom built by Kevin Carter at K&K Audio, and I purchased it secondhand from the original owner.

The metal rings appear to be basic pipe clamps, bolted to the bottom of the box. Not elegant, but effective. If I were to build around these transformers, I would be tempted to cut large holes in a block of nice hardwood to sink the cans into. I might even consider using ebony or myrtlewood or one of those woods purported to have magical sonic benefits, just for the heck of it. :)

The switch is of the highest quality, but I can't identify it. I have tried to find another like it, without success. I've considered calling Kevin about it, and still might someday.

Really never got the passive pre-amp thing, as it's really nothing more than an attenuator box that places larger impeadance load's on the power amp input section. Inserting extra isolation transformer based pot's in the low level stream, certainly can't be helping thing's. Curious how you're handling the TT's 5 mv output and RIAA equalization, with what's basically a passive switch box. Think I'll stick with my Adcom 565.
Turntable duty is handled by a separate phono stage that feeds into the passive. Hey, I'm glad you like your Adcom. I like my passive. I hope that you'd listen to my setup and judge for yourself, given the opportunity. What looks good on paper isn't always the final answer. In the end, you've got to trust your ears and go with what you like.
Very Nice Nate!! Love that Seiden switch and I too am a Big fan of TVC`s. :D
I think simple is great. I Love the clean and clear sound they give (but maybe thats just me)! :yes:
Hey DR, thanks. I'm with you on the sound - I like it enough that I'm intent on trying all different flavors until I settle on my favorite. I've got a couple other TVC and AVC boxes lined up to try. One involves some tedious soldering and I haven't gotten up the will to tackle it yet...
 
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Certainly not trying to upset anyone here, but just pointing out the obvious. There's really not such thing as a passive pre-amp, just an attenuator box placing more of a impeadance load than need be on the power amp's input section. Having to use an external phono section, seem's to throw out the purist intention a bit. Already know what better than a passive attenuator box sound's like, as I've experimented connecting 500mv equipment directly to power amp input's. Sound's just fine, but little flexibilty. If you're running a power amp with level control's, then best to skip the extra box all together.
 
My apologies for the digression Nate, but I wanted to comment a little bit on the following:

Really never got the passive pre-amp thing, as it's really nothing more than an attenuator box that places larger impeadance load's on the power amp input section. Inserting extra isolation transformer based pot's in the low level stream, certainly can't be helping thing's.

There's really not such thing as a passive pre-amp, just an attenuator box placing more of a impeadance load than need be on the power amp's input section. Having to use an external phono section, seem's to throw out the purist intention a bit. Already know what better than a passive attenuator box sound's like, as I've experimented connecting 500mv equipment directly to power amp input's. Sound's just fine, but little flexibilty. If you're running a power amp with level control's, then best to skip the extra box all together.

It is true that the resistive potentiometer is nothing more than an attenuator. However, if properly designed, it will provide low enough output impedance to properly drive the power amplifier connected to it. For example, if one were using a 10Kohm pot (wired as a voltage divider), the maximum output impedance that this pot will exhibit is 2.5Kohm (give or take a few ohms depending on the output impedance of the source driving it). This pot would do quite well driving an amplifier whose input impedance is say 30KOhms or higher.

But the 10Kohm pot might not be high enough of a load for the source driving it. So, some care is needed in designing a passive resistive volume control. Of course, if the power amplifier is an integrated, with input selection and attenuation, I would probably use it alone.

A transformer volume control works somewhat differently. As we know, it transforms voltage on its input (primary) to output (secondary) in direct proportion to the ratio of the turns of copper wire on the primary and secondary. That is, if there are Np turns of copper wire on the primary, and Ns turns of copper wire on the secondary, and a voltage Vp is impressed on the primary, the secondary voltage Vs = Vp x Ns/Np. In other words, Vp/Vs = Np/Ns.

So, as the knob on a TVC is turned up, Ns increases and therefore Vs increases.

But where the TVC excels is in the behavior of impedances that are connected on the primary and secondary. While voltage is transformed in the ratio of Np : Ns, impedance is transformed by the square of the turns ratio, viz. (Np / Ns) ^2.

So, if we connected an amplifier with an input impedance of 50Kohms on the secondary, it would appear to the source (on the primary) as an impedance whose value = 50Kohms x (Np/Ns)^2.

By the same token, the output impedance of the source (say ZS) will appear to the amplifier as ZS x (Ns/Np)^2.

Take the case when Np/Ns = 2.

The 50Kohm amplifier impedance will appear to the source as a 200Kohm impedance, making the amplifier a much easier load to drive.

If ZS, the source impedance = 1Kohm, it will appear to the amplifier as a 250 ohm source.

I guess the point is that theoretically at least, the TVC is a lot less of an impedance problem than a resistive volume control. But it should be noted that as Ns gets closer and closer to Np (volume is turned higher and higher), Np/Ns, and therefore, the square of Np/Ns goes closer and closer to 1. Which in turn means that the reflected impedance is not that much different from the actual impedance, as we go towards zero attenuation.

I would imagine that at normal listening levels, Np/Ns is greater enough than 1.0 to let the beneficial effect of impedance reflection to be achieved.

Further, it is not possible to build an ideal transformer. So, the resistance/inductance of the copper wire and the iron core of the transformer will affect the analysis, but the beneficial effect of the impedance transformation from primary to secondary is still valid.
 
Cool, that's certainly an in depth discription of transfomer's and impeadence matching far more than I'm wanting to go into, but point's out that inserting additional transformer's into the soundstream only further degrade thing's. While some of this stuff look's pretty cool and makes for good conversation, guess I'm more into keeping the signal true at actual usable level's.
 
black wire LAMINATIONS connection?

Hi Nate (Redboy) and guys, i'm doing a passive pre with the S&B TX-102 and need a precious info. The 2 trafos have a black wire, named LAMINATIONS,
that wire have to go to signal ground, chassis, earthed or not connected?

Thanks in advance!

ciao, R
 
Nice stuff Redboy.Is that the silver wired version or the copper?

As you might recall from the previous passive pre thread,I had tried the Lightspeed in my system and really liked it but eventually went back to an active preamp because of the impedance issues.I could see a TVC in my future,even if only to acquire first-hand experience of what they contribute sonically.

It wouldn't cost too much and it would be an education. :yes:
 
Hey, I'm back! Been on vacation for a few days...

This one was the copper wired version, and very nice indeed. I sold it with the idea that it would give me some impetus to wire up the Slagle autoformers I have here, but I got distracted and they sit here...

theo, you should give these things a try if you can track down a pair. :yes:
 
Hey, I'm back! Been on vacation for a few days...

This one was the copper wired version, and very nice indeed. I sold it with the idea that it would give me some impetus to wire up the Slagle autoformers I have here, but I got distracted and they sit here...

theo, you should give these things a try if you can track down a pair. :yes:
You can tell from my previous post that Probably will jump for a TVC at some time.They are a relatively new arrival in popular hi-fi consciousness.ii have been researching the TVC's for at least 7 years myself.I went for the Lightspeed because it had been declared to be more 'invisible' than a TVC.The Lightspeed,as great as it was/is,does not mate well with every system because of the impedance interactions.TVCs do much better in that regard.That is why I'd still like to try a TVC.Just to see how they do in their own right.

Preamps,and by that I mean active preamps,are possibly the most coloured,resolution filtering/losing item after the crucial Source component(what is lost at the Source is not available to the finest preamp,passive pre,TVC etc).Poweramps vary,but not as much as preamps.The better the Source,the bigger the gains in improving the preamp.This is a broad generalisation and there will of course be wonderful preamps and wonderful poweramps,but more often than not the poweramp will do a reasonable job but will be let down by the preamp.

I know that my Source(read;Turntable/arm/cartridge/phono stage)is much better than the rest of my system since the arrival last month of the Audeze LCD-2(rev.2) headphones/Violectric HPA V200 headphone amp combination.I understand only now, how via most systems I am only hearing a fraction of what the Source components are doing.I would love to replicate the sound of the Audeze/Violectric via a Room system.I know now what my Source is capable of.
 
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