how to build a pre using S&B TX-102 transformers

[Sigurd Ruschkow]

I just finished a prototype of a preamp with the TX102 and just a single input and output. ELMA 24-position rotary switch was used to switch between the 19 different attenuation levels.

I am using the +6dB mode as I need the extra voltage for my power amp.

The little wire that was needed is silver coated copper teflon insulated wire.

It was very simple to wire everything up.

With the output floating I got lots of hum and noise so I connected input and output ground together, and my system is now more quit than ever - no preamp that creates any noise

Sound is wonderful!!! Soft, round, polished, lots of bass, maybe too much bass for male voices, detailed, with instruments that has clear focus, and the soundstage is excellent!

I also have the Sowther ones in the same box and also wired up to the same ELMA rotary switch.
I can thus check the sound quality between the Sowthers and the TX102s.
I have not tried them yet, though.



Sigurd

 

[KevinTams]

Got my Tx102's wired in and running today. I had a similar problem to Sigurd in that I had my -ve's floating, the symptoms were a broadband mush of sound, sort of a white noise, but only at the -10db to 0db windings. I spoke to S&B who advised connecting the -ve's input to output, which I did at the RCA sockets, ..... result

Did I say result, I can't bring myself to turn the thing off now, to finish the job, I just keep playing record after record. And just for the record this replaces my passive pre which was a direct wired Alps "blue" pot and p*sses all over it. The improvements are far from subtle and improvements in all areas, imaging, information, tonal quality.

Thanks to everyone involved in this GP, this rates as a great VFM upgrade.

Kev

 

[ThorstenL]

Konnichiwa,

Got my Tx102's wired in and running today. I had a similar problem to Sigurd in that I had my -ve's floating, the symptoms were a broadband mush of sound, sort of a white noise, but only at the -10db to 0db windings. I spoke to S&B who advised connecting the -ve's input to output, which I did at the RCA sockets, ..... result

What must be understood is that you only float the output of the Transformer if there is an external connection between chassis/ground of source(es) and amp.

In my system for example the TV/VCR/DVD Player has earth through the TV aerial and the CD Player has earth trough the mains, as has the phono stage and of coursemy (tube) amplifiers are earthed. As a result I keep the output of the 102 floating and the sound is rather notably improved, even though I was able to minimise any hum coming through the various earth's path.

Hence you best always fit a switch that allows you to select which way, tehn if you ever change anything in the system....

Sayonara

 

[KevinTams]

Kuei Yang Wang

What must be understood is that you only float the output of the Transformer if there is an external connection between chassis/ground of source(es) and amp.

I'm trying to understand this one. My CDP is a Linn Ikemi, which I assume has the signal grounded to earth somewhere within it's circuitry. My power amps have the signal -ve terminated at the power star point, with this connected to the protective earth through a resistor, ( I think100ohm but don't quote me). So both of the transformer windings should have been earthed, but not through the signal -ve. Given that the fix worked means that something is amiss with my earthing, however I've a black silence between tracks with no hint of hum. The case of my pre will be earthed through the protective earth of the power amp. I'm still using the pre in rough form and still playing music, so I haven't yet wired my earths and -ve's as you suggested, maybe tomorrow if I can take it out and finish it.

I've not yet used my phono in circuit as I'm waiting for Origin Live to deliver my Silver arm, I've just bought an Acoustic Solid Small Royal and am itching to fire it up, so at present no vinyl

 

[krishu]

Hi,

happy new year!

I got mine and did already build a simple magnetic pre ... it was soooo easy to do. I chose 0dB configuration and used an alps source selector and an Alps 23step switch. Until now it did not play for more than three records but even now I am satisfied .... an my expectations were huge after all that hype (and the price, of course)

I'll post pictures etc.next week

Cheers
Christian.

 

[darkmoebius]

Question for Kuei...

Can the TX-102's balanced output drive long interconnects (approx. 8 meters) like normal balanced drivers?

The preceding stage is a parallel TDA1541A dac and the amplifiers are monoblock single-stage MOSFET amplifiers with a load equivelent to the mosfet's gate load - Rterm=120K.

I also have the Sowther ones in the same box and also wired up to the same ELMA rotary switch.I can thus check the sound quality between the Sowthers and the TX102s.

Please post your impressions as soon as you get a good feel for the differences.

 

[analog_sa]

Can the TX-102's balanced output drive long interconnects (approx. 8 meters) like normal balanced drivers?

The question really is whether the DAC can drive the long interconnects on its own. What follows the parallel 1541?

 

[darkmoebius]

The question really is whether the DAC can drive the long interconnects on its own. What follows the parallel 1541?

Hi Analog,

I never thought of it that way, but now mentioned - it is incredibly obvious! TX-102'a are passive .
Hence, the preceding active stage provides all the drive/voltage.

The DAC is Tube-Lovers parallel design kit over on Audio Vender's Bazaar. The kit provides three different output stage choices: 6c45 SE, 6DJ8 SRPP and AD844 common based Op-amp output.

Having just re-read the manual, it seems that I can adjust the ouput level by varying the stock 33 ohm I/V resistors. The usuable range is between 20 and 68 ohms, the lower values resulting in greater output. I'll just have to hook my DMM and see what the true voltage range turns out to be.

I was hoping to maintain the purity of the TVC to amp connection(in theory), but I also have a few Burr Brown DRV134 balanced line drivers and INA2134 balanced line receivers here on my desk. I can always use those in a unity gain config to drive the long interconnects.

If need be, which would be best - inserting the line driver before the TVC or after?

 

[analog_sa]

Hi darkmoebius

Call me prejudiced but i would steer clear from the DRV unless absolutely necessary. A 6S45 will be more than capable of driving the TX and the cable.

If you really must use the DRV it should be before the TX- these transformers really like being driven from a low impedance. Assuming zero driving impedance the output impedance after the TX is mostly determined by the dc resistance of the secondary and is low enough to drive a very long cable.

 

[darkmoebius]

Call me prejudiced but i would steer clear from the DRV unless absolutely necessary. A 6S45 will be more than capable of driving the TX and the cable.

Makes a lot of sense to me. There is something incredibly simple and elegant about the TVC and to add an IC full of resistors, etc. into the picture kind of spoils it literally and figuratively.

I'll just have to see how things work out with all my sources and , if need be, have some of my inputs direct and others via DRV's. In reality, I only have a tuner, DAC, and video sound feed. Vinyl is something for future paychecks.

If you really must use the DRV it should be before the TX- these transformers really like being driven from a low impedance. Assuming zero driving impedance the output impedance after the TX is mostly determined by the dc resistance of the secondary and is low enough to drive a very long cable.

Thanks for the explanation. I read and re-read the S&B page, but just wasn't getting the picture(it was 2am last night). Seems like the TX's will do just fine with my setup. If not, I can always add the DRV's to a few inputs that need help.

 

[wytco0]

Anyone else got their pre working yet? If so please post details.

I wont be able to strat on mine for another couple of weeks.

 

[krishu]

Hi,

I have put my TVC on my website here

I used unity gain, RCA inputs and outputs, connected input and output ground together but SEPARATED ground of both channels as this is already connected in the sources.

Sounds wonderful! Just neutral, no hum, no noise, but yes: dynamics

Cheers
Christian.

 

[Keith Marrison]

I wired up my tx102's at the weekend . These things are superb. As krishu says; neutral and very dynamic. I just keep playing cd after cd. Shame I had to go back to work.
Many thanks to all involved in the group buy.Mine are wired up with rca's on the input and balanced out to drive my Aleph 5 clone.
Anyone want to buy aBOZ.
Cheers Keith

 

[wytco0]

Thanks Krishu and Keith for the info re your amps, I am looking foward to putting mine together.

I will be uisng mine with my DIY UCD180 based power amp which has Balanced inputs. Keith, could you post a few pics of how you have put yours together as it sounds like the configuration I am after?

Thanks.

 

[Keith Marrison]

wytcoO
My TX102's are wired up like this;
Input signal and ground through an elma switch to the 102's with a ground connection to star ground through a 150 ohm resistor{as recommended by Kuei Yang Wang}
Outputs: pin 1 to star ground
pin 2 signal out from 23 pos switch
pin 3 unmarked black or white wire fron 102's
I did'nt bother with any earh switches thinking that I would just loosen the chassis screw to try different arramgements; but with the complete lack of hum and inky slence I have'nt yet tried other earthing .
As my daughter would say; these things rock
Ihope this helps

Keith

 

[wytco0]

Keith Thanks for the info.

I am looking foward to strarting on mine in a couple of weeks.

Anyone else built one yet? if so I would love to hear how you did it and how it sounds. Pictures would also be appreciated.

 

[scottw]

screen tap

I'm in the process of building a maple box for my TVC pre to be lined with copper sheets for shielding. Was trying to decide if it would be best to mount the 102's in contact with the copper shield or keep it floating.

However, I measured R between the screen tap and the 102's mu-metal "can" and one is 0.3R and the other varies some but is usually around 10R or larger. I'm thinking that this is occuring because the screen and core are connected and the core is in weak contact with the can as it sits in the potting wax.

So, with all I have read on the black hole that is grounding and ground loops, I'm thinking that a varying resistance here may not be "ideal". Maybe, because it is only shielding, it will not cause a problem but if the 102's can is grounded and the screen tap is grounded there will be multiple paths to ground; and a nonstable resistance between them.

Any suggestions? Might this be a concern? Anyone else measure R from the screen tap to the Tx can? Master Kuei, any thoughts?

Thanks,

scottw

 

[ThorstenL]

Re: screen tap

Konnichiwa,

I'm in the process of building a maple box for my TVC pre to be lined with copper sheets for shielding. Was trying to decide if it would be best to mount the 102's in contact with the copper shield or keep it floating.

Connect the screen wire, TX-102 and designated system ground (I personally place this on the input side, John Chapman from Bent places it on the output side) to the metallic (screen) parts of the case.

There is no garantee that Can and Transformer are conencted together or insulated, at any extent, Transformer case, core & screen and case screening all belong together as one set of screens.

if the 102's can is grounded and the screen tap is grounded there will be multiple paths to ground; and a nonstable resistance between them.

Actually, remember to consider all screens seperate and as SCREEN, they are not ground (at least not neccesarily), but eventually should be connected to ground.

An extreme grounding system would keep Screen, Input ground and output ground seperate, with the case(screen)returned to Earth seperately and each sides "signal cold" referenced apropriatly.

Sayonara

 

[scottw]

Re: screen tap

Thanks for the reply Kuei.

There is no garantee that Can and Transformer are conencted together or insulated, at any extent, Transformer case, core & screen and case screening all belong together as one set of screens.

Then, it seems, I should solder a drain wire to the Tx can and run it parallel with the screen wire to the single point ground; and isolate the Tx can from the case(copper shield) where it mounts.

scottw

 

[ThorstenL]

Re: Re: screen tap

Konnichiwa,

Then, it seems, I should solder a drain wire to the Tx can and run it parallel with the screen wire to the single point ground; and isolate the Tx can from the case(copper shield) where it mounts.

If you so wish.

I'd probably mount the transformers in contact with the case and also terminate the screen wire there and use a single wire from the screen to SPG. Many ways to fry up that fish.

Sayonara