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Silk STA-522A vs Sowter 9335

68.48.134.123
Posted on February 7, 2010 at 19:47:32
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 Hi all, I hope there is someone out there who might be able to comment on the sonic difference between these two units.

I have a Rega Apollo CD player with 600Ohm output impedance and a Sugden A21ap amp with 47kOhm input impedance. I'm going to wire the transformer to a Shallco shorting 2 deck single pole switch.

Silk uses a Supermalloy core and Sowter uses mu-metal. Both are iron, nickel, and molybdenum with perhaps some copper in the mu-metal type. The Sowter shows 85H inductance, while the Silk shows a seemingly impossible 1100H. Costs are similar, $430 shipped for the Silk and $380 for the Sowter depending upon the daily exchange rate. Sowter claims a wider and completely stable bandwidth. The Sowter offers 26 positions at 2 dB per tap, and the Silk has 23 with a few 3dB steps. The Sowter is made in the UK, which would be consistent with my other gear, and the Silk is made in Thailand. Both appear to be excellent build quality. The Silk is featured in a few pre-built products, but not the Sowter for whatever reason. Which would you choose and why? Is there anyone out there who has heard them both and has some objective opinions?

 

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RE: Silk STA-522A vs Sowter 9335, posted on February 8, 2010 at 10:17:34
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 Maybe I should post this on the Tweaks forum?

 

Try this post ion the DIY Asylum (nt) , posted on February 8, 2010 at 11:43:09
GEO
Audiophile

Posts: 4749
Joined: April 7, 2000
Contributor
  Since: September 9, 2000

 

Why oh why do you want to add a transformer?, posted on February 8, 2010 at 15:36:15
Allen Wright
Manufacturer

Posts: 5652
Location: Schaffhausen
Joined: January 31, 2002
 I can see absolutely no need - the impedances from the CD player t the amp are perfect - is there any other reason?

Regards, Allen

 

RE: Why oh why do you want to add a transformer?, posted on February 8, 2010 at 15:42:15
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 I dont have any way to control the volume right now, so I need to do something. I've considered two options, either an active tube preamp using the 26 (Gary Pimm), or a passive. If I'm going passive, I'm using a transformer volume control!

 

I didn't read it all..., posted on February 9, 2010 at 05:30:58
Allen Wright
Manufacturer

Posts: 5652
Location: Schaffhausen
Joined: January 31, 2002
 ...and see it was a TVC you were talking about.

regards, Allen

 

RE: I didn't read it all..., posted on February 9, 2010 at 14:10:29
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 np

 

RE: Why oh why do you want to add a transformer?, posted on February 9, 2010 at 18:28:53
coolhand
Audiophile

Posts: 537
Joined: June 5, 2006
 Hey Tom... (see link below)
This shortly due offering from Brian of DIY HiFi Supply looks to be something quite special indeed, especially if you're considering a DHT pre, and Brian has been using a TVC for years so I'm sure he has a 'clear' perspective as to the pros & cons of both...!

http://www.diyhifisupply.com/node/747

 

RE: Why oh why do you want to add a transformer?, posted on February 9, 2010 at 20:50:14
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 Thanks - this sounds fairly similar to Gary Pimm's 26 preamp - auto bias active load on the choke, low noise filament supplies are provided by batteries. For now I'm going to stick with the TVC, if I think I can do better with an active stage I'll give it a shot later...

 

RE: Silk STA-522A vs Sowter 9335, posted on February 10, 2010 at 07:34:30
Thorsten
Manufacturer

Posts: 4209
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
 Hi,

First one or two general notes.

First, I was involved in an abortive group-buy for TVC's from Sowter to our (my?) specifications in the late 90's of the last millennium. The original Sowter TVC that came out about a year later seemed largely based on this original specification.

Second, I was subsequently involved in the specification and development of the Stevens & Billington TVC's (no longer available to the DIY Market), which unlike the Sowter spec. item was specified and designed without any economic limit on complexity and material costs (but was limited by commercial availability of the core lamination).

The Silk unit appears based on making an equivalent/improved TVC to compete with the S&B Unit. I have some loose ties with a vendor that supplies the Silk unit nowadays.

As far as primary inductance is concerned, the original S&B TX-102 had 400H primary inductance measured at 100Hz. At 20Hz it measured significantly higher (forgotten how much). Later versions have even more inductance, though I am not sure if the match the 1100H claimed for the Silk unit. I guess I could see to get hold of a pair and test them, however the number is not "seemingly impossible" but certainly achievable.

As far the primary inductance goes it main "technical" relevance is in terms of compatibility with higher source impedances. For example, 85H with 600 Ohm source impedance will give a LF rolloff of -3dB at 1.1Hz, clearly far beyond good & bad.

Yet with a 10K source impedance at low frequencies (not unheard of in tube phono stages for example) the -3dB rolloff would be 18Hz, which is not great. In the same situation the 1100H load would produce a -3dB point of 1.5Hz.

There are two less obvious issues. Higher inductance generally means more turns and more level handling, which reduces the amount of (mainly low frequency) distortion at higher levels.

A further issue is more subjective. It seems all else being equal, TVC's sound better the lower the source impedance. However if the primary has more turns it means it tolerates (again) higher source impedances better in this area too.

Okay, sonic comparisons.

I have only compared Sowter (the first Sowter which appears broadly equivalent to the 9335) to S&B (MKI). I found the Sowter TVC to sound significantly more shut in, less detailed and lacking in dynamics and impact. It was still a notable step up, subjectively, from a good quality stepped attenuator.

Based on others comments (no first hand direct comparison) the Silk TVC is reckoned to be about the equal of the S&B. If so it will perform notably better than the Sowter, in my experience.

I wish I could help more.

Ciao T
Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

 

RE: Silk STA-522A vs Sowter 9335, posted on February 10, 2010 at 10:45:16
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 Ok perfect thanks very much! I certainly didn't expect to hear from one of the folks who originally helped cook the idea up. By the way I was recently offered a pair of the TX102 transformers for 1400 POUNDS from the manufacturer, which I thought was surely a typo when I read it. I think I'll stick with the Silk. I'd like to know if you still use a TVC personally, or if you've found an active solution that betters it.

 

RE: Silk STA-522A vs Sowter 9335, posted on February 12, 2010 at 06:59:44
Thorsten
Manufacturer

Posts: 4209
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
 Hi,

> I'd like to know if you still use a TVC personally,

Given that I am now rather deeply involved on the commercial audio side, my system at home tends to include whatever new product is being cooked up and which needs long term ergonomic/reliability testing.

In the "reference" systems (in acoustically treated rooms at company premises) TVC's remain one of the main comparison standards.

> or if you've found an active solution that betters it.

I think this is the wrong question.

By definition and inherent principles active "preamplifiers" and passive "preamplifiers" are very different.

There are clearly systems where active preamplifiers are needed (passive just will not work or give good results), there are others where they distract from the systems main qualities and strength.

The whole TVC lark was never intended to supplant active preamplifiers, but rather to remove some of the sonic and system compatibility problems found with traditional passive "preamplifiers", so more like "passive on 'roids", not "go away active".

Srajan from 6moons made an excellent observation in one of his reviews (sorry, cannot be bothered to look it up and link it).

He observed that systems that already sounded "right" directly (source, amp, speakers) had a serious upgrade from replacing traditional active pre's with a TVC.

On the other hand he found system combinations where the "personality" of the active pre was needed to provide a correct reproduction.

I personally have always subscribed to systems of the first kind, but as someone who builds practically everything in his system himself (including cables and all) or at least heavily customises everything, I find it easy to achieve such systems.

So I have been "aggressively passive" for a long time. And every time I dally with active preamp's so far I have come back to passive of one description or the other, with TVC's still the best solution most times.

I hope that puts the "TVC" into context.

Some interesting reading from a fellow "aggressively passive" guy (though we do not necessarily see eye to eye on TVC's) is here:

Arthur Salvatore on Linestages

Ciao T

PS, I still have this long term active linestage project, with TVC input, a antique triode (10Y) as amplifier in the WE Repeater Amp design, with output transformer, of course all transformers silver wire wound and high nickel permalloy core and with silver coupling capacitors... I suspect this may be the best of both worlds and oulr only have 6dB gain. But the cost is extreme.
Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

 

RE: Silk STA-522A vs Sowter 9335, posted on February 12, 2010 at 07:50:08
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 I have read the 6moons review. Worst case scenario I'll try it and resell it on Audiogon if I dont like the results =)

A guy named Andy Evans was raving about the 10Y a while ago on the tubes forum as we discussed an active 26 linestage. Several people were hunting for 10Y linestage schematics - would you care to share it?

 

RE: Silk STA-522A vs Sowter 9335, posted on February 12, 2010 at 09:01:27
Thorsten
Manufacturer

Posts: 4209
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
 Hi,

There is not much of a schematic per se.

The standard WE repeater Amp looks like this:



Input Transformer is TVC (S&B TX-102 Silver)

Output Transformer is 4:1 40K:2.5K (S&B TX-101 Silver)

Current Source is 160H/12mA Choke (S&B Anode Load Choke - custom Part in silver)

Two Capacitors are 0.47uF (to input) and 2.2uF (output) Audio Note (Silver)

Cathode resistor Non Inductive Wirewound - Value per Tube Datasheet recommendation for selected operating point, I'd likely use 250V/10mA so 2.2K. I have old UK Mil Spec silver leadout resistors left over in 2.2K/9W

Powersupply to suit, probably glowtube regulators per channel, full dual mono supply with LCLCL plus R/Glowtube and some big old transformers and maybe 5U4 or GZ34 per channel.

Really, not much of a schematic, it's all in the (virtually unobtanium and ultra expensive) parts.

In the Days when S&B still supplied the DIY market at semi-normal prices the signal magnetics would have rub in the 2K UK Pound range, the AN Silver capacitors run nearly the same money.

Add a suitable silver switch and all - even in the best days we'd likely have looked at > 5K UK Pound (and the pound was strong then and the force with Geordie) pure parts cost, by now I'd expect we are looking 10K ++, who knows.

Makes a Silk TVC look like a Bargain, doesn't it?

Ciao T
Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

 

RE: Silk STA-522A vs Sowter 9335, posted on February 12, 2010 at 09:24:00
drlazybones
Audiophile

Posts: 122
Location: Forest Hill, MD
Joined: December 29, 2003
 So it's an auto-bias TVC input parafeed output linestage. I like it.

I can't seem to find a data sheet that mentions the plate resistance of the 10Y: http://www.mif.pg.gda.pl/homepages/frank/sheets/049/1/10Y.pdf, but here's a cheap alternative to the key ingredients, with the possible exception of the output transformer, which you have spec'd at a much higher primary/secondary impedance - is that because the 10Y has a plate resistance in excess of 15k?

Input transformer Silk STA-522A $400
Current source Magnequest EXO-010 $75 each
Output transformer Magnequest B7-15k (15K:500 parafeed output) $99
0.47uF cap Mundorf supremem silver/gold $39 each
2.2uF cap Mundorf supreme silver/gold $66 each

 

RE: Silk STA-522A vs Sowter 9335, posted on February 12, 2010 at 10:32:27
Thorsten
Manufacturer

Posts: 4209
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
 Hi,

10Y is electrically very close to RCA Type 10, anode impedance would be around 6K. The choice of 40K primary is more for minimising the parallel-feed capacitor value.

Your choice of substitutes is yours to make, where I have tried the ones you list (Mundorf Cap's) I would not use them or any from that metalised film family, non of them sound remotely like the ANJ or ANUK cap's. Mundorf makes much better cap's for less money than this range.

No comments on the MQ Transformer or choke, on paper looks okay.

Ciao T
Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

 

RE: Silk STA-522A vs Sowter 9335, posted on February 18, 2010 at 07:29:17
Vis-Viva Technologies LTD


 
Hi T,
i have just built up a pair of 522A's that i got from Brian whilst i was in HK. im having some trouble with some tech things that i would like to discuss with you. please reply to my email address.
Jason

 

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