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Thursday, December 15, 2016

Transformer Volume Control Review

Greetings. We have made a pair of TVC (transformer volume control) for a very nice and patient customer some time ago, and he has been very nice to provide us with his review and also measured data on our TVC. 

For those that are unaware of what it is, you can refer to the links below:

http://jandkaudiodesign.blogspot.my/2016/10/optvc.html
http://jandkaudiodesign.blogspot.my/2016/10/transformer-volume-control-tvc.html

As you can see from the measured data, bandwidth is RULER FLAT from 20Hz - 20kHz, and low frequency -3dB point is at 10Hz, more than most speakers can reproduce. Channel matching is spot on. Most importantly, it sounds absolutely terrific! Do not hear it from us, try it yourself. 

We'd like to THANK Lasse for sharing the pictures and providing a review for us!


QUOTE:

Hi Jolin,


I like the TVC's. They are made with tight tolarenaces regarding channel balance and frequency response from each step. 


I used Sommercable Carbocab 225 (6N copper in compressed carbonized plastic layer and polypropylen insulation) to wire all the taps, which I find very good cable especially compared to it's price. I use Oyaide Tunami cabling otherwise almost everywhere.



The sound quality is the best I have heard, beating the crap out of S*** TVC's and the original TVC's of the Coincident Statement Line Stage. Compared to my previous TVC's the sound is much smoother. The sound of the TVC's is very liquid, refined and microdetailed also at low listening levels. I'd say with Permalloy core they hit just the right spot with Finemet transformers, very very good combination of transformer cores in my opinion because the Permalloy is so smooth and Finemet is so transparent, airy and wide bandwidth. I believe they are "the" core materials in those attributes, and when combined 25% permalloy/75 % Finemet the result "does it all" for my liking.


Please find a picture of the installed units attached. I did not take other pictures than that, I'm sorry and now I have put on the stainless steel covers which block the view of the transformers. The freq response of each step has now "normalized" and is identical in each step. Funny how that changed slightly in the burn in process also.


Thank you for the (snipped - our little secret)!


Best regards,


Lasse

END QUOTE. 

Do note the measurement is made by Room EQ Wizard software. It is limited to 48kHz sampling frequency only and therefore the accuracy for such sampling rate is <= half of the sampling frequency before Nyquist effect kicks in. So, everything after 24kHz is not faithfully measured. The TVC bandwidth is definitely much much more than 20kHz.

Suppose the highest frequency component, in Hertz, for a given analog signal is fmax. According to the Nyquist Theorem, the sampling rate must be at least 2fmax, or twice the highest analog frequency component. If the sampling rate is less than 2fmax, some of the highest frequency components in the analog input signal will not be correctly represented in the digitized output.

TVC measurement - left channel

TVC measurement - right channel

Screen capture of email sent to us
Coincident Statement Line Stage

Update on 12/21/2016 (thanks to Lasse that provided the supplementary information).

* The measurements are from the whole modified Coincident Statement Line Stage preamp. The preamp has been modified with J&K TVC and Noguchi FM-10K-600CT output transformer. Very simple & great sound, zero feedback. 

* Also the sound-card's input/output is not DC connected and the loop back measurement has attenuation at the bass (-3dB @ 7,5Hz).


J&K Audio Design
12/15/2016

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