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Monday, June 11, 2018

Miller Effect on Resistive Attenuator

Have you ever wondered, why TVC, or AVC are much better sounding that resistive attenuator, or resistive volume pot? 

The answer(s) to why transformer / autoformer based volume control is better than resistive volume pots, is quite complex, as there are many factors to it. But, one that stands out, that many may not be aware of, is the Miller capacitance + volume pot effect, that caused the amplifier bandwidth to be reduced significantly when used with a resistive attenuator, or resistive volume pot. This is especially significant if a high value volume pot is used, such as 100K-250K pot.

Everyone knows about Miller capacitance, and why grid stoppers are required, right? But, is he aware that volume pot is part of grid stopper too?

The resistance from the pot has the same effect as a grid stopper (The resistance, starting from input of source, to the volume pot viper section,  is part of the grid stopper!), creating a RC low pass filter with the input capacitance of the tube connecting to the volume pot. This RC low pass filter will attenuate any content above the cut-off frequency. 

The cut-off will be worsen by higher gain tube as the Miller capacitance is multiplied by the gain, in simple calculation sense, a good example, will be 12AX7. (Could it be the same reason where some prefers lower gain tubes in their amplifier instead of a high gain ones?)

Take 12AX7 as an example, the Cin (Miller capacitance) will be ~200pf, give a  take a few or tens of pf. 

Say, with 100K Ohm resistive volume pot, the setting now is at mid point of 50K, indicating that there's a 50K+ "effective grid stopper" connected to 12AX7. Ignore the actual grid-stopper connected for the moment. With that, the resultant cut-off shall be:

f cut-off = 1 / (2 * pi * Rg * C) = 1 / (2*3.142*50,000*200pf) = 16kHz (!!!) 

That's a freaking 16kHz low pass RC filter in the amplifier without one even realizing it. That is sad...

That's why a lot of folks prefer TVC or AVC versus resistive volume pot. That's why most people will say that the realism is better, the highs are airier and with more body once they migrated to TVC or AVC. Once they tried TVC or AVC, they will never go back to resistive volume pot.

Till then. Go figure.

J&K Audio Design

J&K Audio Design Facebook Page

For those that wonder why there isn't much activities in the blog, we apologies for not having to much time to write now. We will, but just not as frequent.

Still, we will find some short intervals between here and there to publish a few pictures or posts on our Facebook page. For those that have not followed us there, or liked our Facebook page, it is time to do so now to keep yourself updated on the latest development, and have some real time interactions there. 

It will be fun. See you there!

J&K Audio Design

Saturday, April 21, 2018

Fully Built Transformer Volume Control

Fully Built Transformer Volume Control - would anyone be interested?

We REALLY hesitated on introducing a fully built transformer volume control due to the amount of manual labor required to solder the TVC to the step-switch. One unit of fully built stereo Transformer Volume Control takes 5-8 hours to solder!

Due to the overwhelming response from readers asking for a fully built TVC as not many are trained on soldering and building audio kits, we are introducing this, for a limited time, for a limited quantity, for batches order only so that we can keep the quality in control. 

Also, we think that Transformer Volume Control is something that an audiophile must own as the improvement in sound is just substantial over the price paid (very high cost / performance ratio), we are doing a limited time promotion on standard configuration standard TVC to keep the cost of making them down. 

Standard standalone 24-step TVC - U$590/pair (RM-2350) (special batch order price only)
* 24-step, potted with turrets
* Hi-B core only (others - will be normal price) 
* Primary 600 Ohm, secondary: 600 Ohm

Note: It will be built in a batch of >=5 sets. You can order 5 sets or more, or wait for 5 sets to be accumulated before build starts. If you order >=5 sets, you can customize it slightly, please email for details.

Fully built stereo unit - U$990/unit (RM-3950) (special batch order price only) 
* built with standard 24-step TVC above
* full aluminum chassis
* 24 step attenuator switch 
* double-screw chassis 
* input grounded, or output grounded, or floating (need to ground at chassis)
* single set of stereo input and stereo output

Note: It will be built in a batch of >=5 sets. You can order 5 sets or more, or wait for 5 sets to be accumulated before build starts. If you order >=5 sets, you can customize the parts used (some at extra cost), please email for details.

Sample fully built TVC is as follow: 
* outlook and materials may change depending on parts availability

TVC - fully built
23 step TVC only (shown is 33-step as sample only)

Silver Plated OFC wiring

33-step version shown as sample only
Made in Taiwan 24-step switch

What's the difference between this and the custom made version? Custom made (more expensive) version offers superior cores - NanoCrystalline (aka Finemet), Permalloy and Amorphous, and is customisable (different primary/secondary impedance, different step-up/down ratios, configurable and etc), different grade of wires, solder, and etc. Sound quality wise, custom made version is a grade higher too (that justifies the price!). 

Still, this standard version is excellent sounding - with extended frequency range, solid vocals/body and clarity! The difference between TVC and resistive stepped attenuator is easily differentiated even by non-audiophiles! You owe yourself to own it, trust us!

Till then, grab hold of this opportunity to get yourself a fully built TVC, or a raw Transformer Volume Control, for your long awaited birthday present, Christmas present, 1st draw pay gift to yourself, wedding anniversary present, and(or whatever reasons you can cook up)!  

While it lasts... don't regret after promotion is over, or before we regret it.

J&K Audio Design

Thursday, March 29, 2018

J&K DAC Review

J&K Audio Design DAC Review - submitted by customer. 

OCTOdac: Fidelity and Musicality Beyond Sound.

Two years in the making, from design to sourcing and subsequently the final built, the entire journey was a huge learning curve and also one filled with utmost satisfaction. Credits to J&K for bearing and taking the journey with me.

Listening: Round One - First Impression
It was flat and dull!... Seriously! With all the additional caps in the DAC unit, it does sound like a punctured tyre trying hard to complete the journey while waiting to be inflated back in shape. Not forgetting the tubes were NOS dating back to the 30s and 40s.  Well, that was the first impression. It did not take long for the DAC to gradually open up and reveal herself. After warming up probably for about 2 hours, the character of design became more apparent. Clean, dark, transient, deep, wide and warm. If I were to put them into simple words, that would be it.  Sonically,  if there’s such words it would be musical neutral yet analoguely warm. Why I didn’t mention accuracy? That in my humble opinion is subjective to the overall setup, room acoustic and head knowledge of the audiophile. One man’s meat, may be another’s poison. A Concert Grand Piano will definitely sound different from a Full Upright Piano… let’s not go down that dark dark alley of audio apocalypse. For mention’s sake…. The design and backbone of this DAC is capable of processing the difference. Everything falls back on the listener.

Listening: Round Two – Width and Depth
Fast forward one week later, after daily non-stop playback of 10 – 12 hours, the full blossom of the DAC is at full bloom. Sonic control was just enough, not like the army general howling battle cries, but enough to keep the darling at arm’s length. Stage depth and width was and still is, beyond walls. Keeping things in perspective, the speaker fades and the band / orchestra / ensemble takes center stage. Dynamics were fast and attacks were strong yet gentle to the ear. Guitar rifts up and down the frets keeps the listener on the edge of our toes, anticipating the next bar or expressive fingerpicking. Attacks of the Flamenco accompanied by the shoe taps of the tap dancer reverbs across the room.

Listening: Round Three – Instrumentals
Electronic sounds like techno and new age were less defined as this DAC was designed with NOS in mind. Old School sound with a touch of new component technology. The thumb of the techno bass and electronic drum were less engaging. Head bangers will find this very upsetting. Though it raises some hair, it doesn’t thump the heart to a point of cardiac arrest. Moving down the spectrum, Rock, Soul, R&B audiophiles will not find any lacking in this. The depth of the bass, tightness of the drum skin and mood of the R&B and Soul are felt across the spectrum. Nothing is short changed during playback. Going further down the stream to acoustic instruments is where this DAC shines! Though only decoding at 20-bits, no details are spared. Starting with the Quattro bass, each slap, slide, pop, bend and vibrato is clearly audible. Brass instruments are bright and zingy. Woodwind blows mellow and sweet. Strings are majestic and swift, each pull of the bow is well defined and expressive. It truly takes a lot out from a DAC to realistically reproduce the sound of a live quartet or orchestra performing in front of the listener. I would say OCTOdac holds up pretty well. Of course system matching and room acoustic also comes into play and both are equally important.

Listening – Round Four (Vocals)
The separation job done by the DAC was superb! Be it in a choir, solo or acapella, the vocals are spot on. Emotions are positively passed on to the listener. Vocal expressions are represented in a way that will keep you anticipating on what will come next. Layers of sound are clearly defined. Vocals lean toward the neutral side. Not excessively warm, neither is it freezing cold. Dim the lights, sit back and crank up the volume. Indeed a hair-raising experience, bordering the fine line of being horrifically silent. Probably Chucky lurking round the corner of the room.

The OCTOdac was fully custom designed with flexibility and future upgrades in mind. The Processing (DAC) Module is truly modular and hot swappable. In the event I would like to have a more vocal centric sound, I can simply build another DAC and swap with my current PCM1702. Satisfying my incurable itch for symmetry, the GainStage was build and design to match my current monobloc amplifier.

DAC configuration & description

Processing (DAC) Stage
Inputs: Fully dedicated S/PDIF and Digital Coaxial.
Output: Single-ended (RCA) analogue outputs.
Convertor: Dual Mono BurrBrown PCM1702 20-bit
Digital Power Trans:  EI - Z11 (Level 2)
Analogue Power Trans: Super Hi-B Dual Core (Level 3)

Gain Stage (monobloc units)
Tube Compliments: 6J5 (driver) , RGN1064 / #1805 (rectifier).
Super Hi-B Dual Core Tube B+ Power Supply
Tube Output Trans: Western Electric Core 15K – 600
Tube B+ Choke: Western Electric Core

The OCTOdac filled the missing piece in my audiophile quest. Truly a bang for buck, value for money and fully customized piece of gem. It doesn’t just bring you music, it carries along with it the joy and emotions of sound. Adequately defining the true meaning of Fidelity and Musicality Beyond Sound.

Saturday, March 10, 2018

ED8000 tube amplifier schematic

When I'm talking about NOS Telefunken tube amplifier, it gets me excited and makes me sleepless! 

For those that are unaware of the previous article, please visit:

Here goes revision 1 of our proposed ED8000 tube amplifier design. There are tonnes of methods to build ED8000 tube amplifier. Below ED8000 tube amplifier schematic is just one of them, a simple one in fact. It needs only 1pc of 5687 to drive both Left and Right channels, with the use of 1:2 step-up input transformer to provide sufficient gain to drive ED8000 tube to full power.

P/S: circuit has not been tested yet, further fine tuning may be required.

Other than the usage of 1:2 input transformer, there is the innovative use of a 200H plate choke for 5687 as load to keep the B+ low to match the B+ of ED8000, where B+ is quite low compare to other tube amplifiers such as 2A3 or 300B. If resistive load is used for 5687, then the Vplate of 5687 needs to be lower so that the B+ needed does not exceed 177V. 

Or, use interstage transformer! With interstage transformer, ED8000 grid leak resistor can be removed, together with the coupling capacitor, which is an even more elegant and better sounding design. Of course, interstage transformer comes with a slightly heftier price tag.

All the components for the ED8000 single ended tube amplifier schematic are carefully calculated for the best effects and are not simply plugged from the sky. If you copy the design, please do not change the values of the components used. If you change it, and it does not sound good, blame yourself! LOL. 

The B+ can be slightly tuned by adding a small capacitor of 0.1U - 0.68U after 5U4 rectifier tube rectifier. This converts the choke-input rectification to pseudo capacitor-input, and raise the B+ slightly.

If you build it and like it, let us know! If you need the irons, let us know too! If you see errors in the design, let us know. It was designed in a matter of minutes.


J&K Audio Design

ED8000 Tube Amplifier

Let's talk about a slightly different topic today, ED8000 tube and how to use ED8000 in Single Ended Amplifier!