Need advice on a TKD stepped series attenuator

[red76]

Hi All,

What's your take on TKD attenuators? I would rather opt for Mickey's DACT but they won't fit in my amp. I know that some older Audio Research attenuators with 'smooth' steps are prone to damage and has bad tracking. I want to know if these are similar to these or not, if they are not good, I might just opt for an Alps Black Beauty. Thanks for your input.

red76

TKD 2P-2511S:






Alps Black Beauty:

[joe3rp]

These are very good potentiometer. However the series aspect of multiple resitors has should be considered. Number of resitors x number of leads - solder...etc

The solution (with new problems) has been to hook these up in shunt configuration. This will result in only 1 high quality discrete resistor between the input and the output. This configuration can be adopted in most audio taper potentiometer, it is a matter of finding the correct value in order to amtch the input and output reistance of the driving stage and amp input stage.

Thset-up basically has a resistor connected to the wiper side of pot, this is the same connection to the output...ver simple and pure. The potentiometer then pulls the input signal to ground to attenuate...simple.

But now the problem comes in, the input, will see a variable impedance ranging from the minimum value of the choosen resistor (at max attenuation) and the max resistance being the resistor value + pot value.

Maybe look at eh goldpoint site...to explain series, ladder and shunt volume controls configuration.

A proponent of shunt volume control is the very much respected Mr. RIVO!

[red76]

joe3p said:

However the series aspect of multiple resitors has should be considered. Number of resitors x number of leads - solder...etc

Hi joe3rp,

Thanks for pointing out the Goldpoint site! It was very informative. Could you elaborate more on the 'problems' you stated above with series atten. w/out connecting it as a shunt type, if you don't mind? The Goldpoint site does not expound on this. Thanks again.


From Goldpoint's site:

"All Goldpoint stepped attenuators improve sound quality and provide better channel-to-channel signal level tracking, compared to potentiometers.

I generally recommend the reliable Mini-V (series type) attenuators. They serve as easy, direct potentiometer replacements/upgrades and yield 95% (or more) of the advantages of using a stepped attenuator: better sound quality and improved channel-to-channel signal level matching.

Theoretically, Mini-L ladder attenuators will sound the best, although reports from users generally state that Mini-H shunt attenuators sound just like ladders. But compared to our Mini-V series type attenuators, you may need to have really good equipment, including your loud speakers, and a good listening room to perceive and appreciate the sonic differences. In some systems, using a series type attenuator yields all the sonic improvement a listener cares to (or is able to) discern.

Additionally, both ladder and shunt attenuators sometimes present a different kind of problem, compared to series type attenuators. They sometimes create popping or clicking sounds while switching them from one level setting to the another. The amount of popping or clicking depends upon the actual circuit the attenuator is installed into, or upon the other equipment in the system.

Popping or clicking sounds when using ladders is usually due to "DC offset" present at the volume control in the system. Fixes for this include capacitively coupling the output of the ladder attenuator, or adding a resistor to ground at the output of the ladder attenuator. (Note: Some systems with ladder attenuators installed have no popping or clicking problems.)"

[joe3rp]

The discrete series resistor like the tdk (25 steps?) the goldpoint and DACT are composed of resistors connected in series (therefore the name). If you look at the drawing in the goldpoint site...these series assume you are in the midpoint position (12 oclock) ....before the signal from the input reaches the output, it will have to pass to two solder connection then a resistor (mulitply by 12 to 13 times)....in short more components to add something to signal. Note that a well designed SET amp will only need the signal to pass through a resistor, triode, resistor, triode, capacitor, power triode then output transformer...or 7 stages...the series resistor about 13 stages. If you are at lower level setting, the signal passes through even more resistors. At full volume, it willnot pass through any resistors...GOOD! But then how often do you play volume control all out....unless it is a passive!

A plastic conductive pot ...like the ALPS BLACK is a single conductive and a wiper....so only 1 resitor.

However the quality discrete resistors (DACT or TDK or GOLDPOINT)...maybe make up quality sound.

[mozilla]

That's the argument for using an autoformer type of attenuator as the impedances are matched throughout the entire range.

If you are at lower level setting, the signal passes through even more resistors.

The multiple resistorsin the path account for the loss of dynamics & highs in most passive preamps.

An autoformer bypasses this problem, it is especially good when listening late at night at low listening levels as the sound you hear is similar to what you get at high levels without any loss of dynamics of highs. Furthermore, the frequency response does not shift as you change volumes.

Check out the S&B transformers here:
http://www.stevens-billington.co.uk

All you need to do is hook em up to a 23-position switch (with no resistors) & RCA jacks & you're done.

Or do a seach for Dave Sagle over at AA. He winds these for about $200.

[rtsyrtsy]

That's the argument for using an autoformer type of attenuator as the impedances are matched throughout the entire range.

Hyperion, sorry to put you on the spot but mind sharing some of your thoughts on the Bent audio passive "pre" that used the silver S&B Mozilla mentioned?

I had it in my system for a while and boy did the CJ PV11 cower in fear of being replaced. Remote volume pot pa lang, the CJ turned green w/ envy na. Then when music flowed...I have to admit I was biased (not the way you do tube power amps) since the Bent was effectively less tubes in my gear but the sound...oh well, I'll leave the articulation to you, Master Darth.

[johnmarc0]

Guys,

I do agree with Joey that ladder types do pass more resistors, but that is the whole point , the sum of the series resistors is what the driving component/system sees i.e. the load impedance regardless of where the wiper taps are. That means the driving system, sees only one impedance and the driving system does not create voltage standing waves (which results to audible distortion and sometimes equalization) as the wiper taps are moved.

The wiper on the other hand selects taps on the series ladder network and selects the voltage to be 1dB step lower (regardless of voltage level input).

I do agree that H attenuators will sound better but on "some" systems only where the driving component have a floating ground as H attenuators are back to back pi type attenuators and good for balanced systems and much more better for push pull types than SET. SET have ground as reference and using an H attenuator defeats the purpose of the back to back pi arrangment (the resultant of H with lower point grounded is a ladder network, i can shoot the attnuator equations if you need it).

carbon type pots lin or log are better yet, the problem with this type is that they use carbon contacts instead of high surface bearing minimal friction materials like gold and silver contacts.

lin or log pots eventually disentegrate in sound quality as the carbon brush wiper builds up residue due to friction between the wiper and carbon bed, which usually results to crackling sound.

On autoformer attenuators, I do not trust them yet! period. Autoformers use a different concept instead of using resistance in a ladder network, it uses reactance in a ladder network. having spent two semesters in electromagnetics and a semester of electrodynamics dictates that reactive materials and devices not only creates voltage standing waves but also phasor reflections(or simply phase distortion). Phase based reflections can only have two results either harmonic distortion (which screws up an SET's performance) or equalization (which changes or shift's a music materials amplitude across several frequencies). An autoformer is not much different in principle as the voltage stabilizer used in computers. They are very much load sensitive and has elliptical frequency response (compared to flat with resistive devices).

Loss of dynamics is caused by reactive devices as signals pass thru the curvature of the ellipse of a reactance component. Some loses voltage while others do not. Resistors on the other hands loses voltage but has no exceptions across the freq band. It maintains the dynamics albiet to loss in amplitude. Loss of amplitude does not mean loss of dynamics as dynamic response is mainly driven by active devices (tubes or SS) and their non linear boundaries. In audio systems, capacitive reactance (capacitance) is the main culprit for loss of dynamics i.e. capacitance in grids of tubes, in gates for mosfets and junctions of transistors and even capacitance along the signal path.


JM

[joe3rp]

the main culprit for loss of dynamics i.e. capacitance in grids of tubes, in gates for mosfets and junctions of transistors and even capacitance along the signal path.

JM

This is really about my other post...pero hindi mo napansin...

Do you think in designing an Interconnect....a very very important (+others inductance, resistance) factor is low capacitance.

Would you havean idea as a good target.....how many picoF per foot

[red76]

Hi Folks,

I didn't expect to have these number of responses . Anyway, TVCs are too much $$$ for me right now (especially S&B). I'd rather have a more sophisticated system anyway designed to accomodate a TVC to reap its max potential. Sowter also makes TVC's similar to S&B:

http://www.iagaudio.com/steppedattenuator.htm

I bought Sowter step-up trafos (w/ chassis) from them for around $250, they take time to respond to emails but deiliver nonetheless. But most of you folks can DIY easily (JM, ArnoldC) so buying bare trafos directly from Sowter would be more economical.

For Sir JM:

On another note. If your only given a choice between the 100k TKD SERIES attenuator (w/ max atten. of 85dB and up) and an 100k Alps Black Beauty what would you use for a simple 3 stage SET?

And BTW, what's your peronal take on TVC's w/ primary and secondary windings (NOT Autoformer ala variac)?

Thanks.

red76

[johnmarc0]

This is really about my other post...pero hindi mo napansin...

My aoplogies po ser, hehehehehe

Do you think in designing an Interconnect....a very very important (+others inductance, resistance) factor is low capacitance.

Would you havean idea as a good target.....how many picoF per foot

Yup, capacitance is a really important criteria just like inductance and resistance, but the idea for transmission lines different as reactance is concerned, in interconnects we have to design reactance to act towards infinity i.e. two cylinders in parallel where the length dictates inductance and the space bet cylinders dictates capacitance, this reactances must be continous so that resultant reactance is infinitesimal or approaching zero. zero reactance means resistance, so the reactances cancel each other reaching pure resistance. so that is why.

1. rigid coax interconnects sounds better than standard stereo interconn cables. coax are like two cylinders superimposed over the other.

2. when we use thin single wire interconnects, whe get better and consistent performance by braiding as braiding introduces more capacitance, normal parallel lines creates more inductance than capacitance. Braiding performs electrically like coax at audio frequencies.

3. The longer the interconnects sometimes results in less coloration. As short interconns does not see electrical infinite reactance, creating constructive distortion or coloration. longer runs makes transparent interconnects. (though I still have to test that notion comparatively with braided versions).

Also, as food for thought, back in the late 70's we used analog rotary phones, which has no amplifying device just a dynamic speaker and carbon mic (the carbon mic eats 0.3mA at -48V exciting a 600 ohm linestage). It runs 10 to 20 Kms from my house in cebu to the city telephone exchange. Speech run two ways (duplex) through twisted quadruple wires (two twisted pairs braided together). I can not remember any loss in dynamics and speech is damn clear and detailed. That my friends is the ultimate interconnect. Would you agree?

JM

[joe3rp]

Also, as food for thought, back in the late 70's we used analog rotary phones, which has no amplifying device just a dynamic speaker and carbon mic (the carbon mic eats 0.3mA at -48V exciting a 600 ohm linestage). It runs 10 to 20 Kms from my house in cebu to the city telephone exchange. Speech run two ways (duplex) through twisted quadruple wires (two twisted pairs braided together). I can not remember any loss in dynamics and speech is damn clear and detailed. That my friends is the ultimate interconnect. Would you agree?

Bossing,

You are correct there. Audiophiles like to use the voice as the reference in most listening tests, because voices are basically very familiar to us...midrange. And when you use the telephone...you can identify the person on the other line as your mom or dad...or your girlfriend that you can talk to for hours...and hours....

[mozilla]

Hey. Sorry folks, I'm getting confused. What's the diff between a TVC and an autoformer? I keep using the term autoformer but when I went back to check my corrspondence with some AA DIY'ers I realize I built a TVC -- though a very el cheapo one.

JM, kindly explain the diff. TIA

[red76]

Hi JM,

I hope that you may answer some of the questions I posted last night:

For Sir JM:

On another note. If your only given a choice between the 100k TKD SERIES attenuator (w/ max atten. of 85dB and up) and an 100k Alps Black Beauty what would you use for a simple 3 stage SET?

And BTW, what's your peronal take on TVC's w/ primary and secondary windings (NOT Autoformer ala variac)?

Mozilla wrote:

Hey. Sorry folks, I'm getting confused. What's the diff between a TVC and an autoformer?

Hi Moz,

I can only answer the basic main difference. An autofromer TVC only has a single winding. S&B's TVC has two separate windings (a primary and a secondary) AFAIK. Other than that, I am an ignuramus on the topic

red76

[mozilla]

Here's a link to computing [url=http://homepages.tcp.co.uk/~nroberts/shunt.html]Shunt attenuators:
[/url]

and one for [url=http://homepages.tcp.co.uk/~nroberts/atten.html]stepped attenuators
[/url]

[mozilla]

Hi Moz,

I can only answer the basic main difference. An autofromer TVC only has a single winding. S&B's TVC has two separate windings (a primary and a secondary) AFAIK. Other than that, I am an ignuramus on the topic

red76

Thanks Red!

Anyway, just to add to the discussion, here are some links to interesting discussions on TVC's & the like:

From Doc John Cheap Audio

From Thorsten's group

[johnmarc0]

Hi JM,

I hope that you may answer some of the questions I posted last night:

For Sir JM:

On another note. If your only given a choice between the 100k TKD SERIES attenuator (w/ max atten. of 85dB and up) and an 100k Alps Black Beauty what would you use for a simple 3 stage SET?

And BTW, what's your peronal take on TVC's w/ primary and secondary windings (NOT Autoformer ala variac)?

red76

I have better experience with alps, to competently qualify the two, I have not tried tkd so bets are off on my judgement. I would be ok with 85dB attentuation, on some alps I can squeeze 100dB attenuation, but since your a 3 stage system predriver-driver-power tube and most probably your power sensitive (lalo na if u have tons of 6sl7 mu in the predrive), It would be a good idea to go series attentuator, but my only reservations is that what will be the impact of the TKD on overall harmonic distortion and coloration. Since it is in series and not terminated to ground like parallel, it may not see a constant impedance. The series resistance and the grid capacitance of the tube forms a time constant network (or inverse of a freq cutoff filter).

The response may be good or maybe better, but I would love to see and listen to it if you have the TKD installed. It will definitely create coloration by equalization (time constant variance is equalization in micro seconds), the question is, will it be better than traditional signal path capacitor coloration. I dunno and wanna find out.

I use interstage trannies on my VT52, it tames down midrange honky drivers, and rolls off the bass. But it sounds bad on transparent speakers as the bass coloration becomes much more apparent. The mutual winding TVC will also have the same effect. The TVC is much more like a MC step-up tranny, My VT52 right now uses a TKS27 mc step up tranny as input, it works fine with low power input and I get a voltage stepup of 18 (300 ohms: 100K Ohms) equivalent to a 6sn7, but once I cracked in higher line levels, it goes down the drain (the core saturates at levels higher than 0.85Volts RMS on 600 ohms) , it was so bad it only works with my 11 year old DENON pre solid state pre as it has fast coherent feedback. On passive, cant go better than 12 o clock.

JM

[red76]

Thanks for sharing your views and your system highlights JM.

My amp is a simple 3 stage cascaded 6SN7 (ala Fi Primer) SET 300B. Obviously has tons of gain w/ 150mV input sensitivity.

BTW, just found out that the TKD has the switch position #2 (first click from OFF *switch #1*) at 50dB. Seems just right for a passive attenuator in my amp don't you think? I have variable gain from my phonostage (and an analog volume control for a future digital source)

red76

[johnmarc0]

there you are, your on a roll!

JM