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T.M. Wanka
Reply with quote  #1 
Hi,

for quite some time I am using stepped attenuators in ladder configuration as volume control. However this is based on readings and the opinion of others, I have not compared different networks.

Now I want to implement a remote control. I have been looking around and most of the time I see relay switched r-2r networks, rarely ladder type.

Is the ladder type really superior? Will the resistors in series to ground have any audible disadvantage?

Thank you in advance,

Tom
sailor
Reply with quote  #2 
I went from a stepped  resistor pot to a high quality alps motorized on one of my GG and could hear no difference. But you can't switch directly  from one to the other for comparison. I have ordered a ladder and in a couple of weeks I can give you my opinion on your question.
If there was any difference it would be in the quiet passages, in the quiet detail. Resistors produce noise and the lowest musical sound that you can here is the sound level above the noise level.
One question did come to mind, no matter if its 1 resistor or 18 resistors the amount of resistance is the same in a given pot, say 50K. IE: Ladder in a 50k pot say  One resistor say 45k for signal 5K resistor for ground. In a stepped say you would have 18 resistors for 45K for signal and 5 resistors for 5K to ground. They both have the same resistance just more parts. So is it the overall resistance or the number of parts of equal quality that's important? I would think that some one with a scope could answer this question.

T.M. Wanka
Reply with quote  #3 
Hi,

Quote:
Originally Posted by sailor
But you can't switch directly  from one to the other for comparison.


I hoped, someone had done this before. A few relays, a USB controller and a shell script that switches between the two volume control from a random number generator should allow a blindtest. I hoped I did not need to do that again.


Quote:
I have ordered a ladder and in a couple of weeks I can give you my opinion on your question.


That would be great. I had very bad experiences with Alps in my old Copland CTA 401. Low volumes had extreme and easily audible Channel differences. It started to crackle so I bought a new one and that was not too much better. I got something like that: http://cgi.ebay.at/200470870443 , ladder type, and it worked like a charm.

I also used a rotary switch with resistors soldered to it, like that: http://www.diyfidelity.com.au/product_info.php?cPath=26&products_id=32


So I know that works good. But I wanted a remote control, that is no problem, just tons of relays and lots of money. An r-2r has fewer parts, and is much cheaper. And I still can change the resistors.


Quote:
So is it the overall resistance or the number of parts of equal quality that's important? I would think that some one with a scope could answer this question.


The question is, if the noise of two resistors in series sums up, or the louder masks the other. Might depend on the frequency.

So please, report if there is a reason to stick with ladder,

thank you in advance,

Tom
CharlieM
Reply with quote  #4 

Rather than contradicting what is stated in "Audio Reality,"  I think the following can be made to fit:

From Sonic Craft:
 
"Reactive and resistive components alter audio signals (hopefully for the better), but they will never improve the quality of the input signal.   "A chain is only as strong as its weakest link".  In the audio chain, the error of a weak link is multiplicative more than not."
 
Also, from Michael Percy's catalog regarding attenuators:
 
*Ladder L-Pad: usually constructed as a pair of mono controls, this type control features a switchable series and shunt resistor for each position so the audio signal passes through only a single series element no matter how many dB of attenuation, input impedance is constant, output impedance varies, absolutely the best choice for interstage use in electronics where constant load is desired, excellent for passive preamps too, Vishays can be used for primary positions.

*Series Attenuator: for compact stereo attenuators, a string of resistors encircles the control, the sum of which equals the impedance of the control, the greater the degree of attenuation, the greater the number of resistors the signal must pass through, input impedance is constant so use interstage in electronics is a common application, good for passive preamps also and the sonics are surprisingly good if quality resistors are used, practical budget alternative to an L-Pad."

 
I only use mono ladders now at 100K (and I don't now use the 10K resistors that are called for between the attenuator(s) and the tubes in the GG).  I get up to change the side of an LP, so getting up to adjust the volume is usually no big deal for me.   However, there are times when if I could just hit a remote to adjust volume..... like when the little woman starts an inane dialog about........

Like everything in Audio, there are compromises.  One compromises the absolute clarity of a ladder for the ease of use of a remote controlled motorized series type.   There is a lot to be said for that. 

sailor
Reply with quote  #5 
OK, I hooked up my 2 GG preamps to the same amp and speakers one at a time.
They are not exactly alike. The one with the remote volume control also has a tube power supply and better caps. The other is almost stock except a series resistor volume. They don't sound exactly the same. But they are very close. I now have my new ladder resistor volume control but I have not installed it. I will put it into the one with the tube power supply and by pass the remote volume and compare it to the series resistor version. But I can't do it until next week. Results to follow.
You keep mentioning relays and other parts, are you speaking of a standard motorized volume plus required parts to run it. If so only the volume control is actually in the signal path.
Yes the total noise is the sum of the noise of everything in the signal path. But you should never hear this noise because it is so low. However as I mention before: The noise floor sets what the quietest music or detail you can hear. So the quieter you play your music the more you will notice the loss. MP players work by removing detail so. If your stereo sounds like an MP player you have a lot of noise.

By the way resistors have 2 types of noise. one is fixed the other varies with the temperature of the resistor and is usually the greater.  So the cooler the resistor the lower the noise. If you check your resistors out in a catalog it will be stated in PPM/ C 10, 25, 50, 100 or etc. Most metal film are 50ppm/c. Resistance causes the heat the more power and resistance you have on a resistor the more noise because it will heat up. Volume controls have very low amounts of volts and amps flowing threw them. This is why I think there may be little difference between 1 resistor and 10 if the total resistance is the same.

Walter
Reply with quote  #6 

Has anyone used a Lightspeed Attenuator with a Transcendent amp?  As publicized on DIYAUDIO.com, it is a form of series / shunt resistor using optocouplers as the resistive element.  I have used it to good effect as a passive attenuator.  I plan to build one into the GG.

don a.
Reply with quote  #7 
My GG pre has been modded with optocoupler volume/balance control.
The increased resolution over the "stock' carbon pot isn't small.
It's made a great pre-amp better.
don
PAUL
Reply with quote  #8 
I built my GG kit about three years ago and have enjoyed the clean, clear, fast sound very much.  I made many for the mods talked about here and elsewhere, (alps blackBeauty pot, better output caps, metal film resistors in signal path, bypassed electrolytics, etc). Sounds good to me and all that have heard it.
On a lark I bought the Warpspeed LDR.  By itself, just as a attenuator it blew away the GG. Not enough gain, but it certainly sounded wondeerful.
I have not put it in the GG yet.   Right now I am listening with the LDR in the Dodd buffer.  This sounds great up to a point.  It starts distorting when I turn the volume up to max.  Must be an impedance mismatch, so I am going to try a different tube.
I have not decided if I am going to try the LDR in the GG yet
Don a, what are you powering your lightspeed with? 

don a.
Reply with quote  #9 
Hi Paul:
I didn't do the mod myself.
There were 10 (Silonex) optocouplers used. 2 (matched) for the attenuation, and the remaining used in the bias loading resistor and the feedback circuit, each having it's own trim pot.
I can connect you with the person who did the mod if you wish--
don
T.M. Wanka
Reply with quote  #10 
Hi,

first, thank you all for your feedback, I will check the LDR.


Quote:
Originally Posted by sailor
You keep mentioning relays and other parts, are you speaking of a standard motorized volume plus required parts to run it. If so only the volume control is actually in the signal path.


I mentioned that twice.

First for blindtests (I cannot trust my ears). Depending on what device you want to test (if possible) you have relays on both devices and switch from one to the other and back. For example I had a tube output stage for my CD player, I disconnected the original output stage and connected both stages with relays so that only one was connected to the dac and preamp at the same time. Than - with a USB controller - I had my computer switch to one, wait 20 seconds, then switch again. Which of the two stages was connected was a result from a random number of /dev/random (a unix random number generator) and it was written to a file. So I was technically blinded, I did not know, which stage was connected at any time. I tried to find out, if it as the other or the same. After the test I compared my notes with the file to see if I could reliable identify differences (I could not, output was calibrated for both output stages so there should have been no volume difference for both stages).


Second is the volume control, there are ready DIY remote control kits like this one; http://www.diygene.com/store/Hi-End%20Volume%20Control%20DIY%20Kit%20LED%20Remote%20Control%20V-03

with variations, usually they use series or r-2r networks. You can also build one with 48 relays per channel for a true ladder option, that works exactly like a 2 x 24 position rotary switch. Lots of parts, lots of work, I would like to avoid that unless ladder type is clearly better.


However the LDR looks promising, there are cheap remote controlled potentiometers available no good reputation for audio use but perfectly for the LEDs.

Thank you

regards Tom
T.M. Wanka
Reply with quote  #11 
Hi,

Quote:
Originally Posted by T.M. Wanka
However the LDR looks promising, there are cheap remote controlled potentiometers available no good reputation for audio use but perfectly for the LEDs.


sorry, that should read "digital or on-chip potentiometers".

regards Tom
PAUL
Reply with quote  #12 
Tom;
one of the things that make the WarpSpeed work so well is that it uses a multiturn precision pot.
This is what allows for a smooth and gentle control.  I am at least into the 2nd turn when the music comes on and have great control of the level.
From the responses on the LDR forums its hard to fine a remote control that uses a multiturn.
I lot of complaints I have read is that most LDR are hard to control and do not completely shut off the signal. This is why I did not jump on board until the WarpSpeed came along.
WarpSpeed has solved this problem...The only thing I do not like is part of the circuitry is potted.
I hope to try to put the LDR into the GG this weekend

steve f
Reply with quote  #13 
My Grounded Grid was optocoupled modded, along with balance control, and parts upgraded.  The mods were performed by my buddy Erick (Buzz) of Greenvalve Audio.  The Grid by itself is a wonderful product. Erick's mods take it into 'price no object' sound quality.  Don A, who did your mods?

Steve
don a.
Reply with quote  #14 
Steve: Erick did mine as well!
Best
don
PAUL
Reply with quote  #15 
I find it fascinating that that rarely I have seen a response of someone on any of the forums admitting that after spending money or time on a mod that did not make their wigit sound so much better.
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