Yes the can, so you may not be imagining things.
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Sowter attenuater transformer volume control. From their website:
"The transformer action of these attenuators assures the loading circuit sees a low driving impedance regardless of switch position. This ensures the maximum bandwidth potential and minimum distortion of the circuit can be realized at all gain settings."
We've done a lot of mods on Dynaco equipment over the years in fact that is how we got started back in the 70s. The volume control on the older PAS-3 was always a problem. Eventually we had some custom switches made up so we could install a stepped control in the unit.
The impedance of the control is important. The stock control on the original PAS-3 was 250K. If you install a larger value it will mess with the 12AX7 at the input of the circuit as the volume control and the input capacitance of the tube interact (Miller Effect). However if you go below 100k don't expect any bass out of the phono section!
IOW you do have to choose the value carefully. BTW it will not matter how nice the control is if these parameters are not observed- the same electrical rules apply to the best controls as the do to the cheapest.
I believe that the volume potentiometer (pot) is the single most important component that can have detrmental effect on sound quality, this is why they all sound different to each other.
All volume controls have pin point touch contact that are purposely made light in pressure as not to wear out the resistive track or contact points, all the music signal has to try to pass through these contacts.
These contacts/track are also mostly made dissimilar elements/metals which can have a "diode effect" which tries to rectify the ac music signal, this is a form of distortion.
In order what I believe is the best type of volume controls.
1: Lightspeed (ldr based) Attenuator or TVC (transformer based) = no contacts in the siganl path.
2: Mercury Wetted Relays = with gold or silver contacts in a mercury bath, they also resist tranishing /arcing, also are becoming illegal.
3: Good quality relays = with gold or silver contacts
4: Switched resistor = double leaf, each side of the wiper contact
5: Switched resistor = single leaf on one side of the wiper
6: Potentiometer (Pot) = conductive plastic track
7: Potentiometer (Pot) = carbon track
Atmashere, you raise an important point. I was thinking of replacing the stepped resistor attenuator (Goldpoint, 100kOhm) with an inductive volume control in my amp that uses a 12AX7 followed by 12AT7. The stepped attneuator sounds great. I want to see the sound can be improved by using an inductive (autoformer) volume control. However, the inductive volume control impedance is highly dependent on frequency. At 1 kHz it is about 1 MOhm (yes, megaOhm) and at 20 Hz about 20 kOhm. There is a 3.3 kOhm input resistor that goes to the grid of the 12AX7. Can inductive volume control significantly affect the frequency response in this case?
I know we aren't supposed to be off topic here but is the Pope Catholic?? IOW, yes.
Georgelofi, we've done a lot of experiments with controls and I find that I can't agree with your regarding relays. Universally they were inferior to a good quality rotary stepped switch. However, switches are quite variable so I can see good relays being better than some switches. But if you have higher quality switches the relays don't stand a chance.
From what I understand of light-activated devices, one would have to be quite careful in doing a substitution in the case of this preamp! The light activated devices I have seen can cover a pretty wide range of resistances- the higher values, even if a better device, will still introduce coloration that an inexpensive control of the right value wont have due to the Miller Effect issue. IOW things are getting dicy if the control is able to exceed 250K.
With experiments with volume controls go back as far as the 1970's, this is what has bought about the ldr Lightspeed Attenuator.
Almost all rotary switches have a stiff disc wiper made out of a different material to the springier metal that the leaf/leaves are made out of.The two contact points in relays are at least made out of the same material.
It is comon knowledge that two different metals that are a touch contact with current/voltage passing through them will creat a "diode effect" electrolosis or glavaic.
Herve Delartz of DartZeel backs this up as well, this is why he does not use contact volume controls either in his $25k NHB-18NS preamp but uses ldr's which have no contact.
Quote interview with Herve:
Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light. However, until all the patents are in place, I would prefer not to specify the details.
Yes you are right with these TVC's as well, they do also have inductances, have you ever seen what happens to 20khz square wave through them, they can either ring their brains out or be severly bandwidth limited. What goes in doesn't come out unscathed in nearly all ones I have tested on the bench.
10K square wave on every tap (unloaded) of one particular inductive volume control.
Same test on another popular inductive volume control.
So yes I have seen the high frequency performance at 10K of a number of inductive volume controls. My take is you cannot lump them all together.
Understanding the nature of square waves, moving to 20Khz in frequency would tell you the same about one and less about the other. Moving to 1Khz would still tell you the same story about far and far more about the other.
I'm sure the signal is not as well preserved as resistor attenuator or LDR units. But music isn't composed of square waves and I don't make a of habit of listening to 20 kHz square waves. I have heard your LDR unit and like it a lot, but you don't sell a kit that can be installed in an amp..have you considered it?
No but it's what all and I mean all audio desigers use, it's a good indication of if what your looking/measuring at is as close to a "piece of wire" nothing added or taken away, and all designers use these non musical wave forms to see what's going on.
No I don't do kits but here I show all how to build one themselves.
Almost all rotary switches have a stiff disc wiper made out of a different material to the springier metal that the leaf/leaves are made out of.
'Almost all' *but not* all. I can think of several off the top of my head that use similar metals and some of those are not even 'high end' parts.
This is for a control going in a PAS-3 or similar circuit. If the values are not observed there will be a price paid in the form of bandwidth.
Never had a problem with miller effect and inductive volume controls. Mainly because with an autoformer, worst case is at full volume when the output impedance of your source drives the miller directly. As you attenuate the autoformer transforms the excess voltage into current so things just get better. I have seen situations where an autoformer actually extends the bandwidth of a device over a resistive based attenuator because of its ability to increase drive as you attenuate to better deal with things like miller and cable capacitance.
I'm with dave on this one.
However if you are just replacing the stock part, you can find replacements that will sound better for under $30.00.
Is this an older preamp? If so, you may have bigger fish to fry as far as the sound goes. All the older ones need new filter caps in order to work right.
OTOH if you are really trying to push the performance, it is possible without going completely nuts and many of the updates/mods are more important than the volume control. It does not make a lot of sense to install an expensive volume control unless you are also planning or already have these updates!
Hi Dave, thanks for clarifying my confusion. I have your autoformer preamp(Bent Audio TapX), which competes with some of the best preamps out there (both active and passive), as long as you keep the interconnects short and impedances appropriately matched. However, I think an autoformer will work even better installed directly in the input of the amp, as I have found with resistor stepped attenuator.
He was talking about how the volume control has changed the sound. And I say given the same value they all sound different to each other. I believe because of materials used and contact point pressure, given the same value they are the single most worst component that can change the sound in equipment. They are fundamentally flawed. It's just like having loose/dirty rca plugs/sockets if you clean them with contact cleaner (plug and socket) you will hear a massive difference to your sound, and these have ten/hundred times the contact area than the miniscule area a pot has.
Hi George, what isn't flawed in audio? From what I understand, even the LDR preamps have issue with impedance matching, drift, and tolerance (ie, difficult to make a balanced preamp using LDRs). LDR preamps do sound excellent, may even surpass the best resistor or transformer/autoformer based preamp, but I don't think they're for everyone, just as any other passive preamp. But I do appreciate the fact that you popularized this technology for us to enjoy.
He asked "Am i imagining things?" I say no he's not and give him the reasons that's all.
And I'm not saying the Lightspeed Attenuator is the answer, even it doesn't quite sound as good as going direct. In fact I've said many times if you want to hear the truth of what the source is giving, then listen to your source directly pluged into the poweramp with a very quite cd. Then listen at the same level with a pre (active or passive) in the way at the same level, then go with the one that sounds closest to the direct sound. Because this is the one that is least imprinting (colouration/distortion) it's own signature onto the music signal compared to the direct sound, and therefore is the closest to the most transparent sounding eg: (a piece of wire with or without gain)
I don't think anyone on this thread has denied that the volume control makes a difference. However there are engineering principles in play and they are such that if ignored, the result could be that a $4.00 volume control from Radio Shack can sound better than the best light-activated volume control system available.
There are plenty of other situations where that is likely not the case. IOW this cannot be taken out of context- the parameters of the surrounding circuits cannot be ignored. So if a light activated device is to be used, it would have to be one that is designed for the circuit.
Here is a good article for those who are interested to see how much their active preamp or passive volume control, is adding colourations/distortions to their sound.
It's called the "Ravel's Bolero Test" and you need a CD or LP of it or like it to conduct the test.
http://www.high-endaudio.com/RC-Linestages.html click on Bolero Test, scroll down to "CD Player?" if you have a cd player
It is basically doing what I suggest you do 2 posts back
Atmasphere, I was trying to understand your post and if I read you correctly, are you saying that the circuit has to be engineered to accept and maximize sound quality for any particular type of volume pot?
There are some audio engineers that think a good standard volume pot will outperform many of the other more expensive designs. Croft is one of them.
Phd, you are correct. Start with the right value. Only then do you switch things up, if you will pardon the expression :), with better quality.
Dracule1, both. First, the site commits a web 1.0 error, that of endless rant/scrolling. Second, many of the conclusions don't seem to arise in a scientific manner, instead are based on deductions without understanding of the math behind them that is at play in each instance.
I think some folks who are familiar with the Manley Steelhead, would say that it's a respectable piece.
As good as it is,it's not as clean as the Lightspeed Attenuator that I am using now.
Very easy to hear the loss of detail when running my Esoteric cd/sacd player into the Steelheads line input and running the variable(volume control)outs to my power amps(Acoustat servo tube OTL).
Using Antony and Johnstons the Crying Light, for example, his multi tracked voice and background instruments are no longer buried when I listen with the Lightspeed in the chain.Details which I never knew were missing are now easily heard.Sounds cliched, but it's what I am enjoying now.
I also decided to try the Manley phono stage in fixed mode to the Lightspeed, and again the sound was better.
Had I never tried the Lightspeed I would still consider the sound of my sources to be quite respectable.I am not denegrating the sound of the Steelhead ,used as a linestage, but others have stated that it sounds it's best when used as just a phono stage.So is it's volume control the culprit?I'm now thinking yes.
My take on the Lightspeed is that it imposes less of a sonic smudge on the music as some other volume controls do.
I've had some fine preamps in the past and really enjoyed my time with the MP3,S-30 from Atmasphere running a stacked pair of Quad 57's.
Unfortunately,the MP3 is true balanced, so I wouldn't have been able to properly impliment a Lightspeed and bypass it's volume control.I will say that the MP3 made balanced cable comparisons a thing of the past.
But in the single ended world of the rest of the pre amps that I have owned,I have to say that I'm hearing more detail now using the Lightspeed than I did with any of the other pre amps,all of which cost ten times or more than the Lightspeed and many with some very good resistor ladder volume controls.
Does the volume control effect sound quality?
My answer is yes.
Hi Lacee, I tried to look at a pic of the Acoustat servo tube OTL amps, and it looks to have passive volume controls on the input to them, if so, if you or someone can remove them from the circuit (not just bypassed) then the Lightspeed Attenuator will jump up another order of SQ magnitude for you again.
Thanks for the advice George, but this and several other mods have been done to the Acoustat servo amps,all the better to showcase how good the Lightspeed is.
The Acoustats I have are not stock,they were modded by DTS audio,I power the servo amps with Shunyata Annaconda power cords which are plugged into a Furutech GTX Gold receptacle on a dedicated 20 amp line.
The IEC on the amps were replaced with top of the line Furutechs,and the connectors(3 per amp)are also upgraded rhodium from Furutech, and the RCA on the Acoustats are the upgraded Furutech rhodiums.Interconnects are Nordost Heimdal.I use AMR gold fuses in the amps with the WA fuse chips and transformer chips.
The speed and clarity of this system was great when I was using the Steelhead as a pre/phono.
Using the Lightspeed and bypassing the Manly for cd and using only it's fixed outputs for phono has improved the clarity even more.
Yes, I've lost the mono control on the Steelhead by running fixed output, and I have to switch the IC from the Esoteric to the Steelhead for vinyl, but the sound improvement is well worth the effort.
And for me, that's why I do the things I do.
Did I hear "gear head" stream from the peanut gallery?
Been called worse, but if you really are into the music,you owe it to the music to give it the gear it is deserving of.
What good are 10,000 lp's if you've only heard 25% of the music recorded on them ?