This was discussed in the 80+ page MyRef C build thread and never created so here it is. You are encouraged to describe how you attenuate Mauro's omni popular contribution to the world of audio here. I suppose we can start where Uriah left off. Is 10K the optimum Rt for the Europe mains only?
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If anyone here has used a higher value attenuator to control the MyRef, would you tell us about it?
I can't believe everyone with these amps is using a 10K attenuator, come on guys, tell us what differences it made, if any.
I just bought a Chinese 21 step DACT type 20K pot from Gigaworks for 10 bucks on Ebay and tried it with several amps including a MyRefC. I am very impressed with the sound quality. It sounds as good or better than the Twisted Pear preamp that I had been using.
PJN
PJN
PJN
Thanks, this is exactly the kind of information we need here. What improved specifically, bandwidth, tonal accuracy, soundstage or PRAT? Mauro had recommended a value half that in the MyRef so if anyone else can explain why, that would be another step forward.
Thanks, this is exactly the kind of information we need here. What improved specifically, bandwidth, tonal accuracy, soundstage or PRAT? Mauro had recommended a value half that in the MyRef so if anyone else can explain why, that would be another step forward.
I had been using two different preamps with my amps, a class A discrete pre with a LDR pot designer by Greg Ball (SKA amps), and an older Twisted Pear chip based preamp design(Kookaberra) which uses a chip to attenuate the volume. Both are nice but the class A outclasses the TP. I was looking for something cheap to use with a class D am and a Chipamp.com LM3886 amp projects that I had recently built. I didn't want to go to the expense of building another pre, and had never just tried a passive pre just using a pot. I was going to get one of the less expensive pots that use a bunch of descrete resistors since many have said that they are superior to standard pots like Alps and the like. Then I came across the really cheap DACT type pots that used SMD resistors so I took a shot and picked one up. I picked 20K because it had been recommended for the class D amp that I have been messing with. I compared the pot with the T.P. Kookabarra pre with a recC, a class D, and a LM3886 chip amp. In all cases the sound was very clear, blacker background, it seemed more direct than with the active pre, maybe the soundstage was deeper. The active pre sounds nice but in a direct A/B comparison it seems to smooth things out, it seems that some low level detail is getting lost. I think that I prefer it over the active pre, at least for now. For ten bucks I think that I'm going to buy a few more, you can't go wrong. I haven't compared it to the Class A pre. But I did compare the Class A to the Kookabarra using a RevC and it had a lower noise floor, allowed more detail to come through, blacker background, deeper image, and had a smoother sound. Don't get me wrong the Kookabarra does sound nice and cost a lot less to make than the class A, but the class A discrete pre made the Kookabarra sound slightly harsh in comparison. By the way the RevC sounds better than the modified Class D amp that I just put together, it's not in the same class. But I have to say that I am impressed with the chipamp.com LM3886 amp, the revC is better but the LM3886 isn't too far behind.
PJN
PJN
PJN
That is an awesomely descriptive post! We need more just like them to advise those building them.
udailey
I've read your post that states a lower pot value (ie: 5K) will sharpen the amp and raising the value will sweeten it. I like comparisons that fall into one of the four categories above so would you say that a higher value pot will make the MyRef more euphonic? Do you make this assertion based on experience with the same volume controls except for the value? What do you think is going on here to create this effect?
That is an awesomely descriptive post! We need more just like them to advise those building them.
udailey
I've read your post that states a lower pot value (ie: 5K) will sharpen the amp and raising the value will sweeten it. I like comparisons that fall into one of the four categories above so would you say that a higher value pot will make the MyRef more euphonic? Do you make this assertion based on experience with the same volume controls except for the value? What do you think is going on here to create this effect?
I'm not sure what the effect of line voltage might have on attenuator choice (just trafo input to same AC output).
To answer the original question, I have tried a Lightspeed clone and TX102 transformer volco. Both are very good, but I haven't tidied up the grounding in my MyRef chassis (safety earth is fitted, of course), and I have a slight hummmmm with the LS.
i'm using a tubed preamp that was about 3 times the cost of the myrefc. it's a silvaweld swc-1000bfa and the transparency of a passive aside, the liquidity of this unit is something i will never trade for. before this i was using the amp straight from modded lite dac 60 with asio foobar internal volume control that's suppose not impart any digital loss. and i think it's correct that myref doesn't need an active buffer because with that previous setup the dynamics and soundstage were just as big if not bigger... actually it's a hair bigger on both aspects. but my silvaweld has a 300b in the power supply and sounds like it's in the audio path!... and of course it gives me that hologram imaging that only tube can. i guess that's enough rant from me. 😉
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jonclancy
I wasn't thinking along the lines of mains power output as I was about the power variance and cleanliness. I was going on the assumption that there might have been a reason to choose a lower value pot other than the obvious one of source compatibility/matching. What would be the likely sonic result of using a 100K value attenuator instead of the 5-10K recommended by Mauro?
PreSapian
I may be a little confused by your post but I have interpreted it to say that when using your computer as the volume control feeding your modded lite dac 60, you thought the soundstage may have been larger but not as well defined as with your current silvaweld tube line stage. You also believe it may have had greater "dynamics" prior to putting in the silvaweld. Please narrow the meaning of dynamics so it falls within the four parameters above. Was it quieter or more immediate (better PRAT)?
I wasn't thinking along the lines of mains power output as I was about the power variance and cleanliness. I was going on the assumption that there might have been a reason to choose a lower value pot other than the obvious one of source compatibility/matching. What would be the likely sonic result of using a 100K value attenuator instead of the 5-10K recommended by Mauro?
PreSapian
I may be a little confused by your post but I have interpreted it to say that when using your computer as the volume control feeding your modded lite dac 60, you thought the soundstage may have been larger but not as well defined as with your current silvaweld tube line stage. You also believe it may have had greater "dynamics" prior to putting in the silvaweld. Please narrow the meaning of dynamics so it falls within the four parameters above. Was it quieter or more immediate (better PRAT)?
I think that you meant to say "stepped attenuator" instead of "pot", when referring to devices that switch between many different sets of discrete resistors. Below is a link that has simple explanations of the different topologies of stepped attenuators, and their advantages and disadvantages.
Stepped Attenuator Types
I am not sure why this thread needs to be specific to the myrefC. The amplifier can be treated like a normal power amplifier that has no volume control. You just put a preamplifier in front of it, in order to get a volume control. So this thread could just be a generic thread about preamps, which are sometimes in the same enclosure as the power amp and sometimes not.
One type of preamp is the passive type, made with either a potentiometer (a resistor with a variable center tap) or a stepped attenuator (which is made with resistors and switch(es)) but consisting of resistive voltage dividers, either way. Below are some (edited) general notes that I once wrote in another thread, about some of the things that should probably be considered, for audio attenuators.
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Generally, you'd want the output impedance to be very low and the input impedance to be high, but maybe not "too high".
The other pieces of equipment that are connected to your attenuator will have their own output impedance (connected to your input) and input impedance (connected to your output). Those input and output interconnections will each act like a resistive voltage divider (two more attenuators!).
So if your input impedance is too low, relative to their output impedance, the loss of signal level might be significant. Also, for low attenuator input impedances, their output might not be able to drive enough current at the voltages it's trying to produce.
Similarly, if your output impedance is too high, relative to their input impedance, signal level loss might be significant.
Another consideration is that there will also Always be capacitance and inductance facing both ends of the attenuator, in the interconnects or in components in the source or receiver or both in the interconnects and in actual components. And the attenuator's input and output impedances (mostly resistances) will Always interact with those inductances and capacitances, resulting in a particular "transfer function" for that portion of the signal path (i.e. output circuitry, cabling, attenuator, cabling, input circuitry).
A transfer function describes the frequency response (gain vs frequency and phase vs frequency) through a linear time-invariant system and completely describes and defines the output's transient and steady-state characteristics for every possible input.
i.e. The attenuator's input and output impedances can cause changes in the gain and phase angle of the signal, versus frequency, when ideally you would want either no change at all or a change that is exactly constant versus frequency.
The only example that comes to mind at this hour is when the output impedance is too high. In that case, it could interact with cable capacitance, and/or an existing RC low-pass filter in the other equipment's input circuitry, to either create a low-pass filter or lower the cutoff frequency of an existing low-pass filter, possibly affecting the sound.
So it seems like it would be "a really good idea" to keep the attenuator's input and output impedances as constant as possible, so that the frequency response of the system wouldn't change as the volume control is changed.
Yet another separate consideration is resistor noise. All resistances generate noise, all by themselves. The higher the resistance, the more noise is generated. So lower resistances are better (as are lower currents and voltages, as it turns out), except when it makes the input impedance too low.
Here is a very interesting article about the different types of resistors and resistor noise:
Resistor Types--Does It Matter? .
In low-noise circuits, I try not to use any resistors above 10k Ohms, and usually use much smaller ones if I have that luxury. But for an attenuator, sometimes you might want the input impedance to be more than that, for example.
Obviously, there are some trade-offs to consider. One might even want to have different impedances available for solid state and tube interconnects, for example.
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Some further thoughts:
Passive attenuators can be absolutely great when their input and output impedances work well with the devices they are connected between. And they are usually relatively easy to design and build. But I'm guessing that theoretically a lower-noise passive attenuator could be built, which would not be practical to use alone because of its very low input impedance, but which could be used with an active input buffer amplifier and an optional active output buffer which then would, as an active preamp, introduce less noise into the system than any passive preamp could.
A preamp with active buffer amplifiers would seem to also be the most robust solution in terms of compatibility with many different types of input and output devices, because it could have a very high constant input impedance and a very low constant output impedance.
Sorry to have blathered-on about all of that for so long.
Cheers,
Tom
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it's definitely quieter. blacker background and also a hair deeper bass. transients are about par. lateral sound stage was actually bigger with just the dac straight to the amp. depth wise it was rather flat, though- 'wall of sound' type of a deal.
but with the preamp, soundstage fills the room, enveloping me from all sides. shortcomings of the preamp, however, could be contributed to the poor quality interconnect that's introduced with it.
but still, i like the preamp in the chain much more :grin:
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Tom, I'm under the impression the LDR approach like Uriah uses in his offerings is a third type or method for attenuation. "The best buffer is no buffer at all".
Where does this type/approach fit into your view of the landscape?
All attenuators will work. But, the builder must ensure that the resistances before and after the attenuator are compatible with the reactances inherent in the connections/equipment.
The LED/LDR is simply a resistive attenuator that is controlled by light rather than mechanically.
The LED/LDR is no different in terms of ensuring that the equipment that it is connecting is compatible.
Uriah has made the LED/LDR control adjustable to change the attenuator impedances more easily. It is still a resistive attenuator.
The LED/LDR is simply a resistive attenuator that is controlled by light rather than mechanically.
The LED/LDR is no different in terms of ensuring that the equipment that it is connecting is compatible.
Uriah has made the LED/LDR control adjustable to change the attenuator impedances more easily. It is still a resistive attenuator.
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I have not run the MyRef yet, but my thoughts on attenuators are: If the input end is connected directly to the interconnect, the total input impedance the source sees is much flatter with lower attenuator resistor values. Therefore, the resistance should be as low as the source can driver or higher. Seems to make sense to start from the lower value and swap in higher values to see how the sound changes.
Thanks Andrew. My next question would be - what is the nature/advantage/disadvantage in using what I understand to be a preamp that actually produces gain/increase to the source as apposed to straight resistive attenuation. I may be misunderstanding that preamp function
Hi,
extra gain is required where the existing lower gain system has headroom to allow extra volume if required.
A buffer can be added to any source where that source is incapable of driving the cables and receiver.
A passive pre-amp, no buffer and no gain stage, acts as receiver for signal coming from the source/transmitter.
The same passive pre-amp acts as a transmitter/source when sending signals to the receiver and cables.
If any of the above transmitter-receiver combinations cannot operate correctly, then a buffer may correct that driving incompatibility. This addition of one or more buffers would convert that passive pre-amp to an active pre-amp.
If the system plays too quietly and has headroom for additional gain then an active pre-amp with fixed gain or variable gain can provide the extra volume required.
extra gain is required where the existing lower gain system has headroom to allow extra volume if required.
A buffer can be added to any source where that source is incapable of driving the cables and receiver.
A passive pre-amp, no buffer and no gain stage, acts as receiver for signal coming from the source/transmitter.
The same passive pre-amp acts as a transmitter/source when sending signals to the receiver and cables.
If any of the above transmitter-receiver combinations cannot operate correctly, then a buffer may correct that driving incompatibility. This addition of one or more buffers would convert that passive pre-amp to an active pre-amp.
If the system plays too quietly and has headroom for additional gain then an active pre-amp with fixed gain or variable gain can provide the extra volume required.
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Clear and simple - just what I needed. This is exactly my situation in that I am very happy with the Ref-C and the Lighter Note, but my current speakers - The Sunflowers - sound great but are on the inefficient side. I'm hoping my bi-amp project will serve to correct the power deficit without any degradation form adding an active crossover (dbx-234) to the signal path. BPA-150 for woofer and MyRef-C for mids and tweeters. In part I'm taking my lead from this article.
BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
If the results are not as I hope, I'll be looking in other directions.
Thanks Again
Active speakers have a reputation for sounding louder than passive speakers.
Test the set up without extra gain stages and see if you are happy.
If more gain is needed from some sources then add in a variable gain stage either to all the lower level sources or to a universal pre-amp.
I would suggest that a switched gain stage that is unity gain stable and has options for 2times and 4times gain would cover most needs. i.e. switchable to +0dB, +6dB +12dB.
Test the set up without extra gain stages and see if you are happy.
If more gain is needed from some sources then add in a variable gain stage either to all the lower level sources or to a universal pre-amp.
I would suggest that a switched gain stage that is unity gain stable and has options for 2times and 4times gain would cover most needs. i.e. switchable to +0dB, +6dB +12dB.
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