On the use of a preamp to improve sound quality with VTA70

corndog71 wrote:It's not about making it louder.  There's a different component to what the preamp's active stage does to the signal.  It fleshes it out.  It exposes the dynamics of the music.  I know there's a better explanation for it but it eludes me.  My observations were consistent with various active vs passive preamps.  There's a trade off either way.  Ultimately, active preamps offer more control as well additional gain at the line level.  They're helpful too if you have multiple amps to drive.  For instance in my rig I'm not just running the signal to my M125s, but also a pair of subwoofer amplifiers.

I agree, and I want to experience these immeasurable qualities a preamp may bring to the listening experience. That is why I bought a couple to evaluate.

rjpjnk wrote:Peter, Let's just agree to disagree on this one and move on.

I think we do agree about this .... You probably mean the other peter (W)

Peter W. wrote:
Transients - not RMS.

A snare-drum rim-shot will typically be around 125 dB in free air at the drummer's ears. Down about 4 dB at 20 feet. Attack to decay (below 80 dB) is less than one (1) second.

If, using reasonably efficient speakers, 1 watt = 96 dB, 106 dB will require 10 watts, 116 dB will require 100 watts and 125 dB will require ~900 watts. A more reasonable 120 dB will need ~300 watts (all numbers approximate and rounded to lower whole number). Most well-designed power-amps are entirely able to make such transients, if allowed (driven to) do so. Remember, transient capacity is a function of peak-power capacity over time. Not RMS power continuously.

And that is the point-of-departure. A source that will not drive your amp to reproduce said transient will not provide the full dynamic range of the original source. Full Stop.

I agree, at least based on my one experience with my phono system.  When I switched my phono step up transformer from the 30 turns setting to the 15 turn setting, I would hear a bright clinking/clanking sound on some loud piano high notes -- sounded like hitting a glass jar with a butter knife.  Other odd sounds at random times.  When I switched back to 30 turns that phenomenon went away.  In both situations I still had plenty of volume knob turning available.  (I believe the problem occurred at any volume, not just when it was cranked up -- I'll have to try again and see if I get the same result at low volume.)

What I visualize is that my phono preamp is clipping during those loud transients.  It can't produce more than x volts because the signal it receives is y milivolts and there's not enough gain to get to z volts, the transient peak.  With the 15 times voltage with 30 turns on the transformer there is enough gain to produce the transient.

These transients can be very short duration such that you might not particularly notice or they may occur at random times like I did and not hear them as being associated with a particular instrument or note.

There may be other transient issues going on with my system, but not aware of because I'm used to them.  At some point I'll need to try an active line preamp...

dave

peterh wrote:

rjpjnk wrote:Peter, Let's just agree to disagree on this one and move on.

I think we do agree about this .... You probably mean the other peter (W)

Correct. I added a W just now.

solderblob wrote:

I agree, at least based on my one experience with my phono system.  When I switched my phono step up transformer from the 30 turns setting to the 15 turn setting, I would hear a bright clinking/clanking sound on some loud piano high notes -- sounded like hitting a glass jar with a butter knife.  Other odd sounds at random times.  When I switched back to 30 turns that phenomenon went away.  In both situations I still had plenty of volume knob turning available.  (I believe the problem occurred at any volume, not just when it was cranked up -- I'll have to try again and see if I get the same result at low volume.)

What I visualize is that my phono preamp is clipping during those loud transients.  It can't produce more than x volts because the signal it receives is y milivolts and there's not enough gain to get to z volts, the transient peak.  With the 15 times voltage with 30 turns on the transformer there is enough gain to produce the transient.

These transients can be very short duration such that you might not particularly notice or they may occur at random times like I did and not hear them as being associated with a particular instrument or note.

There may be other transient issues going on with my system, but not aware of because I'm used to them.  At some point I'll need to try an active line preamp...

dave

I'm not familiar with phono preamps and the use of step-up transformers, but his is interesting Dave. If I remember correctly you said the transformer is after the phono preamp, and before entering your poweramp, which has only a passive attenuator for volume. correct?

Is the 30/15 turns setting on the primary or secondary? How many turns on the opposite side?

rjpjnk wrote:

solderblob wrote:

I agree, at least based on my one experience with my phono system.  When I switched my phono step up transformer from the 30 turns setting to the 15 turn setting, I would hear a bright clinking/clanking sound on some loud piano high notes -- sounded like hitting a glass jar with a butter knife.  Other odd sounds at random times.  When I switched back to 30 turns that phenomenon went away.  In both situations I still had plenty of volume knob turning available.  (I believe the problem occurred at any volume, not just when it was cranked up -- I'll have to try again and see if I get the same result at low volume.)

What I visualize is that my phono preamp is clipping during those loud transients.  It can't produce more than x volts because the signal it receives is y milivolts and there's not enough gain to get to z volts, the transient peak.  With the 15 times voltage with 30 turns on the transformer there is enough gain to produce the transient.

These transients can be very short duration such that you might not particularly notice or they may occur at random times like I did and not hear them as being associated with a particular instrument or note.

There may be other transient issues going on with my system, but not aware of because I'm used to them.  At some point I'll need to try an active line preamp...

dave

I'm not familiar with phono preamps and the use of step-up transformers, but his is interesting Dave. If I remember correctly you said the transformer is after the phono preamp, and before entering your poweramp, which has only a passive attenuator for volume. correct?

Is the 30/15 turns setting on the primary or secondary? How many turns on the opposite side?

The setup is cartridge, step up transformer, phono preamp, passive attenuator, then power amp.  The transformer secondary is 15 turns ratio or selectable 30 turns ratio as follows from Ned Clayton, builder of the SUT:

"They have a 1:15 winding ratio, and are spec'ed for 200 to 45,000 ohms impedance ratio. These also do have a 50 ohm center tap, which is selectable via the box's "hi/lo" gain switch. The "hi" position doubles the step up ratio from 15 to 30 times."

Don't know how many turns...



dave

Ahh, ok. Got it. So the numbers 15 and 30 are turn ratios, not number of turns. Now I follow.

So this transformer essentially provides the option of doubling the signal voltage entering the phono preamp. You say it sounds better at the higher level (30:1) setting. If clipping of the preamp were the issue it would be worse at the 30:1 setting than at the 15:1 setting. So I doubt it is clipping you are hearing on the low setting. Not sure what could be causing the clinking sound you mention on sharp hits. Truly a mystery. Maybe it's just a matter of keeping the SNR higher with the hotter signal into the phono preamp?

rjpjnk wrote:Ahh, ok. Got it. So the numbers 15 and 30 are turn ratios, not number of turns. Now I follow.

So this transformer essentially provides the option of doubling the signal voltage entering the phono preamp. You say it sounds better at the higher level (30:1) setting. If clipping of the preamp were the issue it would be worse at the 30:1 setting than at the 15:1 setting. So I doubt it is clipping you are hearing on the low setting. Not sure what could be causing the clinking sound you mention on sharp hits. Truly a mystery. Maybe it's just a matter of keeping the SNR higher with the hotter signal into the phono preamp?

I think you're right and my idea that the phono preamp is clipping might be bogus.  I tried to duplicate the malfunction last night and couldn't.  But I just checked and I see that had the Mk3s in pentode mode.  So later I will try it in triode mode.  If the problem occurs then, that pretty much confirms it's not the preamp clipping....

UPDATE #2

I have now had a few hours of listening, measuring, and calibrating time, and try as I might, I really cannot hear any difference between the direct path and the PAS 3X path. I also measure no difference using REW and a calibrated mic for frequency response, THD, and impulse response for what that's worth.

I conducted the tests by installing an A/B switch allowing me to conveniently switch between a direct path from my iPhone to the VTA70 and an indirect path going from iPhone to PAS then to VTA70. I first set all the PAS tone controls flat (In the PAS 3X this causes an actual electrical bypass of the tone circuits), Loudness and Scratch filter Off, and balance center. I then took some measurements of pink noise to calibrate the volume of the PAS path to exactly match the direct path.

Then I just sat in the sweet spot and played a variety of music and flipped a hand held A/B switch after blindly turning it around in my hands so I had no idea which path I was listening to at any time. At first I could not tell which was which, and neither one sounded better, but then after a few minutes I noticed the channel balance was slightly off in the PAS. To deal with this I adjusted the balance and volume on the PAS until I measured identical SPL response to pink noice in each channel and continued with the testing.

So I'm not hearing the magic here guys, but I'll tell you what. I LOVE this PAS! Not for improving the sound, but it is really fun. It has a very nice volume control and I actually enjoy the balance and stereo blend function (Allows for easily listening to just one channel with both speakers or mixing to mono for experiments). And it has excellent tone controls! Can't believe so many people bypass them. They are smooth and powerful, and seem to boost just at the right places. Also, the frequency response plots I captured show that when the controls are centered the spectrum looks identical to the direct path, so they really do get out of the circuit. I don't feel I really need them, but it is nice to know they are available if I want. Or if one of my sons comes home and wants to hear bass that shakes the floor.

Also, the PAS makes the overall system a *lot* louder on full volume. The position of it's volume control that causes the output to match the direct path is about 2 O'clock, so anything past this is louder than I could achieve with a direct path. Of course there is potential for overdrive in this region. But you know, spikes and all that transient stuff goes here...

The PAS does add a little noise. A tiny bit of hum, and some rushing hiss. I have to put my ear up to the speaker to hear it, but it's there.

So... I guess some will say it must be a great preamp if I can't tell it's in the circuit.

In any event. I am not saying that preamps can't improve the sound or add special dynamics, just that I can't hear them with the equipment I've got. It is absolutely possible that my equipment (iPhone, PAS 3x, VTA70, Klipsch Heresy III) is just not good enough to show the differences. Though I have heard it said the these speakers are pretty revealing.

The good news is that the PAS actually does not seem to be degrading the sound other than the slight hiss and hum mentioned above. But no new and improved dynamics have appeared in the music. That was nothing but wishful thinking I'm afraid.

Thanks for sharing your observations.

Observing the nature (of things) and not blindly rely on what other say is the way newton and galilei
enhanced our knowledge of the world. I like the idea of an A/B switch around the amp!

If you can enjoy the music equally with or without a preamp I would suggest saving the expense of the extra stage and cabling.

I agree. From a purely HiFi point of view, I should not use the preamp or its associated cables. But for now I am enjoying having some knobs to turn for a change.

rjpjnk wrote:I agree. From a purely HiFi point of view, I should not use the preamp or its associated cables. But for now I am enjoying having some knobs to turn for a change. :)

You also have :
- an input selector
- tone controls, might be needed for some recordings
- tape out , may be used to drive a computer line input ( but you might need a buffer )
- balance control and a unique blend control
- a volume control , you don't need to have your power amp close

For what it's worth, here's what Paul McGowan thinks:

https://www.youtube.com/watch?v=Dh27E7YKN9s

Thanks! That was a great video. He seems pretty believable. I especially liked that he used to ascribe to the purely technical viewpoint that there is no preamp like *NO* preamp, but then later changed his mind. I want to believe this is not related to the fact he now sells preamps.

He seems to understand that technically speaking, the preamp can only degrade the sound quality from any measurable point of view, i.e., SNR, dynamic range, frequency response, time/phase delay, etc. Yet, still the end result comes out sounding better somehow.

He makes the interesting point that the preamp has to surpass a certain quality level in order to achieve this. I assume he means it must of such high quality that whatever sonic enhancement it brings outweighs the physically unavoidable degradation of having another element in the signal path.

He does specifically refer to the benefit of such a very good preamp as "enhancement" and specifically not preservation. I love the point about the music suddenly being all over the room and producing a deep and immersive experience, full of life. I want that. By comparison, when he amplified the raw digital signal directly with the poweramp it still sounded good, but missing some pizzazz. Which begs the question of why we place so much effort into preserving the fidelity of the original signal I suppose.

If a very good preamp offers tasteful enhancement I think that is a definite value added.

I wonder if he would consider the VTA SP12/SP14 products to be of good enough quality to achieve this? I am glad to hear he agrees that tubes are the way to go.

rjpjnk wrote:Thanks! That was a great video. He seems pretty believable. I especially liked that he used to ascribe to the purely technical viewpoint that there is no preamp like *NO* preamp, but then later changed his mind. I want to believe this is not related to the fact he now sells preamps.

He seems to understand that technically speaking, the preamp can only degrade the sound quality from any measurable point of view, i.e., SNR, dynamic range, frequency response, time/phase delay, etc. Yet, still the end result comes out sounding better somehow.

He makes the interesting point that the preamp has to surpass a certain quality level in order to achieve this. I assume he means it must of such high quality that whatever sonic enhancement it brings outweighs the physically unavoidable degradation of having another element in the signal path.

He does specifically refer to the benefit of such a very good preamp as "enhancement" and specifically not preservation. I love the point about the music suddenly being all over the room and producing a deep and immersive experience, full of life. I want that. By comparison, when he amplified the raw digital signal directly with the poweramp it still sounded good, but missing some pizzazz. Which begs the question of why we place so much effort into preserving the fidelity of the original signal I suppose.

If a very good preamp offers tasteful enhancement I think that is a definite value added.

I wonder if he would consider the VTA SP12/SP14 products to be of good enough quality to achieve this? I am glad to hear he agrees that tubes are the way to go.

https://www.theatlantic.com/science/archive/2016/08/occams-razor/495332/

A good read.
Beware of false premises, as well.

I recall PS Audio as a major proponent of "passive preamps" a few decades back. PS Audio was Paul McGowan's (and Stan Warren's) old (and Paul's new, again) company. FYI: Agreement on this topic has not been achieved among the celebrities of our hobby... Apparently the original PS Audio didn't survive the arguments. I believe Paul sells active preamps these days. I do not know what Stan is up to--post Superphon and Supermods. I believe Stan was the principal passive preamp protagonist at PS Audio (pardon the alliteration).

j beede wrote:I recall PS Audio as a major proponent of "passive preamps" a few decades back. PS Audio was Paul McGowan's (and Stan Warren's) old (and Paul's new, again) company. FYI: Agreement on this topic has not been achieved among the celebrities of our hobby... Apparently the original PS Audio didn't survive the arguments. I believe Paul sells active preamps these days. I do not know what Stan is up to--post Superphon and Supermods. I believe Stan was the principal passive preamp protagonist at PS Audio (pardon the alliteration).

The posted video seems to agree with this. In it, the author says he used to be a major proponent of "No Preamp", which I believe has to be understood to mean passive, since we must allow for some way to turn the volume down. Apparently it wasn't until he heard his friend's active tube preamp that he changed his mind. Stories like this are what inspired me to do some investigation myself, and that's what led to this thread. The investigation is ongoing.

Aside: There must be an interesting story behind how a pair of resistors ever came to be know as a "passive preamp". For that matter, even an active preamp spends most of its time reducing the input signal in the case of line level inputs. It seems a bit of a misnomer to call either of these "amps". It might be more correct to call them passive attenuators and active attenuators, for that is what they do, make signals smaller.

Transducers (microphones, guitar pickups, phono cartridges) need preamps. Line level signals need attenuation, unless you like full volume all the time.

Regarding Paul McGowan's passive preamp, I guess it might not have been a big seller if it was a box with nothing in it.

Actually, there are some really expensive stepped attenuators in some of those passive boxes. I cannot imagine how they justify their cost.

I have an idea. I may build a even higher quality passive preamp that is just two extremely accurate fixed resistors and some very expensive solder. It would always have a fixed voltage reduction ratio, so you would have to buy a different preamp for each volume level you like to listen too and swap them whenever you want to change the volume. But they would be the ultimate in sonic purity and do away with contact noise.

Or has this already been done?

rjpjnk wrote:Actually, there are some really expensive stepped attenuators in some of those passive boxes. I cannot imagine how they justify their cost.

I have an idea. I may build a even higher quality passive preamp that is just two extremely accurate fixed resistors and some very expensive solder
Or has this already been done?

How about a few resistors an some alligator clips...

One very important consideration in this age of primarily digital sources is the fact that signal attenuation in the digital domain (cd players with volume controls,computers, dac/preamps, etc)is generally achieved by reducing bits, and therefore resolution.

If using digital sources, they should be run at full output and attenuated by an analog preamp or at least stepped attenuator in the analog domain.

Lots of discussion about this in the PS Audio forum, and elsewhere.

Thanks for bringing this up. I've heard this too, and being the rebel I am I am starting to doubt its veracity as well.

I need to look into this more. Could it be a leftover concern from early digital days?

Sure, it is possible to reduce the volume purely in the digital domain. For example, if you just shift all the numbers one bit right (divide by 2) before sending them to the DAC this will result in half the analog output level. But this is also throwing away one bit of information forever, and this means a loss of resolution. This is a very bad way to control volume. As you correctly point out, it is far better to supply the full digital range to the DAC and then attenuate the resulting analog signal.

So I'm totally on board with this, but here's the question. Are any modern manufacturers of digital audio devices currently implementing such an obviously terrible method of volume control?

Do you know of any device that does this?

I can say with certainty that the iPhone 5s/6s (with analog output jack) does not. SNR testing clearly shows the volume attenuates cleanly to the very last click. If the attenuation were done in the digital domain it would lose 6dB of SNR per bit removed.

If you're interested in high fidelity, you would not want to use the internal dac OR the analog output stage of an i-device.

Rather, you would want to wirelessly stream (at 16 bit resolution) to an airport express, mac mini or imac, then, using its minitoslink output on to a high quality external dac then to an analog preamp like the SP14.  Which provides the desired analog attenuation.

Here's the dac I use for superb sonics.

http://www.ankaudiokits.com/Non-Oversampling-Valve-Rectified-Tube-DAC.html