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The new DIY preamp designed during pandemic
- Thread starter pma
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- Thread Starter
- #22
1) yes I am, I have no objections and it has become my main system preamplifier.
2) I agree that from pure audio signal point of view that takes into account 20Hz - 20kHz range only the high slew rate is unnecessary. However, the real world is more complicated, we have HF unwanted signal components and short spikes at the output of digital signal sources that spread the spectrum into tens of MHz, though not very high level. We have RFI induced voltages, we have cell phone and wifi networks. All and all, fast high slew rate opamps simply do better under this conditions.
I asked the second question because of personal experience. I recently bought a Topping Pre90 (sent back in the meanwhile), which is a beauty when it comes to measurements. Alas, although there were plenty of details, transparency and so on, I wasn't pleased with the sound for 3 reasons :
1. tonal balance (too bright to my taste and when comparing to 2 other pres). EQ couldn't fix it and a hypothesis was that it might be of dynamic origin
2. Sensation of "no flesh to the bones" which was probably due to the former
3. Flat, "fused" sound, without the 'relief' some good stuff can bring you.
The global result was paradoxical, since you hear things never heard before (and after too for that matter) which could be correlated with SINAD performance.
Tonal balance and flat character reminded me of japanese amps of old, before Transient Intermodulation Distorsion was described by Ottala. Culprit then was insufficient slew rate of the first stage with large gain and negative feedback to get low distorsion figures. Considering the higher input signal levels than before (2 or 4 V) and high open loop gain of opamps, I was wondering if some kind of TIM could be involved in preamps, hence my question. (After all, even if there is no "integration" curve of saturation in the first stage, with 2xVcc = 30V, 10 is about all the gain it takes to make an opamp's first stage clipping with 2V input before NFB applies)
Furthermore, large amounts of NFB reduce distorsion, but produce higher order distorsion products which resemble the "real world" you're speaking about.
I have no clue to what could cause the 'relief', which makes possible focusing on one particular track. I guess pro stuff used during record making process allows that, because I can only imagine that one of mastering purposes is to obtain this result.
BTW, I don't know if TIM is part of standard preamp devices measurements ...
1. tonal balance (too bright to my taste and when comparing to 2 other pres). EQ couldn't fix it and a hypothesis was that it might be of dynamic origin
2. Sensation of "no flesh to the bones" which was probably due to the former
3. Flat, "fused" sound, without the 'relief' some good stuff can bring you.
The global result was paradoxical, since you hear things never heard before (and after too for that matter) which could be correlated with SINAD performance.
Tonal balance and flat character reminded me of japanese amps of old, before Transient Intermodulation Distorsion was described by Ottala. Culprit then was insufficient slew rate of the first stage with large gain and negative feedback to get low distorsion figures. Considering the higher input signal levels than before (2 or 4 V) and high open loop gain of opamps, I was wondering if some kind of TIM could be involved in preamps, hence my question. (After all, even if there is no "integration" curve of saturation in the first stage, with 2xVcc = 30V, 10 is about all the gain it takes to make an opamp's first stage clipping with 2V input before NFB applies)
Furthermore, large amounts of NFB reduce distorsion, but produce higher order distorsion products which resemble the "real world" you're speaking about.
I have no clue to what could cause the 'relief', which makes possible focusing on one particular track. I guess pro stuff used during record making process allows that, because I can only imagine that one of mastering purposes is to obtain this result.
BTW, I don't know if TIM is part of standard preamp devices measurements ...
- Thread Starter
- #24
Hi, yeah, sometimes there are no simple answers. I do not know the Topping Pre90 circuit design (maybe we could ask @JohnYang1997 ) however I think that you would probably get a kind of answer that it is all in your imagination. As I do not know the Pre90 design I am not able to comment on it.
Re TIM, yes some of us still measure TIM at least at the design phase. You may do it in analog manner and then get very wide spectral content due to fast rise time that you may control, or get a usual DIM test signal as provided in Arta e.g., however then it is limited to Fs/2 and corresponding limited rise time and it is something like DIM48 or so.
These are interesting points however I am not sure there is a fertile soil at ASR for it, I would rather guess there is not. Not much tolerance often.
Re TIM, yes some of us still measure TIM at least at the design phase. You may do it in analog manner and then get very wide spectral content due to fast rise time that you may control, or get a usual DIM test signal as provided in Arta e.g., however then it is limited to Fs/2 and corresponding limited rise time and it is something like DIM48 or so.
These are interesting points however I am not sure there is a fertile soil at ASR for it, I would rather guess there is not. Not much tolerance often.
Speaking of imagination and ASR tolerance:
If we consider Bruno Putzeys as a trustworthy person, he recently said "when audiophiles report a particular listening experience, that experience is real. Trust that. Just don’t trust the explanation they proffer." in a Sound&Vision interview.
I'm also an amateur musician and I'm able to play on the piano whatever song I hear for the first time, write down a multi part song on music paper without tonal reference or tune a violin by ear with just the help of my tuning fork, and sometimes without.
So, while I consider myself as an objectivist (my job is IT engineer), I hear what I hear, and I'm sure of that. And before you object, by personal experience, I'm very aware of placebo effect, but don't ask why.
I own a pair of Hypex monoblocks because they sound clearly "right", but they were on a short list based on their objective measurements and build quality. My strategy is to make a shortlist of what is properly done and measures well, then listen and pick by ear.
So, I want it all, details, transparency AND entertaining sound, because believe me it's on the recording, even 16/44.
Pre90 just didn't pass listening test.
As a musician, maybe amateur, I had to "play" a little with all studio stuff (semi pro DAW and sound processing plug ins on par) for my own compositions and believe me, mastering engineers have all the tools they need to make a track sound anything but boring or flat.
Therefore, I just try to find a scientific explanation to what I hear, be it good or bad.
For the time being, nobody is able to measure the interpretation of a sheet of music. But make no mistake, a good musician will always be recognized from an average one. Same for sound gear.
It should just make all of us honest and admit there are some factors we are not aware of, hence don't measure yet.
Ignoring this is just not scientific IMO. My hypothesis is that some dynamic phenomena are involved. There should be no offense to anybody, but shall anybody pick the gauntlet up ?
It is very disappointing if somebody questions impressions on the behalf of measurements which might not be exhaustive. Ignoring a problem is the best way to never solve it.
At that stage, I know for sure after listening to the Pre90, that the amount of information on a CD is astonishing, and I credit SINAD for this. Transparency and details checked. But OTOH some flaws (to my ears) are begging to be fixed. I'd like to listen once in my lifetime, a fully professional mastering stuff to know what the true "reference" sound of a recording is. And before you ask, I do research about the stuff they use before amp and speakers
- Thread Starter
- #27
BAL1 input to BAL output +6dB, BAL2 input to BAL output +12.62dB. That's how it is set. But just changing one resistor on PCB you can get up to +60dB gain from the balanced input, still reasonable distortion of 0.04%.
dtaylo1066
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Fantastic job! Did you make a PCB or is it point to point wired underneath?
- Thread Starter
- #29
I never use point to point wiring or breadboards
. The PCB (double-sided with groundplane) is always a part of the circuit parameters, especially regarding suppression of hum components and EMI pick-up.
- Thread Starter
- #31
PicoScope is small and thus it is ideal for traveling, as we usually have our notebooks with us. I even had it with me in Japan when I was working on a plasma power supply regulation.
It has limitations (8-bit resolution, no input filters in spectrum mode), however if you know what you are doing it is a good tool. There are more types in their product range, mine is one of the cheapest.
https://www.picotech.com/products/oscilloscope
What voltage did you drive the plasma , I got upto 200KV @ 1.2Mhz 150KW load, evil thing.
- Thread Starter
- #33
I was working on the development of unique Water Stabilized Plasma system (WSP), we have several installations in Japan. It has arc voltage of 250Vdc and operating current is 200 - 550A. The arc power is up to 150kW. Plasma velocity at the exit nozzle is up to 7km/s. Used mostly for spraying of ceramic powders. (Oops I corrected the power from the typo)
I love to have seen that, cool. Thanks.
did some work on a gas CO2 Laser and that was fun, for a company called Laser Energy in Somerset, the guy who own it was Terry Cryer, a great guy.
did some work on a gas CO2 Laser and that was fun, for a company called Laser Energy in Somerset, the guy who own it was Terry Cryer, a great guy.
Here is small one I made to keep slugs of garden.
- Thread Starter
- #38
Below is the link to the RightMark Audio Analyzer report that I measured yesterday
syn08
Senior Member
- Thread Starter
- #40
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