Yes Sir. It is an audio circuit and the same considerations apply.
I am constantly amazed with the trashy solutions audio manufacturers with high end pretensions come up with. So, no, the fact that Bryston are using it is no excuse. Do you actually believe Bryston sounds any good? I know they have a great warranty, but..
Voltage regulators sound very much consistent with the underlying technology - low feedback regulators sound like low feedback amplifiers, whether that is good or bad to you.
I believe the interaction between regulators and amplifiying circuits to be complex and require a lot of experimenting to get right. You may end up with a lot of good ideas if you do a search including regulators and Jonathan Carr.
Dear Mr. Analog,
Thank you very much for your kind and extremely valuable reply.
Actually I have a Bryston .4b preamp that has a power supply +/- 24 V based on fixed regulators.
And it does not satisfy me completely (dynamics).
I understand that I have still a long way to go.
I will do the suggested search.
Jonathan Carr is another one of my myths.
Thank you very much indeed.
Kind regards,
beppe61
Thank you very much for your kind and extremely valuable reply.
Actually I have a Bryston .4b preamp that has a power supply +/- 24 V based on fixed regulators.
And it does not satisfy me completely (dynamics).
I understand that I have still a long way to go.
I will do the suggested search.
Jonathan Carr is another one of my myths.
Thank you very much indeed.
Kind regards,
beppe61
PB2 said:
Dear Pete,
I am very plaesed to hear from you.
I must confess that I built just a one-channel prototype based on the schematic found with poin-to-point wiring with nice results.
With regards to the null test I would be very grateful if you could give me some links to web pages concerning the topic.
If I understand well, you think that my present Bryston .4b preamp is not all that bad.
The problem is that, as I said before, I find it a little musically uninvolging. I had the occasion to listen to a tube preamp in front of a transistor power amp and the outcome was better.
I think that the preamp plays an important role in an audio chain.
A lot of audio people prefer tube preamp.
As always I am quite disoriented.
And as always any your suggestion would be very valuable and much appreciated.
Kind regards,
beppe61
ITALY
beppe61 said:
Hi Beppe good to hear from you also,
Good to hear that your building, I think it's good to just get started and build a few designs, have you ever thought of building different designs with an A/B switch to compare them? Many people claim to hear significant differences but when controlled tests are made there's often no difference.
Your .4B is probably not bad at all but perhaps you could A/B compare it to the one you built.
There's the possibility of very small differences in top notch preamp designs probably due to very small frequency response differences across wide bandwidths, could even be gain mismatches, or interface loading differences. All of these should be very small and nearly inaudible.
I'll try to give you a short simple summary of null testing. Let's say that a power amp has a voltage gain of 10, then ideally the output is exactly 10 times the input voltage. We can use a voltage divider to divide the voltage at the output back down by a factor of 10 and then subtract the input from this output. The difference represents all possible errors and forms of distortion. One problem is that frequency response and phase errors will cause the difference not to null, but these are linear rather than non-linear errors, so compensation is sometimes needed. I don't like the name used here by this author "sound impairment monitor" see his "External SIM" section, note that he references Baxandall: http://sound.westhost.com/sim.htm
There are also threads on this board that discuss the subject and the Hafler XL280 manual which is online, I'll try to find the link.
Pete B.
PB2 said:
Dear Pete,
You are very scientific on this null tests.
If I understand correctly that null test would be the best method to assess the quality of an amplification device, isn't it?
However in reviews of audio equipments I see distortion spectra more often.
They use a tone of fixed frequency (100 or 200 Hz) at a level 0dB and then search for distortion products (small peaks around the test tone).
Strange is that amps that produce a lot of distortion are judged as better sounding (like tube amps).
And on this affirmation, there are magazine that don't present any measurements at all (like The Absolute Sound for instance).
They report only on listening tests.
This is most confusing, especially for the uneducated mass of hi-fi hobbists like me.
Another factor that bother me mostly is the following.
Let us take a line preamp device.
It has to do only a slight voltage gain (usually from 3 to 5 times) and a current gain (adaptation of impedance). Please excuse my rude English.
And you can find preamps that do this task with one, two up to 20 and more active devices.
If measurements are everything why we don't see preamp all based on the Analog Devices AD797 op-amp, that has unbeatable distortion performances and a very limited cost?
I think that the best way to judge a audio rig on a whole could be the test disks.
For instance I have one from Sheffield with a track called "WALKAROUND" to evaluate how well a system can reproduce a sonic image. This is a very challenging task.
And in my present system the effect is not so great indeed.
There is no or little depth.
A friend of mine say that the component that affect more the spatial reproduction abilities are speakers. I must tell you that I am not so sure.
My opinion is the following. Please correct me if I am wrong here.
As the more directive frequencies are the high frequencies, it could be the ability of the system to reproduce correctly this part of the audio spectrum that influence this characteristic.
Usually I see frequency response measured at 0dB.
Never I see frequency response at let say -70, -80dB.
It could be that some system obscure the high frequencies of low level and these are the signals that give the sensation of space.
What do you think?
I am sure that a system that reproduce correctly that WALKAROUND track is, as Doug Sax says, a "really damn good system !".
I think that I wrote too much and too bad for now.
Anyway thank you very much for your kind trying to educate me on a scientific basis.
Kind regards,
beppe61
Hi Beppe61
I am beginning to appreciate your sense of humour.
Recently a very kind gentleman sent me the circuit of a cheap ($1000) Audio Refinement (YBA) 6-channel pre. Amazingly, all the channels follow identical, tube-borrowed topology and the entire pre is powered by non-regulated but heavily filtered PS. It also seems to sound decent. I do not in any way claim this to be a great topology but find it interesting that contemporary commercial designs like this exist.
I am beginning to appreciate your sense of humour.
Recently a very kind gentleman sent me the circuit of a cheap ($1000) Audio Refinement (YBA) 6-channel pre. Amazingly, all the channels follow identical, tube-borrowed topology and the entire pre is powered by non-regulated but heavily filtered PS. It also seems to sound decent. I do not in any way claim this to be a great topology but find it interesting that contemporary commercial designs like this exist.
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analog_sa said:
Dear Analog_sa,
Thank you very much for your kind words.
I swear I tried to learn some basic electronics on the books.
But I failed miserably.
Thank you immensely for your schema.
This is exactly what I am looking for. I would like to express my humble considerations hereafter. Please correct me if I am wrong.
1) At present it doesn't seem possible to assess the sound quality of a circuit only on the basis of a set of measurements.
2) The mere fact that a topology is old doesn't mean that is also bad. Just look at tube amps and preamps.
3) I think simple is beautiful. Very few components used in their best working conditions to achieve the maximum intrinsic linearity.
In a line preamp (my present nightmare), for instance, two active opportunely selected devices can be enough. One for the voltage gain and one for buffering.
4) A lot of highly regarded contemporary designers have changed to topologies with a minimum of feedback or with no-feedback at all.
5) Yes. In a buffer the feedback is 100%. But they are needed to get current and low impedance. So buffers are convenient and pretty much inevitable.
6) The quality of power supply is enourmous. For instance a well executed batteries based power supply can elevate a very good preamp to a stratospheric level.
7) If the damages to the signal is done at low level, then you can only amplify them. I must say that in my experience I found a lot easier to find nice power amps then nice preamps, especially in the solid state field.
8) A lot of people are worried of coupling caps. I am much more worried about quality of caps. Film and electrolytic.
Now, if only that very kind gentleman could disclose to us the kind of fets used and the value of voltage supply.
May be I am too demanding here.
Anyway those are the topologies I am looking for.
Simple and nice.
I am looking forward to hearing from you and everyone else who wants to enter in the discussion.
Thank you very much again for your valuable suggestions.
Kind regards,
beppe61
Hello
I presume that the high value of C26 do reduce the slew-rate of the circuit ?
But is C26 are there for stability purpose, how about reduce it to 27pf ?
Btw, here is the complete Radford ZD22 preamp circuit.
Thank you
Bye
Gaetan
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