About freq response test procedure on preamps
Hello, i have noticed that in the lab tests of preamps usually the frequency response is measured for an output of 1V into a standard load (like 100kohm).
And usually the frequency response is extremely linear.
I have a maybe silly question.
Will this freq response be so linear also for much lower outputs, like 10-20 mV ?
I ask this because i think that the linearity at low levels is very important to give a preamp a good "transparency".
I think that at the lowest levels the noise, for instance, could overlap the audio signal.
I mean it could be much more difficult for an equipment to be linear at low levels
Thanks in advance for any kind advice.
Regards, gino
Hello, i have noticed that in the lab tests of preamps usually the frequency response is measured for an output of 1V into a standard load (like 100kohm).
And usually the frequency response is extremely linear.
I have a maybe silly question.
Will this freq response be so linear also for much lower outputs, like 10-20 mV ?
I ask this because i think that the linearity at low levels is very important to give a preamp a good "transparency".
I think that at the lowest levels the noise, for instance, could overlap the audio signal.
I mean it could be much more difficult for an equipment to be linear at low levels
Thanks in advance for any kind advice.
Regards, gino
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Actually at lower levels it should be the same or in some cases even better.
On the distortion tests, if they are showing noise plus distortion, you will see what looks like the distortion dropping until it starts to clip and rises rapidly. The noise is really what is showing up at the low level.
On the distortion tests, if they are showing noise plus distortion, you will see what looks like the distortion dropping until it starts to clip and rises rapidly. The noise is really what is showing up at the low level.
Hi, the fr should be measured over it's intended load resistance range. Not many these days have to see a 100k Amp etc input ! A good pre out should be able to drive, say 2k comfortably.
Low mV should be just as linear as 1V. Low mV @ the Amp input will be very quiet out of the speakers.
Low mV should be just as linear as 1V. Low mV @ the Amp input will be very quiet out of the speakers.
The OP may be confusing linearity with frequency response flatness. Two different concepts.
FR may be different at high level vs normal level (at least for a power amp), but it is very unlikely to be different between normal level and low level (especially for a preamp).
FR may be different at high level vs normal level (at least for a power amp), but it is very unlikely to be different between normal level and low level (especially for a preamp).
different frequency response vs level is a nonlinear behavior - will be associated with distortion from the nonlinearity
Slew Rate distortion is often speced by the highest full amplitude frequency sine that can be reproduced below some distortion threshold
Slew Rate distortion is often speced by the highest full amplitude frequency sine that can be reproduced below some distortion threshold
I should correct my post. If the noise plus distortion curve is a straight line starting at the low level that can be due to just the noise. If there is a bit of a curve at the start or some bounce around what should be a straight line that can be a level induced distortion, such as crossover distortion.
Distortion at the zero crossings are often perceived as annoying.
Distortion at the zero crossings are often perceived as annoying.
High gain small signal transistors are better than power devices.
Class A is easier in a preamp
Lots more feedback may be available.
Preamps are driving closer to a linear load so much easier.
Class A is easier in a preamp
Lots more feedback may be available.
Preamps are driving closer to a linear load so much easier.
Hi and thank you a lot for the helpful reply
I am quite clear in my mind with the things to do, but need time
First ... buy a scope. It is fundamental.
Then to spot a nice schema for a line stage. I have some ideas for this.
For instance lately i listened to excellent recordings made with analog tape recorders, then transferred to digital.
My point is that those recorders must have highly trasparent circuits.
This a good point to start for nice schematics, that surely can sound excellent (looking at their service manuals i mean).
Then i will have to address parts selection, layout and PS design and construction
Then add the best attenuator i can allow ... and it will be done.
It is a very long process ... but first the scope.
I must "see" the noise ... the distortion to be able to fine tune the elements above.
Problems ... it is not easy to know which are the tape recorders used and if they were stock or modified.
This is tricky. But the quality of those recordings is really breathtaking.
So real that are scaring. The sound as they say is "palpable" 😱
Perfect for my taste.
Thanks and regards, gino
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Hello and thank you very much for the suggestion.
Do you think that simple circuits have a "potential" for better sound ?
This is my true feeling lately, but i have no technical basis to explain this.
Thanks a lot and kind regards, gino
My own personal opinion is that such circuits can consistently deliver a good subjective result. This gets debated over and over and over... that the amplifier should be as a transparent and "perfect" technically as possible. Thing is, all those with such amps often don't seem happy with them when used for their primary purpose... music reproduction.
You will only know by trying such designs 🙂
You will only know by trying such designs 🙂
Thanks a lot for the very helpful advice.
I have the same feeling ... for instance i am sure that if we had a look at the circuits of the best analog open reel tape recorders we would see quite basic topologies, nothing out of this worlds.
Of course well implemented and realized, but always quite textbook circuits.
I have to find a place selling service manuals ... maybe an Ampex ... or a Nagra, Studer ...
Thanks a lot again.
Kindest regards, gino
I have the same feeling ... for instance i am sure that if we had a look at the circuits of the best analog open reel tape recorders we would see quite basic topologies, nothing out of this worlds.
Of course well implemented and realized, but always quite textbook circuits.
I have to find a place selling service manuals ... maybe an Ampex ... or a Nagra, Studer ...
Thanks a lot again.
Kindest regards, gino
I have the opposite feeling. Of course, it depends on what you mean by textbook circuits. Most textbook circuits are actually quite poor, but they are useful stepping stones for newbies.ginetto61 said:
My guess is that in the very best analogue equipment you will see excellent, innovative circuits using clever application of good engineering principles but nothing esoteric or wacky - for wacky you need to go into 'high-end' audio.
Thanks a lot for the link !
To be honest i asked a recording label to know which tape recorder they were using
They did not tell me ... and i can understand.
Sometimes they say but they add that they have modded it, so ...
Even only the line driver for the outputs must be excellent if the result is so astonishing, i believe. Then a decent attenuator and stop ... line preamp.
Thanks again and kind regards, gino
P.S. i much prefer solid state
Hi and i am sorry but i was not able to know which tape recorder they were using ... but the result is sincerely astonishing ...
so the recorder must be very very good indeed with transparent electronics inside
http://www.amazon.com/Blue-Coast-Collection-E-S-E-Sessions/dp/B000VI5BZA
An externally hosted image should be here but it was not working when we last tested it.
If i only knew i would immediately search for the service manual of the recorder. I am sure that some line driving circuit could be spotted.
Kind regards, gino
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You're welcome 🙂
Its always interesting to look at different circuit topologies from different manufacturers.
Its always interesting to look at different circuit topologies from different manufacturers.
There are some vary famous preamp circuits from Erno Bolbery in the old Audio Amateur. Of course, I am not sure they actually sound any better than a modern op-amp. Might look up the schematics of the old Haflers. (all on their web.) Lots of preamp/line cards used FETs you can't get any more. I think Pass has a few preamps out there and of course, one of the all time benchmarks is the JC-1 from John Curl. All of these will be different, so it should be educational.
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