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Old 30th March 2013, 09:37 PM   #31
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by Cassiel View Post
Yeah, one filament gets all the food while the other starves. I wonder what's wrong with this socket, dirt inside the pin I presume. Value of R2 is 130K.



I can understand your distrust, graphs get me dizzy though - you won't see them coming from me. I am merely stating that my preamp's bass is kinda soft in a direct comparison against the Bryston preamp.

What I am going to do is experiment a lot. I have done this with tube output stages and now it's the turn to do it with preamps.
Yes, you will be doing just that; a lot of experimentation. It will be like throwing darts with a blindfold on.

Reading a graph is easier than reading numbers. You don't need to even have numbers on the axis to get an idea where your frequency response is relative to any one point on the graph.

This plot uses the free software HolmImpulse. It is one of my speakers, but you can do the same thing with a line stage as if it was a loopback test.

Al you need is:

1. A computer
2. Sound card with a line input and line out
3. Some cables
4. HolmIpulse software

You do one sweep with the preamp bypassed and use that as a calibration run.

The sweep takes about a second or two to get meaningful information. You can then do the same with any other line stage to get a reference, but in either case the response should be ruler flat. If it is not, at least any changes you make you can see if you are making progress and you won't need a blindfold.

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Old 31st March 2013, 12:50 AM   #32
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I am still waiting to see quantitative measurements.
Fine Loren -easy enough to hook up.

I have a 'protoboard' here; give me a day or 2 - 3 (other commitments) and I will give you gain, frequency response, input impedance, output impedance. My distortion analyzer is on the blink right now but that does not seem to be in dispute. I have all the component values and there is a 12AU7 lying around here somewhere.

I will take the fed power amplifier input impedance as a low 22K. If anybody knows of a lower impedance commercial amplifier, kindly state. (My own notion is that they are mostly 100K.)
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PS: OK, Loren, just missed your post while typing/doing other things, and possibly misunderstood. You perhaps want quantative measurements specifically from Cassiel's amplifier, not in general to prove the case/circuit.

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Old 31st March 2013, 01:58 AM   #33
Cassiel is offline Cassiel  Libya
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Well, since Loren insists....

I'm almost sure I did something wrong, maybe Loren can tell me.
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Last edited by Cassiel; 31st March 2013 at 02:11 AM.
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Old 31st March 2013, 02:42 AM   #34
Cassiel is offline Cassiel  Libya
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lol I don't understand this program. I'm hooked.
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Old 31st March 2013, 08:53 AM   #35
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Originally Posted by Cassiel View Post
Do you know any tricks to improve bass response? Compared to a Bryston and a Mark Levinson's it lacks a little in that department.

Apparently the engineers cannot fix the bass in this thread But then again, where have they heard a ML?

Several issues with your preamp.

First the 6SN7 simply cannot produce the bass that a good solid state circuit can. Not even if you connect 20 in parallel. Maybe it's due to microphonics. Who knows? In fact very few tubes are capable of near solid state - like bass. I only know the 6H30 but maybe there are others.

Second. You need a seriously overdone power supply - plenty microfarads in a CLC arrangements + solid state regulator.

Third. Despite my general dislike for the sound of cathode followers, a 6H30 follower does extremely impressive bass. With a CCS it may even become tolerable in the upper ranges.

And most importantly, all choices are about compromise. It is tremendously hard to preserve the midrange and fix the bass. If it were easy, all high end amplifiers would use exclusively tubes

Last edited by analog_sa; 31st March 2013 at 08:55 AM.
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Old 31st March 2013, 10:43 AM   #36
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Originally Posted by Cassiel View Post
Well, since Loren insists....

I'm almost sure I did something wrong, maybe Loren can tell me.
Yes that doesn't look right at all I think probably your levels are too low for starters (your impulse response should be a hell of a lot cleaner than that!!

What did a loopback of the sound card look like?

Certainly if the FR curve presented is indicative of the FR of your preamp then I'm not surprised you think it sounds bass shy rising response from about 500Hz up around 5db by 10Khz, and starts rolling off at around 80Hz down by 5 db by 20Hz....

edit: I can't find my loopback cable, but here is a quick and dirty measurement of my Sound Card preamp that I use for buffering stuff I'm testing. Not sure what is going on above 20K (I'm pretty sure it didn't used to do that) but it gives you an idea as to what you should be seeing. Note you should go into options and change to raw response rather than gated as well, when you are doing line level measurements

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Old 31st March 2013, 03:29 PM   #37
Cassiel is offline Cassiel  Libya
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Originally Posted by analog_sa View Post

Several issues with your preamp.

First the 6SN7 simply cannot produce the bass that a good solid state circuit can. Not even if you connect 20 in parallel. Maybe it's due to microphonics. Who knows? In fact very few tubes are capable of near solid state - like bass. I only know the 6H30 but maybe there are others.

Second. You need a seriously overdone power supply - plenty microfarads in a CLC arrangements + solid state regulator.

Third. Despite my general dislike for the sound of cathode followers, a 6H30 follower does extremely impressive bass. With a CCS it may even become tolerable in the upper ranges.

And most importantly, all choices are about compromise. It is tremendously hard to preserve the midrange and fix the bass. If it were easy, all high end amplifiers would use exclusively tubes
Good to read this, it saves me a lot of time. So they can't compete with SS in the bass department, can they? It's OK, I still prefer tubes.


Quote:
I think probably your levels are too low for starters
I think I have sorted out my amplitude problems. I'm still wary of false readings.
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Old 31st March 2013, 03:44 PM   #38
Loren42 is offline Loren42  United States
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Originally Posted by analog_sa View Post
Apparently the engineers cannot fix the bass in this thread But then again, where have they heard a ML?
...First the 6SN7 simply cannot produce the bass that a good solid state circuit can. Not even if you connect 20 in parallel. Maybe it's due to microphonics. Who knows? In fact very few tubes are capable of near solid state - like bass. I only know the 6H30 but maybe there are others...
I am not sure where you get your information, but that is untrue for a line stage amp. The difference in frequency response between vacuum tubes and solid state will be indistinguishable.
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Old 31st March 2013, 06:51 PM   #39
DF96 is offline DF96  England
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Originally Posted by analog_sa
Apparently the engineers cannot fix the bass in this thread
I thought the engineers were still waiting for a genuine bass problem to be demonstrated. Demonstration has to precede diagnosis, which then must precede solution.

Last edited by DF96; 31st March 2013 at 06:52 PM. Reason: typo
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Old 31st March 2013, 10:11 PM   #40
Loren42 is offline Loren42  United States
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I thought the engineers were still waiting for a genuine bass problem to be demonstrated. Demonstration has to precede diagnosis, which then must precede solution.
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