John Curl's Blowtorch preamplifier part II - Page 3410 - diyAudio
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Old 3rd February 2013, 12:22 AM   #34091
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I don't need any stinkin' measurements to verify what my ears hear. What test equipment do you use today, kgrlee? Any?
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Old 3rd February 2013, 12:27 AM   #34092
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Thanks for reminding me, kg, I had a THD distortion measurement running when I went to lunch, and I forgot about it. It would have run all night.
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Old 3rd February 2013, 12:57 AM   #34093
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Gpapag, what do you think of this enclosure's group delay:
http://www.moonaudio.fr/Photos%20tai...up%20delay.jpg

Quote:
Originally Posted by elektroj View Post
Those pots in SSL consoles are nothing, compared to number of Blackmer gain cells that the signal must go thru.
I hated SSL since they copied the Neve flying faders in a make believe way. While Neve had invented them to get rid of those awful VCAs, SSL had copied the motor for the look, but kept the VCAs.
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Last edited by Esperado; 3rd February 2013 at 01:03 AM.
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Old 3rd February 2013, 01:30 AM   #34094
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Quote:
Originally Posted by elektroj View Post
Those pots in SSL consoles are nothing, compared to number of Blackmer gain cells that the signal must go thru.
Maybe one more, 'rather' than a pot, would be better.
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Old 3rd February 2013, 03:01 AM   #34095
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It appears that many people do not know how audio designers, like me, do their job.
Let me give a small, sample of today's effort.
Hi Demian, I hope you pick up on this message. I normally would contact you by phone or email, but let's give them a sample of what we do for a living (at least some of the time).
I received both your and Bascom King's emails on the servo/bias problem.
I can't reply effectively without a little more investigation of the circuit.
I have prototyped the second stage (the problem one) and have it running, (more or less) on my test bench. I need a balanced drive to do it right, so I am trying to use your ST1710 (with diff drive) and make the measurements with the HP339, etc.
However, I am having grounding and sync problems, so I might just have to go back to the ST1710 entirely for this test.
In order to parallel your efforts, I got Tim and Hal (my techs) to mod up the servos externally on a solderless breadboard, in order to allow for quick changes, etc.
Unfortunately, it is Tim's first effort with a solderless breadboard, and now I have about $100 in tech time with no useful result at the moment. I have to decide whether I want to go forward with what I have or redo it.
In any case, I am looking in parallel with the two of you to get this problem resolved.
My personal opinion is that we must compare notes on exact values in the bias and the gain set resistors, because as there are 4 of us (with Peter included) in different locations looking at the same circuit, I suspect that we are not necessarily using the same values.
We are going to have to, once again, generate a schematic that all of us can sign off on, just to minimize the confusion.
For the record, I think that the servo return/bias resistors should be about 200 ohms. This worked for the JC-2, why not here? If 100 ohms works OK, then we will go with it.
Let's get together on the schematic. I have DesignWorks Professional 5 up now on the PC, but the schematic entry is pretty dated, and will have to be updated. IF I had the exact values that seem to work, or what resistive values we have changed to, then I could update the schematic, but I am going to need verification from each of you as to what resistive values you have in your particular prototype. Let's get together on this.
As far as the RIAA 'deviation' I trust your judgement, and perhaps now that I have the HP, I can independently verify it, once again, if it becomes necessary.
Regards, John Curl

This a sample of our internal communications and the problems we have to solve on a weekly basis. Any questions?
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Old 3rd February 2013, 03:29 AM   #34096
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> Any questions?

What's the supposed end product of your collaboration ?
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Old 3rd February 2013, 03:50 AM   #34097
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Old 3rd February 2013, 04:05 AM   #34098
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So, once again, you you have chosen the old technology (motorized pot) instead of trying something innovative or to improve a new and promising known one ?
How are-you not bored to walk always on the same side of the same road ?
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Old 3rd February 2013, 04:42 AM   #34099
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I just use the best available. If solid state were better, I would be glad to use it. I am not really interested in redesigning someone else's electronic volume control. I would prefer it ready made, or at least, ready designed. I have other considerations that I have to pay attention to, and I do not get an added salary for re-inventing something that already exists.
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Old 3rd February 2013, 04:56 AM   #34100
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Thanks for the link, elektroj. I did not know that site. Perfect reading!
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