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-   -   Doug Self Preamp from Linear Audio #5 (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a.html)

Carl_Huff 8th October 2015 04:51 PM

Quote:

Originally Posted by rsavas (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post4476712.html#post4476712)
... But for this tone control all you really need is a Lm317/337 combo esp if you are going to use cap multipliers as extra filters. Take a look at the Elektor 2012 pre-amp PS, it does the job.

Hello rsavas,

It is nice to see you here. Your points are valid. My only real knock on the Elektor power supply is that it does not fit in a 1U chassis. The Elektor design is robust but bog standard and not unlike the power supplies from the Elliott Sound pages as suggested previously by George Brooke. I am confident that you are right and that either of those proven designs would work.

My request was for someone to offer a creative alternative that breaks away from all of that power supply boredom! It is always good to study and learn something new. MadInventor's contribution was to that end.

kouiky 8th October 2015 05:17 PM

Linear Technology's LT3042 can be arranged to drive a D44VH1NPN for very low noise and a high CMRR and PSRR. That would be my chosen path.

I might be mistaken, but does your board lack guard rings? I notice the components are spaced quite far.

Carl_Huff 8th October 2015 05:27 PM

Quote:

Originally Posted by kouiky (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post4477009.html#post4477009)
Linear Technology's LT3042 can be arranged to drive a D44VH1NPN for very low noise and a high CMRR and PSRR. That would be my chosen path.

I might be mistaken, but does your board lack guard rings? I notice the components are spaced quite far.

I just looked at the LT302 app note. Looks to be an interesting part!

Nope no guard rings. I for one have never seen guard rings used at audio frequencies.

kouiky 8th October 2015 05:34 PM

Those Linear Tech regulators have impressive noise performance, and they were only $4 each, last I checked.

I've found that some opamp datasheets recommend guard rings, and Marantz was one off the top of my head that did exercise such trace practice. But, if your measured performance is good and stable, then no worries.

Did you happen to capture any bandwidth and curve results? I'm interested in some of the metrics and behaviors of this preamp. PS: Good job taking the initiative here.

Carl_Huff 8th October 2015 05:58 PM

Quote:

Originally Posted by kouiky (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post4477034.html#post4477034)
... Did you happen to capture any bandwidth and curve results? I'm interested in some of the metrics and behaviors of this preamp ...

I have confirmed that the tone controls do in fact behave as as described in the article using a spectrum analyzer. I tried to measure noise but I quickly got frustrated as the noise performance of the circuit is too close to the noise threshold of my aging AP Portable One test set.

Jan Didden has generously made the article available online at: Linear Audio | your tech audio resource

I invite you to download it. It's a great tutorial. Doug put a lot of time and effort into writing it.

MadInventor 8th October 2015 10:04 PM

Quote:

Originally Posted by rsavas (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post4476712.html#post4476712)
Curious why one would use a lm317 as a voltage reference, for a series pass regulator? I would suggest to use a TL431 or similar, if you need something that is variable.

This PS was NOT designed for Carl's project, if it was, it would be quite different. It was designed for this:
Quote:

It can be configured for about 3-4vDC to maybe 100vDC and up to maybe 4A.
I use 431 family (LMV431, LM4041, THLV431) a lot, but not to do 55 to 70 vDC. Even more resolution would be lost using a 431 (voltage divider down below 36v) when a 317/337 can literally do those voltages. Then there are different stability issues with 431. They almost give TO-92 LM317s away. The trimmer variability is a very small percentage of output, parts do age. I would design a PS for Carl's project using large front end caps, and let the regulator do a little less ripple error correcting. Would leave the output capacitance low ESR, small value < 1000uf total, including preamp capacitance. Having the case at 1.75 in. and 1A current, will cause its own issues, with power dissipation.

Mad

prasi 9th October 2015 09:26 AM

Hello Carl,
Have you decided on the price ?
Also if I want to build a seperate enclosure for your pre-amp tone control , any recommendation for Trafo, PS and soft-start and protect ckts?
reg
prasi

Carl_Huff 9th October 2015 04:15 PM

Quote:

Originally Posted by prasi (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post4477762.html#post4477762)
Hello Carl,
Have you decided on the price ?
Also if I want to build a seperate enclosure for your pre-amp tone control , any recommendation for Trafo, PS and soft-start and protect ckts?
reg
prasi

Hello prasi,

The details of the kit are described in the the very first post of this thread. "The cost for a 2 channel kit will be $50 plus actual cost to ship." The kit includes the hard to find parts. The balance can be purchased from Mouser Electronics. I will be providing a BOM and a reprint of the Linear Audio #5 article written by Doug Self.

There is a delay ON that avoids turn-on thumps. The project as presented is intended to fit in a 1U chassis. However if the power supply is to be internal to that chassis the box might likely have to be 2U in height.

I could be a source for a punched laser etched chassis if enough people make that request. We shall see.

Most any +/- 15v power supply that can sink 1A will work. There are several about. I have designs on hand and could provide PCBs and BOMs to anyone needing one. The trafos recommendations usually come with the selected power supply.

Carl_Huff 9th October 2015 04:18 PM

MadInventor,

I am looking forward to see what you contribute.

If you make the outputs adjustable between 12 and 17 volts you will hit the sweet spot for most builders on this forum.

prasi 9th October 2015 04:58 PM

Oh, sorry, I must have missed it while admiring the photos of the beautiful PCB!!


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