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Old 9th June 2012, 11:22 PM   #31
kevinkr is offline kevinkr  United States
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I've updated the BOM and replaced the original with the revised BOM, note that the difference is the addition of a second page covering the high voltage supply. I've yet to add the filament supply.

Note with regard to the high voltage supply there is no reason if desired not to go with independent regulators for each channel - that is exactly what I am doing for mine. Only one power transformer, and choke are required - the input filter caps C1, C3, and C4 do not change. Just double quantities for all other parts.

Don't forget sockets for the PSU as I forgot to include them in this cut of the BOM.

Acceptable pass tubes for use in this supply design include the 5881, 6L6, 6BQ5, and 6BD5GT - note the different pin outs where applicable.
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Old 11th June 2012, 01:52 AM   #32
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Added the detail for the filament regulator to the BOM. Note that in addition to the LT1084 5A regulator you will need a silpad, suitable insulated hardware and if not using the PSU chassis as a heat sink, some sort of suitable heatsink..

Dissipation in the regulator could be 12W or more depending on line voltage and transformer selected. Use a heatsink with thermal resistance to ambient of less than 2C/W.

Note that the filament supply wants to sit fairly close to ground so as not to overstress the 6S3P filament insulation so this really precludes using this filament supply to power the 12AX7A in the high voltage regulator because of the near 200V differential between filament and cathode.

Note also that with regards to "C4" in the high voltage regulator this could be changed to 110uF total using a pair of 220uF/350 - 450V caps in series shunted with 220K 1W resistors to assure that the voltage divides equally between them. This would be good for a few dB additional ripple reduction.

Listening to this thing every day, digital now on the back burner.. I'm quite pleased with the overall performance.

Lest there be any confusion this design was intended for use with a wide range of cartridges, LOMC types like my SPU should be used with a step-up transformer to maintain good SNR despite the high gain. (I've been asked about this a few times.)
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Old 11th June 2012, 02:01 AM   #33
kevinkr is offline kevinkr  United States
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While I obviously can't review my own design I can describe a few of its sonic attributes. Perhaps this will help a few people to decide whether this is the sort of sound they would be interested in.

I would describe it as fast, detailed, with very good imaging, and has very extended frequency response. Very open sounding. It is also quiet, and very clean..

Compared to my last design it has much less character which I take as a good thing, the previous design tended to be a bit warm and euphonic sounding, and lacked both the detail and imaging of this design. (It was quite decent.)

I aim for neutral, and whether or not it actually is, I believe it comes about as close as I know how at this point in time. For the objective as I've mentioned it also measures well.
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Old 11th June 2012, 02:25 AM   #34
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Quote:
Originally Posted by kevinkr View Post
While I obviously can't review my own design I can describe a few of its sonic attributes. Perhaps this will help a few people to decide whether this is the sort of sound they would be interested in.
Any chance of a needledrop thru this phono stage?

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Compared to my last design it has much less character which I take as a good thing, the previous design tended to be a bit warm and euphonic sounding, and lacked both the detail and imaging of this design. (It was quite decent.)
12AX7's?

jeff
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Old 11th June 2012, 02:33 AM   #35
kevinkr is offline kevinkr  United States
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Hi Jeff,
Not currently set up to do digital captures, but perhaps at some point in the future.

The previous design was based on D3A triode connected front end, and a 5842 output stage, both stages with gyrator loading - the gyrators being implemented with 5687 dual triodes. The main issue with this older design is the high input capacitance. Both designs use passive EQ and quiet tube regulated supplies.
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Old 12th June 2012, 08:54 AM   #36
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Try the D3a as a pentode in the front end. Lower input C and IMHO, deals with the criticism you have of the sound.
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Old 12th June 2012, 03:09 PM   #37
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Try the D3a as a pentode in the front end. Lower input C and IMHO, deals with the criticism you have of the sound.
Yes, my exact thought and this is in the cards - essentially a new design though as the current design is built around the characteristics of its triode front end and gyrator loading.
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Old 14th June 2012, 06:30 PM   #38
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Well the chassis for the power supply arrived the other day, so now all I am waiting for are the transformer and choke from Edcor.

I think I failed to take my own advice and was looking at my new supply chassis last night and realized that it is going to take some very careful planning to get everything to fit.

I'll post a picture at some point of the chassis and the ensuing build. You'll want to avoid my mistake..
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Old 15th June 2012, 06:50 PM   #39
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Why is it that no matter how many things we build, trying to get the power supply to fit is something that occurs time and time again
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Old 16th June 2012, 01:18 AM   #40
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Why is it that no matter how many things we build, trying to get the power supply to fit is something that occurs time and time again
It's particularly embarrassing as I always warn against building in too small a box, and I appear somehow to have not taken my own advice.

What's even funnier is that I made this box somewhat larger than the one destined to contain the supply for my next 26 dht line stage which has an additional filament supply this one does not. What to do..
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