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Old 8th August 2003, 09:20 PM   #1
JDeV is offline JDeV  South Africa
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Default Preamp PSU questions

I am thinking of building the following preamp and want to know if it is really neccesary to use 200mA chokes, and why 25 x 470uF caps and not just 1 x 10000uF ?

Here is bottom part of circuit, top part in next post:
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Old 8th August 2003, 09:21 PM   #2
JDeV is offline JDeV  South Africa
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Default Part 1

Top part.
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Old 8th August 2003, 09:39 PM   #3
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Default Casanova

Looks suspiciously like your building a clone of Robert Ang's Audio Note M7 clone/variation.

neccesary to use 200mA chokes

A much higher current choke will likely have substantially lower series resistance and therefore a lower Zout. That's probably what they were after.

why 25 x 470uF caps and not just 1 x 10000uF ?

He's obviously aiming for low ESL/ESR, though for a regulated non DHT filament, I can't see a reason for it.

I'd use schottky's in the filament bridge and adjust the values of the last two caps in the B+ to ensure it's stable.
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Old 9th August 2003, 09:40 AM   #4
EC8010 is offline EC8010  United Kingdom
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Default Boutique components

I'll probably be shouted at for saying this, but that drawing looks like a collection of very expensive components with very little evidence of any understanding of circuit design.

The 6072 is a low-noise valve expressly designed for audio that used to be used in AKG microphones. DC heaters help reduce hum, as does a well filtered HT supply. Regulated DC on the heaters stabilises cathode temperature, which is a good thing (and cheap to do), without needing lots of boutique components. Since the output impedance of the HT supply is primarily that of the final capacitor, the low DC resistance of over-sized chokes will have very little effect.

I'd suggest that you use the 6072 section, but make your own power supply arrangements with whatever you have handy. As Brett suggested, it is well worth using Schottky diodes for the LT. Also use a separate transformer for the LT from the HT to prevent HT rectifier spikes appearing on the LT. After rectifying and smoothing the LT, use a regulator of your choice to set 6.3V on the valve pins. Use a low-leakage (ceramic or PTFE) valve base to minimise noise.

To make the project more interesting, you might like to consider a valve HT regulator in place of lots of expensive iron.
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Old 9th August 2003, 09:43 AM   #5
dhaen is offline dhaen  Europe
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Hi,

The heater smoothing circuit looks like over-kill to me.
If you take Bretts suggestion of a Schottky bridge, and increase the 1 ohm resistor, you'll be able to reduce the smoothing cap requirements. Have a play with PSU Designer to see what's going on.
As for the multiple parallel caps? Sometimes it's just to get it into a low profile box.

Cheers,
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Old 9th August 2003, 01:35 PM   #6
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6072 is a very good sounding valve. I like it mostly in phono stages but no doubt it also sounds good at line level. BTW WIM (MR Valve) in JHB has lots of new old stock 6072s. The heater PSU has a strong effect on the final sound even with IDHTs. However the solution shown is probably not optimal - just a single Elna Cerafine 10,000uF before the cap multiplier should do the trick with little capacitance close to the the valve. A larger improvement than the crazy multi-cap mish-mash can be had with a high current choke in the heater supply.

cheers
peter
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Old 9th August 2003, 02:41 PM   #7
JDeV is offline JDeV  South Africa
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Thanx for all the good news.
After looking around locally (whole of South Africa) , I was just about to look for another circuit. All those fancy caps will cost a small fortune to import. I noticed that the 6072A can be replaced by the 12AY7. Is this wise or must I rather get the 6072A. I got 4 x 12AY7's at moment, but of mixed brands (RCA, GE, Heintz & Kaufman) - so I must buy new ones anyway. What should the PSU trafo. rating be? 100VA good enough?
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Old 9th August 2003, 02:44 PM   #8
JDeV is offline JDeV  South Africa
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Default Re: Casanova

Quote:
Originally posted by Brett
Looks suspiciously like your building a clone of Robert Ang's Audio Note M7 clone/variation.

Quite right.


http://www.audio-genesis.com/casanova.html
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Old 9th August 2003, 03:00 PM   #9
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Default Re: Re: Casanova

Quote:
Originally posted by JDeV
Quite right.

http://www.audio-genesis.com/casanova.html
I recognised the schematic.
Robert's using a different pre now, a choke loaded or WOT 76 iirc.
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Old 10th August 2003, 02:14 AM   #10
SHiFTY is offline SHiFTY  New Zealand
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Make sure your first filament supply cap can handle the ripple current, it might be quite high...
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