Is modding an existing PSU instead of building one a good idea ?

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Avgatzeblouz

Avgatzeblouz

Well-known member
Joined
Nov 6, 2015
Messages
161
Location
Montréal
Hi everyone,
being not really as tech savvy as most of you guys, I would appreciate your input on this topic : for my next builds, pairs of U67 and M49b, I wonder if I could save some time and money by getting power supplies from Advanced Audio (https://advancedaudio.ca/collections/diy/products/power-supply-7-pin-tube-microphone), and get them adapted to the mic needs ? Scotty, from Advanced audio, told me he could adjust his PSU to any requirement I could have, he adjusts the voltage based on 2 diodes.

So, what's your input about this ? Are those PSU clean enough for the task ?

Thanks !
 
As far as i know, he just takes the standard aphex 460 PSU and mod it with 2 zenerdiodes.
Chunger sells them: http://store.studio939.com/product/tps100-tube-microphone-power-supply
Or if you're in Europe: https://www.thomann.de/be/the_tbone_psu_sct2000.htm?ref=search_rslt_t+bone+psu_109922_1
Are those clean enough? Well, i haven't used them yet, but i've heard great things about it.
But: When you're building for example a M49, you must build the M49C version. The psu isn't clean enough for the B-version.
 
wlinart said:
But: When you're building for example a M49, you must build the M49C version. The psu isn't clean enough for the B-version.
Click to expand...

Not true ;)

What "isn't clean enough"? Enclosure? Transformer? R-C? Zeners? Origin?
There are mostly two versions of chinese PSU (in case of transformer voltage) - ca. 220VDC and ca. 300VDC (after bridge).
Of course better is to use lower voltage to drop it easier. Rest depends only on how you will optimise the drop before zener diodes.
If you only change Zeners - then you are right, but this is unproper for many microphones, not only M49 "b".
Heater supply section also can be improved.

There's another question - which tube you are using as substitute for AC701 and how you wil optimise microphone circuit, including biasing etc. ? If this is only different tube, with all the components values as in original schematic, then - hmm... - not really lucky build ;)
 
Hi, and thanks for your answer, I am eager to learn. I have FAB BV11 and Phaedrus AC701k electronic tube. For the other components, my plan is to follow the original schematics. Either by using Poctop PCB, or ptp. By clean, I mean correctly regulated.

Thanks again,
Manuel.
 
Avgatzeblouz,

The Apex 460/alctron PSU is a fairly standard 220 volt psu with a 6.3 volt for heater with a zener diode on the HT to drop it off at 135volts. The phaedrus thingy is a AK701 emulator now AK701s were made for a 4 volt heater, and if you were using a real one you'd need to ad a resistor or VR to drop the voltage but I don't know how the phaedrus thing works so i don't know if it'll take more volts, probably will though, i doubt it can possibly be as fussy as a valve filament.

But seriously, why don't you find a nice subminiature tube to use, you'll learn an awful lot more and valves are magic ;-)

Anyhow the alcron is fine for any valves that uses a 6.3 heater current, sure Neumann were a little more fussy with their voltage than AKG, but you should be fine. U47s however are a much more fussy beast which has been covered many times elsewhere

Beware of the WooWoo people talk about tube/valve mics, they are probably the most simple circuit you can make with a valve, just make sure you have a really excellent output capacitor, no electrolytic or ceramic!
 
Solidstate replacements aren't my thing completely.
For 4V heaters it could be made with use of 7805 voltage regulator and resistor divider (1k/3.9k) after it.

 
... Or two series diodes (maybe Schottky) after it? ;) Or even just an appropriate-value RC filter...
 
ln76d said:
Not true ;)

What "isn't clean enough"? Enclosure? Transformer? R-C? Zeners? Origin?
There are mostly two versions of chinese PSU (in case of transformer voltage) - ca. 220VDC and ca. 300VDC (after bridge).
Of course better is to use lower voltage to drop it easier. Rest depends only on how you will optimise the drop before zener diodes.
If you only change Zeners - then you are right, but this is unproper for many microphones, not only M49 "b".
Heater supply section also can be improved.
Click to expand...

Well, I've read that statement a lot on this site, which was why i said it here, but if isn't true, all the better :)
 
Timjag said:
Avgatzeblouz,

The Apex 460/alctron PSU is a fairly standard 220 volt psu with a 6.3 volt for heater with a zener diode on the HT to drop it off at 135volts. The phaedrus thingy is a AK701 emulator now AK701s were made for a 4 volt heater, and if you were using a real one you'd need to ad a resistor or VR to drop the voltage but I don't know how the phaedrus thing works so i don't know if it'll take more volts, probably will though, i doubt it can possibly be as fussy as a valve filament.

But seriously, why don't you find a nice subminiature tube to use, you'll learn an awful lot more and valves are magic ;-)

Anyhow the alcron is fine for any valves that uses a 6.3 heater current, sure Neumann were a little more fussy with their voltage than AKG, but you should be fine. U47s however are a much more fussy beast which has been covered many times elsewhere

Beware of the WooWoo people talk about tube/valve mics, they are probably the most simple circuit you can make with a valve, just make sure you have a really excellent output capacitor, no electrolytic or ceramic!
Click to expand...

Hey, thanks  a lot. I already have a pair of electronic tubes, so I'm gonna stick to that. According to all the answers I got on this thread, it might be good just to ask Advanced audio to mod their PSU to reduce the heater voltage to M49b needs. That seems like a valid option.
Thanks a lot everyone !
 

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