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Old 22nd March 2007, 04:15 AM   #1
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Default How to use DC supply with phono preamp?

I've tried to work this out with Jim Hagerman, but maybe I'm not asking the right question. I want to use a 12V DC power supply with the Bugle, rather than 9V batteries (opamps are rated for up to 18V and a 15V supply is recommended in the manual). I tried wiring the positive and negative holes on the board to the positive and negative terminals on my DC power supply, but I get no sound or simply a hum or buzz. Yet it works fine with batteries.

This is the Bugle, with battery holders attached, but the two pairs of holes are immediately below them, and small capacitor in front of each.

Click the image to open in full size.

And the last page in the manual here has a full schematic for those who can read them.
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Old 22nd March 2007, 10:38 AM   #2
audioPT is offline audioPT  Portugal
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Hi!

You need at least a symmetrical power suplly.

You can do it in two ways:

With your 12V transformer, make a 'virtual ground' using 2 resistors and 2 capacitors with, at least, 2.200uF each;
Or making a half bridge supply from the transformer directily.

See picture...

But remember... This is a RAW supply... don't expect a good or even a reasonable performance...

I recommend using 9V Bat with Bugle
Or a excellent dedicated low noise power supply
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File Type: gif apt_raw_psu.gif (4.8 KB, 560 views)
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Old 22nd March 2007, 03:38 PM   #3
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It's a PowerOne regulated 12V 12.5A unit, which I thought was a step up in quality from the Pyramid 13.8V 3A unit I had used previously. Are there any simple regulators like a TREAD that output 12V?

And how were the resistor values calculated? Because I don't believe I have any 470ohm on hand, but I do have higher and lower values. Does the closeness of their match determine how good the ground is?
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Old 22nd March 2007, 03:44 PM   #4
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You need a 'supply splitter' to generate a virtual ground. The one suggested above is a start, just a start though... The resistor values are not critical.
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Old 22nd March 2007, 03:56 PM   #5
audioPT is offline audioPT  Portugal
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Here is a 'simple' supply splitter.

CCS with current mirror

There is also a 'Rail Splitter' from Texas: TLE2426
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Old 22nd March 2007, 09:30 PM   #6
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So why exactly do I get hum/buzz/no music when I use the DC supply and everything works fine with batteries? And would I be wrong to presume there are power supplies that I can use without having to build a supply splitter?
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Old 22nd March 2007, 09:45 PM   #7
audioPT is offline audioPT  Portugal
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Strange... You have a funny name 'Fokker' (no hard feelings)

Ok... from the begining...

That pre-amp. Bugle, needs a positive voltage, ground and a negative voltage to work.

This voltage can be from +5, 0, -5 to +15, 0, -15...

Now, if you have a 12V transformer, you only get +12, 0... where are the -12V? You don't have it, so no music.

Quote:
Originally posted by JWFokker
...Are there any simple regulators like a TREAD that output 12V?
Here you have ONLY +12, 0 V
You will need 2 TREAD PSU's to put the Bugle working
One for +12,0 and the other to 0, -12


Quote:
Originally posted by JWFokker
So why exactly do I get hum/buzz/no music when I use the DC supply and everything works fine with batteries?
Exactly because the Bugle isn't supplied with power in the right way.
Even if you use a 'simmetrical' PSU, you will hear some hum/buzz if this PSU isn't designed to supply a phono pre-amp.

Quote:
Originally posted by JWFokker
And would I be wrong to presume there are power supplies that I can use without having to build a supply splitter?
You presume well, IF that power supplies ARE Simmetrical, i.e. with +15, 0, -15V or other voltages
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Old 22nd March 2007, 09:57 PM   #8
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Looks like I found one:

http://www.electronics123.com/s.nl/i...=8&category=41

A Velleman P8042. Variable between 1.2 to 24VDC output. I just need to pick up a decent AC transformer. If I remember correctly, I need to get a higher voltage than what I want to output, right? So a 15VAC transformer would be good, or should I go higher?
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Old 22nd March 2007, 10:08 PM   #9
audioPT is offline audioPT  Portugal
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Quote:
Originally posted by JWFokker
Looks like I found one:

http://www.electronics123.com/s.nl/i...=8&category=41

A Velleman P8042. Variable between 1.2 to 24VDC output. I just need to pick up a decent AC transformer. If I remember correctly, I need to get a higher voltage than what I want to output, right? So a 15VAC transformer would be good, or should I go higher?
Ok... Fine!...

For your case, feeding Bugle [ to Jim Hagerman], you will need a 2x15VAC... You ONLY can have simmetrical voltages if you have 2 secondaries on the transformer or if you use the schema in my second post for one secondary...
If you go for this kit, you must buy also 2 x 2.200uF capacitors to substitute the 470uF ones that came with the kit...

BTW, Bugle is a good pre-amp, it deserves better PSU

BTW2... Why not Bugle's Power Supply?
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Old 23rd March 2007, 12:38 AM   #10
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You know, that's probably the best idea. I had forgotten about it when trying to figure out how to get my power supply to work with the Bugle. I wonder though if I can just use a 12V transformer in the Bugle power supply, rather than the 15V it calls for, because I installed an AD8620 opamp in place of one of the OPA2134PA's to eliminate DC offset, and the AD8620 is only rated up to 13V.

Thanks for all your help.
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