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Old 12th September 2007, 06:07 PM   #1
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Default Bias Supply Quality / Importance

How important is the bias supply to the performance of ESLs? I'm building a headphone amp and trying to decide between a higher voltage multipler straight from the wall, and a 115v to 230v transformer and a smaller multiplier. Also, how important are the capacitor types (polypro, film-foil, teflon) and diode types (i.e. fast recovery, schottky, avalanche etc.) in these supplies? Also, what about ripple supression in these supplies?

Max bias I'll need is 600v...

Thanks!!
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Old 13th September 2007, 07:49 PM   #2
Calvin is offline Calvin  Germany
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Hi,

Q: how important?
A: quite unimportant?

Q: use Tranni?
A: functionally it is even, but IŽd prefer a trannie because of galvanic decoupling to the power line. In Germany and many other nations it is not allowed to take the voltage right off of the wall.

Q: importance of Caps
A: unimportant. Use the cheapest that fullfill the voltage and capacity requirements. You donŽt need Foils for this.

Q: diodes?
A: unimportant, just fulfill the voltage requirements. Use cheap standard highvoltage types like 1N4007 or series connections of those.

Q: ripple rejection
A. the usually used and always positive(e.g. for safety) high ohmic value resistor between cascade and the transducer itself reduce ripple ( RC-Filtering). Adding a blinker-circuit reduces influences further by completely intermediate decoupling the ESL from the supply. As a bonus You get a very sensitive control device.

jauu
Calvin
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Old 13th September 2007, 07:57 PM   #3
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In addition:

The hot side of the HV-supply can be filtered with a high value resistor or a neon oscillator ('blinker') and the resistance of the coating as well.
But what about the side of the HV-supply which is connected tom the trannie. Do we need something there to avoid noise etc.? It is directly from the mains.
Any suggestions?
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drs M.J. Dijkstra
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Old 14th September 2007, 06:00 AM   #4
Calvin is offline Calvin  Germany
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Hi,

IŽd use whats standard
- a good switch with small cap over the contacts
- a fast fuse
- a MP-cap
- Varistor
-additional filtering is not necessary, but if it makes You feel better, IŽd suggest a complete input block (mains connector, switch, fuse-holder and filter as one component)

jauu
Calvin
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Old 14th September 2007, 04:37 PM   #5
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Calvin:

thank you for your help. What do you think about something like this, which would be battery-powered:

http://www.emcohighvoltage.com/CASeries.pdf

also, as for the blinker-circuit, do you have a schematic I could look at?
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Old 14th September 2007, 08:10 PM   #6
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I talked to Emco today, they won't sell in small quantites. However, I found a circuit that uses a 555, perhaps this is what you mean by a blinker:

http://www.quadesl.com/speaker/diyesl/hv_supply.pdf
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Old 15th September 2007, 06:35 AM   #7
Calvin is offline Calvin  Germany
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Hi,

no, MJ and I donŽt talk about that supply....thereŽs no component blinking in that circuit!
The circuit we mean looks like this:
Click the image to open in full size.

jauu
Calvin
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Old 15th September 2007, 02:14 PM   #8
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well, I was considering the square wave generator ('555) a blinker anyways, thanks for the clarification. I assume that this is a 90v DC breakdown voltage that the schematic refers to? I see a lot that are 65 AC / 90 DC breakdown voltage. How does the neon bulb act as a control device?
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Old 16th September 2007, 03:19 AM   #9
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The neon lamp monitors the voltage on the capacitor. If the voltage rises above about 90V, the lamp turns on. The voltage will rise when the charge on the diaphragm of the speaker leaks away into the air or through other paths. When the lamp turns on the diaphragm will recharge. This will lower the voltage across the capacitor turning the lamp off again.

I bought modules directly from Emco about 15 years ago. I didn't have any trouble at that time, but maybe the fact that I was an engineer working at HP helped. Try Pico, they have some very small HV DC-DC converter modules and may be more willing to sell small quantities or have distributors who will.

I_F
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Old 16th September 2007, 11:43 PM   #10
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Quote:
Originally posted by I_Forgot
The neon lamp monitors the voltage on the capacitor. If the voltage rises above about 90V, the lamp turns on. The voltage will rise when the charge on the diaphragm of the speaker leaks away into the air or through other paths. When the lamp turns on the diaphragm will recharge. This will lower the voltage across the capacitor turning the lamp off again.

I bought modules directly from Emco about 15 years ago. I didn't have any trouble at that time, but maybe the fact that I was an engineer working at HP helped. Try Pico, they have some very small HV DC-DC converter modules and may be more willing to sell small quantities or have distributors who will.

I_F
thanks for the explanation. So, may I ask why this "cycling" of the bias voltage is desired?

As for the DC-DC power supplies, do you feel that it is better than a simple voltage multiplier? Remember, I only need maximum of 600 V bias, as this is for a headphone amplifier. How would the HV DC-DC supply compare to say using a Hammond 229A230 which is 6 VA and would be wired for 230V CT @ 25 ma and then a simple voltage doubler circuit? Like this:

http://photo.head-fi.org/data/500/alwayson.gif

Maybe I could add the neon to this supply, if it makes sense... just looking for a nice solid recommendation and then I'll go from there and experiment!

Calvin:

as for your recommendations of:

- a good switch with small cap over the contacts
- a fast fuse
- a MP-cap
- Varistor

I'd love to see a schematic if you have one tucked away somewhere. I'm not sure I'll use the switch, but it would be nice to know how to size the fuse, and where to place the MP-cap (I'm assuming something like 0.022 at line voltage across the primaries) and what to do with the varistor (probably a heat indicator as in power amps?)

Thanks!
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