[d.g]

Hi all, looking for some ideas/advice on transformers for a small headphone amplifier I have, it uses a 240v>15v AC wall transformer ( DC conversion is done inside the amplifier case)

I am considering the possibility of upgrading the power supply but am not sure where to start - nor am I sure if a benefit in SQ will be found.

Any ideas for the home DIYer? I have no experience in building circuits but am Electrical/electronic Engineering trained and can follow diagrams and build if required!

 

[Juaquin]

You might want to check out AMB's σ24 and σ25 if you're looking for a nice supply. You could also use a small trafo and Tangent's TREAD.

 

[nikongod]

Quote:

Originally Posted by Juaquin /img/forum/go_quote.gif You might want to check out AMB's σ24 and σ25 if you're looking for a nice supply. You could also use a small trafo and Tangent's TREAD.

For circuits with DC inputs (and no regulators after that) those are awesometoast, for amps with AC inputs they may not run so well.

If the amp relies on a voltage multiplier (SS or transformer) to power some part of its self, or isolate, or generate positive and negative voltages things could go poorly.

I would look at the info posted by pink floyd elsewhere for amps that require an AC power input.

 

[d.g]

Thanks, I did a search but that username just fetched back one thread about dacs, any idea which section this information was in specifically?

 

[joe_cool]

d.g: Can you read a schematic?

 

[d.g]

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif d.g: Can you read a schematic?

With a little assistance yes! That one has me scratching my head a little as to what everything is, and is the input voltage 9v?

 

[nikongod]

Quote:

Originally Posted by d.g /img/forum/go_quote.gif Thanks, I did a search but that username just fetched back one thread about dacs, any idea which section this information was in specifically?

He is banned here. You will have to go to his site.

link

 

[joe_cool]

Quote:

Originally Posted by d.g /img/forum/go_quote.gif That one has me scratching my head a little as to what everything is, and is the input voltage 9v?

Yes, the input is 9VAC from a transformer. One side is grounded and the other side passes thru a power switch to the rectifiers.

D5 serves as a half-wave rectifier and delivers about +12VDC to C11 and the 7805 regulator.

C3, D1, and D2 form a half-wave voltage doubler and deliver about +24VDC for the 7815 regulator. D2 is the "catch" diode. When the transformer voltage is negative it charges C3 to about 12VDC. When the transformer voltages is positive it adds to the 12VDC already trapped in C3 and delivers about 24VDC through D1 to C1 and the 7815 regulator.

C6, D3, and D4 do the same thing in reverse to deliver -24VDC to the 7915 regulator.

The transformer is a 9VAC 500ma wall-wart with a barrel plug. It's very easy to provide the correct transformer for international locations and the high voltage is kept out of the case. This means certification (UL, CSA, etc.) is provided by the manufacturer of the transformer.

Now, what kind of headphone amp do you have? If you're not good with electronics terminology maybe pictures would be helpful.

 

[Juaquin]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif For circuits with DC inputs (and no regulators after that) those are awesometoast, for amps with AC inputs they may not run so well.

Yeah...totally missed that.

You could of course bypass the internal AC->DC circuitry (depending on the amp design) and wire up a nice DC supply directly to it internally, but who knows if it would be worth it.

 

[nikongod]

Quote:

Originally Posted by Juaquin /img/forum/go_quote.gif You could of course bypass the internal AC->DC circuitry (depending on the amp design) and wire up a nice DC supply directly to it internally, but who knows if it would be worth it.

Compared to a single-wave voltage multiplier I'd bet that running nicer dedicated power supplies results improvements, although I agree whether its worth it is the real Q.

 

[cobaltmute]

Quote:

Originally Posted by d.g /img/forum/go_quote.gif Hi all, looking for some ideas/advice on transformers for a small headphone amplifier I have, it uses a 240v>15v AC wall transformer ( DC conversion is done inside the amplifier case)

As nikongod pointed out, does your wall transformer output 15V AC or 15VDC? This will affect what you can do.

 

[d.g]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif He is banned here. You will have to go to his site. link

Cheers, will have a look at that!

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif Yes, the input is 9VAC from a transformer. One side is grounded and the other side passes thru a power switch to the rectifiers. D5 serves as a half-wave rectifier and delivers about +12VDC to C11 and the 7805 regulator. C3, D1, and D2 form a half-wave voltage doubler and deliver about +24VDC for the 7815 regulator. D2 is the "catch" diode. When the transformer voltage is negative it charges C3 to about 12VDC. When the transformer voltages is positive it adds to the 12VDC already trapped in C3 and delivers about 24VDC through D1 to C1 and the 7815 regulator. C6, D3, and D4 do the same thing in reverse to deliver -24VDC to the 7915 regulator. The transformer is a 9VAC 500ma wall-wart with a barrel plug. It's very easy to provide the correct transformer for international locations and the high voltage is kept out of the case. This means certification (UL, CSA, etc.) is provided by the manufacturer of the transformer. Now, what kind of headphone amp do you have? If you're not good with electronics terminology maybe pictures would be helpful.

Ah, I need 15v AC though for my amp, there are a couple of pictures attached, its a Neco Soundlab Mosfet - Neco builds these and sells them on ebay. Here is a link eBAY URL

 

[theearbone]

I just got a used Neco MOSFET, and on the first day tested the AC cupply from the wallwart and it was stable to a tenth of a volt, then repeated the test with a 18V Clairtronic toroidal that I had in an ABS box for another amp and that was not as good and the one included with the Neco.  So I wouldn't invest £20-40 bulding an external transformer in a box PSU for this amp.
 
The power supply of course extends onto the PCB, and in the new V2.1 Neco has changed the electroytic capacitors near the opamps to larger value onnes, they look like Samwha VA series, which are high spec but pretty cheap caps:  http://www.rapidonline.com/Electronic-Components/Capacitors/Radial-Electrolytic/130-deg-Low-impedance-miniature-electrolytics/77042
 
Neco might even be persuaded tp do an upgrade for people with the v2.
 
A second more expensive change would be swapping the voltage regulator for an aftermarket super regulator, you'd need a +18V model; I think only Brent at audioupgrades.co.uk supplies 18v models, but I might be wrong.  Larger options like the JLH ripple eater simply won't fit in the case.
 
The other capacitors could be swapped for higher spec pricer options, the best on paper smallish PSU capacitors are probably the Rubycon ZLH, these are pricey and probably not the best bang per buck upgrade.  In my experience a good cheap upgrade are the resistors on the signal path, especially when the signal is weakest: in the case of the Neco this is the resistor that leads into the opamp(underneath the PCB); resistors on signal path by the mosfets; the feedback resistor going back into the opamp.  The V2.1 also has an upgraded volume control and headphone socket, space would probably not allow for a fullsize stepped attenuator.
 
I have ordered some fancy resistors and will report any gains they provide.

 

[theearbone]

The changes made were  replacing the input resistor with same value Shinkoh Tantalums at £3.30 each and then Takman metal films for feedback and signal entry to mosfets, thats six resistors at 76p each, so about £10 woth of bits + P&P.  The effects were:
 

1. A serious removal of high fequency fuzz, things just more defined up there.  Especially noticeable in vocalists sses.
2. Improved instrument placement, the central sounds are not spreading out wide.  This is the same kind of effect you get when improving the regulation to DAC chips.
3. A more natural sound, acoustic instruments just sound more like they actually do.  Things also a bit weightier.

 
Overall this tenners worth of parts made more difference to this amp than adding a £170 PSU did to the Slee Solo Green version. 
 
From memory there are another 7 resistors per channel that can be changed, I'd expect further small improvements for doing those with Takmans.