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rjm rjm is offline

Richard Murdey

diyAudio Member

About Me

  • About rjm
    Biography
    Canadian citizen, Japanese resident.
    Location
    Kyoto
    Interests
    Audio Circuitry
    Occupation
    Research Scientist
    Country
    Japan
    Real Name
    Richard Murdey
  • Signature
    RJM Audio (phonoclone.com / G+)

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  • Last Activity: Today 12:14 PM
  • Join Date: 2nd May 2004

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Posted 21st May 2015 at 01:32 PM by rjm Comments 0
This post, about a push-pull MOSFET output stage for a headphone amp, got me thinking again about the Audio Technica AT-HA5000, which is something of a benchmark in its class. The "basic" signal circuit (not a complete schematic, it's clearly missing some ancillary details) is attached below. Probably out of MJ originally.

I think with any circuit like this, the differences are less about the MOSFETs and the operating points and more about the front end and what tricks you do with the power supply. That, and how you make sure it doesn't go up in a puff of vaporized silicon taking your headphones with it.

The Audio Technica schematic has nice old-school Zener regulators, a discrete JFET front end, a long tailed pair + current mirror for voltage gain and "proper" BJT Vbe multiplier and driver stage. Q7 is presumably in thermal contact with Q10,11 providing overtemp protection, and the output has a protection relay (not shown in detail) for...

Posted 20th May 2015 at 06:00 AM by rjm Comments 12
The circuit was originally hosted on Headwize, but the site seems to have gone offline.

It was a single stage resistively-loaded MOSFET follower, a unity gain current buffer used to drive headphones.

Some updated versions provided below. As noted in the comments the "Reverso" version with the CCS on the V+ and a p-channel mosfet has better PSRR performance, especially with voltage divider network R6,R7,C4 on the collector of Q2.

So good in fact that I switched around the n-channel version to use a negative voltage rail to obtain the same result!

Posted 18th May 2015 at 08:15 AM by rjm Comments 0
I was perusing this thread earlier today. Which led me to what I think is the original source, at least as a modern, relatively clean headphone amp version of the original original (by way of ESP).

Some comments from our own Nelson Pass are seemingly relevant.

AC coupled, and simplified to a single supply voltage, the circuit can be run at +5 V operation (USB, etc) with fairly decent performance.

The circuit is optimized for 16 ohm headphones.

Posted 11th May 2015 at 09:15 AM by rjm Comments 0
Posted in Uncategorized
From now on every effort will be made to consolidate to the following values, 1/4W metal film:

1, 4.75, 10, 47.5, 100, 150, 221, 475, 1000, 1500, 2210, 4750, 10000, 22100, 47500, and 100000.

Also, the 1/4W 47 ohm and 68k carbon comp. resistor is widely used as damping and bleeder functions, respectively.

Exceptions will be made for the RIAA eq. of the Phonoclone and VSPS circuits, and the business end of the X-reg, where specific, non-standard resistance values are required.

*****

On resistor selection-

I honestly don't know if one resistor sounds better than another. I do know, however, that one resistor can be more expensive than another. At Mouser your basic 1/4W metal film resistor can run between 5 cents and 2 dollars in 100 unit quantities. Setting aside sound quality, it's not at all clear that you are getting any kind of material benefit at all by getting the expensive parts. Instead, it really...

Posted 10th May 2015 at 03:23 AM by rjm Comments 0
There is something freakish about a brick-sized block that sits there and plays room-filling music ... with no wires attached whatsoever and no obvious moving parts. It gave me the same "I'm living in the future!" sense of wonder I got buying my first 1 TB hard drive.

It doesn't take too much searching the internet to discover that among wireless portable (bluetooth) speakers, the TDK A33 is highly recommended for its exceptionally good sound quality. That comes with a massive caveat, however: Most of the people writing these reviews only have Bose, Beats, and the internal speaker of their iPhone as references for comparison.

So does the A33 sound good in a hifi context?

Read on to find out...

No, okay don't bother. The answer is "no".

But it doesn't sound bad. I'm listening to it now as I type this, hooked up via the AUX input to my Onkyo PCI-200SE sound card, with the A33 tucked under the...
Recent Comments
Great and nice stuff...
Posted Yesterday at 07:12 AM by kasey197 kasey197 is offline
Sorry, yes I just realized...
Posted Yesterday at 01:59 AM by abraxalito abraxalito is offline
@kasey197 I uploaded...
Posted Yesterday at 01:50 AM by rjm rjm is offline
In pursuit of even more...
Posted Yesterday at 01:45 AM by abraxalito abraxalito is offline
ah here it is : ...
Posted Yesterday at 01:42 AM by kasey197 kasey197 is offline
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