diyAudio - View Profile: rjm
Go Back   Home > Forums > Members List

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

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+)

Statistics

Total Posts
Blog
Wiki
General Information
  • Last Activity: Today 02:15 PM
  • Join Date: 2nd May 2004

Friends

Showing Friends 1 to 1 of 1

Blog

View rjm's BlogRecent Entries
Latest Blog Entry

Posted 25th February 2015 at 01:24 PM by rjm Comments 1
The HD600s.

Ok, so why donít you like the K702s?

I didnít say I didnít like them. Just that I think the HD600s are better.

Itís pretty simple really:

The K702s have a strident, hard upper-midrange "bump" that I find disagreeable. Yes, it makes tracks sound more ďliveĒ, but itís also fatiguing and a bit clinical, and - as many others before have noted - makes the sound overall somewhat thin. In direct comparison the HD600s seem full the point of boominess, but I'm willing to accept that midbass plumpness for the Sennheiser's warmer, luxurious midrange. In imaging, the K702s trend to a wide, distant, airy soundstage while the HD600s run towards a closed in, intimate presentation. In that sense the K702 are more like listening to speakers, and I can certainly see people being attracted to that.

These are both top-shelf headphones at the top of their game, I don't mean to imply that the AKGs are bad. The two...

Posted 22nd February 2015 at 02:24 AM by rjm Comments 2
I've added an additional RC filter stage (R3, C4 in the schematic below) before the Zener diode, substantially reducing the amount or ripple on the transistor base by cleaning up the voltage applied to the Zener reference. (The original Z-reg is described here.)

Circuit shows C2 with a value of 300 uF. Typically much larger values are used. I kept the filter capacitance to a minimum here to show circuit working with a reasonably high ripple (1 V p-p) on the input. The rectifier diodes used here are of no particular consequence, I just wanted the simulation to generate a realistic sawtooth for the input.

***

OK, this doesn't do as much as I originally thought. The improvement is mostly below 100 Hz, whereas the ripple is mostly in the 100Hz-1kHz band. There's perhaps 3 dB less output ripple, but that's about it. You can verify this yourself in LTSpice, just cut the wire between C4 and the junction or R1-R3 and rerun the sim.

Posted 14th February 2015 at 12:47 PM by rjm Comments 6
Rhymes with "custard"...

Each channel has a BB OPA134PA - socketed - for voltage amplification and an eight transistor discrete buffer with 2 ea. 2SA1837. 2SC4793, C546B, C556B. Dual mono layout (more or less ... the circuit board itself is shared and not completely symmetric).

There's a pair of NE5532s at back for balanced-unbalanced input conversion, and a pair of transistors (TIP122 TIP127) with trim pots and circuitry between the input and the main amplifier which looks a bit like voltage regulators to me but I can't see where they fit in to the scheme of things.

Pretty decent quality for the price. (I paid $350/delivered)

First impressions of the sound are quite positive, plenty of depth and decent smoothness. Letting it cook overnight now and will put it in the main system tomorrow.

****

Comparison notes vs. Sapphire (with Sennheiser HD600s)

H10 immediately impresses...

Posted 7th February 2015 at 07:47 AM by rjm Comments 0
I recently obtained a pair of AKG K702 headphones to complement my long-standing reference Sennheiser HD 600s. I figured since I'm building headphone amplifiers it would be a good idea to have a reference grade low impedance model as well as the high impedance HD 600s to use for evaluation.

First though, a note on sensitivity:

K702: 62 ohms, 105 SPL/V
HD600: 300 ohms, 97 dB/mW

Different units. Grrr!

At the same volume position I quickly discovered the HD 600s play slightly louder than the K702s. The datasheet values predict the K702s should be about 3 dB louder, so it seems the sensitivity is off by as much as 6 dB.

In numbers,

K702: 62 ohms, 105 SPL/V ... 93 dB/mW from datasheet, 87~89 dB/mW (99~101 SPL/V) in practice.
HD 600: 300 ohms, 97 dB/mW ... 102 SPL/V.

The K702 requires as much as ten times more power to drive than the HD 600s. The voltage sensitivity is about 3 dB lower than...

Posted 31st January 2015 at 01:28 PM by rjm Comments 0
A couple of years ago I built a standard op amp + diamond buffer headphone amplifier, called the Sapphire.

It's a fairly common circuit, from eBay on up its not hard to find similar designs. The Sapphire is distinguished by its full dual mono design, Zener voltage regulators (Z-regs), and by keeping the buffer circuit outside of the op amp feedback loop.

Regarding the feedback loop, there are two schools of thought:

1. Put the buffer inside the feedback loop, so the op amp does active error correction on the output signal, and the buffer provides the high speed currents required to make that correction.

2. Put the buffer outside the feedback loop to isolate the load from the op amp. The load currents are provided by the buffer, but the output signal relies entirely on the low output impedance of the buffer for accuracy.

The explanation is too long to bother with here, but I am strongly in favor of using a buffer...
Recent Comments
thanks for sharing....
Posted 26th February 2015 at 08:19 PM by mlloyd1 mlloyd1 is offline
I doubt it would make...
Posted 23rd February 2015 at 12:18 PM by rjm rjm is offline
Thanks for replying....
Posted 23rd February 2015 at 08:59 AM by asaifa asaifa is offline
The NE5532 are dual...
Posted 22nd February 2015 at 11:32 PM by rjm rjm is offline
Hi. Thanks for writing...
Posted 22nd February 2015 at 02:24 PM by asaifa asaifa is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 02:30 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2