diyAudio - Other Audio Things
Go Back   Home > Forums > Blogs > rjm

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
Other Audio Things Audio items not from RJM Audio
Old

Audio Op Amps

Posted 26th June 2015 at 02:59 AM by rjm
Updated 13th July 2015 at 02:23 AM by rjm

I'm often asked "which op amp sounds better".

The reply is usually a scowl and muttered "does it look like I care!?" Which is something of a lie... I do care about getting op amps to sound good. It's the phrasing of the question I dislike.

Op amps do not come in "good, better, best" flavors. All it is - and this is pretty obvious I would have thought but apparently not - all this is about is matching an op amp to the job it's going to do; the circuit it's going to be sitting in.

The op amp you'd choose to use as a DAC IV converter is different from the one you'd choose to back a 100k volume potentiometer in a preamp is different from the one you'd choose for an MC phono preamp input stage...

Why do you think there are like a gazillion different op amps to choose from in the first place? It's because there are about a gazillion combinations of op amp characteristics and properties ... not because...
Attached Thumbnails
Click image for larger version

Name:	bryston.png
Views:	180
Size:	141.7 KB
ID:	1669  
rjm's Avatar
rjm
diyAudio Member
Views 418 Comments 1 rjm is offline
Old

Jenson JE-990 discrete op amp

Posted 8th June 2015 at 07:45 AM by rjm
Updated 9th June 2015 at 12:09 AM by rjm

LTSpice copy (protection diodes removed) of the original JE-990 circuit. Even with BC327/337 subbed in for all the original transistors the simulation works without further modification.

C1 seems to be critical for stability. C2 and C3 damp overshoot seen on the simulated square wave response, hinted at by the high frequency rise in frequency response shown in the screen grab below.

My impression is that this circuit is of the heavily optimized, no-stone-left-untouched variety.

Sourced from m.nats page and The John Hardy Company.
Attached Thumbnails
Click image for larger version

Name:	je990.png
Views:	98
Size:	76.8 KB
ID:	1660   Click image for larger version

Name:	jensen 990.png
Views:	296
Size:	98.7 KB
ID:	1661  
Attached Files
File Type: asc 990-2.asc (6.7 KB, 110 views)
File Type: pdf DIY.JE-990.DOA.V1A.pdf (77.7 KB, 68 views)
File Type: pdf 990.pdf (1.80 MB, 67 views)
rjm's Avatar
rjm
diyAudio Member
Views 303 Comments 2 rjm is offline
Old

AT-HA5000

Posted 21st May 2015 at 01:32 PM by rjm
Updated 27th May 2015 at 01:54 AM by rjm

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...
Attached Thumbnails
Click image for larger version

Name:	AT-HA5000.png
Views:	199
Size:	98.0 KB
ID:	1636  
Attached Files
File Type: asc HA5000 mod 01.asc (6.0 KB, 106 views)
rjm's Avatar
rjm
diyAudio Member
Views 439 Comments 0 rjm is offline
Old

Szekeres 2015

Posted 20th May 2015 at 06:00 AM by rjm
Updated 18th June 2015 at 11:26 PM by rjm (added schematic of original version)

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!
Attached Thumbnails
Click image for larger version

Name:	szekeres 2015 reverso.png
Views:	111
Size:	51.2 KB
ID:	1651   Click image for larger version

Name:	szekeres 2015 negative.png
Views:	89
Size:	41.3 KB
ID:	1654   Click image for larger version

Name:	szeke2.gif
Views:	130
Size:	6.0 KB
ID:	1668  
Attached Files
File Type: asc szekeres 2015 reverse split CCS.asc (3.8 KB, 90 views)
File Type: asc szekeres 2015 negative.asc (3.3 KB, 87 views)
rjm's Avatar
rjm
diyAudio Member
Views 499 Comments 12 rjm is offline
Old

JLH-2005 headphone amplifier

Posted 18th May 2015 at 08:15 AM by rjm
Updated 27th May 2015 at 01:52 AM by rjm

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.
Attached Thumbnails
Click image for larger version

Name:	JLH2005 LV 23.png
Views:	242
Size:	44.3 KB
ID:	1644  
Attached Files
File Type: asc JLH redux LV 23.asc (5.8 KB, 70 views)
rjm's Avatar
rjm
diyAudio Member
Views 369 Comments 0 rjm is offline
Old

A headphone amplifier gain calculator

Posted 2nd May 2015 at 05:30 AM by rjm
Updated 2nd May 2015 at 05:33 AM by rjm

You input the headphone sensitivity and impedance, and it spits out what I think is the ideal amplifier gain.

Even if you disagree (personal preference, difference input levels, etc.), the difference will be consistent regardless of headphone as long as the specified parameters are correct.

The gain value setting is tailored to normal line level input and listening fairly loud with the volume control at 9~10 o'clock. The output series resistance is assumed to be zero ohms.

Adjust as desired, and note that 3~6 dB either way will still be a usable. If your amp has a large output series resistance the gain Av should be scaled up as,

(Routput + headphone Z)/(headphone Z)
Attached Thumbnails
Click image for larger version

Name:	gain calculator.png
Views:	81
Size:	11.7 KB
ID:	1622  
Attached Files
File Type: zip headphone amplifier gain calculator.zip (6.8 KB, 45 views)
rjm's Avatar
rjm
diyAudio Member
Views 365 Comments 0 rjm is offline
Old

Doin' a "Gilmore" : a discrete transistor headphone amplifier

Posted 10th March 2015 at 12:17 AM by rjm
Updated 13th March 2015 at 10:42 PM by rjm

Recently I spent some time updating the diamond buffer of Sapphire headphone amp circuit. Later I stumbled on Kevin Gilmore's headphone amp circuit. Well, I'd read it before, but it had slipped my mind.

On seeing the Gilmore circuit again the thought process re. a Sapphire+Gilmore went something as follows,

"Toss out op amp, convert the Gilmore dual-LTP front end to bipolar, bolt the Sapphire3 buffer stage to the back, and substitute in the Sapphire3 current sources. Wrap in a mild feedback loop."

The result is shown attached. The Vbe multiplier is still a simple resistor (R33) ... that may need to be refined to add thermal throttling. The offset servo is not shown, but the action is shown as Vadj. Alternatively a trim pot would be placed between R30 and R32 to provide a small measure of offset adjustment. Most of the open loop gain is controlled by R14,R15 ... it seems to me that some work could still be done in that area. Despite going...
Attached Thumbnails
Click image for larger version

Name:	Gilmore-Sapphire3.png
Views:	421
Size:	87.5 KB
ID:	1594  
Attached Files
File Type: asc Gilmore-Sapphire3.asc (9.8 KB, 145 views)
rjm's Avatar
rjm
diyAudio Member
Views 556 Comments 0 rjm is offline
Old

Which is better, Sennheiser HD600 or AKG K702?

Posted 25th February 2015 at 12:24 PM by rjm
Updated 25th February 2015 at 11:41 PM by rjm

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...
rjm's Avatar
rjm
diyAudio Member
Views 556 Comments 1 rjm is offline
Old

Z-reg II improved simple Zener voltage regulator

Posted 22nd February 2015 at 01:24 AM by rjm
Updated 28th February 2015 at 06:17 AM by rjm

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.
Attached Thumbnails
Click image for larger version

Name:	z-reg ii.png
Views:	389
Size:	55.0 KB
ID:	1586  
Attached Files
File Type: asc Z-reg ii.asc (3.2 KB, 119 views)
rjm's Avatar
rjm
diyAudio Member
Views 584 Comments 2 rjm is offline
Old

Gustard H10 Headphone Amplifier

Posted 14th February 2015 at 11:47 AM by rjm
Updated 12th April 2015 at 02:59 AM by rjm

Technical Specifications:

Signal Input : 2x XLR female , balance
2x RCA, unbalanced
Maximum input level : +21 dBu, impedance 10kΩ
Input impedance : XLR: 10kΩ, RCA: 68kΩ
Input Sensitivity : +6 dBu
Main amplifier gain : +8 dB
Main amplifier gain adjustment range : -4 / +2 / +8 / +14 / +20 dB
Frequency response : 0-55kHz (-0.5dB)
Damping Factor :> 400 @ 50Ω
Dynamic range :> 128dB (A -weighted )

THD + N (1kHz 1W @ 100Ω): <0.00035%
THD + N (1kHz 0.5W @ 32Ω): <0.0007%
Crosstalk :-110db (1kHz)

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...
Attached Thumbnails
Click image for larger version

Name:	DSC_7276s.jpg
Views:	1994
Size:	468.5 KB
ID:	1577   Click image for larger version

Name:	DSC_7264s.jpg
Views:	617
Size:	434.0 KB
ID:	1578   Click image for larger version

Name:	DSC_7271s.jpg
Views:	593
Size:	354.0 KB
ID:	1579   Click image for larger version

Name:	DSC_7265s.jpg
Views:	330
Size:	376.9 KB
ID:	1580  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 2488 Comments 6 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 08:30 AM.


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