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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...
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From Tube CAD Journal by JRB

Posted 25th June 2015 at 08:05 PM by alexcp (My DIY projects)

For every hobbyist-built amplifier in existence there are probably one thousand amplifiers which are planned on being built and maybe one hundred amplifiers that have all their parts collected in a box waiting to be built and ten amplifiers that are partially built and collecting dust in a closet.

(see full post here)
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AKM's new "VERITA" AK4490EQ 120dB 768kHz/32-bit 2ch New Generation Premium DAC

Posted 15th June 2015 at 09:47 AM by hollowman

Click the image to open in full size.
Supposedly, Astell and Kern are using this in their latest AK-380 high-end/high-$ DAP:
Click the image to open in full size.
I proto'd this DAC recently (along with AKM's new premium ADC)....what can I say ... I'm floored! This is the best digital I've ever heard to date.

Some hold-outs of antiquated multi-bit DAC religiosity may never be able to step outta their cognitive dissonance -- or warm-fuzzy nostalgia -- 'cause of their loss of virginity with their first loves (= classic R2R multi-bit) oh G A W D ... memories are so precious ... man -- I'm lookin' at my Philips CD650 and gettin' misty-eyed ....WAKE UP DUDE!!!
Folks, this is 2015 and technology does EVENTUALLY improve (tho', it takes time and is often 3 steps fwd, 2 back).

Unless Philips decides to revamp their TDA or SAA lines, AKM's your ticket ... or...
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capacitance measurements with the hp 4192A

Posted 10th June 2015 at 01:10 PM by rjm

Work stuff. I was writing Labview vis for an hp 4192A LF impedance analyzer and needed something to measure to check the data acquisition program. So I stuck some of my audio capacitors I happened to have into the 16047A test fixture "just to see".

I have no idea what these measurements are telling me other than yes, the 0.47 uF capacitors are indeed 0.47 uF ... up to about 0.5 MHz anyway. Maybe someone can do some technical analysis. I was struck though by just how quickly the inductance of these big film caps kicks in. As audio coupling caps they are fine, but if you are silly enough to use them as power supply bypass for example...

There are some reproducibility issues I'm still coming to grips with, but the differences shown in the plots is definitely from the capacitors themselves and not the leads or random variations. I've measured them several times over with similiar result.
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Posted in The Lab
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Resources for acoustic measurements

Posted 8th June 2015 at 03:32 PM by MartinAndersen
Updated 8th June 2015 at 05:43 PM by MartinAndersen (new link)

This is my collection of everything related to speaker measurements. Better to share it than hide it away in my bookmark collection

Understanding Cabinet Edge Diffraction
"One of the most misunderstood topics in audio is the subject of diffraction. Diffraction, acoustic phase, and how listening rooms impact our reproduction of sound, based on what I see posted in many discussions on the internet, are subjects of much confusion. In this article I will attempt to clear some of the fog on the topic of cabinet diffraction, and hopefully, present it in such a way as to make it much easier to understand."
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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.
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New system hard disk

Posted 8th June 2015 at 02:47 AM by panson_hk

Thanks to the SMART feature of the hard disk and the utility which warned me the disk was dying. I was able to backup a WIN7 system image before things happening. Restoring the image on a new hard disk was done smoothly.
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Bargain beaut - headphone amp

Posted 2nd June 2015 at 05:44 AM by abraxalito
Updated 9th July 2015 at 09:43 AM by abraxalito

When I found this on Taobao a few days ago I could not believe the price wasn't a mistake, or that it was just for the case with nothing inside. But it turned out to be real, so I ordered one - it arrived just now so I'm taking it apart before having a listen. The case oozes quality and the volume control feels silky smooth.

Here - (lehmann) ܵĺţȫ䣬һ-Ա

When I've had a listen (gotta search for my 1/4" adapter) I'll get into modding.... Incidentally for those on 110V, it does have a mains voltage selector switch. Amazing.

I traced out the circuit (still haven't listened) and found its pretty much as shown on the Taobao page. 78/79 15V regulators feed BD139/140s and a TL072 sits between the volume pot and the discrete OPS. This stage resembles a diamond, but instead of the more familiar current sources to the rails, it has 1500ohm resistors. LTSpicing this arrangement (schematic shown) reveals its...
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JBL Paragon Superclone

Posted 30th May 2015 at 06:23 AM by mlise
Updated 30th May 2015 at 06:25 AM by mlise

I have new 2234/35 cones in the 2224H baskets making them into 2234H's. I bought some lead aquarium plant weights to load them up, but broke down and bought genuine JBL OEM mass rings for a mere $85 each. They appear to be zinc (pot metal) so I an be comforted I won't get lead poisoning listening to the speakers. Just have to glue the mass rings in and the dust caps on to make the drivers 2235H's.
The Eminence ASD1001 was my low budget plan for a mid, but I saw 2450J's were actually relatively cheap, so I now have the most modern neodymium magnet version of the 4" diaphragm tweeter JBL makes. The massive ferrite magnet versions cost twice as much.
In this far, I figured I might as well spring for a pair of 2405H's instead of the Beyma clones I already bought. Thanks to e-bay for refunding the first FUBAR pair of 2405H's, I found a second really nice pair.
I wound up air core inductors to make an N7000 dividing network (mid to tweeter x-over) and have the rest...
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Why might a diamond buffer sound better?

Posted 25th May 2015 at 07:00 AM by abraxalito

Here's an interesting post by Charles Hansen (of Ayre fame) about his preference for diamond buffers in amp output stages -

He's saying that diamond buffers sound better but that he has no idea why this would be.

Simulating the PSRR of the diamond vs a traditional EF2 reveals a significant difference - about 6dB better PSRR for the diamond. Could this explain the SQ improvement? Charles designs his amps without GNFB so you'd tend to think that his OPS PSRR is really rather critical.

Since making this discovery I've been on the look-out for opamps with diamond buffer OPSs - OP260 was one I found (courtesy of Esperado) but there are a few from Linear Technology which I've ordered up a few of. In particular, LT1886 and LT1723 look very interesting as potential amp/buffer stages in DACs. LT is fairly unique in that they publish a simplified internal schematic in all the DSs I've looked at...
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