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Jenson JE-990 discrete op amp

Posted 8th June 2015 at 08:45 AM by rjm
Updated 9th June 2015 at 01:09 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 03:47 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 06:44 AM by abraxalito
Updated 9th July 2015 at 10:43 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 - 莱曼(lehmann) 耳放 莱曼构架的好声耳放,全铝机箱,一体耳放-淘宝网

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 07:23 AM by mlise
Updated 30th May 2015 at 07:25 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 08:00 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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Posted 21st May 2015 at 02:32 PM by rjm
Updated 27th May 2015 at 02:54 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...
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Szekeres 2015

Posted 20th May 2015 at 07:00 AM by rjm
Updated 19th June 2015 at 12:26 AM 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!
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JLH-2005 headphone amplifier

Posted 18th May 2015 at 09:15 AM by rjm
Updated 27th May 2015 at 02:52 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.
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Why do I need a preamp?

Posted 14th May 2015 at 08:22 AM by cspirou

One of the things that confused me a bit when I started this hobby was the distinction between a preamp and an amp. Looking up info on a preamp usually was met with a definition that a preamp controls volume and switches inputs, which never made sense to me because my amp always had volume control and multiple inputs.

Well it turns out that what I (and most people) considered an amp was actually an integrated amp. It never really made that much sense to me to separate the functions in a separate chassis and I would roll my eyes seeing preamps worth at least as much as the price of a good amp. Discussions about the different sound of a preamp are a bit weird for me too. While I don't doubt that different preamps sound different, it seems like people are just separating components to do some mix and matching.

However after being in this hobby for a bit of time I have discovered some solid reasons to have a separate preamp(besides wanting to separate everything)...
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Posted 12th May 2015 at 05:08 AM by Mike94531
Updated 12th May 2015 at 05:12 AM by Mike94531

Finally finished these up....I attempted to paint them with a hammer finish spray paint..boy did they turn out bad!

So I found a roll of carpet at Lowes and bought a couple cans of spray adhesive.

The speakers sound pretty good..we'll see how they sound when I get around to building my Pass F5 far I only have the boards I bought from the store...expect a few months for sure at the rate I get things done!

Yes, that is real carpet...$20 for the roll..I know I won't win any beauty contests with them but for garage speakers I think they are pretty nice, I also saved some money by using left over wooden hanger rods for the center section supports!

Not sure what kind of grills I am going to put on them for protection out here in the garage, I might have to print something out when I get my 3D printer in a few weeks.

I also included a snapshot of the tool path my CNC Bridgeport used to cut the holes in the front...
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