diyAudio - Blog Entries
Go Back   Home > Forums > Blogs
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

op amps for audio

Posted 23rd January 2012 at 06:36 AM by rjm (RJM Audio Blog)

Douglas Self on op amps for audio, which I read before in slightly different form, on another web site somewhere, many years ago... today was a refresher course.

Excerpts from op amps in small signal audio design, by D. Self [Part 1, part 2, part 3, part 4].

I suppose I should get with the times and start using the LM4562 seeing as it is available in DIP8 now. (I had this memory that it was only SOIC, go figure...) Pity it's dual only. On the other hand, that leads to some neat ideas, like a compact version of the Sapphire amp for example, or the X-reg.

I am struck by how few choices we really have when it comes to practical op amps for audio in single DIP8 packages. There is the NE5534, TL071 and TL051, the OPA134, the OPA604, and OPA27, OPA627. Maybe the AD797 but I have yet to see the point. Given that the TL1071 and derivatives are outdated and replaced essentially by the OPA134, and given the excessive cost (and questionable sonic benefit)...
rjm's Avatar
diyAudio Member
Posted in The Lab
Views 1876 Comments 2 rjm is offline

Anyone notice parallels here with Intel?

Posted 23rd January 2012 at 12:25 AM by abraxalito
Updated 23rd January 2012 at 12:27 AM by abraxalito

Could Kodak's demise have been averted? | Technology | The Observer

My best bet for why Kodak is history comes towards the end of this relatively short piece:

More insightful analyses point to the fact that Kodak had a near-monopolistic grip on a market that was giving it a 70% margin on its products and processes, and that therefore the people who ran the film part of the business were the ones who carried most weight in corporate discussions.
abraxalito's Avatar
diyAudio Member
Views 688 Comments 0 abraxalito is offline

Bt schematic

Posted 22nd January 2012 at 03:59 PM by klewis
Updated 23rd January 2012 at 12:19 AM by klewis
Pavel's scheme
klewis's Avatar
diyAudio Member
Posted in Uncategorized
Views 1047 Comments 0 klewis is offline

The new system, up and running.

Posted 22nd January 2012 at 10:52 AM by rjm (RJM Audio Blog)
Updated 25th January 2012 at 07:57 AM by rjm

So now we have the model 0247 DAC/preamp/headphone amplifier and model 0347 power amplifier in the main system. That's the old Denon DP-2000 TT, Phonoclone 3, and Onkyo D-605SR speakers.

The gain of the 0347 is 30 dB, so with the 0247 doing duty as a preamp the overall gain is a tad high, but it's perfectly useable. I'll look at the passive preamp options (including the model 0447) at a later date.

Anyhow, the big news is it completely destroys the non-inverting LM3875 Gainclone I have been using for the last decade, so badly, in fact, I'm starting to wonder if my Gainclone was busted. In comparison with the 0347 it sounds like a distorted, uncontrolled mess.

Since my speakers are really very modest in quality (though at 82dB and 6 ohms, a bit of a rough load) I wasn't expecting much difference one way the other, so this comes as a severe shock.

Unfortunately I'm not within reach of a good reference system to give the 0347 a real evaluation....
Attached Thumbnails
Click image for larger version

Name:	IMGP1513j 1280.jpg
Views:	1205
Size:	348.1 KB
ID:	576  
rjm's Avatar
diyAudio Member
Views 1677 Comments 1 rjm is offline

Sony SA H7900, motional feedback active speakers

Posted 21st January 2012 at 10:42 AM by hbc

Following my "conversion" that valves really do sound better than transistors:

My home stereo, which is compromised by having to be small person resistant, has been in a state of flux. I worked out that the most economical tube fix was to by a receiver from ebay, so I got a 1967 ish one, 17 tubes, push pull EL84s etc, it is original and it works, but the RIAA is way, out the FM stereo decoder needs re alignment, and all the output tubes share a common cathode resistor, 2 ECC83s in series.... so it went on the bench and has stagnated... also most of my speakers don't really suit it.

So to fill the gap I thought I would drag out a pair of Sony SA H7900 active speakers I acquired about 8 years ago, not just active, motional feedback woofers and electrostatic tweeters no less, and bass reflex(?) what could possibly go wrong?

Attached Thumbnails
Click image for larger version

Name:	IMG_0192.jpg
Views:	5454
Size:	380.3 KB
ID:	573   Click image for larger version

Name:	IMG_0193.jpg
Views:	4590
Size:	391.9 KB
ID:	574   Click image for larger version

Name:	IMG_0194.JPG
Views:	1946
Size:	734.1 KB
ID:	575  
diyAudio Member
Posted in Uncategorized
Views 6278 Comments 0 hbc is offline

47 Labs Treasure 0347 : trials and tribulations

Posted 20th January 2012 at 11:48 AM by rjm (RJM Audio Blog)

And not even sure what a tribulation is, but I'm sure I've had at least one building this amp.

Like the 0247 it's not so much difficult as it is painstaking hard work. The output transistors have to be mounted "just so" so the boards screw to the case properly, the wiring of the thermal protection transistors and gluing them to the output devices is tricky and easy to mess up.

I triple-checked and was rewarded by, it seems, error free boards. I messed up and wired the mute switch incorrectly though (the photos show it wrong, in case you come across this blog post looking for help) and I think the switch has a fault somehow as L and R channels appear to me mixed together. Taming the offsets gave me considerable grief but I think its all OK now.

Tomorrow I'll hook it up to the speakers and see what happens.
Attached Thumbnails
Click image for larger version

Name:	DSC_3005 1280.jpg
Views:	2976
Size:	311.5 KB
ID:	569   Click image for larger version

Name:	DSC_2991 1280.jpg
Views:	3403
Size:	401.7 KB
ID:	570   Click image for larger version

Name:	DSC_2969 1280.jpg
Views:	2458
Size:	243.7 KB
ID:	571   Click image for larger version

Name:	DSC_3007 1280.jpg
Views:	4330
Size:	290.9 KB
ID:	572  
rjm's Avatar
diyAudio Member
Views 2943 Comments 1 rjm is offline

Measuring Noise

Posted 19th January 2012 at 03:28 PM by klewis
Updated 19th January 2012 at 03:32 PM by klewis

For LED's - Christer's thread
An interesting method of grading zeners for noise, that I have used for years, is to monitor the noise across the devices with a scope while using my HP bench supply to bias them. The noise spectrum changes quite dramatically as you come into breakdown and then drops to it's minimum at it's prefered current flow. I note the current and voltage after it has settled down. I choose the ones to use by voltage match and bias them accordingly.

One other trick, if you want to know how quiet your supply is, choose a suitible coupling cap and hook the output of it up to a line input on your preamp and listen to it. Try this with and without a load and during normal operation of the supply. A good supply is dead quiet. author: MikeBettinger
klewis's Avatar
diyAudio Member
Posted in Uncategorized
Views 844 Comments 1 klewis is offline

A different design aesthetic.

Posted 17th January 2012 at 10:52 AM by rjm (RJM Audio Blog)
Updated 25th January 2012 at 10:21 PM by rjm

I like the concept of appearance in high-end audio. I mean, where the look of the equipment makes a statement about what it's all about inside.

The 0347 is proportioned like a vintage tube receiver, but in miniature. It even has the lit, transparent front panel where the radio tuning strip would have resided. The heavy grey hammertone and very simple, basic hardware are reminiscent of Heathkit or Dynaco. In short, the appearance evokes the spirit of a simpler, more innocent age of vintage hifi without being a slavish replica.
Attached Thumbnails
Click image for larger version

Name:	DSC_2962 1280.jpg
Views:	854
Size:	276.3 KB
ID:	568  
rjm's Avatar
diyAudio Member
Views 1181 Comments 0 rjm is offline

Another package in the mail...

Posted 14th January 2012 at 10:30 AM by rjm (RJM Audio Blog)

The 47 Labs "Treasure" stereo amplifier kit model 0367 has just arrived here at RJM Audio central command.

61,500 yen delivered, a tad more than the model 0247 headphone amplifier / DAC. Basically lose the volume control and DAC board, gain a bigger transformer and a thick aluminum bottom plate that serves as the heatsink... the amplifier circuit itself is almost identical, just with a slightly bulked-up output stage and the addition of certain safety considerations such as fine tune-able bias current and thermal protection for the output transistors.

Which makes an unusual circuit for a power amplifier: the output stage is a unity gain current buffer running open loop. For a headphone amp that's justafiable because the bias current is such that the amp will almost always be running in class A. For a power amp rated 40 W into 4 ohms, it's class AB.

Mr. Tsukahara seems pretty pleased with the result though, and I am anxious to try it...
Attached Thumbnails
Click image for larger version

Name:	DSC_1012 1280.jpg
Views:	947
Size:	360.8 KB
ID:	567  
rjm's Avatar
diyAudio Member
Views 1039 Comments 0 rjm is offline

This vs. that.

Posted 12th January 2012 at 11:41 PM by rjm (RJM Audio Blog)
Updated 26th January 2012 at 05:42 AM by rjm

47 Labs 0247 vs. RJM Audio Sapphire

I wasn't even aware that the folks at 47 Labs were developing a headphone amplifier until after the Sapphire was finished, and I'm sure they didn't know what I was working on, so it's all the more remarkable just how similar the two designs are. Two separate answers from two separate people sharing the same general design philosophy.


- Solid state op amp voltage stage front end and solid state push-pull buffer running open loop for the output stage.
- Gain of 5-6x (14-16 dB)
- 20-30 mA bias current in the output stage.
- All BJT circuit** (see footnote)
- Use of "diamond buffer" circuit element. (Albeit in very different ways)
- 10 V voltage rails, split supply.


- My voltage stage is an OPA134, or any 8 pin DIP op amp IC. 47 Labs voltage stage is a fully discrete current feedback op amp with a diamond buffer...
rjm's Avatar
diyAudio Member
Views 1086 Comments 1 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 09:29 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2