Design Con 2015
Breaking News
Comments
Newest First | Oldest First | Threaded View
Jay Sinnett
User Rank
Rookie
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
Jay Sinnett   8/10/2011 2:31:15 PM
NO RATINGS
In the circuit description of the 5532, Doug says he doesn't understand the function of Q14. I am not the designer, but I think he was on the right track when he referred to clamping. It's plain to see that Node 3 rides at about 2Vbe above the neg supply (Q8 + Q9). If node 3 (the collector of Q9) starts to go below 1Vbe, then Q14 turns on and sucks current out of Node 2, limiting the drive to Q8 + Q9. In effect, this prevents the collector voltage of Q9 from ever going below about 1Vbe. In other words, it prevents Q9 from going into "hard saturation." Hard saturation causes slow recovery time - so the purpose of Q14 is to keep the circuit recovery time fast whenever the output stage has approached the negative rail. At least that's my guess.

sinsinsin49
User Rank
Rookie
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
sinsinsin49   8/5/2011 7:07:26 AM
NO RATINGS
What I don't understand is that the modern, real audio opamps: LME49990, OPA1611, and OPA211 were omitted! They all are superior in performance compared to those that have been presented. With properly designed LME49990 based circuitry it is actually possible to do 24-bit quality analog work. Please explain.

kendallcp
User Rank
Rookie
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
kendallcp   8/3/2011 9:50:32 PM
NO RATINGS
That's not quite accurate. You need to multiply the noise spectrum by the frequency response that it's exposed to, and then rms it up (square it and integrate over the bandwidth). If the response is a single-pole low-pass, that 1.57x factor (over sqrt(BW))pops up automatically from the integration. The methods are equivalent if the noise density is flat with frequency, but it often isn't.

Hughston
User Rank
CEO
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
Hughston   8/3/2011 9:35:32 PM
NO RATINGS
To calculate the noise in the audio bandwidth you have to add all the noise components in an RMS fashion then multiply them by a bandwidth factor like 1.57 x sqrt (BW). The factor depends upon the slope of the filtering beyond the 3 dB points. 1.57 in this case is for single pole filtering. There are app notes for this on the ADI and Intersil web sites.

Rene Prevo
User Rank
Rookie
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
Rene Prevo   8/3/2011 11:29:01 AM
NO RATINGS
The article talks about low noise, but what are levels of the noise in the audio range (1Hz to 20000 Hz)? RP

Dr. HD
User Rank
Rookie
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
Dr. HD   7/29/2011 9:22:37 AM
NO RATINGS
doh! The AD8597, 8599 and 797 parts are of course from Analog Devices. Note to self: the clue's in the part number!

Dr. HD
User Rank
Rookie
re: Op amps in small-signal audio design - Part 3: Selecting the right op amp
Dr. HD   7/28/2011 11:18:37 PM
NO RATINGS
It isn't true that the LM4562 has no "single" version. The LM4562 is actually the dual of the LME49710 and is therefore exactly the same as the LME49720. The LM4562 was released first, and the single version was then developed. By the time the single was released, National had changed their numbering scheme; the original plan was to phase out the LM4562 number and use just LME49720, but the former had gained too much traction in the market place. Interestingly enough, the LM4562 is less expensive, in small quantities at least. National have some other very impressive op amps in the LME series, most notably the LME49713, which is a current-feedback op amp with similarly ultra-low distortion, ultra-wide bandwidth, ultra-high slew rate, lower noise, and higher output current capability (at least ±93 mA) Other op-amps worth mentioning are the new AD8597 (single) & AD8599 (dual) from TI. These have been released since Doug's book was published and are recommended by TI over the AD797; which is very nice of TI given that the AD797 is considerably more expensive!



Top Comments of the Week
Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

Want a Voltera Desktop PCB Printer?
Max Maxfield
9 comments
I just received an email from my chum Javi in Spain. "Have you heard about Voltera (VolteraInc.com)? It's a Canadian company that is going to offer desktop-size PCB printers for fast ...

Aubrey Kagan

Have You Ever Been Blindsided by Your Own Design?
Aubrey Kagan
37 comments
I recently read GCHQ: The uncensored story of Britain's most sensitive intelligence agency by Richard J. Aldrich. The Government Communication Headquarters (GCHQ), Britain's equivalent of ...

Martin Rowe

No 2014 Punkin Chunkin, What Will You Do?
Martin Rowe
2 comments
American Thanksgiving is next week, and while some people watch (American) football all day, the real competition on TV has become Punkin Chunkin. But there will be no Punkin Chunkin on TV ...

Rich Quinnell

Making the Grade in Industrial Design
Rich Quinnell
15 comments
As every developer knows, there are the paper specifications for a product design, and then there are the real requirements. The paper specs are dry, bland, and rigidly numeric, making ...

Special Video Section
The LT8640 is a 42V, 5A synchronous step-down regulator ...
The LTC2000 high-speed DAC has low noise and excellent ...
How do you protect the load and ensure output continues to ...
General-purpose DACs have applications in instrumentation, ...
Linear Technology demonstrates its latest measurement ...
10:29
Demos from Maxim Integrated at Electronica 2014 show ...
Bosch CEO Stefan Finkbeiner shows off latest combo and ...
STMicroelectronics demoed this simple gesture control ...
Keysight shows you what signals lurk in real-time at 510MHz ...
TE Connectivity's clear-plastic, full-size model car shows ...
Why culture makes Linear Tech a winner.
Recently formed Architects of Modern Power consortium ...
Specially modified Corvette C7 Stingray responds to ex Indy ...
Avago’s ACPL-K30T is the first solid-state driver qualified ...
NXP launches its line of multi-gate, multifunction, ...
Doug Bailey, VP of marketing at Power Integrations, gives a ...
See how to ease software bring-up with DesignWare IP ...
DesignWare IP Prototyping Kits enable fast software ...
This video explores the LT3086, a new member of our LDO+ ...
In today’s modern electronic systems, the need for power ...