brian@ucsd.EDU (Brian Kantor) (09/14/88)
As part of my design for a really wonderous hi-fi preamp, I've been trying to choose the right op-amps to use - or indeed, to discover whether simple discrete transistor or FET amplifiers might be better. For the RIAA phono preamp section, a simple LM540 with about 20dB of gain winds up with a frequency response well past 20kHz, and a slew rate of better than 3V/uS, which is pretty respectable (I think). For the tone-control section, a pair of MC1556s make a nice high- and low-frequency shelving equalizer with maximum of 20dB of boost and cut, and knee frequencies of 2kHz and 200Hz respectively. This part of the circuit will be bypassable by a "FLAT" switch. Finally, I think a LM540 will do nicely for providing the required 10dB or so of preamp gain to drive the power amp to full output from line-level input signals, and also the tape deck dubbing outputs. I could use an LM715, but it lacks the output capability to drive more than about 30pF of load, and I'm afraid that the several tape deck inputs in parallel would probably be more than that. These are based on a 10-year-old IC op-amp design book. Are there better chips for this purpose made these days? Any recommendations? Brian Kantor UC San Diego "There is more harmony in films than in life." - Francois Truffaut
chan@ames.arc.nasa.gov (Jeff Chan) (09/15/88)
From article <1152@ucsd.EDU>, by brian@ucsd.EDU (Brian Kantor): > As part of my design for a really wonderous hi-fi preamp, I've been > trying to choose the right op-amps to use - or indeed, to discover > whether simple discrete transistor or FET amplifiers might be better. > > For the RIAA phono preamp section, a simple LM540 with about 20dB of gain > winds up with a frequency response well past 20kHz, and a slew rate of > better than 3V/uS, which is pretty respectable (I think). >... > Finally, I think a LM540 will do nicely for providing the required 10dB > or so of preamp gain to drive the power amp to full output from > line-level input signals, and also the tape deck dubbing outputs. > ... > These are based on a 10-year-old IC op-amp design book. Are there > better chips for this purpose made these days? Any recommendations? Can't tell for sure, Brian, but it sounds like one of Walt Jung's books. See his update titles "Audio IC op-amp applications, 3rd ed" on Sams for revised reasoning and recommendations for op amps. It is very current (1987 copyright, I think). On a consumer note, the book updates only some of the basic theory parts and all of the audio parts of IC op-amp cookbook, so both books may be useful to have. The 540 is still good, but there may be fresher designs out that will do what you want better. Jeff C. Internet: chan@ames.arc.nasa.gov UUCP: ames!chan
ti@altos86.UUCP (Ti Kan) (09/15/88)
In article <1152@ucsd.EDU> brian@ucsd.EDU (Brian Kantor) writes: >As part of my design for a really wonderous hi-fi preamp, I've been >trying to choose the right op-amps to use - or indeed, to discover ... deleted description of LM540, MC1556s for RIAA phono stage, tone control and flat gain stage... Yes, now there are some much better op-amps for audio preamp applications. If low noise is prime concern, the Signetics NE5534A is the best. It combines superlative noise specs with high slew-rate (13V/uS), and low cost. For lower noise yet, Precision Monolithics' OP27 has less noise than the NE5534, but the slew rate is much worse (0.5V/uS). For superb slew rate (but not necessarily low noise), the National LM318 has a slew rate spec of 70V/uS. There is also a NE5532A that is a dual NE5534 with internal compensation. Signetics also has a new NE5535 that is also suitable for audio applications. For the most up to date information on these things, and articles of audio projects, I recommend the "Audio Amateur" magazine (not available from bookstands: Subscription only). -- -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_- Ti Kan, Altos Computer Systems UUCP: ...ucbvax!decwrl!sun!aeras!elxsi!altos86!ti -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
mjj@stda.jhuapl.edu (Marshall Jose) (09/16/88)
In article <1152@ucsd.EDU> brian@ucsd.EDU (Brian Kantor) writes: >As part of my design for a really wonderous hi-fi preamp, I've been >trying to choose the right op-amps to use .... > I've been poring over databooks for the roughly the same purpose, namely the design of a studio-quality (whatever that is) mixer. Basically, I've been looking for the following qualities: - low noise (~3 nV/root-Hz, 1/f knee around 1 Hz) - high PSRR at high gains - stable operation at G=.5 through G=500 - < $10.00/piece I narrowed my choices to the following: o PMI OP-27 o Signetics NE5534 o TI TL071 (maybe) All have several second sources. Only the first two are good for low-noise pre-amplification, BI-FET noise performance notwithstanding. Hope this helps. Marshall Jose WA3VPZ mjj@aplvax.jhuapl.edu || ...mimsy!aplcen!aplvax!mjj
jim@trsvax.UUCP (09/17/88)
And the typical reply when a hard-to-find magazine is referenced is... Where can we get in touch with Audio Amateur Magazine? (addr, phone, etc..) James T. Wyatt (UUCP:decvax!microsoft!trsvax!jim) KA5VJL Hey Man... I don need no steenkin disclaimor