Search found 3705 matches

by JR.
Thu Aug 07, 2008 8:59 am
Forum: Pro Audio Design
Topic: Graeme Cohen - Microphone Amplifier History and Design
Replies: 10
Views: 40471

Re: Graeme Cohen - Microphone Amplifer History and Design

I'm kind if busy at the moment but I have some cool stuff I can scan in... engineering sketches of movie cameras mounted into old model A (T?) Fords and such. AFAIK Muzak was not connected to RCA but a letter from the president of WE was addressed to my dad c/o MUZAK. Another data point is we actual...
by JR.
Thu Aug 07, 2008 7:38 am
Forum: Pro Audio Design
Topic: Graeme Cohen - Microphone Amplifier History and Design
Replies: 10
Views: 40471

Re: Graeme Cohen - Microphone Amplifer History and Design

My dad worked for WE and RCA, among sundry other related companies (Vitaphone, Muzak,,) . He was sent over to England in '30's to record coronation of King George (?). He was a recording engineer for RCA in NYC when he died in 1950's. I have some of his early engineering notebooks which are dated an...
by JR.
Sat Aug 02, 2008 2:12 pm
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 163644

Re: Benchmark Mic Preamp from 1984 - Active Preamp History

AFAIK the 5534 per it's specification won't drive 300 ohms rail to rail. According to Graeme, the input op amps only swing half rail making the use of 300R resistors possible. These op amps are also running class A in so far as their outputs are always sinking. I asked Graeme some time ago about us...
by JR.
Sat Aug 02, 2008 10:41 am
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 163644

Re: Benchmark Mic Preamp from 1984 - Active Preamp History

I don't see much market for a stand alone mic preamp. What about all those studios who need to get a mic or two into their HDD recorder? I used one just the other week to run an AKG condensor mic into a laptop. It is true that if the OM1556 hybrid was used in a traditional mixing desk front end appl...
by JR.
Sat Aug 02, 2008 9:26 am
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 163644

Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Yup.. Another point that is mentioned and perhaps worth discussing is the nominal impedance of the feedback network. I've looked at this a little in the context of very low noise front ends for A/D and you can get into current drive issues with standard opamps if you work at very low impedances. AFA...
by JR.
Sat Aug 02, 2008 7:15 am
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 163644

Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Thanks, I wish I could use that excuse, but I just skimmed through the pdf linked to and missed that "E" is apparently grounded. I guess "E" stands for earth (?). :oops: I'd have to spend more time looking at an actual implementation to find the claimed advantage of that topology...
by JR.
Fri Aug 01, 2008 7:00 pm
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 163644

Re: Benchmark Mic Preamp from 1984 - Active Preamp History

I'm not up on my semiconductor physics but I recall back in the '70s when working with monochips (semi custom ICs), you could get real resistors below a couple hundred ohms, but large resistances were made from pinch (?) resistors, and they were not very quiet or linear. I recall an early national I...
by JR.
Fri Aug 01, 2008 5:40 pm
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 163644

Re: Benchmark Mic Preamp from 1984 - Active Preamp History

:D small world thanks to WWW. I appreciate his clarification that he doesn't consider it invention, and the distinction that his design passes CM signals through to the outputs. Passing the common mode through to the output doesn't really strike me as a benefit. When dealing with raw signals I prefe...
by JR.
Fri Jul 18, 2008 5:02 pm
Forum: Pro Audio Design
Topic: Old: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 212
Views: 409067

Re: A Direct-Coupled Input-Capacitorless Active Mic Preamp

I feel like the old duffer repeating his stories, but I recall disapproving one vendor's capacitor in that application (blocking phantom) while at Peavey when the cap vendor made some process change to their part that made their leakage current audibly noisy. In a production environment nobody waits...
by JR.
Fri Jul 18, 2008 10:16 am
Forum: Pro Audio Design
Topic: Old: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 212
Views: 409067

Re: A Direct-Coupled Input-Capacitorless Active Mic Preamp

I think we discussed this once before.. A two gang switch for 10s and 1s could give more than enough range, putting the 1s on a second gain stage would simplify managing gain interactions. I think I've seen thumb wheel switches with stops in them which could be nice as we don't need 100dB of gain. I...