Search found 3662 matches

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: 142968

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: 142968

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: 142968

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 vs, the more common...
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: 142968

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: 142968

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: 348419

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: 348419

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...
by JR.
Thu Jul 17, 2008 11:07 am
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 142968

Re: Benchmark Mic Preamp from 1984 - History

yes 2 1% resistors before the cable capacitance.

JR
by JR.
Thu Jul 17, 2008 10:41 am
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 142968

Re: Benchmark Mic Preamp from 1984 - History

not sure what CFB means ... (Current feedback?) IIRC that console used Transamp mic pre, so gain pot was hanging off the emitters, so I guess yes a current feedback node.

This was before I rolled my own version a few years later in the '80s, after discovering those lovely low Rbb transistors.

JR
by JR.
Thu Jul 17, 2008 10:08 am
Forum: Pro Audio Design
Topic: Benchmark Mic Preamp from 1984 - Active Preamp History
Replies: 39
Views: 142968

Re: Benchmark Mic Preamp from 1984 - History

I actually did a similar derived CM shield drive in a LOFT console back in '70s. I had a mic preamp on one end of the input strip and the gain pot over a foot away. I used 2 cond shielded and drove the shield with CM to reduce cable capacitance effects on gain pot circuit nodes.

JR