A Direct-Coupled Input-Capacitorless Active Preamp deleted

[JohnRoberts]

No not crazy at all.. kind of slick actually. :guinness: While I see little real need to dial in pre gain by single digit decibels, it is hipper to have more resolution than 13 position switch and I'm sure many customers would embrace that.

A friend of mine used similar (single) switches on a custom console for mute/solo groups. Actually it was mute/not-mute groups using a circuit I designed for him. He had several regular reggae clients (is that an oxymoron?), so he liked to be able to just punch up 3 mics and mute everything else, then jump to 3 other mics in a different group, etc. This was long before affordable automation and quiet media, so it was useful to be able to set up a handful of groups and alternately mute or solo each "in place" (in the mix with effects). I don't recall all the details but I think calling a "not-mute" group would override the mute on a channel if it was muted by another mute group.

JR

 

[jdbakker]

[quote author="mediatechnology"]Why not consider an "instrumentation" approach with the left-hand switch setting the 1510/1512 gain in dB decades and having the right hand switch set the gain, in single dBs, in the follower. Sure sounds simple.[/quote]
Good plan. One minor implementation nit: from a noise POV it's better not to have the THAT151x operating at 0dB gain (or: at lower gain than the second stage). So either have the most significant digit gain range implemented as 5/15/25/...dB, with the second stage operating as -5..+4dB trim, or have the 0dB stage switch in a pad.

JDB.
[going in the opposite direction for the HDD rec mic pre: one rotary switch + 20dB button connected to a microcontroller, which implements relay switching of both gain stages and a pad]

 

[Samuel Groner]

LTMag_V04N2_Jun94.pdf gives additional information on how to implement flying rails. See page 20-22.

Samuel

 

[bcarso]

These are bootstrapped rails, to be distinguised from Funasaka's driven rails. Both approaches usually work pretty well for audio, with the latter doing a better job at high frequencies.

 

[JohnRoberts]

Bye, I guess... :sad:

I have long thought there is merit to eliminating input iron, input caps, and gain leg caps... Whether this is viable as a commercial product depends more on packaging and merchandising, as sonic improvements will be subtle. 'Iron'ically some in the higher end claim to like the sound that transformers add. Perhaps you'll also encounter folks who miss the sound contributions of their capacitors, too. :roll: A straight wire with gain IMO needs to be more wire and less magnetic or electrostatic coupling but YMMV.

Folks in the low end A) probably wouldn't be impressed with the concept, and/or couldn't hear the difference anyhow. So perhaps appeals to sub-segment of high end, who actually want a pristine audio path.

JR

PS: FWIW your dc coupled mic pre is what attracted me here, as I have been playing with this notion for years, albeit with a discrete front end approach, and less actual bench time invested.