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-   -   LM3875 Inverted Or Not? (http://www.diyaudio.com/forums/chip-amps/225254-lm3875-inverted-not.html)

tom wesley 8th December 2012 02:16 PM

LM3875 Inverted Or Not?
 
Im thinking of building a valve buffered clone. Does it have to be an inverted setup? Am i over/under complicating things. Is non inverted possible?

AndrewT 8th December 2012 02:25 PM

I get the impression you don't know what you are doing.

Post a schematic and hope that someone can guide you.

peranders 8th December 2012 02:28 PM

You can take a peek at my project but the design isn't set yet and not explained. This will come later on. The schematics will also have variants.

My project is a single/dual E88CC tube buffer in cathode follower mode or "White Cathode Follower" mode + inverted/non-inverted gainclone (LM3886) + power supply.

tom wesley 8th December 2012 02:33 PM

I understand the schematic in so far as ive built gainclones (non inverting kit) and wondered if i could builb a valve buffer for it. The schematics are all a variation on inverted designs. I dont fully understand the implications of using the valve with the chip

peranders 8th December 2012 05:58 PM

You will get a rather low input impedance of the inverting amp so a buffer could be good to have and why not a tube buffer in order to get some tube flavored sound.

tom wesley 8th December 2012 06:11 PM

But is it feasible to do with non inverting amp?

Robert Kesh 8th December 2012 06:53 PM

Quote:

Originally Posted by tom wesley (Post 3276395)
But is it feasible to do with non inverting amp?

yes, though no longer as necessary to have a buffer. you would just do it for colour.

perhaps people only use inverting to justify using a buffer to themselves, and hence valves.

KSTR 8th December 2012 07:06 PM

Unless you have whimp of a preamp, inverted config doesn't necessarily need a pre. You can get pretty high input impedance (like 10k) when using a T-network for the feeback path.

planet10 8th December 2012 08:45 PM

Quote:

Originally Posted by tom wesley (Post 3276395)
But is it feasible to do with non inverting amp?

Thorsten Loesch's design -- one of the originally published gainclones -- is inverted. The inverted version includes everything "before" it in the feedback loop so a buffer is really required. Buffered, inverted gainclones, in my experience, are best of breed. If using a cathode follwer, for best performance requires a CCS on the tail of the CF.

dave

madtecchy 9th December 2012 09:21 AM

Quote:

Originally Posted by KSTR (Post 3276478)
Unless you have whimp of a preamp, inverted config doesn't necessarily need a pre. You can get pretty high input impedance (like 10k) when using a T-network for the feeback path.

I have tried the t network on my inverting lm3886. The extra connection to ground seems to inject ground noise into the input... Any comments?

Ps can get 10k input impedance without t network in inverted mode


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