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Project Specific Discussions => Preamplifiers => Topic started by: Tubetec on October 12, 2016, 11:42:34 PM

Title: Neve ba283 output stage
Post by: Tubetec on October 12, 2016, 11:42:34 PM
Just picked up a few Neve clone boards from ebay,I intend to get some transformers from AML soon,
But in the mean time for test purposes I found an old TUAC TP-125 ,its a power amp module made in the late 70's .It has a driver stage thats really quite similar to a Neve Ba283 output stage ,complete with gapped transformer ,2n3055,and 2 bc182's .The output impedence is a good bit lower than a stock Carnhill ,4:1 step down,so about -12db gain compared to a stock LO1166.I've put a ten turn pot in place of the gain control /feedback resistor ,so this allows fine tuning of output levels.I'm running the preamp off two series connected six cell Lithium-ion laptop batteries ,of course with balanced charge from a hobby/Rc style charger .I just about have it wired up now ,next its time to test it out ,find a few pics below .Any comments, or questions welcome .More to follow very soon .....
Title: Re: Neve ba283 output stage
Post by: Tubetec on October 12, 2016, 11:45:01 PM
eddystone case,
Title: Re: Neve ba283 output stage
Post by: Tubetec on October 13, 2016, 01:52:07 PM
Had a chance to test out the unit today,exceeded my expectations by quite a bit ,20hz-50khz into 1kohm within a small fraction of a db,almost 40volts pk-pk output with no visible flattening of the sine wave ,gain around 20 db ,which was a surprise considering the low secondary impedence of the transformer. Slight ringing/overshoot on square waves,but this is to be expected with an unloaded secondary ,with no Zobel network in place.24 volt battery supply worked great too ,tons of juice on tap ,and with 4400mah should power a single neve output stage for about 2 days continuously.Finally I have some of the neve magic to put my sounds through ,without having to break the bank .
Comments ,questions ,criticism very welcome . 
Title: Re: Neve ba283 output stage
Post by: Tubetec on October 27, 2016, 08:34:16 AM
I managed to get a hold of some details about the Tuac driver transformer ,its actually a 4:1+1,which fits in better with my test results.I have the secondaries wired in series ,so effectively 2:1,stepdown. Compares very favourably with Neve LO1166,
both from the bandwidth and output voltage/distortion perspective. Repanco/Bartlett transformers can still produce these units at a reasonable cost ,£18 each, delivery charges not included.
Title: Re: Neve ba283 output stage
Post by: gridcurrent on October 27, 2016, 02:46:43 PM
its actually a 4:1+1,which fits in better with my test results.I have the secondaries wired in series ,so effectively 2:1,stepdown. Compares very favourably with Neve LO1166,
are you a member of the "low headroom society"?
advocates are hanging out over at GS.
Title: Re: Neve ba283 output stage
Post by: Tubetec on October 30, 2016, 12:05:30 PM
Hi Grid current ,
Thanks for the reply ,havent heard of the place you speak of ,but I would be interested ,send me some more info when you can .
Title: Re: Neve ba283 output stage
Post by: Whoops on January 02, 2017, 10:41:38 PM
Hi,
would love to help out and give advice but I don't know what you are trying to do.

Maybe you need to explain a little bit better what are your goals with those BA283 boards.

I would do Mic Pres or Line amps with them.

Title: Re: Neve ba283 output stage
Post by: ruffrecords on January 03, 2017, 04:05:08 AM
I am puzzled by the additional four TO3 transistors in the first pic. Did you ever trace out the schematic of this? There seems to be no bias pot as in the Neve design.

Cheers

ian