IanB

Re: RCA Ba2A Pre amp qestions & answers
« Reply #400 on: August 02, 2020, 12:22:57 PM »
It is dead quiet (thanks to all the amazing knowledge and advice in this thread!). I’m so stoked with it! Very grown-up sounding (my first 2 valve pres so a new thing/sound for me).
Doug is right: with a dynamic & ribbon on vocal all 3 knobs are dimed but with a condenser the attenuators might be useful.
The cheap Chinese VU buffer I got is noisy as! Just ordered the JLM one which should hopefully work a treat.
So thankful for the previous 20 pages of gold that got me over the line so smoothly. Cheers boys!
REDD47 next! PSU is built and works (6x4 & 2 x OA2s = 300vdc). Turrets are done. Just gotta wire it up.
« Last Edit: August 02, 2020, 02:22:02 PM by IanB »


Re: RCA Ba2A Pre amp qestions & answers
« Reply #401 on: September 27, 2020, 10:26:06 PM »
Can anyone recommend me the most easily obtainable, affordable, but still great sounding transformers for this application? Input and Output. Wouldn't mind a power transformer recommendation either.

So far I've got.

Input: Jensen JT-115K-E

Output: Cienmag CMO-30/600

Power: Edcor xpwr146

Will these all works?

Also, what is the most effective way to include phantom power in this build?

Is there a power transformer that would work for two of these in one case


Ryan
« Last Edit: September 28, 2020, 01:45:52 PM by FarisElek »

IanB

Re: RCA Ba2A Pre amp qestions & answers
« Reply #402 on: October 28, 2020, 03:13:14 PM »
Can anyone recommend me the most easily obtainable, affordable, but still great sounding transformers for this application? Input and Output. Wouldn't mind a power transformer recommendation either.

So far I've got.

Input: Jensen JT-115K-E

Output: Cienmag CMO-30/600

Power: Edcor xpwr146

Will these all works?

Also, what is the most effective way to include phantom power in this build?

Is there a power transformer that would work for two of these in one case


Ryan

I used UTC 1:10 input and Carnhill 4:1 out. I used a Hammond power tranny. 300v & 6.3v secs. I use AKG phantom box if I need it but JLM does some easy phantom/phase boards - you’ll need a power tranny to suit but JLM will tell you what you need on top of your B+ & heaters.
It’s a really simple circuit & sounds so good! You can’t go wrong eh!

My3gger

Re: RCA Ba2A Pre amp qestions & answers
« Reply #403 on: November 13, 2020, 04:44:21 PM »
Can anyone recommend me the most easily obtainable, affordable, but still great sounding transformers for this application? Input and Output. Wouldn't mind a power transformer recommendation either.

So far I've got.

Input: Jensen JT-115K-E

Output: Cienmag CMO-30/600

Power: Edcor xpwr146

Will these all works?

Also, what is the most effective way to include phantom power in this build?

Is there a power transformer that would work for two of these in one case


Ryan

Jensen should be very good for input, Cinemag takes unbal. DC as required for BA-2 output and also have more appropriate ratio (7:1 instead of 4:1 some use). Ask Cinemag to make sure. Edcor is meant for power amp applications without phantom tap. Maybe try to find proper toroid because it is often cheaper and easier to work with.
Wish i would see more p2p projects, BA-2 is really simple for learning this technique...

JW

Re: RCA Ba2A Pre amp qestions & answers
« Reply #404 on: January 02, 2021, 11:44:10 AM »
Can 4:1 output not drive 600 ohms properly? Because, if it can, it's more gain and the Carnhill VTB 2290 looks like an obvious choice.

EmRR

Re: RCA Ba2A Pre amp qestions & answers
« Reply #405 on: January 02, 2021, 11:53:45 AM »
Can 4:1 output not drive 600 ohms properly? Because, if it can, it's more gain and the Carnhill VTB 2290 looks like an obvious choice.

First ?  will you ever actually be driving 600 ohms?  This affects the answer enormously.

If you are, it's not a ? of whether it can drive it, it's a question of distortion and gain.  The gain loss in the tube of driving a lower ratio into 600 ohms will counter the 'increased gain' of the transformer, mostly a wash.  But distortion will be higher in the driver tube. 

The bigger question is still whether there's sufficient inductance with DC current flow to give complete low frequency response, or whether the bottom will be rolled off early. 
« Last Edit: January 02, 2021, 09:49:20 PM by EmRR »
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

JW

Re: RCA Ba2A Pre amp qestions & answers
« Reply #406 on: January 02, 2021, 09:30:58 PM »
Thanks very much Doug. I have 3 pieces of equipment that I've noticed definitely prefer to be driven by a 600 ohm 'capable' source. (Am I using the right terminology?) But anyway, DIY pultec/LA2A/1176 I certainly prefer to drive them with something like a Neve over my converters' outputs. Feels like they work better.

EmRR

Re: RCA Ba2A Pre amp qestions & answers
« Reply #407 on: January 02, 2021, 09:48:46 PM »
Thanks very much Doug. I have 3 pieces of equipment that I've noticed definitely prefer to be driven by a 600 ohm 'capable' source. (Am I using the right terminology?) But anyway, DIY pultec/LA2A/1176 I certainly prefer to drive them with something like a Neve over my converters' outputs. Feels like they work better.

Yep, all 3 of those count.  Lower the better in those cases. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

JW

Re: RCA Ba2A Pre amp qestions & answers
« Reply #408 on: January 04, 2021, 09:05:05 PM »
As in a bigger step down (for lower impedance) if I'm reading you right? i.e. 7:1 or is it try it and see if it all comes out in the wash at 4:1? I guess the reason I ask is I'm about to put an order into Carnhill. . . . .for some other things.

EmRR

Re: RCA Ba2A Pre amp qestions & answers
« Reply #409 on: January 04, 2021, 10:15:34 PM »
Think of it backwards for the clearest picture:  If you're driving 600 ohms, the 4:1 loading on the tube is heavier, more distortion, lower level from the tube BUT less loss in the transformer.  7:1, lighter load on the tube, less distortion, higher gain, but more loss in the transformer.  How much distortion matters to you?  I can't say.  You might like either one over the other. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


 

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