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Holy Moly... RCA BA-31
Old 5th November 2011
  #61
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I'm new here, but see I'm in the right place. I have several BA-31b's rescued back in '82 with original schematics and in storage since then. I'd like to fire them up & reunite them with my bk-11a's that they originally powered. I see where the ac power should go, but anyone know the pinouts for the xlr in/out connections? Seems to be set up for 600 ohm. Any help is appreciated, thanks
Old 5th November 2011
  #62
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Cathedral Guitar's Avatar
There are several ones currently on eBay starting at $Holy Moly... RCA BA-31199
Old 17th December 2012
  #63
Quote:
Originally Posted by Seamus TM View Post
Not the same thing, I know, but any love for BA-21a around?
Quote:
Originally Posted by Matty Muir View Post
Of course! They're amazing!
I just got a BA-21a and had it racked up by Stephen Haselton of Shoals Audio. It looks and sounds amazing!

What is the difference in sound between the 31 and 21?
Old 17th December 2012
  #64
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Seamus TM's Avatar
 

Quote:
Originally Posted by littlesicily View Post
I just got a BA-21a and had it racked up by Stephen Haselton of Shoals Audio. It looks and sounds amazing!

What is the difference in sound between he 31 and 21?
RCA BA-31A Preamp Schematic
RCA BA-21A Preamp Schematic

Old 17th December 2012
  #65
Quote:
Thank you for the schematics, Seamus. Would any users experienced with both care to comment on the difference in "sound" between the two?
Old 18th December 2012
  #66
Umm.. just realizing the 31, 71 etc are solid state preamps and the 21 is tube. Sorry for getting to the party late. Pardon me while I make a sheepish exit :-)
Old 18th December 2012
  #67
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Seamus TM's Avatar
 

Quote:
Originally Posted by littlesicily View Post
Umm.. just realizing the 31, 71 etc are solid state preamps and the 21 is tube. Sorry for getting to the party late. Pardon me while I make a sheepish exit :-)
Not that it inherently means something, but that's why I posted the schematics for you to see.

I've never heard a 31x, so I couldn't say how the sound differs from a 21a.

I'll be hearing our 21a along with a whole heap of other US designed tube pres from the 50s and 60s soon, though!

Old 3rd January 2013
  #68
Anyone have both a BA31a and BA71a that can speak to hum levels?
I'd imagine due to the internal powering of the 31a, it will have a bit more hum than the 71a.
Thoughts?
Old 4th January 2013
  #69
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bdmctear's Avatar
 

Quote:
Originally Posted by littlesicily View Post
Anyone have both a BA31a and BA71a that can speak to hum levels?
I'd imagine due to the internal powering of the 31a, it will have a bit more hum than the 71a.
Thoughts?
Have never noticed any hum in our BA-31s. Don't have a 71a to compare to.
Old 4th January 2013
  #70
Quote:
Originally Posted by bdmctear View Post
Have never noticed any hum in our BA-31s. Don't have a 71a to compare to.
OK, thanks.
Old 4th January 2013
  #71
Quote:
Originally Posted by Seamus TM View Post
I'll be hearing our 21a along with a whole heap of other US designed tube pres from the 50s and 60s soon, though!

any report?
Old 1st March 2013
  #72
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Quote:
Originally Posted by littlesicily View Post
any report?
Sorry, I missed this.

Not quite yet.
We're still working on getting everything racked up.
RCA, Collins and Gates: oh my!
Old 1st March 2013
  #73
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My pair of BA71B that I just finished "racking" in an old Heathkit enclosure.





Love 'em!

Cheers,
--
Don
Old 1st March 2013
  #74
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Quote:
Originally Posted by idylldon View Post
My pair of BA71B that I just finished "racking" in an old Heathkit enclosure.





Love 'em!

Cheers,
--
Don
Hey, those are Gates knobs!
Looks awesome, man!
Old 1st March 2013
  #75
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idylldon's Avatar
 

Quote:
Originally Posted by Seamus TM View Post
Hey, those are Gates knobs!
Looks awesome, man!
Yes, those are Gates knobs. I also have a couple Gates Biamotes that I modified to be what they truly are, a single-channel mic pre.

Cheers,
--
Don
Old 1st March 2013
  #76
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Seamus TM's Avatar
 

Quote:
Originally Posted by idylldon View Post
Yes, those are Gates knobs. I also have a couple Gates Biamotes that I modified to be what they truly are, a single-channel mic pre.

Cheers,
--
Don
That's the way to do it!
Old 4th December 2013
  #77
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Quote:
Originally Posted by littlesicily View Post
Anyone have both a BA31a and BA71a that can speak to hum levels?
I'd imagine due to the internal powering of the 31a, it will have a bit more hum than the 71a.
Thoughts?
Just activated a ba-31b, and the first one had a bit of hum when i turned it up, as did the second one, but that was way up.

As an aside, the first amp cut in and out when on, the second one was fine. Anyone have an idea what the problem could be? I'm thinking to just re-cap it and try again...
Old 4th December 2013
  #78
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Quote:
Originally Posted by idylldon View Post
My pair of BA71B that I just finished "racking" in an old Heathkit enclosure.





Love 'em!

Cheers,
--
Don
Nice job! Would you share the schematic of the job? Particularly interested in the areas you added non-original features, like pad, 48v, variable input, etc.. I have some ba-31b's that I use straight in/out, but would like to rack them with these features. Any help would be great, thanks!
Old 5th December 2013
  #79
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Seamus TM's Avatar
 

Quote:
Originally Posted by littlesicily View Post
any report?
Forgot about this thread.

So, I went through a bunch of stuff this past year and ended up keeping (and loving) Gates SA-70 and Collins 6Q-1.
The RCA BA21a still aren't racked up, though...
Old 5th December 2013
  #80
Quote:
Originally Posted by Seamus TM View Post
Forgot about this thread.

So, I went through a bunch of stuff this past year and ended up keeping (and loving) Gates SA-70 and Collins 6Q-1.
The RCA BA21a still aren't racked up, though...
What sources are you liking the Gates and Collins on?
Old 5th December 2013
  #81
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Quote:
Originally Posted by littlesicily View Post
What sources are you liking the Gates and Collins on?
Pretty much everything.
The Collins is woollier than the Gates.
A lot of fun.
I've tried a bunch of tube pres in the last couple of years, and the only one that I like as much as the Gates would be a Fearn.
Old 5th December 2013
  #82
Quote:
Originally Posted by Seamus TM View Post
Pretty much everything.
The Collins is woollier than the Gates.
A lot of fun.
I've tried a bunch of tube pres in the last couple of years, and the only one that I like as much as the Gates would be a Fearn.
That's saying something about the Gates.
Is it fixed gain or variable? Pretty colored sounding I imagine?
Old 5th December 2013
  #83
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Seamus TM's Avatar
 

Quote:
Originally Posted by littlesicily View Post
That's saying something about the Gates.
Is it fixed gain or variable? Pretty colored sounding I imagine?
It's fixed gain, but it has a variable interstage volume control.
Colored is pretty subjective (blah blah blah).
In my world, API is clean, so I probably wouldn't be the one to ask.
I find that it has a nice thick softness to it.
Old 5th December 2013
  #84
Quote:
Originally Posted by Seamus TM View Post
It's fixed gain, but it has a variable interstage volume control.
Colored is pretty subjective (blah blah blah).
In my world, API is clean, so I probably wouldn't be the one to ask.
I find that it has a nice thick softness to it.
Haha...well I'd say API is about as clean as I go, also.
Old 5th December 2013
  #85
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Quote:
Originally Posted by Acmebob View Post
Nice job! Would you share the schematic of the job? Particularly interested in the areas you added non-original features, like pad, 48v, variable input, etc.. I have some ba-31b's that I use straight in/out, but would like to rack them with these features. Any help would be great, thanks!
For this project, I took the easy way out and used JLM's "Go-Between" and their power supply.

JLM Audio Shop

Cheers,
--
Don
Old 8th June 2014
  #86
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Hey folks, I just finished racking Brian's BA-31's (the one's mentioned at the beginning of this very thread). They really needed recapping and Brian wanted to add the standard mic pre features (48v, -20 pad, phase) as well as a line pad since they like to run stuff out of protools back through the RCA's. The line pad is a great feature, the details can be found here... Uneeda Audio - Build your own attenuator pads

I also added the variable gain mod outlined by PRR at groupdiy... Question for RCA BA-31A experts
This isn't a pad, it actually changes the gain of the circuit. I've done the mod to seven units now, it works great.

Lastly earlier in the thread VoiceManMike has a pic of a complete BA-31 unit laying in a one unit rack chassis. I have no idea how this worked. Brian's are the ones with the battleship gray powder coated finish, they were about 1/8 of an inch to tall. The top panel wouldn't have fit on, maybe the ones with the silvery faceplate are narrower, dunno.
Attached Thumbnails
Holy Moly... RCA BA-31-bri_1.jpg   Holy Moly... RCA BA-31-bri_2.jpg   Holy Moly... RCA BA-31-bri_3.jpg  
Old 8th June 2014
  #87
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Interesting thread.. i just wonder why they leave it in the high end forum?
Old 8th June 2014
  #88
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emrr's Avatar
Because they compete with many new things that are considered high end. Whatever high end means. They were high end for the time they were made.
Old 8th June 2014
  #89
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Quote:
Originally Posted by emrr View Post
Because they compete with many new things that are considered high end. Whatever high end means. They were high end for the time they were made.
i got a thread about rfz compressors removed because the devices are too cheap with just up to 1000.- for the monochannel unracked.. So i wonder why a 100.- rca amp should be weighted differently.

but i totaly agree that its stupid to measure a highend audio value with an actual sales price just because that low bargain price of some old units could interfear with some often not especially expensive sounding actual series 500 products.
Therfore i am really surprised to see such bargain tips in the highend subforum which as it states is for the expensive stuff only. maybe the mod has some dozends rca's in the cellar and wants them to become expensive? Has the thread effected the prices of these modules already?

i like that they are powered with +\- 30 volts.. i like to get some.
Old 8th June 2014
  #90
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The prices have hardly moved for years. 31's have centered around $300 for 15 years probably, with some wild variation both up and down. The part GS is not built to manage is the difference between unracked parts cost versus finished plug-and-play. These and many other 'bargain' pieces cost considerably more when finished off and ready to use. Maybe consider something like Langevin AM-16 versus the Mercury replica piece, and price a restoration/rackup all the way through. They can end up about the same.
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