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RCA BA6a attenuators
Old 27th February 2017
  #1
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CJ1973's Avatar
 

RCA BA6a attenuators

Would love to know what people are using to attenuate the higher inputs and outputs on these items.
Would appreciate some links even or a tech in LA.
Old 27th February 2017
  #2
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I think I did a T pad. I'll have to check.
Old 27th February 2017
  #3
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It's a 600Ω load. Here's a calculator. T-Pad / H-Pad Calculator - Resistor Values for Attenuation

It's really easy to make.
Old 27th February 2017
  #4
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Quote:
Originally Posted by jjblair View Post
It's a 600Ω load. Here's a calculator. T-Pad / H-Pad Calculator - Resistor Values for Attenuation

It's really easy to make.
To be honest I have no idea of what all this means
Thank you though. Would anyone be able to make them?
Old 27th February 2017
  #5
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Quote:
Originally Posted by CJ1973 View Post
To be honest I have no idea of what all this means
Thank you though. Would anyone be able to make them?
Anybody who knows how to solder. Every engineer should know how to solder. This might be your time to learn!
Old 27th February 2017
  #6
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Quote:
Originally Posted by jjblair View Post
Anybody who knows how to solder. Every engineer should know how to solder. This might be your time to learn!
I'm actually a songwriter and musician who happens to produce music.
I should just ask a tech to do it. I'd suck at it.
Old 27th February 2017
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Quote:
Originally Posted by CJ1973 View Post
I'm actually a songwriter and musician who happens to produce music.
I should just ask a tech to do it. I'd suck at it.
Ha! Fair enough. Should be easy for them. God luck.
Old 27th February 2017
  #8
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Quote:
Originally Posted by jjblair View Post
Anybody who knows how to solder. Every engineer should know how to solder. This might be your time to learn!
Did you do it on the input or output or both?
Any item you recommend here?
Thx!!
https://www.pacrad.com/catalogsearch...q=Attenuator#2
Old 27th February 2017
  #9
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Quote:
Originally Posted by CJ1973 View Post
Did you do it on the input or output or both?
Any item you recommend here?
Thx!!
https://www.pacrad.com/catalogsearch...q=Attenuator#2
I think I only did the output. I believe all the pads on that page are input pads, and are H pads. You're going to want to make sure it's a 600Ω pad, because that's the impedance the output transformer is going to want to see. Best to have a tech make it.
Old 27th February 2017
  #10
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Quote:
Originally Posted by jjblair View Post
I think I only did the output. I believe all the pads on that page are input pads, and are H pads. You're going to want to make sure it's a 600Ω pad, because that's the impedance the output transformer is going to want to see. Best to have a tech make it.
Great thanks.
I found this on line and made me think if i need both input and output as well, which to me somewhat makes sense as the preamps could be driven harder?
Would love your thoughts
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RCA BA6a attenuators-img_1599.jpg  
Old 27th February 2017
  #11
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I don't know that driving the preamp harder is that big a deal. There's a ton of headroom in this circuit.
Old 27th February 2017
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14dBm is max input, so a hot modern DA output will overload the transformer. Verge of limiting is quoted as -24dBm with input all the way up, input has a 40 dB variable range. Input has both 150 and 600 ohm taps brought out to the connector, so that verge of limiting would translate closer to -30 dBm if you are using the 150 ohm taps. You could use whichever suitable H, U, O or T pad you prefer for either input. A 20dB pad is probably the right range for modern high level signals from a converter, though anything slightly lower wouldn't get into extreme compression easily. So 10dB could prove a better value in some instances. 15 dB; whatever suits the way you work.

Output already has a 0-20dB range 600 ohm T pad. It should also have a 620-680 ohm resistor across the output connector, as the output control expects a 600 ohm load to deliver the quoted dB steps. Maximum output with limiting disabled is quoted as 38.5dBm = 7W. Verge of limiting with output pad set set to 0 is roughly 30dBm = 1W. If you have 10dB limiting and turn the output down to -20, you should still be within the acceptable range of most AD converters, and not need an additional pad. If the knob position freaks you out, you might like an additional 600 ohm T pad between the output control and the output load resistor so the knob doesn't run so low, but that's all mental, the result is the same.

YMMV depending on how you like to run a BA-6, from barely touching to total slammed at all times.
Old 27th February 2017
  #13
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BA-6a

Input attenuator generall not required, as evidence by 55+ years of operation within +4 and +8 bus structures. Now some of the ears that drive the limiter from their racked 1073's with the 10 dB fader loss bypassed, do claim that an input pad is beneficial.
From +4, the input attenuator is neither way down nor close to full up, and the limiter functions just fine.

Output attenuator is needed.
If you are one of the few that work in the +4 bus world, a 19 dB output pad is ideal, this allows the pot to in the "sweet" zone, between 10 and 2 o'clock. two series resistors of 270 ohms each and a shunt resistor of 68 ohms works well.

The output attenuator is the last device in the BA-6a circuit and itself provides the necessary termination for the amplifier/transformer, ASSUMMING there is at least 6 dB of attenuation dialed in the attenuator, OR you have a terminating pad installed (like the one mentioned above).

Your friend McCurry can fill you in with more details.
Old 28th February 2017
  #14
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Thanks heaps Doug Williams and Cathode for your invaluable information. Really appreciate you both taking the time and chiming in. It makes sense for me to at least have the option so now I have to have a cool tech make them formme as I'm just totally clueless! Lol
Thanks again!!
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