BA284 gain?

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simonsez

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Hi all,

any info how much gain of single stage Neve BA284 card?

best,
Simon
 

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looks like gain would be 1+2200/390  while cap coupled 1800 is in parallel with 390 increasing gain to roughly 7.8X

I am unclear what "T" connects to because termination there could affect gain.

JR
 
JohnRoberts said:
looks like gain would be 1+2200/390  while cap coupled 1800 is in parallel with 390 increasing gain to roughly 7.8X

I am unclear what "T" connects to because termination there could affect gain.

JR

which better way to get more gain? wiring the input transformer as 1:1, or  connect  T to V in series with resistor to increase gain.
 
Yeah the T connection is the normal way of changing gain ,as you said , a switched resistor chain is normally here which varies the feedback over the stage .
There are more elaborate full drawings of Neve Ba  ,with suggested values of resistor and the resulting gain .
 
simonsez said:
which better way to get more gain?

wiring the input transformer as 1:1,
removing attenuation is always preferable to adding gain
or  connect  T to V in series with resistor to increase gain.
A variable R from T to V would increase gain, that is probably what T is there for...

It is capacitor coupled because changing other gain setting resistors in the circuit would change DC operating point.

JR
 
simonsez said:
which better way to get more gain? wiring the input transformer as 1:1, or  connect  T to V in series with resistor to increase gain.

The transformer is a step UP type so wiring it 1:1 (if that is possible) would reduce the gain. A resistor between T and V is the usual way to set the gain. Lots of info about this on the web.

Cheers

Ian
 
simonsez said:
any info how much gain of single stage Neve BA284 card?
There is a document on the Internet called "Neve-1073-fullpak.pdf" that contains exactly the information you seek. Specifically there is a table that lists the gain associated with various bypass resistor values on point T. For example, it claims that you can achive as much as 48dB with a resistor of 8.2R (I have verified this with an LTSpice simulation which shows simulated gain of 48.1dB but I have never measured actual gain or stability of this particular configuration). You must also specify a feedback resistor on point S although the value is largely not influential so you should probably just use something like what is used in known circuits like 15K or 18K. In the typical 1073 circuit, first stage gain is defined by 15K FB and 91R bypass which yields gain of 30dB.
 
squarewave said:
There is a document on the Internet called "Neve-1073-fullpak.pdf" that contains exactly the information you seek. Specifically there is a table that lists the gain associated with various bypass resistor values on point T. For example, it claims that you can achive as much as 48dB with a resistor of 8.2R (I have verified this with an LTSpice simulation which shows simulated gain of 48.1dB but I have never measured actual gain or stability of this particular configuration). You must also specify a feedback resistor on point S although the value is largely not influential so you should probably just use something like what is used in known circuits like 15K or 18K. In the typical 1073 circuit, first stage gain is defined by 15K FB and 91R bypass which yields gain of 30dB.

The output stage of the BA284 was typically run at 20dB gain or less. The internal operating level of Neve mixers in those days was about -8dBu . For a line out you wanted +4dBu which is a gain of 12dB. However there is about 4dB gain in the output transformer so you only need 8dB. Even if you are post a group fader with 10dB in hand you would only need 18dB. I do not recall one ever being run at a gain above 20dB.

Cheers

Ian
 
1073  line input transformer wiring as step down (-12dB),  wiring it as 1:1 will easy overdriving the input .
I found the resistor/gain table, will play with it.

thank's all
 

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Note that the change in impedance should be considered. You might get higher noise than necessary if the impedance of the input device or input transistor of the BA284 doesn't match the impedance of the transformer primary / secondary + load resistor.
 

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