Neve BA283AM questions(s)
« on: February 12, 2018, 01:18:42 PM »
Hello all,

I am a student in a EET program in the U.S. I am building a 16x2 summing mixer for a final project for school. I have gathered all of the schematics, and documents I could find from here, Geoff Tanner's website, and other sources regarding the Neve 283 amp cards.

I am using the BA283AM output circuit for make up gain for the summing mixer. I am looking for a wiring diagram of how to actually hook up just this circuit from a Carnhill VTB9071 10k:10k transformer, and also the output to the Carnhill VTB9049 output transformer. I'm hoping one of the many people that has already done this can help me.

I understand the output from the resistor buss for both + & - signal will need to be connected on both ends. If I am reading the documents correctly, Pin M is the +24V, and Pin J is circuit ground (common). I am having a hard time deciphering where everything else goes.

I have all of my parts and am ready to breadboard the circuit. I know there are pre-made PCBs available for these circuits. I am required to have my own manufactured as part of the project criteria.

I really appreciate the tremendous pool of knowledge here on this forum, and want to thank anyone in advance for any help or advice they can offer.

George


API

Re: Neve BA283AM questions(s)
« Reply #1 on: February 12, 2018, 03:36:23 PM »
Have you had a look at the Neve 1272 and 1271 schematics?

ruffrecords

Re: Neve BA283AM questions(s)
« Reply #2 on: February 12, 2018, 04:49:25 PM »
Here is a link to the Neve 1073 documentation which illustrates how a BA283 is typically wired up:

http://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

The output section on its own is probably not enough for the gain make up of a summer but it depends on what kind of summer you mean. Do you have a schematic of it you can post?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Neve BA283AM questions(s)
« Reply #3 on: February 12, 2018, 10:17:35 PM »
Hi API,

I haven't been looking at the 1272 so much. I seem to remember reading that they were the actual buss amps used in the Neve consoles, and that a lot of folks convert them into mic pre-amps. I will have another look.

Thanks,

George

Have you had a look at the Neve 1272 and 1271 schematics?
« Last Edit: February 12, 2018, 10:26:24 PM by Gsrokmix »

Re: Neve BA283AM questions(s)
« Reply #4 on: February 12, 2018, 10:25:46 PM »
Hi Ian,

I do have that package of docs, but it's still unclear to me the actual physical connections I need to make just to that output stage w/ the 2N3055.

I have attached a very ruff schematic of what I was hoping to accomplish. I have bunches of 10k Holco, Shinkoh, and some other esotericy resistors, and I wanted to try each kind in the summing network & see if I can hear any difference. As they are all 10k, if 10k on every line will bring the gain of each pair down too much, I was thinking of just wiring 2 in parallel on each to get 5k. I also seem to remember reading somewhere that 6.8k seemed to work well with a similar circuit.

Thanks again for any advice!

George

Here is a link to the Neve 1073 documentation which illustrates how a BA283 is typically wired up:

http://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

The output section on its own is probably not enough for the gain make up of a summer but it depends on what kind of summer you mean. Do you have a schematic of it you can post?

Cheers

Ian
« Last Edit: Today at 02:51:34 PM by Gsrokmix »

ruffrecords

Re: Neve BA283AM questions(s)
« Reply #5 on: February 13, 2018, 06:26:27 AM »
That might just work. I would be tempted to change the 10K input resistors to 4K7 so the input impedance is close to 10K, With 8 input the loss will be 8 times or18dB. The bus impedance will be 9K6/8 which is 1200 ohms which is a reasonable source for a 10K:10k transformer. To maintain the bus impedance and keep the loss constant you will need to ensure unused inputs have their hot and colds shorted together.

I think the only error is on the secondary of the transformer. At the moment you have it pretty much connected across the base and emitter of the first transistor. I think the transformer secondary needs one side grounded. So the BA283 pins connections should be:

A strapped to J
J is 0V
M is +24V
K is the gain boost pin. Connect a resistor from K to J to boost gain
Output transformer goes between  H and B
Input transformer secondary goes between L and J

Without a gain boost resistor the amp has a gain of about 12dB and there is another 6dB in the output transformer so there should be a nominal 18dB overall which just what you need. You can always coax a little more gain if you need it using the gain boost resistor.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

My3gger

Re: Neve BA283AM questions(s)
« Reply #6 on: February 13, 2018, 11:12:10 AM »
I have bunches of 10k Holco, Shinkoh, and some other esotericy resistors, and I wanted to try each kind in the summing network & see if I can hear any difference.

You could also sell this resistors to audiophiles if there is enough of them, after making wanted tests.
Most of us find metal films (~3W max are readily available) work best because of low noise, high stability, low price, no distortion to speak of, and "no sound". Other  parts and circuits will take care of sound.

Re: Neve BA283AM questions(s)
« Reply #7 on: February 13, 2018, 01:37:41 PM »
Hi Ian,

I forgot to mention that I do also have the Grayhill switched normally used in the "EZ1290" and I'm assuming original circuits? Will this switch provide some extra gain? Does this swich change the feedback resistance which would change the gain?

Thanks again so much!

George


That might just work. I would be tempted to change the 10K input resistors to 4K7 so the input impedance is close to 10K, With 8 input the loss will be 8 times or18dB. The bus impedance will be 9K6/8 which is 1200 ohms which is a reasonable source for a 10K:10k transformer. To maintain the bus impedance and keep the loss constant you will need to ensure unused inputs have their hot and colds shorted together.

I think the only error is on the secondary of the transformer. At the moment you have it pretty much connected across the base and emitter of the first transistor. I think the transformer secondary needs one side grounded. So the BA283 pins connections should be:

A strapped to J
J is 0V
M is +24V
K is the gain boost pin. Connect a resistor from K to J to boost gain
Output transformer goes between  H and B
Input transformer secondary goes between L and J

Without a gain boost resistor the amp has a gain of about 12dB and there is another 6dB in the output transformer so there should be a nominal 18dB overall which just what you need. You can always coax a little more gain if you need it using the gain boost resistor.

Cheers

Ian

Re: Neve BA283AM questions(s)
« Reply #8 on: February 13, 2018, 01:40:38 PM »
I had taken possible unused channels inducing noise into consideration, and came to the conclusion that even a fairly modest mix could produce 8 stereo sub groups, so I figured that I would just plan on using all inputs instead of installing switches to disable certain inputs.

Thanks,

George


That might just work. I would be tempted to change the 10K input resistors to 4K7 so the input impedance is close to 10K, With 8 input the loss will be 8 times or18dB. The bus impedance will be 9K6/8 which is 1200 ohms which is a reasonable source for a 10K:10k transformer. To maintain the bus impedance and keep the loss constant you will need to ensure unused inputs have their hot and colds shorted together.


Re: Neve BA283AM questions(s)
« Reply #9 on: February 13, 2018, 01:46:32 PM »
Hi,

Yeah the Shinkoh's were particularly expensive, the other ones I have not so much. The Shadow Hills Equinox (the unit I will be comparing mine to) uses Dale metal films, which I also have. I have heard / read so much about whether or not certain components change the sound, I just wanted to listen for myself & put the issue to rest for me personally. I have the proper polystyrene, & tantalum caps for this build, so I want to see if the summing resistors alone make any difference to my ears. The SH unit has 3 different output transformers to choose from (I know there are a pair of Jensens in there) & I always choose the Iron when I use that unit.

Thanks,

George

You could also sell this resistors to audiophiles if there is enough of them, after making wanted tests.
Most of us find metal films (~3W max are readily available) work best because of low noise, high stability, low price, no distortion to speak of, and "no sound". Other  parts and circuits will take care of sound.


MagnetoSound

Re: Neve BA283AM questions(s)
« Reply #10 on: February 13, 2018, 02:36:30 PM »
Quote
Hi Ian,

I forgot to mention that I do also have the Grayhill switched normally used in the "EZ1290" and I'm assuming original circuits? Will this switch provide some extra gain? Does this swich change the feedback resistance which would change the gain?

Thanks again so much!

George




I am not Ian, so forgive me ...

The 1290 and it's siblings (1073 etc) have extra gain stages (two!) that the gain switch adds into the path and adjusts, both by attenuation and by shunting the feedback loops, so don't expect to gain anything much  (no pun intended) from using the fancy switch with a single stage board.

You can of course use the switch to vary the feedback shunt of the single stage in the way that Ian has already alluded to, by switching different resistors from pin K to ground.

You have effectively built a 1271 20dB line amp, as was commonly used for line level patch returns.
Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

Re: Neve BA283AM questions(s)
« Reply #11 on: February 13, 2018, 02:36:54 PM »
I see, so unless I just add the first stage, and build that circuit complete, I will have to do as Ian suggested to get some more gain from the single 2nd stage.

Thanks very much!

George

I am not Ian, so forgive me ...

The 1290 and it's siblings (1073 etc) have extra gain stages (two!) that the gain switch adds into the path and adjusts, both by attenuation and by shunting the feedback loops, so don't expect to gain anything (no pun intended) from using the fancy switch with a single stage board.

You can of course use the switch to vary the feedback shunt of the single stage in the way that Ian has already alluded to, by switching different resistors from pin K to ground.

You have effectively built a 1271 20dB line amp, as was commonly used for line level patch returns.

MagnetoSound

Re: Neve BA283AM questions(s)
« Reply #12 on: February 13, 2018, 02:40:33 PM »
I see, so unless I just add the first stage, and build that circuit complete, I will have to do as Ian suggested to get some more gain from the single 2nd stage.

Thanks very much!

George

Yes, although unless you are feeding fairly feeble signals into the summing bus to begin with, you may well not need to.

Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

Re: Neve BA283AM questions(s)
« Reply #13 on: February 13, 2018, 02:50:17 PM »
My thought was to mix hot out of the sub outs, and whatever gain was lost due to the summing network could be made back up, leaving some headroom on the 2-buss for mastering. I'm looking for the sound of the circuit rather than unity gain all the way though, noise of course being a consideration.

Thanks again!

George

Yes, although unless you are feeding fairly feeble signals into the summing bus to begin with, you may well not need to.

ruffrecords

Re: Neve BA283AM questions(s)
« Reply #14 on: February 13, 2018, 03:18:08 PM »
I would not worry too much about noise for an 8 channel unit. With all 8 channels connected the noise power will be 8 times as great but that is only 9dB worse than one. If it does worry you you could add a mute button to each channel - you will probably get extra marks for that!

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Neve BA283AM questions(s)
« Reply #15 on: February 15, 2018, 05:30:28 PM »
Hi Ian,

I'm a little confused by the configuration you suggested below. I do not see a pin H anywhere on either of the 283 circuits. The schematics I am looking at also show the output transformer across M & B?

Thanks again for you help & understanding.

George

A strapped to J
J is 0V
M is +24V
K is the gain boost pin. Connect a resistor from K to J to boost gain
Output transformer goes between  H and B
Input transformer secondary goes between L and J

MagnetoSound

Re: Neve BA283AM questions(s)
« Reply #16 on: February 15, 2018, 05:46:54 PM »
The reason for that is that your schematic is not fully annotated.



Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

Re: Neve BA283AM questions(s)
« Reply #17 on: February 15, 2018, 06:39:53 PM »
Thank you Dan!

George

The reason for that is that your schematic is not fully annotated.



Re: Neve BA283AM questions(s)
« Reply #18 on: February 17, 2018, 10:51:28 PM »
Hi again,

Is the cap in series with the 1.5k resistor across pins 5 7 8 of the output transformer a .01uF? Is a polyester film cap ok for this?

Thanks again!

George

ruffrecords

Re: Neve BA283AM questions(s)
« Reply #19 on: February 18, 2018, 02:58:50 AM »
Hi again,

Is the cap in series with the 1.5k resistor across pins 5 7 8 of the output transformer a .01uF? Is a polyester film cap ok for this?

Thanks again!

George

Yes and yes.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'