Advise for Active Summing Amp Neve BA283

[dinesh]

Hi,

I am looking to build a 16 channel active summing amp based on Neve BA283. The Idea for front end is the 1st stage of BA283 & then all 16 transformer inputs to 2 BA283's for Stereo Summing. Is it a good idea? Like know your reviews. If any one can help to draw a schematics will  be appreciated. Like to know what value of resistor I need to put for the summing of 16 channels.

Regards & Thanks
Dinesh

 

[Joechris]

I think you will find all your answers hidden in this forum, but I can sum up some guide lines. If this is a line mixer you dont want the first stage of Ba283. Neve used the second stage in some pan/aux modules with an inductor instead of the output transformer since they didnt need the bal out, but just low output imp to drive the pan/aux sends. The first stage is not indented to work with more than about -10db output level.
The 1272 has 36 db of gain, so you can bring down the input level down to about -12db with a level and pan pot, and the summing network could have a loss of about -25db and you would  be ok.
Geoff Tanner wrote this at his forum:
"lower the bus resistors to 6800 ohms. So that's 13 x 6K8's =523 ohms = much nicer. (8k2 for 16 channels!) So the final bus impedance is 523 ohms in parallel with 1200 ohms (the 10468 transformer) = 364 ohms  The bus level is 20 x Log (364/(6800+364)) = -25dB to which you add the feed level from the module, say for argument's sake -10dB, to finish up with a
bus level of -35dBu. This level is made back up to regular line level by the gain of the bus amp." 
So you have to deside if you want level and pan, if you want a line in transformer or a reciver chip, and if you want a low imp drive amp after the fader or keep it passive, with a lowish value levelpot
to drive the a 10k pan network.

j

 

[dinesh]

Hi J,

Thanks for your reply. I was looking for a Transformer Line input. Is it worth to add 16 Transformers at input section? Is there any advantage of it or Discrete input is good enough? If I add the 2nd stage of BA283 with inductor, from where i can get the inductors.

Looking forward from you.

Best regards
Dinesh

 

[Joechris]

Well this is all very subjective. I asume you want a mixer that sounds like a Neve desk, and mabye you get all the flavor you want from the 1272 summing amp.
For a bal master insert point after the 1272, you should build a second set of 1271 as your mixer output, witch is a 1272 with a line in transformer and a fader inserted. (could be without the first gainstage). This will give you even more flavor. Build this first, set it up as a two channel mixer with 1k resistors. One channel with transformer, and one unbal without, and have a listen. (pad down the unbal input if you use a 2:1 ratio tran). 16 transformers are expensive, and building 16 BA283 2nd stages with inductors is a lot of work, Im not shure its worth the trouble. Do you want level, pan and auxes, if so, mabye you should have a fader buffer amp. A BA340 could be a choise if you want to stick to Neve design and 24V supply. Igor migth have a pcb for those, but I dont know if he sell them seperatly.

j

 

[avilen_tanaka]

This is my first post.
I'd like to thank you for your cooperation.


>Geoff Tanner wrote this at his forum:
>"lower the bus resistors to 6800 ohms. So that's 13 x 6K8's =523 ohms = much nicer. (8k2 for 16 channels!) So the final bus impedance is 523 ohms in parallel with 1200 ohms (the 10468 transformer) = 364 ohms The bus level is 20 x Log (364/(6800+364)) = -25dB to which you add the feed level from the module, say for argument's sake -10dB, to finish up with a
>bus level of -35dBu. This level is made back up to regular line level by the gain of the bus amp."

Could you please let me know what Geoff Tanner's original post was?

For example, what is the correct way to think about bus resistance in a summing mixer that has BA283NV on each channel?
I plan to put in a BA283AM and an output transformer as the master amplifier.
In this case, assume that there is no PAN and AUX.
If there are 8 channels, let's say the bus resistance is 6800ohm. Dividing this by 8, I get 850ohm.
I understood that I need to think of it as resistance, including output transformers.

Sorry if I'm asking a ton of questions.
I will study and come back.

Best,

Tanaka

 

[noizetoys]

I have an original Neve 16 channel monitor panel that is essentially a large summing mixer. The only active components are the summing amps.
- It is wired with line input transformers (31267 or the modern Carnhill 9046) to isolate and unbalance the signal.
- The transformer feeds the unbalanced signal to the panel controls, which are all passive (no buffers or amplification).
- The panel has four buses (with two "s's" not three) and two post fader sends using a one knob/two button configuration.
- The buses and sends feed the bus rails through a 15k resistor.
- The bus rails feed line amps (wired for summing) which can be either a 1272, 3405, or 3415. These modules use a 10468 (or Carnhill 9045) as the summing device followed by series of amplifiers to make up the gain loss.
- 1272's use a 283AM: NV for preamp gain, AM for output gain/drive
- 3415 (and its predecessor the. 3405) use 338/438 (was there a 638?) preamp gain, and a 340/440/640 or 512 for output gain/drive
- The line/summing amp are usually wire to have a preset amount of gain to make up for the signal loss on the bus.
- Each of the line amps has connections for an external level control via pot or fader (on many summing amps, this is a small, recessed variable resistor used to keep the unit within 'spec'). How this is wired depends on the module (see their respective schematic)
- Finally, the amp feeds an output transformer (gapped or untapped depending on the circuit).

If you wanted to put a buffer amp after the input transformer, which is not strictly required, you could use the 283AM (the output section of a 283) or a BA106. You would not use the 283NV, as it is stated above, it wasn't designed for that purpose.

 

[ruffrecords]

Just to put this into perspective, all Neve buses were unbalanced, used anything from 6K8 to 15K bus feed resistors (for various reasons) and always fed a 10468 transformer before being fed into a gain make up amplifier.

If what you want to build is a balanced input line level summing mixer then you can do it with some modification of the original Neve circuits. If you want to be able to route or pan individual inputs then the approach would be different. If you can describe precisely what it is you are trying to do we cangive you more detailed help .

Cheers

Ian

 

[Stack]

Several years ago, I needed a multitrack monitor mixer for a Quad Eight analog recording console. My mixer, basically custom made Clarostat
Plastic conductive, on 5 different pots per channel. We only used iso resistors and I always wanted more gain, other than the 5534 summing outputs. A pan pot amp, individual iso transformers per channel’s got me in a construction mindset over re creating what we’d done earlier and just, going for it straight away, once again. Rupert Neve, IMHO, came the closest to what I believe could put a smile on my face again. They want 4,000.00 for 16 channels. For most application mixes, I believe that’s about all I’d ever need to stay cool and satisfied with what I have for tools and need.

 

[Stack]

Put the amps in where they’re needed. No more, no less.

 

[avilen_tanaka]

I have an original Neve 16 channel monitor panel that is essentially a large summing mixer. The only active components are the summing amps.
- It is wired with line input transformers (31267 or the modern Carnhill 9046) to isolate and unbalance the signal.
- The transformer feeds the unbalanced signal to the panel controls, which are all passive (no buffers or amplification).
- The panel has four buses (with two "s's" not three) and two post fader sends using a one knob/two button configuration.
- The buses and sends feed the bus rails through a 15k resistor.
- The bus rails feed line amps (wired for summing) which can be either a 1272, 3405, or 3415. These modules use a 10468 (or Carnhill 9045) as the summing device followed by series of amplifiers to make up the gain loss.
- 1272's use a 283AM: NV for preamp gain, AM for output gain/drive
- 3415 (and its predecessor the. 3405) use 338/438 (was there a 638?) preamp gain, and a 340/440/640 or 512 for output gain/drive
- The line/summing amp are usually wire to have a preset amount of gain to make up for the signal loss on the bus.
- Each of the line amps has connections for an external level control via pot or fader (on many summing amps, this is a small, recessed variable resistor used to keep the unit within 'spec'). How this is wired depends on the module (see their respective schematic)
- Finally, the amp feeds an output transformer (gapped or untapped depending on the circuit).

Thank you for your comments.
I'm very happy to hear that there is no one around me who has this kind of expertise!

neve BA106 is below, isn't it? I'll do some research.
I can't find many pictures of the actual BA106. I'll try to find some.
https://www.technicalaudio.com/pdf/Neve/Neve_BCM10/Neve_1895_Switching_Unit_BCM.pdf
Now, let's consider placing the Carnhill 9046 at the input and using the BA106 as a buffer, and since the BC107 is no longer available, I'll substitute the MPSA18. I thought so, but BC107 is available as a current product.
How did you come up with the bass resistance of 15k ohms? For example, the mixer I'm trying to build is small compared to a large console mixer. Even if the number of channels is 8, is 15k ohm enough? I want to understand this idea of bus resistance.
With my little knowledge, I tried to find out how to calculate the bus resistance, but I couldn't figure it out.

If you wanted to put a buffer amp after the input transformer, which is not strictly required, you could use the 283AM (the output section of a 283) or a BA106. You would not use the 283NV, as it is stated above, it wasn't designed for that purpose.

The input transformer is Carnhill 9046. After this, the BA106 is placed as a buffer, followed by the BA283AM.
This channel will be connected to the bus at 15k ohm.
Finally, the BA283AM will be placed again as the master amplifier.
After thinking about your comment, I came up with this configuration. Is my understanding correct?
First of all, I want to do some preliminary exercises with a simulator such as LT-Spice.

There are transformers and inductors in each module that attenuate the signal. And there is a built-in amplifier card to amplify the signal. However, in my concept, it is not such a complicated configuration. I'm not sure if I'm doing this right.


Please let me know if I'm making any serious mistakes, and I'll go look it up on the web and relearn it.

Best,

Tanaka

 

[avilen_tanaka]

Just to put this into perspective, all Neve buses were unbalanced, used anything from 6K8 to 15K bus feed resistors (for various reasons) and always fed a 10468 transformer before being fed into a gain make up amplifier.

If what you want to build is a balanced input line level summing mixer then you can do it with some modification of the original Neve circuits. If you want to be able to route or pan individual inputs then the approach would be different. If you can describe precisely what it is you are trying to do we cangive you more detailed help .

Cheers

Ian

Thanks for your comments, I really appreciate it.

What I want to create is a small line mixer.
My residence is not very spacious and I want to create a mixer that can be handled on a tabletop.
The requirements are as follows.
What I am having trouble with is that even if I could simply mimic the circuit and create it, I don't understand the bus resistor. Why do I need to drop it to 6800 ohm? I don't understand this either.
---.
1. 8 channels in total.
2. I want to control the volume for each channel. I want to control the volume on the master as well.
3. No need for PAN or AUX.
4. I want to use the old Neve circuit as a reference.
5. I don't care about the cost for the purpose of enjoying my own personal creation.
6. My creation style is basically DAW based, so as long as I can use a line, I am good to go.
---.

Best,

Tanaka

 

[avilen_tanaka]

Several years ago, I needed a multitrack monitor mixer for a Quad Eight analog recording console. My mixer, basically custom made Clarostat
Plastic conductive, on 5 different pots per channel. We only used iso resistors and I always wanted more gain, other than the 5534 summing outputs. A pan pot amp, individual iso transformers per channel’s got me in a construction mindset over re creating what we’d done earlier and just, going for it straight away, once again. Rupert Neve, IMHO, came the closest to what I believe could put a smile on my face again. They want 4,000.00 for 16 channels. For most application mixes, I believe that’s about all I’d ever need to stay cool and satisfied with what I have for tools and need.

Thank you for your comments.

Yes, I agree. The cost is unnecessarily high.
I would like to create and enjoy it anyway.

 

[noizetoys]

You don’t need both the 106 AND a 283AM, only one. In reality you don’t need either but if you want to do it, won’t hurt anything (other than your finances).

If you look up John Klett’s website, he has info on how to calculate bus resistors for a Neve circuit. I wrote 15k for the bus resistors because that’s what is in my panel. Yours would be different because of the lower number of channels. Also depends on the transformer you use.

Lastly, the 1272 uses a 283AV (both AM and NV are filled). There are a number of threads n this site about how to use a 1272 circuit for summing. Just do a search.

Hope this helps.

 

[noizetoys]

This might also help you understand what’s needed. It’s about a monitor panel like mine, but it does a good job of explaining bus resistors, etc.

https://repforums.prosoundweb.com/index.php?topic=2303.0

 

[avilen_tanaka]

You don’t need both the 106 AND a 283AM, only one. In reality you don’t need either but if you want to do it, won’t hurt anything (other than your finances).

If you look up John Klett’s website, he has info on how to calculate bus resistors for a Neve circuit. I wrote 15k for the bus resistors because that’s what is in my panel. Yours would be different because of the lower number of channels. Also depends on the transformer you use.

Lastly, the 1272 uses a 283AV (both AM and NV are filled). There are a number of threads n this site about how to use a 1272 circuit for summing. Just do a search.

Hope this helps.

I see.
I'll experiment once to see what my preferred configuration looks like, and conversely, what problems arise.

This might also help you understand what’s needed. It’s about a monitor panel like mine, but it does a good job of explaining bus resistors, etc.

https://repforums.prosoundweb.com/index.php?topic=2303.0

Thank you. The way to calculate the bus resistance is very interesting.
It is the information I was looking for. I appreciate it.


Thank you again.

Tanaka

 

[SIXTYNINER]

.....original Neve 16 channel monitor panel that is essentially a large summing mixer. The only active components are the summing amps.

Any chance for an image about ?
cheers

 

[ruffrecords]

Thanks for your comments, I really appreciate it.

What I want to create is a small line mixer.
My residence is not very spacious and I want to create a mixer that can be handled on a tabletop.
The requirements are as follows.
What I am having trouble with is that even if I could simply mimic the circuit and create it, I don't understand the bus resistor. Why do I need to drop it to 6800 ohm? I don't understand this either.
---.
1. 8 channels in total.
2. I want to control the volume for each channel. I want to control the volume on the master as well.
3. No need for PAN or AUX.
4. I want to use the old Neve circuit as a reference.
5. I don't care about the cost for the purpose of enjoying my own personal creation.
6. My creation style is basically DAW based, so as long as I can use a line, I am good to go.
---.

Best,

Tanaka

OK, that is a reasonable specification. You do not say if the inputs and output are balanced so I will assume they are. You don't want pan pots so I will assume this is an 8 into 1 mixer. Here is one way to do it.

1. Unbalance the inputs with a transformer. In a Neve mixer this would have been done with a 31267 transformer wired 10K:600. You could use the equivalent Carnhill transformer wired the same way. The signal is now 12dB lower than the input level.
2. Use a 1K log pot for the volume control .This will be reflected via the transformer to the input as an impedance greater than 10K
3. Feed the pot wiper via a bus resistor to the bus. As this is a mono bus we do not have to worry about crosstalk. But we do want to minimise interaction between channel so we choose a bus resistor at least 10 times larger than the pot value. A typical Neve value would be 15K.
4. The bus loss is equal to the number of inputs i.e. 8 times or 18dB. This is the amount of gain we need to make up.
5. With only 8 inputs there is no need to use the Neve standard method of a transformer input to the bus amplifier. We can just wire the bus straight to the BA283 first stage and set its gain for 18dB.
6. The output of this stage can feed a 10K pot as the master volume. The pot wiper feeds the output stage of the BA283.
7. We still need to make up the 12dB loss from the input transformer which we do in the output stage.

Cheers

Ian

 

[noizetoys]

@SIXTYNINER I haven't completed the mixer quite yet.

Here's the panel itself and what I'm planning for it to look like when I'm finished.

 

[Golgoth]

@noizetoys Wow! That looks incredible. Do you by any chance have one spare of these round skirted pan knobs that you would sell? Thanks!

 

[noizetoys]

I don't, actually. I think I may have bought the last that ones that Dan Alexander had. I have (10) 8014 routing modules that came with a more 'standard' looking knob.

You might want to try Vintage King. I've bought a few Neve items from Mike Nehra, the owner and he/they have a large collection of Neve parts. He's on Reverb and eBay as 'lindsaymomof3'.

Good luck!