Noob summing bus project

[keeeth]

I’m a total beginner to DIY audio. Further than soldering a new pot on here or there or making up cables I’ve never really done anything. I have a very basic understanding of components/circuits but it’s very very basic.
I’ve wanted to learn for a while, but I’ve never managed to get round to it. However after being let down by somebody who was going to build a summing bus project for me I’m thinking I may just try and do it myself.

I’m planning to make a start by following these instructions:

http://www.diyrecordingequipment.com/4203/how-to-build-a-diy-passive-summing-box/

But mine will be a bit different. I have about 16 belclere input transformers. I think they’re called TF10016. I’d like to put those on all the inputs. I also have a pair of Neve 1276 modules which I’d like to use for the make up gain.  I’ll probably buy a power supply kit from JLM to power those. I’m looking to do it as 8 stereo pairs and I’d also like to put mute switches on all of those.

I have a number of questions I’d like to ask but I suppose the most important one is do you guys think that’s all do-able by a beginner?

Thanks in advance

 

[ruffrecords]

I believe the Belcere TF10016 is roughly equivalent to the 31267 so you can probably wire it as 10K:2K4 or 10K:600.

If you use transformers on each input you don't need to follow the link you posted because you have now unbalanced all the inputs and you can do a simpler unbalanced passive mix as was used on Neve consoles.

The 1276 is a line amplifier with a 31267 input transformer. For an unbalanced passive mixer you don't need the transformer. I am not sure the 1276 will have enough gain to make up the passive mix bus loss.

Cheers

Ian

 

[keeeth]

Hi

Thanks for your answer. I was looking to use the 1276 amps mainly for the colour they will give me. Is there a way to still use them with the way you suggested? 

I'm having them modded so they give me more gain. It's basically the same thing as converting a 1271 to a 1272 so it should, I think give me about 40db.

I've attached a block diagram of what I'm thinking. This is just with the parts I've got now. I'm planning to add to what's there if I need to.

How would you say is the best way to achieve what I'm looking for?

Cheers

 

[ruffrecords]

40dB gain will be more than enough. Geoff Tanner, also ex-Neve says " (a 1276) could be converted to 1272 specs by fully populating the BA283AMA, re-wiring the internals, and changing the input transformer" so I hope this is the modification you are having done.

Your basic block diagram looks fine to me. You just don't need to use the input 1276 transformer. As you have stereo inputs you don't need to worry about crosstalk so your bus loss needs to be no more than 1/N where N is the number of channels or about 18dB in your case.

Cheers

Ian

 

[keeeth]

But wouldn't the transformer on the 1276 amps be where I'm getting most of the colour on my mix bus from?  I don't want to lose that. Do you mean it's just unnecessary or will it mess up the circuit if it's there?

Yeah the mod you mentioned is the one I think. Someone else is doing that for me so I'll check on it.

So can I just wire it as my block diagram shows then or do I need to add any other parts?

Cheers

 

[ruffrecords]

But wouldn't the transformer on the 1276 amps be where I'm getting most of the colour on my mix bus from?  I don't want to lose that. Do you mean it's just unnecessary or will it mess up the circuit if it's there?

Yeah the mod you mentioned is the one I think. Someone else is doing that for me so I'll check on it.

So can I just wire it as my block diagram shows then or do I need to add any other parts?

Cheers

The things that create colour tend to be the parts working at larger signal levels. For transformers this usually means output transformers and I would suspect that is where most of the colour comes from in the 1276.  The Belcleres at the input working at +4dBu or more will add there own colour but the bus signal going into the 1276 input transformer will be about -20dBu and hence much less likley to cause the transformer to add colour. But there is not reason not to include it, I only meant it was not necessary.

Cheers

Ian

 

[keeeth]

Ah ok I see what you mean. Is there anything I can do to get the input transformers on the 1276 have more effect or is it not worth it? Could I for example. Add a transformer before the 1276 to get the level up and therefore make the 1276 input transformer have more effect. Or have I got that all wrong?

Sorry if these are daft questions, I'm honestly a total beginner so I'm trying to find my way round this project and get it all solid in my head before I start. I'm comfortable with building it, I just don't have a clue how to design it.

 

[ruffrecords]

The input transformer will have a subtle effect at low signal levels but other than that there is not a lot you can do to make it add colour. As I said before, you get more colour from a hard working transformer and that will be the output transformer.

I just watched the Sound City film on BBC4 and they had Rupert Neve on there explaining how the dc flowing in the output transformer contributed to the 'sweet sound'.

Cheers

Ian