Summing amp-need to choose between my own design and one from ebay

[atlanteansparrow]

Hello folks,

This is my first post at DIY and although I've been following some of the interesting threads that appear on this board, this is the first time I really need your tech and sound advice.

Here's the thing: I have a studio and been thinking about getting a summing amp for quite a while now.
I have the possibility of building my own project summing box, which I'll build with a technician or for more or less the same money, buy a summing box made by Velvet audio.

What I can build is a tube 8x2 summing device with four 12AU7A RCA tubes as input, a couple of 12BH7 Westinghouse black plates for the output and Jensen output transformers. It has no pan pots or individual level controls as well as no input transformers.


The other option is a Velvet Audio SA-14-4 Vintage line mixer. It is based on a Neumann dual summing amp with floating balanced inputs & outputs. The level and pan controls are realized by a passive circuit.
It comes with Haufe transformers.
The gain controls are working as a pad. The master volumen enables a maximum gain of +10dB. The Pan pots have a center click.
The unit has 14 balanced mono inputs + 3 balanced stereo inputs. An additional feature is a stereo balancing amp for the fourth stereo input.
The SA-14-4 is running with an external power supply. It works from 100V to 240V main voltage.
The included dual summing amp is a Neumann V475. The dual balancing amp is a BFE Filtek V1157.


I'd be very interested in knowing your points of view regarding the two options. This is a tough one for me, what potential do you see in my tube summing box? Do you think it is worth going that direction? Or would you just go the other way? any experiences with Haufe transformers and thatt Neumann model?

Of course the ultimate decision is mine, but I think it's wise to listen to what you people have to say.

Thank you very much!



M

 

[helterbelter]

Hi,

Well, the valve project sounds really cool to me, haha.

But there's also a 3rd option : Racking a V475 yourself !

There are quite a few Neumann V475 summingboxes built by people here. I've got one myself, (although I'm currently into rebuilding it), and it sounds great. But, the racked V475's built here have a very simple setup : multiple stereo inputs, and a stereo output. Just a mastervolume, (rotaryswitch, not a fader).... So, no panners, no channelfaders. This stuff is what you control inside your DAW. This is a pretty inexpensive project. About 150 to 200 euro's and you're ready. But if your goals are different than just "outside the box"-summing, then the VA will be more what you need.

For racking a V475, check this :
http://www.groupdiy.com/index.php?topic=13857.0

 

[helterbelter]

Oh, sorry : Welcome to the community ! 

 

[helterbelter]

"The SA-14-4 is running with an external power supply. It works from 100V to 240V main voltage."

So, he probably uses a switching powersupply.... 

 

[atlanteansparrow]

Thanks Helterbelter for your welcome and replies!

Yeah looking at it that way it doesn't really make a lot of sense paying U$S 2000 for the VA, I mean all those level and pan pots won't really make a real contribution to the sound of the thing...it's only the Neumann summing amp really. Then again somewhere in this forum I read someone's post mentioning that you better do all the panning and leveling outside the DAW in order to make a real difference in stereo imaging and sound.

My biggest concern regarding my tube project is that I have a previous experience with valves (using the so called vintage line sowter transformers) that resulted in a noisy amp with not so much headroom. It was a mic preamp project based on the V72 with four gain stages. It uses the Siemens 804 tubes and then put a couple of 5687s for the output. Don't get me wrong, it does have a nice colour but with a -40db hum and hiss and little headroom using it becomes a bit of a nuisance.
Now I'm on the process of rebuilding it.

So I'm quite keen on trying the summing box project but I'm also pretty much aware of the possible drawbacks. I've never heard the Jensen output transformers for tube gear either. Does anyone know how they stand against the (solid state) Haufe?

It's a bit of a decision since I'll be passing all my audio thru this box and here in Argentina it's very difficult if not imposible to try all this gear options without purchasing and having them shipped here first.

What can I do to avoid the problems I mentioned above? I was going to use 5687 output tubes and then changed for 12BH7s because they better fit the specs for the Jensen transformers.
And if the Jensen weren't so great, are there any better output transformers out there? Besides tone, headroom and low noise is my main concern.


Thank you!