Poor Man's Tube Mixer

[ruffrecords]

Well that makes it a whole lot easier for you and anyone doing their own thing with it.
So does each input comprise of two independent but identical stages?  I'm assuming the trimpot is a level pre-set that can also determine the 2K5 source impedance for your eq but?
Edit:  scratch that last bit, you have this on your eq boards already

It is a very simple retro design based on my very first tube mixer but using the 6922 instead of the 6SN7.

The basic mic pre is 1:10 transformer (20dB gain) followed by 6922 mu follower (28dB gain) to an unbalanced direct out. Each mic out also feeds a 10K fader which feeds pan and mix buses. Mix buses are passive and gain make up is provided by another 28dB mu follower. This will likely be too much gain make up hence the need for a trimpot. This also reduces bus impedance and improves crosstalk.

Edit: If you want EQ per channel you will need gain make up for that. The REDD EQ has about 14dB of insertion loss so if you use another 28dB block for EQ gain make up you will have another 14dB of overall gain getting you past the 60dB mark.

If you look at the block diagram I posted and assume every op amp symbol represents a 28dB mu follower you won't go far wrong.

Cheers

Ian

 

[SWAN808]

Here's a pic from their web site:

https://www.metcaseusa.com/en/Technomet/M6436325/m6436325_fpnl_tisw_TitleImageSwap500x408.jpg

Seems a bit reminiscent of the old RCA consoles.

Cheers

Ian

cool project...how much are these metcases with slanted front?

 

[Winston OBoogie]

If you look at the block diagram I posted and assume every op amp symbol represents a 28dB mu follower you won't go far wrong.

Thanks for the run down Ian. 
I walked right past the block diagram in post 7.  Got it and understand it now

P.S. 
"Poor Man's" is a fine name for a DIY audio project. 
"Po' Boy" is a sandwich one eats when in New Orleans.

 

[JohnRoberts]

Not sure why a "poor boy" needs a tube mixer...

A Po Boy is something else entirely.  Good luck.

JR

 

[Winston OBoogie]

A Po Boy is something else entirely.  Good luck.

Yep.  Lived on them for 3 months when working in N'Orlins.

Sorry for my O.T.  diversion Ian.

 

[kambo]

4 mic pre is a very annoying* number have! either have 2 or 8 or + as option...

* i personally find it not friendly.... either u wish for 8 mic pres u had, or u endup only use 2 from dec, and use rest from outboard... never seen any good practical reason of having 4 mipre...
there is also nothing i would specifically use only 4 mic pre with a stationary tube mixer!

edit: this all  very personal experience, not trying to criticize in a bad manner btw , all sounds good!
edit 2:  i think 8 single tube tube mu follower classic stages, with patch option to double the gain would be the killer option... not many cases u wouldnt needed 35-45dbgain to be honest! far rooms, and ribbons etc.. plug them to external if u r multiminign to 12 mics etc! but 8 is a good number to have..

 

[ruffrecords]

@kambo. It is an unfortunate fact that there are lots of possible products.  I chose four mic pres because I have  built tube mixers and lunch boxes with that number in them more than anything else.

Would you really want an 8 channel 2 bus tube mixer with no EQ etc or just 8 tube mics pres?

Cheers

Ian

 

[kambo]

Would you really want an 8 channel 2 bus tube mixer with no EQ etc or just 8 tube mics pres?

Cheers

Ian

8 ch mic pres, 2 bus, with variable filters,  eq on master!

 

[5v333]

I like the idea of making stuff as minimal as possible.
Not having great amount of possibilities makes one work with knowledge and creativity.
Choosing - positioning and pointing mics is similar to gain eq and compression.

However it could be cool if theres a simple way to connect preamps or other sources to your mixer to expand the amount of inputs...
Maybe some inputs that goes directly to the summing net without preamps, faders etc..

Keep it up!!

 

[ruffrecords]

8 ch mic pres, 2 bus, with variable filters,  eq on master!

Can you clarify what you mean by variable filters?

Cheers

Ian

 

[ruffrecords]

However it could be cool if theres a simple way to connect preamps or other sources to your mixer to expand the amount of inputs...
Maybe some inputs that goes directly to the summing net without preamps, faders etc..

Keep it up!!

That is already there, a couple of direct inputs, one connected to the L and one to the R bus. Check out the block diagram in reply#7

Cheers

Ian

 

[kambo]

Can you clarify what you mean by variable filters?

Cheers

Ian

HPF/LPF with continuous frequency instead, fixed frequency filters
ie:
normally HPF : 80Hz, 100Hz, 150Hz etc filter switches,
replaced with one knob go from 0hz to 300Hz, and opposite to  LPF 

 

[JohnRoberts]

You need to take a poll of what people want, how many channels, features, etc...

To keep them honest they need to place a deposit to buy a mixer from you, if you meet their request...  8)

JR

PS: I spent decades at trade shows with kibitzers telling me to add just this one extra feature and I'd sell a million mixers. :

 

[5v333]

That is already there, a couple of direct inputs, one connected to the L and one to the R bus. Check out the block diagram in reply#7

Cheers

Ian

Doh..!

 

[kambo]

extentions easy,,, Ian thinks of it ))

i was thinking,
8 micpre infront with filters .. since u already have insets, that cold be used for extension on EQs, comps etc  on top row, as a separate 500 kind a  extention unit!

 

[TwentyTrees]

Yep - fully agree with John and others on the danger of scope creep here! On a personal level I’d be happy with 4 pres (I don’t often use more that  4 at once in my project studio), particularly as the summing inputs would make using external pres pretty straightforward. Using standardised gain blocks then opens up a world of potential user customisation.

Also - finally a chance to use up that shoebox of 1:10 mic transformers I’ve ripped out of Shure minimixers!  ;D

 

[ruffrecords]

HPF/LPF with continuous frequency instead, fixed frequency filters
ie:
normally HPF : 80Hz, 100Hz, 150Hz etc filter switches,
replaced with one knob go from 0hz to 300Hz, and opposite to  LPF

Ah, now I understand. Unfortunately that is not something I plan to provide - I don't even have a design for the kind of HPF/LPF.

Cheers

Ian

 

[ruffrecords]

Yep - fully agree with John and others on the danger of scope creep here! On a personal level I’d be happy with 4 pres (I don’t often use more that  4 at once in my project studio), particularly as the summing inputs would make using external pres pretty straightforward. Using standardised gain blocks then opens up a world of potential user customisation.

Also - finally a chance to use up that shoebox of 1:10 mic transformers I’ve ripped out of Shure minimixers!  ;D

Thanks for your input. I am only too well aware of feature creep from my days long ago when I did this kind of thing for a living. Part of the purpose of this thread is to clarify what people want and don't want. So far it seems I got it about right for most people. The only puzzling thing is nobody has commented on the echo and foldback buses. Taking them out would be very easy and save a couple of transformers and tubes.

Cheers

Ian

 

[TwentyTrees]

... the echo and foldback buses...

Essential stuff in my world at least - I hate tracking vocals without a little comfort reverb to help pitching and delivery, and a separate foldback / cue bus is always useful. I also use lots of parallel compression at mix, so both those buses come in handy there too.

[Edited as I did go a bit off topic there...]

 

[Tubetec]

Wow, the wish lists are getting longer and more unrealistic by the moment 

For me usually the first treatment I reach for is to trim the bass end ,per channel  , very often a good balance can be found with careful  mic selection and a touch of low cut filter.  I also found with some of my experiments that relatively simple circuits with switched values of coupling capacitor and relatively shallow curves worked adequately for most HPF jobs .