Another Channel Strip

[alexc]

Hi All

Some pics of my latest franken-build - a channel strip using :

- JLM powerstation psu
- JLM 99 pre with lundahl traffo, 2520 doa in first position, 990 doa in second
- JLM fet DI and go-between
- Foote led meter pcb
- Gyraf pultec with haufe and lundahl traffos with a 12BH7 in the srpp
- MNats/Gyraf 1176 rev J with no input traffo and a haufe output traffo
- veroboard relay bypass for eq and comp

I get a noise floor from -65dBu(mic, line) to -61dBu (guitar) with an output of around +24dBu
with the compressor and eq active. Bypassing the eq makes no real diff to noise floor, bypassing
the comp drops the noise by around 10dBu.

So best noise is -72dBu with only the preamp and the output section of the 1176 in circuit.

It sounds fanastic of course  

This is the third of these channel strips I've done, the first two being with neve style inputs
and eq make up. it is  the best performer of the three, although not by much.

Tricky bit was finding the right combo of ground connections for the various bits to get
the best noise performance. Basically trial and error (70%), luck (20%) and theory (10%)
Also, getting all the power rails right took a little effort.

But I have to say, I am happily surprised at how good the performance is and how quiet
it is. The 1176 is not the quietest design in the world! And I am not the neatest wiring guy around
- although they are all sound mechanically and safe.
Its just that I don't really go in for wiring looms on prototype, one-offs.
And I am always trying to find the weakest link, noise wise so moving wiring and so on around.

I added a thresh-hold pot (1M linear) to the 1176 (as provided by mnats on his revD pcb but not on the rev J/H)
and that made a huge difference to the control-ability of the 1176. I can now get less compression without
having to sacrifice so much thru-gain meaning my signal to noise at the output of it all is much better.

This was probably the key difference in the usability of the unit of the previous my  ones.
I always struggled to get less compression without reducing the 'level' knob to the point where the signal
would sound dull and lifeless. I can say all my future 1176 builds will include this control.

All in all a great experience that has really pushed my skills forward a long way in all sorts of ways,
especially in understanding of gain staging, signal to noise and  perfornance testing.

Thanks for checking it out!

 

[deuc224]

:'(

cuz i know i will never have the know how to build something like that.

 

[okgb]

Horrible !
How can you put that much functionality & usefullness
into something and make it look good ?

I'm kidding of course nice work
looks like a fair bit of sheilded cable ,
now 23 more channels to go ?

 

[lsskmki]

Hah, what a conincidence. I just finished my Mid pultec (with dual op amp balancing& makeup stage)  + 1176 channel last week in a 2U case. No tubes in mine though, but unexpectedly low noise floor.

Nice front panel design there!

 

[gyraf]

Very nice indeed!

What is the gain of the SRPP with the 12BH7 tube? Will it go to unity gain on the Pultec with a 2:1 output transformer?

Jakob E.

 

[creal]

Nice build, i think your enjoy with this babe.

 

[sahib]

Good stuff. I know you've already mentioned but your wiring is  quite a sphagetti junction, works though.

Great front panel, 70s hi-fi looking and I like it very much.

 

[Stagefright13]

Wow that's awesome! That's a great idea making a whole channel strip. Don't even know why I didn't think of that before. Now I wanna do something like that! Thanks for the inspiration!!

Congrats! Looks really cool to.

John

 

[zayance]

Nice one Congrats!

 

[alexc]

Thanks kindly everyone    That was my 10th unit completed and put to work.

My thanks as always to those people who contributed design and pcbs for these fine modules
as well as all the knowledgable folks at this great place.

The 12BH7 gives around around 3dB less gain in the SRPP with the lundahl.
Response is 3dB down at around 30Hz and about 2dB down at 20KHz or so.
Pretty good performance I think.

I used it because my heater 'pre-regulator' was too close to thermal shutdown
with the 6922 tube. The difference of around 65mA when using 12.7V heater gave me the  margin I needed
at the cost of a couple of dB of EQ makeup. Not really a prob as I never really not use the EQ!

Plus it sounds really good, as did the 6922. I think the tube definately gives the box
more 'weight' than with SS make up amps I used in the other 2 builds like this I did.

On a good elec guitar with noisless pups, I get a very authoritive sound but with amazing
touch sensitivity and detail. Plus it's pretty easy to get some subtle crunch.

And the 1176 threshold control means I can now use the 'slam' (gyraf mod) without the comp being to crazy!

My goal is to design a single board strip one day. Eliminate alot of the spaghetti.

For the moment, it's just too much fun throwing together leftover modules of all the different 2chn units
I've done.

I mean, how can you not?