1o73 Line-in boards - mission accomplished

[Cosmonaut]

0dbfs your project looks so cool, but what about the paning circuit?will you use pots,lorlins or what?

Thanks for this amazing project!

 

[0dbfs]

I've got two Rolls Folcrom passive summing boxes to use for external LCR assign and summing. I can parallel the inputs to those in the patchbay to make this a 16x4 or a 32x2 mixer with L/R assign switches (or 1/2/3/4 for 16x4) for the 32 channel system. The folcrom boxes are about $700 retail. Pricey for what it is. I've got them already and it's another project I don't need to spend time on so I'm cool with it for now. I can DIY some more for additional busing as well as a panel of rack mounted patchable attenuators.

That makes my implementation of the LN72 channel amp a simple 16x16+16 gain control and level's box. With 20+ lbs of iron hanging off the back end and some magic in the middle.

I hope I can fit it all into 6RU's without melting anything important and come up with solutions for the issues/thoughts in previous post.

Best,
j

 

[0dbfs]

Looks like space-wise I can stack 2x LN72's and fit the four trafo's stacked behind the boards into a 10.5"/6RU case using various L-Brackets.

It appears that Martin was able to fit 8 channels-wide of the ez1290 into a 19" box....

Also looks like I can probably use a pot for the input sensitivity. I'll have to sort out the desired taper to see what tracks. Since the I/P trafo drops the line-in signal several dB as it hits the divider network it will likely be more susceptible to interference by mounting a pot off the PCB. Maybe shielding the connections to the pot will address that if it poses a problem.

Need to come up with front-panel measurements for 16x channel-strip spacing.

Best,
j

 

[0dbfs]

Hi Martin,

I've spent some time checking out these boards before stuffing and these are really very cool. Thanks for a great project that is nicely purpose-built and very flexible at the same time!

I see you have extended certain traces (and left room to drill holes) for some of the additional connections for the pre-amp FB loop and unbalanced output positions. That is really cool. I would recommend (or request) adding a hole/via in the PCB at those points if you do another run.

I am considering bringing these positions out to the front panel for controls with either a switch or a pot as well as having the 10468 I/P trafo switchable to be reversed for either line or mic level. ie; step-up or step-down. Still need to stuff and test these things but seems probable.

Looking for thoughts on these mods:

- Making 10468 I/P trafo "reversible" with a switch.
- Bringing the pre-amp stage FB control out to the front panel either on a switch or a pot.
- Bringing the output-driver stage FB control (specified as 1.5kR on this board and potentially "variable" as per the original docs) out to the front panel.
- Extending the I/P pad (sensitivity) switch out to the FP with either more positions or a 5k Log pot.
- 10k Log fader for the divider between stages.

Phase and Phantom can be addressed externally if required. ie; 16x JLM go-between's (or similar) normaled into the patchbay.

Seems like this configuration (or similar) would allow these boards to be used in service as line level channel amps and [at least] medium-gain mic-amps with various "coloring" and gain-staging available based on the FB settings between the two stages not to mention the pads/dividers and trafo switching... Maybe also bring a 47R||RV1 switch out for driving lower impedances when patching the channel out into || bus destinations or when multed to multiple outboard attenuators.

Thoughts or comments?

Best,
j

 

[sr1200]

Dumb question time... (sorry most of this stuff is way over my head, but im trying to learn)

Im thinking of employing a pair of these in a summing box at the end of the chain for "make up" (i guess you could say)  What im thinking though, is that I would only want a trim pot (fader) and perhaps leave the pre gain full open. (im guessing the pot/switch looking thing mounted to the board is similar to the EZ1290 and a stepped gain switch)  Is there a way to jumper that board to open it up leaving the fader to do the dirty work?

 

[0dbfs]

sr1200,

I am learning too and after reading up on this circuit and some of the options I think it's a really very cool and flexible building block for so many things.

To answer your question: Yes. There are several points that you can use "fixed-wiring" and various resistors to set the gain of the device. The original BA183/283 cards brought these options out to pins on an edge card. The input setting via the grayhill switch is an attenuator between the input transformer secondary and the "pre-amp" stage on the BA283. You could omit the grayhill and just wire in a jumper link for the desired position.

You may also want to tweak using the other options in the circuit that appear to have been purposefully designed or implemented to affect the gain-staging through the two gain stages once you have the card assembled and can run some audio through it.

Best,
jonathan

 

[kestep]

Debating on putting 2 of these in a DY analog summing box (at the end of the chain as L/R gain makeups). I'm somewhat new at this and have a "newbie" question... For this application, do I need separate input and output transformers for each card? Are they shared?

 

[kazper]

Debating on putting 2 of these in a DY analog summing box (at the end of the chain as L/R gain makeups). I'm somewhat new at this and have a "newbie" question... For this application, do I need separate input and output transformers for each card? Are they shared?

You probably figured this out but, separate transformers for each chanel.

 

[mrdarwin]

Hi every body!
I've got two EZLN72 boards.
I would like to try to build a passive Eq like pultec with ezln72 amplifier stage. I will use filters part of a Gpultec for example, connected to boards.
I'm not comfortable with transformers, ratio, etc...
Is it necessary to use 2 input xformers? 600:600 input filters(lundahl 5402 like gpultec), VTB9046 input ln72? Ratio and impedance will be matched?

I know lundahl is for balanced input, filter part can work with unbalanced input...
In other way, I was thinking about doing this routing: input/VTB9046/gpultec filter board/ln72/VTB9049/output.

Thanks!

 

[Whoops]

The schematic link in the first post is dead:
http://www.technicalaudio.net/neve/neve_pdf/1073-EH10023.pdf

Martin can you please post the schematic again?

thanks