24 channel mixer the "Stereotype"

thanks Gary, it's been an adventure. I stuffed one channel and one input board today and ran a few tests. A few silk screen errors and the fader is on the wrong side, but it works! passed some test tones and we did a sweep on the AP and it looks good. Maybe one or two tweaks to the BOM but nothing major.

don

hakanai said:

If someone wants talkback, that is actually already built in. The input stage can easily get 12db of gain and the fader buffer can get 30db. So now it's a mic level channel, just without 48v. So channel 12 can be your talk back channel with any dynamic mic.

Click to expand...

Hey don, so I'm just a little curious about gain staging.. In the input stage, would it be possible to go above and below unity gain with a resistor in series with rotary switch or pot?

And the same question about the fader buffer, but would the fader be controlling the 30db of gain or would there need to be another switch or pot and the fader is just a trim..

Sorry for the nooby questions, just trying to figure out if its possible to boost/vary the gain on the channel amplifiers, rather than just trim the output.

looking sweet Don

peace

The input stage is setup for fixed gain. The trim on the schematic is a common mode trim (although I guess you could use it for some gain at the expense of common mode noise performance). Common mode noise performance is essentially how well your balanced signal rejects noise. If you want gain in the input then you need to change the feedback resistor and resistor to ground on the + input. Higher values = more gain. The input stage should happily do +20db of gain (according to the 2520 application notes).
The fader buffer has a gain trim and with the values I stuffed it should be good for a large range of gain. I trimmed +12 into the test channel. The fader is the only front panel control over level. So when we say "gain in hand" that is a reference to gain in the fader. That is there so that you can go beyond unity gain while mixing if necessary (for all sorts of reasons).
When I said you could turn a channel into a mic level input, I meant this strictly as talkback. This circuit is not design for mic inputs and is missing some things mic pre's have internally. The idea behind the suggestion was that a standard dynamic mic could be used and the gain could be fixed internally. you would then set all the auxes on that channel to post fade and it would give you a talkback section. You wouldn't care about all the sub-optimal stuff going on because it's just talk back, who cares. I would also leave out the LR drop on resistors just to make sure no weirdness gets into the main busses.

Fuccimain said:

Sorry for the nooby questions,

Click to expand...

no apology necessary. These are the questions that get me thinking about the circuit differently and lead to me learning things as well

Cool, thanks for this Don,

I wasn't really interested in the talkback but more of trying to use the input section as more of a line amp, as I thought the input DoA could give more than 12db of gain. So when you say increase the feedback resistor and the resistor to ground off the positive input, would you say that they would have to be increased together? Like say I wanted to put in a 3 way switch for unity, then plus 10db and plus 20db, for example, I would have to increase the resistor values for both feedback and +to ground for each step up in level? Just trying to understand how this would work in a sudo line amp sorta way.

Peace

Looking good Don

When I am looking at my 'most desired' but 'doable' diy console, it does seem to come up very similar to your design 

Minimal, high quality and diy maintainable circuitry, able to handle big faders with solo, mute, L/R assign and a bunch of pre/post aux's. Traffo-less inputs, direct outputs and ACA summing. Scalable without breaking the bank.

Looks very interesting indeed.

Nice work  ;D ;D

thanks alexc! Sorry for the long silence. I have been preoccupied with another project that has finally had some custom parts come in. I will be getting the mixer moving again in the next week or so. Hopefully I'll have some more pictures soon.

don

Hi!


This 24 channel mixer can be added to Send / Return / Bus Output gain ?


how to install?

Are you asking about inserts on the buses? the classic api summing board is setup for an insert and fader, so I thing the answer to your question is yes. Let me know if I am misunderstanding.

Don

Hi!

yes a inserts on the buses !

How much money do you use to do this DIY ?

DIY can give me this information?

Thank you!

mylesgm said:

very cool indeed!

Click to expand...

How much money do you use to do this DIY ?

DIY can give me this information?

Thank you!

zayance said:

Finished this. It's been used for about two weeks now, all is good i'm happy with it.
Thanks to hakanai for the Summing/Pan Boards.
Thanks to Jeff @ Classic api, for the help and clarifications, and for all the goodies.
Thanks for Gary (gar381) for all the DOA kits, boy that was a lot of soldering......
Thanks to Frank @NRG for the panel work.

Nothing much here, added a Headphone amp based on Wayne Kirkwood's Schematic, thanks to him as well, it's made on a double sided home etched board...
Yes the Heatsink is FAT for the headphone amp, it's what i had in hand so....
I preffered 1731's all the way, i tried with 2520 on a couple of tracks + ACA Booster section, and it wasn't my thing, but it's easy to swap so......
Added a JLM 40LED VU and that's that, working great.
I made one board with Caps on input, and the other board just with jumpers, to hear and compare, still a couple of things to do.....

Click to expand...

any updates on this ?

I have been submerged in a few albums and getting a web radio station off the ground so this has been collecting dust for me, sorry. But I should be returning to this project in the coming days and I have been daydreaming the next phase as well. Which may sound a bit early to some (considering this phase is still not nailed down) but seeing the next step is a great motivator and clarifier for me, so it's a good thing.

Don

working on it
http://www.groupdiy.com/index.php?topic=53603.0

I have a bunch of 10k log faders, are these ok to use, or should I change the fader circuit somehow?

thanks for any input.

s

Fuccimain said:

I have a bunch of 10k log faders, are these ok to use, or should I change the fader circuit somehow?

Click to expand...

Are you asking for use with the input boards or in preparation for the channel boards? the channel boards can use log or linear pots ranging from 1k-100k (10k ideal). The input boards are really only for use with 1k log (10k linear slugged may work as well but is untested).

hope that helps
Don

Hey Don,

no I have the mark 3 stereotype boards (input boards?),. I was going to breadboard some fader buffers, unless the new version you made with the fader boosters can be used with the mark 3.. but yeah, I have 10k faders, not pots, log faders

The new channel boards can be used with the mark 3 boards. You will simply pick off at the fader point and connect to the input of the channel board. The buss outputs on the channel boards us a dual row pin header so you can simply use one row to connect the previous channel and the other to pass through to the next. The whole thing should be done soon. This is of course if you need all the features it offers. if you simply want to buffer the fader so you can use your 10k log faders, then a simple buffer on a breadboard as you suggested would do the trick nicely. My fader buffer schematic is in the other thread for reference.

don

I still have a couple of Hakanai summing boards around that Im planning to solder upp soon.
Anybody tried the APP992 op amp in it? Or does anybody know if there is something making them not suitable for this application?
Here are some of the features:

- ultra low noise (1nV/rt Hz)
- ultra low distortion
- very high slew rate (75 V/uS)
- high class A operation
- drive 75 ohm
- can be powered from +-14V to +-25V , so it can use +-16V, +-18V , +-24V of power supply.
- very stable on unity gain.

Can't see any reason why APP992 shouldn't work in this, I've compared them against GAR1731
and GAR2520 and I like them all. The 992 has a very open naturall sound to them with a solid bass.
1731 has a nice soft coloration and 2520 has a cool presence lift but the 992 has this " elegant expensive" sound.

Good luck!
//M