Adding panpots to tube Raytheon console
- Thread starter BossOrgan
- Start date
Help Support GroupDIY Audio Forum:
Got the power supply and preamp section rebuilt. Tried splitting the output transformer on one channel for a direct output. It does work to give two isolated outputs (one for direct out, one for mix bus), but the gain loss is too much. Not worth it as the direct out doesnt have enough gain to drive my tape machine inputs to full level. Taking a direct out from the full 500ohm secondary works much better.
So im thinking the final topology will be:
separate mic and line (32db pad) inputs -> mic/line switch -> phase switch -> preamp -> direct out/mute/mix buss switch (will use the original program/off/monitor switches) -> daven -> NYD 600ohm pan circuit -> output amps
The direct outs will have their own 500ohm T attenuators, so you can set levels independently for direct outs.
i will add in an echo send similar to the UA610 on each channel, and add in a 6sn7 for makeup gain to drive an echo output.
This means to go from tracking to playback you have to flip two switches (mic/line and direct out/mix buss) for each channel. And when using the direct outs, you cant monitor that channel. I suppose I could use one of the extra console switches to send the echo output to one of the line input channels. Then you would have a way to monitor a channel when switched to direct out.
I also bought a couple Hammond 119DA (600ohm:4/8ohm) transformers which I will use to drive passive monitor speakers direct from the console. Will use some of the extra console switches to make make the speaker outputs switchable on/off.
Cheers!
Tyler
So im thinking the final topology will be:
separate mic and line (32db pad) inputs -> mic/line switch -> phase switch -> preamp -> direct out/mute/mix buss switch (will use the original program/off/monitor switches) -> daven -> NYD 600ohm pan circuit -> output amps
The direct outs will have their own 500ohm T attenuators, so you can set levels independently for direct outs.
i will add in an echo send similar to the UA610 on each channel, and add in a 6sn7 for makeup gain to drive an echo output.
This means to go from tracking to playback you have to flip two switches (mic/line and direct out/mix buss) for each channel. And when using the direct outs, you cant monitor that channel. I suppose I could use one of the extra console switches to send the echo output to one of the line input channels. Then you would have a way to monitor a channel when switched to direct out.
I also bought a couple Hammond 119DA (600ohm:4/8ohm) transformers which I will use to drive passive monitor speakers direct from the console. Will use some of the extra console switches to make make the speaker outputs switchable on/off.
Cheers!
Tyler
So did the spilt winding direct out truly isolate from sounds in other channels on the mix bus, despite the low level? If so, still seems worth pursuing. Use some external gain stage if you need more. Yes, lower level comes with the territory.
I think you will never need an attenuator on the direct out, no matter how you configure it. To drive that stage hard enough to clip ANYTHING, you'd have to be over 10% THD.
I think you will never need an attenuator on the direct out, no matter how you configure it. To drive that stage hard enough to clip ANYTHING, you'd have to be over 10% THD.
With the split secondaries, there is a slight amount of bleed from the mix bus coming thru the direct out. Pretty quiet, but audible.
Did some gain calculations. Each mic preamp has about 33db of gain when using the entire secondary into a 500 ohm load. Drops to 27db (6db loss) with the secondaries split.
I suppose I could scrap the 6j7s and go with dual triodes instead, cascade the triodes and get more gain per channel.... Then split the secondaries.....
But I think i'll just stick to original preamp design, and make the direct outs switchable.... for now anyway. This will be less work, and the direct outs wont have any bleed from the mix bus. They will however have some amount of bleed from the echo bus....
Did some gain calculations. Each mic preamp has about 33db of gain when using the entire secondary into a 500 ohm load. Drops to 27db (6db loss) with the secondaries split.
I suppose I could scrap the 6j7s and go with dual triodes instead, cascade the triodes and get more gain per channel.... Then split the secondaries.....
But I think i'll just stick to original preamp design, and make the direct outs switchable.... for now anyway. This will be less work, and the direct outs wont have any bleed from the mix bus. They will however have some amount of bleed from the echo bus....
BossOrgan said:
Ok. I suspected as much.
BossOrgan said:
Here's the thing. A dual stage 40-50dB pre is gonna overload and need a 20dB input pad with most anything modern. And....the single stage RCA 76 console type pre, which should have MORE headroom than these (direct feed stage) also overloads frequently and needs a pad. It's a quandary that requires running some real world experiments. If you go dual stage, you really have to make it variable gain somehow, and that's it's own big wire length problem in the context of a console, UNLESS you do something short which requires you to open the lid of the console every time you set up gain trims for a new session. I would suggest getting really clear about headroom requirements, input overload points, etc.
ruffrecords
Well-known member
emrr said:
Very sound advice in a fixed gain preamp.
Cheers
Ian
Referring to direct feed.... is it safe for me to try it on these output transformers? I dont know if they will support the DC.... seems like other similar UTC transformers will accept 8ma of DC?.... but these transformers have no markings. They are RC75 size enclosures.
