All things Green Pre

[kato]

The output pot is a trim pot so a perfect log taper probably doesn't make much difference. Most of the time you will probably leave it full clockwise and use the regular gain switch to set levels.

I purchased those Taiwan Alphas for the output and then decided in the end not to use them at all.

Good luck!

 

[Phrazemaster]

Hi kato,

So what did you do then, just use a 10k resistor across the PCB somehow? How did you wire it?

thanks!

 

[kato]

[quote author="peterc"]

would there be a way to effectively mute a mic channel,

You could use a switch to ground the wiper of the ouptut level pot.
[/quote]

I was thinking about your mute question and Peter's suggestion to ground the wiper. It occured to me - if you don't want to wire an extra switch to your front panel, you could get one of those pots with switches built in (like these for example. - 10k log pot w/switch @ web-tronics).

Then again, you effectively "mute a mic channel" just by turning the output pot all the way counterclockwise - but if you want that nice, definitive "click" to tell you it's off - the switching pot would do.

 

[Phrazemaster]

Excellent Kato, thanks very much! I will look into those switches. I'm also interested in having the hpf/phase/Phantom switches lighted. Adding led's, relays, separate power for the relays? I'm researching.

Thanks again buddy,

Mike

 

[Phrazemaster]

Just ran across some great stuff on implementing relays. I want to have momentary illuminated front panel switches, labelled HPF and Phase and +48, so when you tap them they turn on/off their respective functions. As I understand it at this point, relays will be the way to do it. Maybe this has been covered here to death, but I find it quite difficult to use the search feature (yeah I know, the foxtrot thing with the indexing page by page, great workaround, but so time-consuming!).

Anyway, I just wanted to post a cool link I found, which I will adapt for my 4ch green. Of course, I will post my fledgling circuits and throw myself on the mercy of the court of the great ones here for any modifications or advice. Thanks all for a truly super forum, supportive encouraging and fun. I appreciate "knowing" y'all!!

Relays and Flip Flops and Timers, OH MY!

 

[Phrazemaster]

Hi all, maybe this has been covered but I can't find it in the search. I am considering bypassing the 10k log pot altogether, after buying a relatively high quality pot off ebay (noble pots) and seeing the signal path even on this high quality pot. I don't want to run my audio through that mush. I guess I could make another resistor switch network, but this seems like a royal pain, and isn't one gain switch enough?

So forgive the perhaps obvious or maybe overly covered, but why do I need the output fader 10k log pot at all; is there an advantage to having it or does it color the sound? Or is it a smaller adjustment like a trim? And if I don't want to use it, can I bypass it altogether with a jumper or a fixed resistor value? How?

I do research before posting, so sorry if I missed an obvious answer.

Thanks folks,

Mike

 

[Harpo]

[quote author="Phrazemaster"]I am considering bypassing the 10k log pot altogether, after buying a relatively high quality pot off ebay (noble pots) and seeing the signal path even on this high quality pot. I don't want to run my audio through that mush. I guess I could make another resistor switch network, but this seems like a royal pain, and isn't one gain switch enough?

So forgive the perhaps obvious or maybe overly covered, but why do I need the output fader 10k log pot at all; is there an advantage to having it or does it color the sound? Or is it a smaller adjustment like a trim? And if I don't want to use it, can I bypass it altogether with a jumper or a fixed resistor value? How?
[/quote]
This pot is not involved with gain but with loss. It's a fader. You can bypass it by leaving it out and take a piece of wire to link the wiper connection in the middle of the pot (leading to the output stage) to the incomming connection (comming from gain stage, next to the LED's). Doing this link with a switch will give you the "mute" circuit. Wire this switch in the same position as the pot has been, giving you full level out/silence.

The advantage in using the pot is, to adjust your outgoing level to the next stage (mixer, recorder,..) in case you like the distortion of a cranked up overdriven transistor gain stage :green: and all taste in between. For usual, the pot is set full clockwise to archieve max. headroom and cleanest sound and your gain switch is set according your source/mic. If you're searching for lots of colour, a preamp with transformers at in-/output, maybe tube-based, would be a better painting machine.

 

[Phrazemaster]

Dear Harpo,

THANK-YOU for a beautiful and clear explanation. That makes perfect sense!!! I am really new at all this; I'm mostly a tech generalist (software, macro hardware building like computers), but I've always enjoyed putting things together.

Thanks for "putting this together" for me in such an easy to understand way. You rock! :thumb:

 

[peterc]

The original idea behind the pot was to have an "output trim" to have a little variation of level into the next stage.

For e.g. some compressors are very level sensitive, & for some reason the threshold reacts differently at different input levels. Something like the old Fostex compressors dont even have a threshold if I remember correctly, the input level set the amount of compression.


Peter

 

[Phrazemaster]

Thank-you Peter!

 

[kato]

I powered up 2 channels of green. The higher voltages (13-16v range) check out normal but the low values start low and gradually drop down to zero as the channels warm up?

Has anyone else had this situation? Is it a problem?

I pasted in a table with Peter's reference in the first column, and my 2 channels in the next two.

Peter's starting voltage: +14.8, 0 -15.2
My starting voltage: +16, 0, -16

The Strange Behavior Starting with pin 7 of IC1, my initial measurement immediately after power-on is .25. Every few seconds it drops to .24, then to .23. then to .22, .21 etc.
Once I get down to .09, the voltage drop goes more slowly. I leave the probe attached. Over the course of a 3 1/2 minute Hall & Oates song, the voltage eventually drops to .01, and then to .00, occasionally hitting .01 again for a second, then back down to .00.

Same behavior with pins 1 & 2 and 6 & 7 of IC2 and IC3.
If I wait long enough, they will eventally drop to 0.00 volts.
So I labeled them as either ".09 drops" for example or just 0 depending on how long I waited before measuring (see table below.)

This is with no rotary gain switch connected, no output fader connected, and no pad/phase/HPF switches connected.

Any thoughts? Thanks for your insight. I'd love to hear if this has happened to anyone else - or theories of what is happening here.

Thanks! Kato

 

[peterc]

Kato

Remeber I was using a +-15v supply (actually +14.8 & -15.2v) so your slightly higher voltages are fine. When I measured the voltages I did not really do any long term testing of voltages, so they may well drop down to zero.

I think all is OK

Peter

 

[kato]

Thanks for the response Peter!
I figured this was normal but I worried there was one errant component causing the phenomenon. (If anyone else experiences this, please post just for interests sake.)

Again, I assume all is normal - especially since now I've tested two other channels; all 4 do this. Approx voltages jibe with what you have. ¼v quickly becomes .1v and then stays there for a long time. IC3 takes longer than IC2 to descend - almost 10 minutes which would explain why your IC3 pins 1 and 2 have a higher value than IC2.

I can't wait to get these racked up and in service. (Now I just need to get an oscilloscope for setup.) Thanks again for all your help! I will post pics when finished, Kato

 

[Phrazemaster]

Congratulations Kato, it looks like things are moving along for you! Hope to see some pix soon...

On another note (Ab?), a very nubie question. I would post this in the nubie thread, but was advised it's not really maintained, so here goes.

The 1U rack cases, does this mean there is only 1" of vertical room inside the case, and 2U means 2"? I ask because I'm trying to plan my build and layout, and not sure if I should get a 1U or 2U. If the 1U only has exactly 1" of vertical room, then I will probably need to go with a 2U. But it puzzles me because the 2U, for instance, is about 3.5" tall. How much vertical room is in these two sizes? I've tried to get an idea from drawings of Par-Metal enclosures, but can't tell. :shock:

I am building 4 channels of Green Pre Soup.

Thanks for any insights in advance.

Mike

 

[kato]

1U is 1.75" - pretty intuitive, right? :green:

you can fit the greens easily into 1U - make sure your caps are not too tall on your powersupply! Also the one huge cap on the green, you may have to mount it on its side (i did.)

 

[Phrazemaster]

Thanks Kato, man you're the best! Short of disassembling some other gear I have, I was getting my tape measure out and trying to figger out from other cases how much room, then wondering if parmetal internals were standard, etc. Their draft drawings are very hard to read the way they have done them. Curious, do you know how much room is in a 2U case, just for reference?

Thanks again buddy! :thumb:

 

[kato]

[quote author="Phrazemaster"]Thanks Kato, man you're the best! Short of disassembling some other gear I have, I was getting my tape measure out and trying to figger out from other cases how much room, then wondering if parmetal internals were standard, etc. Their draft drawings are very hard to read the way they have done them. Curious, do you know how much room is in a 2U case, just for reference?

Thanks again buddy! :thumb:[/quote]
No sweat bro.

Rack height is a standard. Just take the number of rack spaces × 1.75".

So a 3U case is 5¼" (give or take depending on brand / metal thickness.)

One thing to consider about Par-Metal - their 10-series case has a lip on the front, so if you're trying to fit a VU meter or something that's exactly the height of the front panel, that lip will get in the way. This is not true of their 12-series cases (more expensive.)

I'm using a 10-series Par Metal for my two channels of Green. My risers are pretty tall (I think they're ½") They're too tall for the power supply. (Fine for the green boards.) But the PSU caps were just barely touching the top cover. I changed to smaller risers just for the PSU and all is well.

Keep us updated on your progress! Kato

 

[peterc]

A word of warning, some cases height is not the same as the front panel. Sometimes the actual box is made slightly smaller than the number of U's. Check with the case maker.

1U = 44mm

Peter

 

[kato]

Right. Peter makes a good point. That 1.75" measurement I referred to applies only to the front panel. The case behind it is smaller.

I just measured the inside of a Par Metal 2U enclosure for you:

about 77.75mm of free space (height.)
(compared to 89mm of front panel height.)

 

[lagoausente]

Anyone knows if the LT1357 chip can be used on the green? anyone have tried it?