All things Green Pre

[peterc]

Ju

Are you turning up the 100k trimmer to get the level up? With 7.75v on the output, the 100k trimmer should easily get the red LED lit.

Regards
Peter

 

[fum]

Hey Peter,

I've adjusted the output of the signal gen (connected to the mic pre set at minimum input gain, output pot at max) so that the output of the mic pre reads 7.75V AC.

Once I'm there, now I start turning the the 100K pot. There's plenty of range left on the 100K pot, it just does not make the yellow or red leds come on.

I'll have to check the parts, maybe I have a resistor amiss?

Regards

ju

 

[peterc]

1) PARTS LIST:
I only found 8 .1uf ("good" quality)...and found 6 100nf ("any" quality).
The list has 10, and 4 respectivly..... Since these are really the same values, expressed different ways....two caps/sizes are switched???...what goes where? (edited today)

Use 4 "any"quality in the meter section, & the 2 other "anys" as the last 2 in the audio section.

2) PICOfarads:
What is a good choice for the five 22pf's and one 150pf's ? I am having trouble finding these, and a source. Does voltage make a difference?

All the ceramic/poly caps will have a minimum voltage rating of about 50v, so they'll be OK

3) WIREwounds:
I have some quality Shallcross 100k .15watt wirewound resistors. Would these find a nice home in this pre?.....I am fairly ignorant about ww's in general.

They will be fine.

4) ALPS pot:
I happen to have some 20k Alps Black Beauty's. Is there a way to use that instead of the 10k pot? (I realize they'll have to be wired "off-board").

Should work 100%

5) POWER supply:
A friend suggested I gut an older Digigesign converter box and keep the PSU. It has a +15v, -15v power supply, but what do I do about the 48v ?...(I know.....it's a switching supply, but he assures me, he has used those gutted boxes for headphone preamps with excellent results).

Box will work fine.

Peter

 

[peterc]

Ju

I can adjust so that I get no leds lit. As I turn up, one green, then the other comes into play, but yellow and red will not light.

Check the output of the detector, should vary up to about 12v. If you have a scope, check that the 1st stage of the TL 074 is amplifying the signal, with the given values, there should be a gain of about 5 max.

Peter

 

[dissonantstring]

hello helpful gents.
i'm getting parts ordered for a V14 green pre, but i'm a bit stumped on the 4700uF electro cap. Does anybody know what the lowest voltage rating i can go on this cap? i can only find it in 25V.
i also read in this thread that the 1/2W zener might be too big, but i can't find any 1/4W zeners at Digikey or Mouser. Will the 1/2W zener fit with a little nudging?
any help is greatly appreciated.
cheers,
grant

 

[fum]

did you search the digikey site?

lot's of options there. Do a search on 4700uF, then click on electrolytics.

 

[Freq Band]

Thanks peterc. Got the docs too. :thumb:

Now about getting +48v to these pres.
The PSU in this box I'm using is +15,-15, 0 , only. I have not yet taken readings off it's tranny's secondaries (before regulation).
Which option is best for two channels ? :

1) Tap off (split) of that tranny's secondaries and regulate to the required +48v ?....like here:
http://www.beatbazar.com/guests/ssltech/kps-1/kps1sch.gif

2) Dump the old PSU and build a fresh one that has everything?

3) Build a seperate +48v PSU ?.....like here:
http://members.aol.com/ecc81/ps48.html
or here:
http://www.tangible-technology.com/power/Phantom_frying.html

=FB=

 

[dissonantstring]

hi fum,
i did in fact check the digikey and mouser catalogs earlier and found some 4700uF caps in lower voltages like 25V and 35V, but i was wondering if 4700uF cap needed to be at least a certain voltage?
i'm thinking as long as it isn't in the PP circuit, 25V should be enough, but I just wanted to make sure.
what voltage rating did you use for the biggie 4700uF cap?
thanks for your help.
-grant

 

[peterc]

Grant:

The original 4700uF part is a 6v part.

FB:

As far as I can see, they will all work. The first can be used with the existing trandformer, the 2nd 2 schemes will need an extra transformer.

Peter

 

[fum]

I'm using a Philips, at 16V :grin:

 

[dissonantstring]

many thanks peter and ju!!
:guinness: :sam:
now to finish the hunting and gathering! :green:
cheers,
grant

 

[louder]

alo
just to make sure,about the connection of those two jumper points:
the small jumper gives metering before the output pot,and the bigger jumper after the output pot?.
i fired up my 4 greens,and all the voltages are okay,so the above question it`s the only doubt,for now.
best regards
pedro

 

[louder]

alo
second doubt:
if we connect xlr`s pin1 (in/out),to star ground,no need to use the ground from the psu,right?
best regards
pedro

 

[peterc]

the small jumper gives metering before the output pot,and the bigger jumper after the output pot?.

Nope, other way round, long jumper gives pre-pot metering

f we connect xlr`s pin1 (in/out),to star ground,no need to use the ground from the psu,right?

Correct

Peter

 

[Freq Band]

I have several non-shorting rotary switches. Can I use a shunting resistor to make this work?...as in:


http://www.platenspeler.com/background/attenuator/uk_attenuator_1.html#series_ground

...and I assume the R values might need to be recalculated ??
.........or is there another way to configure a non-shorting?

PS..can a switch be added to make the metering selectable post/pre pot?)

Thanks,

=FB=

 

[TobWen]

I think of a complete redesign of the PCB ... anyone interested??

 

[peterc]

I have several non-shorting rotary switches.

These will work, there might be a loudish click when changing gain settings. Try them.

PS..can a switch be added to make the metering selectable post/pre pot?)

Sure can, seems like a big thing to do..... Most people have a favourite mode of working & stay that way. The output pot is purely an attenuator, so the post output pot level will never be higher than the pre output pot level.

I think of a complete redesign of the PCB ... anyone interested??

This has already been done with the "Super Green". But maybe you have some cool ideas? Bring them on!

Peter

 

[TobWen]

oops, where can I find information about "Super Green" ?

 

[Freq Band]

Super Green:

http://www.akustische-kunst.de/audio/supergreen.html

=FB=

 

[Freq Band]

I promised my self no lame questions...but,

-Can't find BC550, BC560 in Digikey catalog.....search comes up nill.
What's the secret for cross-referencing part #'s ???
Do I need to go to each DigiKey's Manufactur's web site and cross search ?
Or is there a way within Digikey?
(can't use Mouser, must pay with Money Order )

Analog Devices-nada
National Semi-nada
ST Microelectronics-BC550 ="BC547B" only....no result for BC560

Local stores carry NTE (NTE123AP=BC550) (NTE159=BC560)...are those quality? or just pass-able.?.... or does it not really matter?

=FB=