All things Green Pre

[HappyTom]

Hey!

Im about to trim the red peakled for my greenpres.
At what position shall i have the gainswich?

HT

 

[peterc]

Here's some detail from the Setup document.:


Setting the LED meter level (100k trimmer).

I like to set my red LED to light at +20dB. Most modern balanced inputs will handle at least this level without overload. This level will give an extra element margin of overload if the input will handle +22dB for example.

The LED's are preset to light at -40dB, -20dB, 0dB & +20dB.

1. Use a 200 - 300 Hz signal.
2. Monitor the + signal output of the preamp with a multimeter (AC volts).
3. Turn up the output trim pot so no attenuation takes place (fully clockwise).
4. Turn up the output level of the signal generator until the multimeter reads 7.75v (+20dB). This is using a RMS reading multimeter. If a scope is used, the level should be set to 21.9 volts pk-pk.
5. Trim the 100k trimmer until the red LED just lights.

Peter

 

[tmbg]

While we have this lovely thread up, I'm gonna hijack it to ask something I've been meaning to ask for a LONG time, but got sidetracked.

From the same document:

Setting the Peak detector DC offset (20k Multiturn trimmer).

1. Set the rotary gain switch to minimum gain with no input signal.
2. Attach the multimeter + probe (set multimeter to DC mV) to the link behind the 10k Output Trim pot. The other multimeter lead goes to
+ground.
3. Trim the 20k trimmer to read as close to -3mV as possible.

You may have to repeat this step a couple of times to get it accurate. Let everything warm up first for a few minutes.

DO NOT rest your fingers on the diodes & resistors of the peak detector, those 100k & 200k resistors next to the TL074. This throws out the
+measurements by a large margin. Ask me, I know.......

I have no clue which "link behind the 10k Output Trim pot" this refers to, but I've tried everything that I think ought to be that, and none of them are in that voltage range, and none of them are affected by the 20k trimmer. This is the same on both populated boards I've built.

I have been able to successfully set the CMRR on both boards, but this step hung me up, and none of the meter LEDs light at all.

 

[peterc]

The link is marked in green on this pic :

Peter

 

[AudioJunkie]

Another slight change in topic of the Green pre.

Which direction do the LED's go (Cathode to left or right of the board? I'm mounting them off board so i want to make sure I have the wires right.

I remember someone asking a similar question a whie back, but never saw an answer.

Daniel

 

[josan]

And another quick question , I have two boards operational no problems on audio but the led's stay lit except for the red which flashes on peaks is this normal.

 

[Consul]

I'm suddenly seeing an "All things Green Pre" thread... :green:

 

[HappyTom]

[quote author="peterc"]Here's some detail from the Setup document.:


Setting the LED meter level (100k trimmer).

I like to set my red LED to light at +20dB. Most modern balanced inputs will handle at least this level without overload. This level will give an extra element margin of overload if the input will handle +22dB for example.

The LED's are preset to light at -40dB, -20dB, 0dB & +20dB.

1. Use a 200 - 300 Hz signal.
2. Monitor the + signal output of the preamp with a multimeter (AC volts).
3. Turn up the output trim pot so no attenuation takes place (fully clockwise).
4. Turn up the output level of the signal generator until the multimeter reads 7.75v (+20dB). This is using a RMS reading multimeter. If a scope is used, the level should be set to 21.9 volts pk-pk.
5. Trim the 100k trimmer until the red LED just lights.

Peter[/quote]

Yeah, i got the document but i really didnt get it..
Does it mean that as long as i have 7.75v on my meter it doesnt matter at what position i got the gainswich?
Well, when i think about it, it gotta be this way..

HT

 

[HappyTom]

[quote author="Consul"]I'm suddenly seeing an "All things Green Pre" thread... :green:[/quote]

Topic changed.

HT

 

[peterc]

Tom :

Does it mean that as long as i have 7.75v on my meter it doesnt matter at what position i got the gainswich?

Thats right. We're just measuring the final level from the pre.

Daniel :

Which direction do the LED's go (Cathode to left or right of the board?

The Anodes (long leg) face toward the 10k pot. The flat edge of the LED (cathode) is placed away from the 10k pot

Josan :

I have two boards operational no problems on audio but the led's stay lit except for the red which flashes on peaks is this normal.

Use a signal gen or oscillator, sweeping the level to the pre. Check the voltage on the link illustrated above. Voltage should vary between about 10mV to 8V.

Peter

 

[HappyTom]

Gaaaah..
I was just ready setting up the unit when i got the brilliant idea to recheck my rechecked psu's.
With the multimeter on the 48v pin and my eyes on the meter my phone rang, then a little click and a flash..... third time during this project i've shorted the 48v and -15v pins... with the results of a blown reg.
I think i gonna buy some extra this time...

Take care when you measuring the psu!

HT

 

[clintrubber]

Here's some detail from the Setup document.:

I may be missing this completely, but I haven't heard of this document before. Is that setup-doc downloadable ? Or do you send it out to buyers of your green-PCB ?

I'd love to have a complete schematic and/or BOM of your v14 Green mic-pre's (the boards have just arrived), so that setup-doc sounds very much like what I'm looking for.

If you're indeed e-mailing it to people, yes please.
I'm here: chickennerdpig (at) hetnet (dot) nl

Thanks !

Peter

 

[BladeSG]

Hi Guys,

Sorry to change the topic again but I'm interested to know if you guys used 1N4747 Zener's?

I can't seem to fit these in the the PCB holes.... :roll:

Thanks

 

[kvintus]

I have a suggestion. When someone starts a new thread about one of the projects that are often discussed on this forum, it would be a good idea to include a link to the schematics for the project. That makes it much easier for everyone to follow and maybe to help solve the problems.

Just a thought.

/Anders

 

[peterc]

If anyone who needs the setup & voltages docs doesnt have them, please let me know.

All those who bought PCB's should have them.

Peter

 

[T-Beam]

[quote author="peterc"]If anyone who needs the setup & voltages docs doesnt have them, please let me know.

All those who bought PCB's should have them.

Peter[/quote]

Hi Peter (and thanks for all the work with the PCB:s)I dont have them and really would like them....I'm not shure what docs I have so please sent me everthing that is related to Green Pre

[email protected]

 

[clintrubber]

Small question: the zeners are 20V, right ? I also see 15V being mentioned.

FWIW: w.r.t. the gain-switch I reason a break before make would be better since it'd give you lower gain - where a make before break would give increased gain @ switching.

Regards,

Peter

 

[BladeSG]

The BOM says 20V zeners, but they won't fit in the PCB so maybe they were supposed to be 15V ones....... :?

 

[peterc]

The original specs 20v zeners, I've seen other pre's use 15v. I was able to get 20v parts to fit. Could be the power rating is too high? I know the 1/2 watt parts are bigger physically.

For testing, you could leave them out.

Peter

 

[BladeSG]

Thanks Peter. I'll try to find 20V ones that are smaller.