Green Pre questions

[MNA]

Hello everyone! This is my first post on this forum, so perhaps an introduction is in order. My name is Martin and I live in Uppsala, Sweden. I've been playing guitars for most of my life, and the last couple of years I've become more and more interested in recording and production. I have a small computer based studio together with a friend, which unfortunately is used only sporadically. That's gonna change though, if everything works out as planned...

I stumbeled upon the Green Pre project a couple of days ago, and it seems to suit my needs quite well. I'm planning on building a 2U rack unit containing four preamps (kind of like mich's Green I guess), but I have som questions. I have read the metas, and while there is tons of useful information available, I haven't been able to get everything worked out.

1. There seems to be a number of different power supplies to chose from. Which one should I choose, and why? Are there any significant differences? I would like to power all four preamps with the same PSU of course, if that makes any difference. Also, what do I need to consider when picking a power transformer?

2. There also seems to be a number of different versions of the preamp itself. Are there any major sonic differences between the different versions? I don't need metering BTW.

3. If it's an easy mod, I would like to have dual outputs from each preamp, for monitoring purposes. The monitor output does not need to be balanced if that makes things any easier. What would be required to accomplish this? I am able to read schematics, but I'm in no way able to design things myself.

4. Last but not least -- what is a ferrite bead? I haven't been able to translate it to Swedish, and I don't know where to get one. Is it some kind of inductor?

Thanks a lot!

/martin.

 

[matta]

Hi Martin,

Welcome to the world of DIY. I am still a newbie myself, but since my first project is nearing completion, and it is a Green Pre I thought I might be able to answer some of your question, in part.

1. Power supplies: Basically you need a power supply that can give you the following +15V,-15V,0 and 48V. There are a few designs available, Peter C has one that he designed for the Pres and you can safely power 4 from that with a transformer that is 15-0-15 and 30VA, which is what is recommended in the BOM.

2. There are a few versions floating around, I think the main ones are V9, V14 and the new Version 2. Sonically I think the are similar, the new version have additional features like metering, High Pass, Phase and Phantom Power. If you don't need the metering you can still build a version and just not stuff the board with the metering section, that is what I have done with mine (mainly because they were prototypes I got from Peter and the metering was still being worked out).

3. Can't answer this one...

4. My understanding is that a ferrite bead is can be a type on inductor and if I am correct (thought I might not be) the ferrite beads in the Green Pre are used as filters.

I hope that helps, I am sure other will chime in and be able to share more.

Cheers

Matt

 

[T-Beam]

Hi Martin
I'm too quite new to this and the possibilities the web gives you to share experiences, ask question and so on. But when I was younger, around high school, I was a dedicated DIY-builder.....but only smaller projects that one could afford back then. I also went to school for practical education in electronics and stuff.

Well, I got carried away there.....I just want to say welcome too and tell you that I'm sitting and waiting for 5 PCB:s from PeterC (4 Greenpre and 1 PSU) that I'm going to build BUT when I got time for it. If you look in "Black market"-forum there is a thread about that order. One tip more for you is that we have a small Swedish forum for DIY-builders that can be useful for you. I know one guy has built a GreenPre there and a few more are interested. Sign up at http://khz.se/forum/ if you're not at it already.

For the record....I'm from Gävle, and I have even grown up in Uppsala. :grin:
/Tobbe

 

[MNA]

Thanks a lot for the quick reply! I have built a couple of guitar effects before, but I am still new to this.

[quote author="matta"]Hi Martin,

Welcome to the world of DIY. I am still a newbie myself, but since my first project is nearing completion, and it is a Green Pre I thought I might be able to answer some of your question, in part.

1. Power supplies: Basically you need a power supply that can give you the following +15V,-15V,0 and 48V. There are a few designs available, Peter C has one that he designed for the Pres and you can safely power 4 from that with a transformer that is 15-0-15 and 30VA, which is what is recommended in the BOM.
[/quote]
Which BOM is that? http://recording.org/users/kev/green_pre.htm uses a 6W transformer to power two preamps. On PeterC's page I haven't found anything about transformers. I guess I haven't looked hard enough...

[quote author="matta"]
2. There are a few versions floating around, I think the main ones are V9, V14 and the new Version 2. Sonically I think the are similar, the new version have additional features like metering, High Pass, Phase and Phantom Power. If you don't need the metering you can still build a version and just not stuff the board with the metering section, that is what I have done with mine (mainly because they were prototypes I got from Peter and the metering was still being worked out).
[/quote]
OK. But since space will probably be an issue, perhaps it would be better to use the smallest possible PCB -- provided that there are no sonic differences.

[quote author="matta"]
4. My understanding is that a ferrite bead is can be a type on inductor and if I am correct (thought I might not be) the ferrite beads in the Green Pre are used as filters.
[/quote]
Yeah, I think I found it now. Thanks anyway though!

/martin.

 

[MNA]

[quote author="T-Beam"]Hi Martin
I'm too quite new to this and the possibilities the web gives you to share experiences, ask question and so on. But when I was younger, around high school, I was a dedicated DIY-builder.....but only smaller projects that one could afford back then. I also went to school for practical education in electronics and stuff.

Well, I got carried away there.....I just want to say welcome too and tell you that I'm sitting and waiting for 5 PCB:s from PeterC (4 Greenpre and 1 PSU) that I'm going to build BUT when I got time for it. If you look in "Black market"-forum there is a thread about that order. One tip more for you is that we have a small Swedish forum for DIY-builders that can be useful for you. I know one guy has built a GreenPre there and a few more are interested. Sign up at http://khz.se/forum/ if you're not at it already.

For the record....I'm from Gävle, and I have even grown up in Uppsala. :grin:
/Tobbe[/quote]
Oh, great! Thanks! I think I'll etch the PCBs myself, but I'll be sure to check out that forum.

/martin.

 

[Kev]

[quote author="MNA"] Which BOM is that? http://recording.org/users/kev/green_pre.htm uses a 6W transformer to power two preamps. On PeterC's page I haven't found anything about transformers. I guess I haven't looked hard enough...[/quote]

a replacement page is at :
http://www.diyfactory.com/projects/green/green.htm
details haven't changed ... just the location.

the Factory does have much more but I haven't opened the door yet

 

[MNA]

[quote author="Kev"][quote author="MNA"] Which BOM is that? http://recording.org/users/kev/green_pre.htm uses a 6W transformer to power two preamps. On PeterC's page I haven't found anything about transformers. I guess I haven't looked hard enough...[/quote]

a replacement page is at :
http://www.diyfactory.com/projects/green/green.htm
details haven't changed ... just the location.

the Factory does have much more but I haven't opened the door yet[/quote]
Ah, thanks! So if I modify that PCB and fit a beefier (chassis mounted) transformer, I should be able to power four preamps? Perhaps fit caps with a higher voltage rating while I'm at it?

/martin.

 

[tmbg]

beefier transformer, yes. Voltage rating on the caps isnt really going to change much, you're more concerned about things like the max current the regulators and rectifiers can pass, the heat dissipation of the regulators (mostly making sure that they're well heatsinked), etc, also note that increased current demand will increase ripple, so more capacitance will be desirable.

The other biggie is the charge-pump voltage doubler used in the phantom section places a bit of a restriction on the current available... more capacitance there should help.

 

[MNA]

[quote author="tmbg"]beefier transformer, yes. Voltage rating on the caps isnt really going to change much, you're more concerned about things like the max current the regulators and rectifiers can pass, the heat dissipation of the regulators (mostly making sure that they're well heatsinked), etc, also note that increased current demand will increase ripple, so more capacitance will be desirable.

The other biggie is the charge-pump voltage doubler used in the phantom section places a bit of a restriction on the current available... more capacitance there should help.[/quote]
Increasing the voltage rating on the caps was in response to the what was said on http://www.diyfactory.com/projects/green/green.htm: "The caps are being used at near or above there operation voltage..."

The caps are not the same in the schematic (http://www.diyfactory.com/projects/green/green02.gif) and the PCB check plot, the caps in the phantom power circuit are generally bigger in the check plot, like 47u vs 100u etc. Do I need to increase the value of all the caps?

Heatsinking the regulators, any further advice on how to do that properly? BTW, I don't think I will ever use all four preamps with phantom power turned on on each channel at once, if that makes any difference.

Thanks a lot!

/martin.

 

[Kev]

[quote author="MNA"]Increasing the voltage rating on the caps was in response to the what was said on http://www.diyfactory.com/projects/green/green.htm: "The caps are being used at near or above there operation voltage..."

Do I need to increase the value of all the caps?[/quote]

This was in relation to the voltage double/triple part of the circuit.
Yes some of the voltage peaks do get high and the need for higher voltage caps is directly related to the main power transformer you use.

At 15 vots AC things will be fine BUT if you were to drift up to 24 volts AC then I'm sure some parts would be in trouble.

As for the current of the phantom and 4 chanels.
4 basic mics will probably be easy BUT if you were to connect 4 UN-known phantom powered DI boxes then it is impossible to know just how much current will be required.

If you find some larger valued caps at a higher voltage that conveniently fit the PCB ... then there is no harm in giving them a try.

 

[PRR]

EDIT: posted in the wrong thread....

> What would I need to do to add instument inputs?

A DI box. Pads on mike-inputs still give too low an impedance for guitar pickups. Mikes can push long cables, pickups can't. So put a DI box, transformer or active, near the instrument and run a mike-cable to the mike-input.

 

[Kev]

[quote author="PRR"]> What would I need to do to add instument inputs?

A DI box. Pads on mike-inputs still give too low an impedance for guitar pickups. Mikes can push long cables, pickups can't. So put a DI box, transformer or active, near the instrument and run a mike-cable to the mike-input. [/quote]

just a convenient place for a shamless plug

http://www.jlmaudio.com/JLMDI.htm
http://www.diyfactory.com/projects/jlmsimpledi/jlmsimpledi.htm (a work in progress)
there is also the Country Hick
http://www.diyfactory.com/projects/countryhick/countryhick.htm

 

[peterc]

#3:If it's an easy mod, I would like to have dual outputs from each preamp, for monitoring purposes.

You could build the balancing amp from my website & make the gain =1 & hang this on the preamp output.

The actual audio core for the pre is the same for ALL the versions, some have a HiPass, output trim, etc.

Peter