All things Green Pre

[Phrazemaster]

OK, I can't install the isolation kits easily, the way my build is...but how about a compromise: an isolation sheet between the two heatsinks? Plastic?

Here's what I have:

The funny thing is, the heatsinks already touch practically, and even touching on purpose they do not short out as in the previously described experience...Is there anything else that could have accounted for this popping?

Let me know your thoughts, and thanks.

Mike

 

[Phrazemaster]

Update...duh...not plastic! I'm using a piece of cardboard so it won't melt

 

[peterc]

The isolation kits should go between the reg & the heatsink, for future reference. What you have done will work, but in your next build bear in mind that the regulator tabs have voltages on them.

I would definitely not use cardboard, if the regs get very hot, it might be set alight.....

Peter

 

[Phrazemaster]

Hi Peter, thanks for letting me know...I really had no idea! I don't know if it will be possible to get an isolation kit on the regs I have; the caps I have are so large I'd have to take them out too before reinstalling the heat sinks...feeling like a lot of work! But I'll think about it, and thanks.

Mike

 

[Phrazemaster]

OK am I nuts or...

If I buy a thermal isolation kit for my To-220 regulators - basically a silicone pad between the regulator and heatsink - the screw going through the hold in the regulator could still short circuit the reg if there aren't silicone pads on BOTH sides of the regulator...right? I don't see that these isolation kits typically come with 2 pads...am I missing something?

There's some slick ones on ebay in Hong Kong where the hole is built into the heatsink...if it wouldn't take 5 weeks to get it I might even do it!

Mike

 

[peterc]

Typically, if you buy a 'kit', it will come with a shoulder washer/bush that will insulate the bolt from the regulator, some come with 2 bushes that will insulate both the heatsink & reg from the bolt.

Peter

 

[Phrazemaster]

Got it...didn't realize...all that hunting on mouser/digikey before, and never caught wind of it, thx Peter.

Question: based on what I described, would anyone recommend I replace the regulators and the bridge rectifier just in case? I have extras for that purpose, and since I'm gonna bite the bullet and redo the board with the insulators and washers etc, would that be a good idea? Or am I just being overcautious/paranoid?

Thanks,

Mike

 

[peterc]

I would replace them, just me, but it is a mic pre so you are looking for the quietest performance possible.

Even though there are protection diodes in there, and the regs have internal thermal protection... Again my humble opinion.

Keep them for a second project that is a line level project, for e.g.

Peter

 

[Phrazemaster]

Thank-you Peter, I appreciate it. I have not spent all this time to just skimp on things now...Sigh!

Would you also replace the bridge rectifier too?

 

[peterc]

No, I would leave the bridge.

Just the active components.

Peter

 

[Phrazemaster]

Oh dear...by "active components" you mean the regulators...anything else specifically? (and, thanks!!)

 

[Harpo]

The funny thing is, the heatsinks already touch practically, and even touching on purpose they do not short out as in the previously described experience...Is there anything else that could have accounted for this popping?

So you have not been lucky as previously mentioned and one of the 4 diodes inside your bridge rectifier is already blown from exceeding parts current limits by this short.
Both diode protected 78xx/79xx voltage-regulators should still be alife.

 

[Phrazemaster]

Thank-you Harpo...I will go ahead and replace the bridge too!

 

[Phrazemaster]

Wow do I need to also test all the diodes as well...now I'm getting nervous; do I need a total rebuild practically?

 

[Harpo]

Only the bridge rectifier and get the isolation kits.
Replace the voltage regulators if it helps better sleep. I probably won't.

 

[Phrazemaster]

Thank-you! Mucho, mucho appreciated everyone!

 

[Phrazemaster]

Hi Peter, don't know if you got my email message - my email address for you is very old - but I'd like to get another PSU board - the latest version as long as it will work with v14 channels, and I'd also like to get another green pre channel board too, v14 if you still have them. Sorry to do this publicly; not sure how to reach you otherwise.

So...are the boards available, and if so how much?

Thanks!!

Mike

 

[sunyata]

Hi,
Is it possible to change the value of the HP-filter? I find 100Hz a bit high. It would be nice to have the option to choose between 30 or 80Hz for the filter.

I just tried the Green Pre with a Röde Procaster. Wow - great combination!!

Best regards

/Lars

 

[peterc]

http://www.mendelt.nl/greenpre_V14/_Green_trim_HPF%20CCT.gif

Changing the 2 x .1uF caps before the HPF IC will change the filter corner freq. So for 50Hz try .22uF

Peter

 

[sunyata]

http://www.mendelt.nl/greenpre_V14/_Green_trim_HPF%20CCT.gif

Changing the 2 x .1uF caps before the HPF IC will change the filter corner freq. So for 50Hz try .22uF

Peter

Thanks! I'll try that

/Lars