gyraf g9 emergency room in the midwest?

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junkmaster

Member
Joined
Feb 9, 2009
Messages
23
hi y'all, i've slowly been working on a gyraf g9 mic pre over the past couple of years (i know, it's ridiculous)......i've hit a brick wall w/ some grounding issues.....i was wondering if there were any folks in the omaha/kansas/iowa area who might be interested in making a couple bucks and finishing it out out....i promise you won't be polishing a turd....i've sunk $800 plus into this thing and really want to just use it, not fight it anymore...anyways, please feel free to contact me at 402 981 1240....hope this isn't against protocol.....cheers, alex
 
You could try posting some pictures and describing what's going on. Maybe we can help you remotely. I've battled layouts and grounding schemes before (I'm sure almost everyone here has), and I'm sure someone here will be able to help you with you problem. I know how frustrating it can be when something is so close to working, but you just can't seem to get it to do what you want. I have seriously contemplated chucking stuff in the trash before just to be rid of it and be able to move on, but trust me, taking the time to truly figure out what's causing the problem is worth it. Not only will you have a fully working piece of gear, but the knowledge you garner from working it out yourself (or with some help) will serve you in future builds. I've learned a lot about grounding and isolation while beating my head against a wall trying to make a preamp quiet.

Post some pics! Let us know what the problems are! We are here to help each other.
 
Yeah! Post Pics!

I just did an extensive rework of the grounding in my G9 and the HF oscillation mod (if you noticed a horrible HF noise when cranking the gain above about 2 o'clock) and they are now rockin'!
I have no doubt that with a bit of an explanation of the issues, this forum can get your G9s
purring along...
+ if you already have 2 years in, finishing them yourself will be very gratifying.

Cheers!
 
thanks a lot for your replies! i will take some pics and write up a little list of things that are going wrong....the hf oscillation is certainly one of them.......forgive me if i am not quick to respond; i'm probably tied up w/ my three yr old boy.....thanks also for the meta thread link....i've gone through it a million times but am just not savvy enough to puzzle through it on my own.
some quick info....
hf osc when gain/trim cranked up past about 1/2way
passes signal w/ mic but always w/ a buzz (sounds great otherwise!)
all switches seem to function but w/ a loud pop.....i think this is normal(?)
the voltage reg is grounded to a very large heatsink then to the chassis
i don't have a ground from the pcb to the chassis but i thought the mountings screws,volt reg heatsink etc would take care of that problem....the only ground is from the xlrs and the heatsink...could that be making a loop?
well, i'll get my act togeher and post some pics soon....thanks again!! cheers alex
 
The two things I can suggest off the top:
Matta has a step-by-step fix for the HF Osc mod on this page:
http://www.groupdiy.com/index.php?topic=17980.380

as far as grounding, I created a chassis starground point.
strapped pin1 on Input XLRs together and then to star-ground,
I also strapped output pin1s together...
earth pin from IEC plug also to ground.
FWIW: I am contemplating getting a punch of green, panel mount banana jacks
and tying my star ground to that to tie into a rack ground bus.

I don't think grounding from the heat'sink would help...

hope something here helps.
Also, there is the mega-G9 help thread. That will get more knowledgeable people than myself in on your discussion.

Cheers!
 
junkmaster said:
the voltage reg is grounded to a very large heatsink then to the chassis
....the only ground is from the xlrs and the heatsink...could that be making a loop?

Hi,
did you isolate the voltage regulator from the heatsink? In other words: there should be no contact between regulator and heatsink!!!
regards
Bernd
 
thanks you guys....when i have a little time i'll run through the matta link you sent me...also will try new ground points.....i will try strapping xlr out pin 1 to ground....right now they're not....bernbrue i do have the reg isolated but that's a good thing to point out for the record....when i first assembled it i didn't! makes me want to double check it again and make sure the mica washer thingy isn't broken....thanks again for your thoughts.....will report back soon i hope....cheers, alex  :)
 
Yeah a few pics on this forum is sometimes all it takes. I've been helped that way. :) Everyone is very helpful here. :)

Plus you probably REALLY want to get that working correctly they sound awesome!

John
 
Yeah I used mine again today on a Jazz recording. Bass DI and a U67 in the other channel for the drum room mic, they sound great. Jakob was very generous to share this wonderful design with us.

Junkmaster, we are here yo help where we can! Best of luck  getting tot he bottom of the problems, and we WILL get to the bottom of them, together ;D

Matt
 
I cut the traces for my high impedance cables also before I even powered it up. But I drilled holes in the board and mounted the wires from the top.

This really belongs in the G9 thread tho.

John
 
thanks again for the info.....sorry if i started this thing in the wrong place....is there a way to move it to a more appropiate thread? don't want to tick anyone off! or is it ok to continue...? i've taken some pics and will post soon...might take it completely apart tonight for more extensive photos...thanks again, the moral support of other frustrated people gives me hope! cheers, alex    ps matta glad to hear you like it on jazz....i do a lot of acousticy music which is what drew me to the pre design initially....
 
Just take pics right now before ya pull the board. Only some people have problems. It is kinda a big project. At least for me with all the tube stuff. But is one of my favorites ever. Let's see it! I'm guessing the mod can move the thread. :)

John
 
good news...i grounded the xlr outs on pin 3 and reconnected the di jacks....then grounded that to chassis......very clean, maybe a whisper of buzz but i think it's from my old-house ungrounded outlets....no longer getting the hf osc but the last two indents on the output don't work and/or are a distorted mes....but i can live with that....if i get it back together and it sounds good i'll be happy...just wish i had an etched face plate to show off....might have to be a freehand dremel job 'cos of cash....thanks again everbody, i think i just needed a kick in the pants...cheers, alex
 
hi all....i moved my problems over to the g9 help thread as requested....starts on page 25...solved a lot of problems but still have a couple tiny gremlins...i posted a couple pics as well....one channel is almost 100% and sounds amazing....thanks jakob!...the other is at maybe 75%....still sounds good....if anyone has the time to check out my post i'd really appreciate it! cheers, alex
 
good news...i grounded the xlr outs on pin 3 and reconnected the di jacks....then grounded that to chassis......very clean

You've grounded the PIN 3!!! this is the HOT point???
It's realy strange
 
creal....i think i mis-typed about #3 but let me post a reply when i have a minute to look at the thing again....will def check it out....thanks for your acuity! cheer, alex
 
creal.....i was wrong, it's grounded at pin one....no worries! still having mysterious line/mic48v reversal on ch 1 card....besides that just need to do the trace cut and she's ready to go....tried desoldering problem switch and moving it around but still reversed....could it be a faulty switch?...it also doesn't cut off the mic input when i switch it to line....the other channel works just fine....starting to think bad switch.....any thoughts appreciated....cheers, alex
 

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