[Godders]

Nearly there! I'm frankly amazed I've got this far without having to bother the good folks of the Lab.

The pre is up and running and sounding pretty fantastic (with dynamic mics at least :? ).

With 48v engaged and a condensor mic plugged in the level was a bit low and there was a lot of hiss. I inspected the PS and noticed I had neglected to fit D6 (the 56v zener diode).

So after giving myself a slap and fitting the diode the hiss has gone but the level remians a bit low and there's a buzz at higher gain settings. Phantom power is measured at 31.7v (with the trimmer at max) so a bit on the weedy side there.

I'm not entirely sure what the function of D6 is? Did I damage something else like the 48v regulator by firing the unit up without D6 fitted?

Any help/suggestions appreciated. :thumb:

Cheers

Nick

[needlz]

My levels are also quite low but it sounds great with all mic types. I am just concerned that my output is much lower than it should be. My API312 kicks the living heyzeus out of it in terms of total output gain.

[Godders]

I haven't really run it through it's paces but with a dynamic (EV635a) I get a pretty decent level.

I believe the available gain should be in the region of 60dB which is plenty for most things.

[needlz]

I am definitely not getting 60db... If that's how much gain it is supposed to produce, something is definitely hosed. Any ideas of what to check for?

[gyraf]

Maxgain with Lundahl's is some 55-57dB. 60-62 with OEP input.

[Godders]

Maybe my post was a bit too rambly (must waffle less :green:).

What is the function of D6?

Could I damage other components by firing the G9 up with no D6 fitted?

As I said I'm getting a low level and some buzz with phantom power on (measured at 31.7v, trimmer at max).

I previously fired up with no D6 fitted.

No problems with dynamic mics and regualr mic input.

Cheers

Nick

[gyraf]

D6 is the zener reference for phantom (look at the schematic!!)

Prevents phantom from going over some 48V

You could have burned electrolytics downstream from the regulating transistor - from overvoltage.

Jakob E.

[Godders]

Thanks Jakob  :thumb:

I'm still at the very early stages of learning, I'm getting my head around schematics but there are still vast gaps in my knowledge.

I will check out those 'lytics.

Cheers

Nick

[gregcs1]

What do you think about using IDE computer cables for front panel connectons?

[gyraf]

Hard to say. try it, and report back..

[gregcs1]

This is the connection cable I made from floppy connection cable. Making it was real pain in the @ss. It took me almost a hour. It really isn't some piece of art, but I hope it will do the job.

step by step  :?


finished, only 3 to go!  :roll:  :grin:


And some pics of (slowly) progressing G9





Jeah, I know, I screwed up connections (female is soldered on pcb instead of male) but who cares! It'll work anyway!  :wink:

The only thing left (on main PCB) are IC's and T1. I'm still looking around for an IC1 heatsink.

Beside that heatsink, the only thing that gives me a hard time are that god [email protected] lorlins on front panel pcb's. I still don't know how to connect them. Obviously I still have some reading to do.


@gyraf

There are some kind of marks (A, B, C, D) on the bottom of the switches (poles). I also found them on pcb. Are they correctly aligned? Can I just solder a to a, b to b and so on...?


Thanks to all for your answers!

[JerryPbury]

Gregcs1,

Do you have a copy of your BOM in regards to your Capacitors (all) and connectors? I used the only one I could find here and it had a lot of wrong / bad (non-fitting, to large/small etc.) component choices.

Thanks,

Jerry

[gregcs1]

I ordered (almost) everything from Farnell. I was really careful to order components with right spacing. (connectors - 2.54mm) etc... I printed PCB in 1:1 and then measured all crytical connections. Farnell has nice thing on their site - you can actually choose component by lead spacing. So I had no problems except with C21,22 because they were 100uF/100V instead of 63V and were too big to fit in. I changed them and now is ok.

order:

http://freeweb.siol.net/gregcs1/Order1.txt

[JerryPbury]

Thank You!

Jerry

[Mailliw]

Hello,

Recently, my G9's phantom power isn't enough to make the pattern/cut switches work on an AKG414. I measured 14 volts on the XLR pins! It was 48 volts last time I used it.

I had the case off for a second today to adjust the trimmer, but 18VDC was all it could muster. I verified that 16VAC is going into the phantom circuit, but thats all I had time for.

EDIT: The top of C26 (47uF/50V) is ruptured. 16.6VAC is going into the phantom circuit. Right now, the mains AC is 117 volts. Could it have simply been a faulty capacitor?

Thank you,
William

[gregcs1]

C26 and C27 are 47uF, 63V. Maybe this is the cause...

[Godders]

C26 and C27 are 47uF, 63V. Maybe this is the cause...

Hmmm, the board says 63v but the parts list and the schematic on the Gyraf website both say 50v for the 4 P48 triplers (C26-C29).

I bought my board already stuffed with resistors, diodes and 'lytics and I've noticed that C28 & C29 were 100uF, 35v instead of 47uf 50v (or 63v?).

I'm thinking this is probably the source of my phantom power problem but I'd like clarification on the correct voltage before I fit the correct capacitance values.

Cheers

Nick

[gyraf]

Go with 63V capacitors, that'll keep you on the safe side. and keep an eye on polarisation!!

Jakob E.

[Godders]

Thanks as always Jakob. :thumb:

Cheers

Nick

[gregcs1]

Front panel question...

Shouldn't SW3 (phase switch) be 2 pos.? PCB marks says 3pos...  I understand input has 3 pos. (line, mic, 48V) and low cut sw (sw4) has 3 pos (off, low, high) but I don't understand why phase switch has 3 pos (in, out, ?)

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