Caps in G9 signal path

Hey Jakob, (or anyone)

some questions about the G9:

www.gyraf.dk/gy_pd/g9/g9_sch.gif

I was wondering if the first 220n cap after the input transformer is needed?

also what does the 47K feed back resistor with the 68p cap really doing? Is there not enough feed back with the gain selector? without it you could eliminate a cap in the signal path.

Just asking because I was doing some listening of mic pres the other day and noticed the G9 not having as much bottom as some of the other pre's. I thought maybe because there are alot of caps in the path.

Its ok to just call me nuts on this one.....

I think the first cap is there to DC-isolate the grid from the instrument when plugged into the jack.

Which trannies are you using? I have the lundahls in mine and have no issues with the bottom end.

Yea I'm using some triads 1:3 for input and output. I've used them in other pres that don't seem to have the same problem.

I've used the same triads for the passive eq's I made in the SRPP stages and they seem to sound great. could be a bit of an impedance mis match being 3:1 instead of 2:1 but I've never had any problems with level.

Maybe the quality of caps I'm using (mylar) arn't up to snuff.

Could be anything I guess...The pre does not not sound bad in anyway, great on guitars, just not as good as some other pres on say...drum room mics.

As you are using a lower turns ratio at the input (1:3), you should try a bigger cap in there, like 1uF instead of 200nF...

I´m almost sure that those triad you are using can be wired as 1:5 or 1:9 also, so you should try a bigger ratio first.

The input capacitor is needed, because our input grid is raised above 0V. 220nF here is plenty - it is looking into more than 1MOhm.

The 47K feedback resistor is half the feedback attenuator, the selectable resistors are the other half. Both halves are needed.

1:3 is a bit low for the input transformer - 1:6 puts you closer to lowest input noise.

If you feel that you haven't enough low end (and you should have), check your transformers' inductances. For medium-z work like this, you need high inductance to get low frequencies thru'


Jakob E.

Thanks guys,

Ok...rafa your right those triads go to like 1:8 or something. I'll try a higher ratio.

I'm using triads in the Langevin line amp I made and use for a mic pre. I have it on a switch so I can go through all the raitios. Guitar sounds better as I get to higher turns raitio. Not to much gain but enough for loud guitars and drums. Its all starting to make sense now...

Jakob I've always had enough gain with the G9 so I've never thought about using higher ratios.

Out with the soldering iron!!!!!!