Ruby preamp output

[Kaiowas]

Hi everyone!

I built the Ruby FET preamp from runoffgroove.com, is pretty cool, in my amp (marshall G MK10II) sounds beautiful, but if i connect the ruby output to the sound crad input (Audigy 2 Platinum) the output starts to crack if i play a little hard. This is regardless of the volume pot, no matter how it is set, it does the crackle thing.

So i decided to measure the input and output voltages with a sinewave.
Iset the voltage of the input around 0.100V~, and the output was about 3.43V~. If i'm not wrong a line input shloud as high as 1.2V, so i made a voltage divider in the output, but it lost all the tone!!!, it didn't soun "pretty" anymore.

What can i do to set the output to line level, but without losing tone in the process?

Thanks in advance!

[javacody]

Sorry, this might have something to do with the impedance the preamp is seeing.

[Kaiowas]

So i'll start to play with the Zinput resistor.
At least now i know it has something to do with the FET and not with the 386.

Thanks for the advice!

[B Tremblay]

Just to clarify, are you using the entire Ruby amp circuit as a pre-amp?

[Kaiowas]

Well...yes.

I'm using the 2 stages, the FET and the 386 (LM386N-1, not as good as the one proposed in the page but...) stages.

Why? that's a bad thing to do? shloud i leave just one stage?

Thanks

[B Tremblay]

Well, the most likely reason that you're having problems is due to an impedance mismatch (as javacody guessed).  Ruby is an amp, meant to be used with a speaker or headphones.  It is not intended for use as a pre-amp or stompbox.

Since the 386 expects to see a low impedance (between 4 and 16 ohms), so expecting it to drive a different load will present some problems.

For a pre-amp, I suggest you try the Fetzer Valve, or if you want more options, try one of the amp emulators.

[Kaiowas]

thanks a lot btremblay!

I built the fatzer valve, i'm still tweaking it to obtain a fatter response!!

maybe fou could help me achieving that.

Thanks!

[stm]

You can still load the output of the Ruby with an 3.9 to 15 ohms carbon resistor (2 watts power rating to be safe) as a load, and then take the output of the Ruby to your soundcard input.  If output is still too hot you can place a voltage divider at the output made of relatively low valued resistors, like 1k and 220 ohms, to cut signal level down to about 1/5 th.