Increasing the gain in Matchbox reply for Daz

[will]

Hi Daz,

I sent this via the regular forum as I get an error trying to reply to your question via personal message. ****Failed sending email :: PHP :: ****

Hi Will,
I was curious as to what mods you did to the matchbox circuit to get more gain out of it?
Kinds regards
Daz

I didn’t have any J201 Fets so I used 2N5457 Fet’s for Q2 & Q3. Substituting the 2N5457 for Q3 works great with this circuit. Unfortunately you can’t bias Q2 with the 2N5457 with the matchbox configuration. So I swapped the 4.7K and 1.2K resistors below Q2 this allowed me to bias Q2. This reduced the gain of this stage approximately 5 times. So I bypassed the 4.7K resistor with a 22uF cap. This basically maxes the gain of the stage.

If I did it again now that I understand how they operate better, I would reduce the 4.7K resistor to about 1K. This would allow the Q2 Fet to bias easier. I don’t think it would change the sound all that much. I suspect it would scale better to how the original tube circuit operated as we are dealing with much smaller voltages.

To increase gain I would bypass the Q2 source resistor 1.2K with a 22uf cap. Many circuits use 22uf in this position, any cap between 1uf and 22uf will work fine. The larger the more gain. As an alternative you could replace the 1.2K resistor with a 1K potentiometer and connect the 22uf cap to the wiper lug. Now you can dial in the amount of added gain you want for that stage.

I hope that helps.

Regards,
Will

[dubs]

Thanks Will for the info, much appreciated!
Yeahmy PM acting funny too.