Question about Fender Mini Twin amp

[Crontox102098]

Anyone can explain me how this amp can work without biasing IC1B? 

[samhay]

IC1B is biased with R2.

[Crontox102098]

I think im blind... I has not seen +Vb connected to R2... Another question... Can i use this preamp with another little amp (Noisy Cricket or some TDA2822 amp) or with some TDA20X0 based amp?

[mth5044]

It looks like the KIA 6213 is a power amp, so you could place whatever power amp you wanted after the volume control.

[Mark Hammer]

If you take everything between the input jack, and the wiper of your volume pot, what you have is essentially and MXR Distortion+, or DOD250, with a tone control.  If you can feed one of those to an amp, you can certainly feed the output at the volume to a separate amp.

Note that R5/C5 produce a low-end rolloff around roughly 340hz.  I gather the small size of the speakers justified the trimming off of low end that the speakers would not reproduce anyway.  If you are planning to feed the output of the preamp stage to somethng other than 3" speakers, then you may want to recoup some of that bass.  You can do this by simply changing R5 from 1k to 2k2.  This will drop the bass rolloff down to around 150hz, which is good enough for guitar.  Your maximum gain will also be reduced from 501x to 228x.  But given that both the Dist+ and DOD250 are able to produce satisfying crunch with maximum gains of 213x, I think you get more than you give up.  Remember, as well that a guitar signal with more bass in it will also clip a little more when it hits the diodes, so you won't feel like you have forfeited that much potential clipping.