for the good people of the forum;at long last i found a proper schematic for the little blackstar HT-1
on the same day i snapped up one used 'locally' only 150Km round trip! :duh it's christmas already <3)
courtesy of the wierd wired interweb,via Korea.. 8) (an official factory PDF no less!) :tu:
Thank you!
It is even a gift! :dbtu:
Cheers
I am SO going to steal take inspiration from that phase inverter!
Now what kinda bugs me is that the preamp uses diodes for most of the overdrive sound. I wonder if the triodes get distorted at all?
In this case, yes.
Typical examples which don't are Marshall JCM900 and Valvestate 8080 , where clipping diodes are followed by very low gain tube stages (think around 3X gain)
But here the triode pair following them has high gain.
This.
In practice, the first tube stage will not clip at all, but it has a lot of voltage gain, and more importanly output voltage swing. Given that second tube starts to grid clip already at few volts of input signal, and has enough gain to start clipping at plates about simultaneously you do get plenty of ovedrive from the second tube.
What the diodes do is limiting the input voltage range to about 600 mV max (peak). At this point the final tube is already driven to "square wave" clipping and there's very little to gain from that point on. The diodes prevent excessive ovedrive of tubes (e.g. excessive grid current draw, which could be hazardous to tube or introduce "nasty" high order harmonic distortion) and also enforce fairly symmetric signal input to the tube waveshaper stages. At "in between" regions you get a little bit of harmonic distortion from the diodes softly compressing the signal by clipping, and more harmonic distortion from subsequent tube stage, which already at point of diode compression is going to clip rather much.
Thanks J M Fahey and teemuk! I see it clearly now. Very clever, I must say!
I really like both the preamp and phase-inverter designs on this amp. They put many ideas in my head... too many! :duh
Thank you for sharing.This will come in handy one day.Kudos!
The reverb looks like is using internal memory on a dspic.
Thanks for putting it up here. Nice to study other work.