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Amplifier Discussion / Re: Gallien Kruger GT200
« Last post by Enzo on December 03, 2019, 08:42:14 PM »Those sound like bias controls to me.
On your schematic from early on, I see D1,2, but they do not connect to Q9,10, only to the bases of Q7,8. They do connect to other transistors, but not 9,10. They do go to the collectors of Q3,4, which are the bias transistors.
Unlike the common complementary SS output stages, this is two single sides stages in push pull. In other words, the bottom half is identical to the top, just drawn upside down. SO usually we see one bias transistor between the positive and negative sides, we have two positive sides, so we need two bias controls.
The adjustment is for 1.65v on the base of the drivers - Q7,8. Qs3,4 draw current through those diodes to set that voltage. The bias is adjustable exactly because transistors vary. Whenever outputs are changed, there is no assumption the old adjustment will still be correct.
What did you use for PMD10K80?
On your schematic from early on, I see D1,2, but they do not connect to Q9,10, only to the bases of Q7,8. They do connect to other transistors, but not 9,10. They do go to the collectors of Q3,4, which are the bias transistors.
Unlike the common complementary SS output stages, this is two single sides stages in push pull. In other words, the bottom half is identical to the top, just drawn upside down. SO usually we see one bias transistor between the positive and negative sides, we have two positive sides, so we need two bias controls.
The adjustment is for 1.65v on the base of the drivers - Q7,8. Qs3,4 draw current through those diodes to set that voltage. The bias is adjustable exactly because transistors vary. Whenever outputs are changed, there is no assumption the old adjustment will still be correct.
What did you use for PMD10K80?
