Re: Q:Feedback resistor for Traynor YBA-1 Bass Master am

3/5/2006 11:20 AM

Wild Bill

Re: Q:Feedback resistor for Traynor YBA-1 Bass Master am Hi HB!     Once again, it's not that simple!     If you follow that feedback resistor you'll see it goes back to the phase-inverter driver tube. It will feed one of the grids and have a resistor from that point to ground.     In the YBA 1 the resistor is a 4k7, with a cap and a presence pot across it to ground.     So you actually have a voltage divider of the 100k resistor and the 4K7. The ratio determines the amount of negative feedback voltage that feeds the grid. In this case it's around 20:1 (100k/4700).     So you can't just compare the one resistor value with a Fender or a Marshall without considering this other resistor! It would be like measuring that trophy fish only at one end! Marshall's often use 100k/4k7 but sometimes 47k/4k7 and others. Fender values are 820R/100R or 820R/47R. I'm working on a Traynor Reverb Master right now that uses 1k/100R.     It's the ratio that's most important. There may be some sonic differences as to the PI resistor value. I'll bet Mr. Aiken covered this point in his FAQs on phase inverters. I'll let you do your own research there!     HTH     ---Wild Bill