I will use this guy without its front end because it arrived without the input trafo and I have some DIY FE 22 at hand.
Because for the front ends a little voltage regulation does well I was thinking to use Q1 and Q2 as cap multipliers by disconnecting R8 and R9. Should I decrese R7 and R8 to 1k and increase C1 and C2 accordingly?
Because for the front ends a little voltage regulation does well I was thinking to use Q1 and Q2 as cap multipliers by disconnecting R8 and R9. Should I decrese R7 and R8 to 1k and increase C1 and C2 accordingly?
BD139/140 are decent cascodes, but not so much decent cap multipliers, due to lowish Beta
measure their Beta then calc how much of base current you need for intended load
measure their Beta then calc how much of base current you need for intended load
So like I said my friend bought a r2 from the Swap meet.
We received this
A bit of a mess and without a front panel but I took my time with it and started with the cleaning of the amp pcbs
Then some holes had to be drilled
Then with a bit of patience it went out ok
All went well, biased each channel at 1.4a and then I connected the amp to the speakers.
There was a bit of hum. Initially I thought it is coming from the front end but I disconnected the front end and actually it comes from the low capacitance in the power supply filter. The filter pcb is built with 2x15000u caps in each cell and 4x0.47r resistors in paralel so the filter is 30kuf - 0.12r - 30kuf.
I removed 2 of the 0.47r resistors to increase a bit the attenuation and now the hum is lower but still can hear it when I put my ear at 1 cm close to my 96db speakers.
At this point I think he has to buy some new caps of a bigger value or to add a second filter pcb with same values for the components in case he hears somethig on his speakers.
Very nice sounding amp, it played the entire night 🙂
We received this
A bit of a mess and without a front panel but I took my time with it and started with the cleaning of the amp pcbs
Then some holes had to be drilled
Then with a bit of patience it went out ok
All went well, biased each channel at 1.4a and then I connected the amp to the speakers.
There was a bit of hum. Initially I thought it is coming from the front end but I disconnected the front end and actually it comes from the low capacitance in the power supply filter. The filter pcb is built with 2x15000u caps in each cell and 4x0.47r resistors in paralel so the filter is 30kuf - 0.12r - 30kuf.
I removed 2 of the 0.47r resistors to increase a bit the attenuation and now the hum is lower but still can hear it when I put my ear at 1 cm close to my 96db speakers.
At this point I think he has to buy some new caps of a bigger value or to add a second filter pcb with same values for the components in case he hears somethig on his speakers.
Very nice sounding amp, it played the entire night 🙂