Ok all you amp freaks out there....
I'm interested in this particular amp, however I'd like some advice on a few modifications to it.
This is a simple, yet advertised as a low-distortion (0.02 IM) 40 watt amp.
What I would like is some suggestions on removing the feedback-installed bass/treble from it, and instead using a "plain" system of feedback, keeping the amp as linear as possible without that stuff attached in the feedback line.
Essentially, like using with the bass/treble at "0".
Secondly, I'd like to UP it's wattage to around 80, maybe 100W, keeping the original design, but perhaps changing the output transistors, maybe the drivers as well. (higher B+, maybe +/- 65V?)
Nothing too drastic - I like its design, just toying with some mods.
I'm interested in this particular amp, however I'd like some advice on a few modifications to it.
This is a simple, yet advertised as a low-distortion (0.02 IM) 40 watt amp.
What I would like is some suggestions on removing the feedback-installed bass/treble from it, and instead using a "plain" system of feedback, keeping the amp as linear as possible without that stuff attached in the feedback line.
Essentially, like using with the bass/treble at "0".
Secondly, I'd like to UP it's wattage to around 80, maybe 100W, keeping the original design, but perhaps changing the output transistors, maybe the drivers as well. (higher B+, maybe +/- 65V?)
Nothing too drastic - I like its design, just toying with some mods.
Attachments
This uses a complex feedback system, some possitive feedback (signal fed to non inverting input) but mostly negative feedback.
Build it without the tone controls and just include R221a and R222a for the global NFB.
Check the specification of the output transisntors; Hfe 80 minimum, VCEo 80v, not much room to increase the voltage rails just double up to increase the current drive.
The 2SA798 has been obsolete for at least 20 years!
Build it without the tone controls and just include R221a and R222a for the global NFB.
Check the specification of the output transisntors; Hfe 80 minimum, VCEo 80v, not much room to increase the voltage rails just double up to increase the current drive.
The 2SA798 has been obsolete for at least 20 years!
Estimated feedback impedance of the tone control circuit is 10-15kΩ, yielding an (1kHz) amplification of { [ ( 47k // 15k ) + 8.2k ] / 0.39k +1 } ~ 51x (34dB -> 600mV input sensivity; check the specifications if possible).
So, for the same amount of amplification add a resistor of 15kΩ parallel to R221a. Increasing this parallel resistor will increase the overal amplification too.
For twice the desinged output power the amplification would be 100x, rendering this parallel resistor to a value of 90kΩ.
So, for the same amount of amplification add a resistor of 15kΩ parallel to R221a. Increasing this parallel resistor will increase the overal amplification too.
For twice the desinged output power the amplification would be 100x, rendering this parallel resistor to a value of 90kΩ.
1. Remove everything below P221a.
2. Include in parallel P221a 10kom (more / less).
3. Listen ...
2. Include in parallel P221a 10kom (more / less).
3. Listen ...
In checking out the transistors used in that amp, and crossing them over to ECG/NTE replacements, all are still available.
The original output transistors when crossed to ECG/NTE come up as #36 - 37's, rated for 120V and 12 amp.
And I've got an extensive ECG/NTE stock of semi's sitting on the shelves, including that "dual" PNP input, Q201, an ECG #43.
The original output transistors when crossed to ECG/NTE come up as #36 - 37's, rated for 120V and 12 amp.
And I've got an extensive ECG/NTE stock of semi's sitting on the shelves, including that "dual" PNP input, Q201, an ECG #43.