Now some pictures "after" and remarks:
- I have received version 4 of L12-2 as kits so I was able to make some changes:
-didn't soldered C5 coupling capacitors of 33uF but instead added those green ones MKTs 10uF on main board
-added potentiometers to bias adjust as Calvin suggested as well as small 1uF films to almost each big capacitor
- I left feedback capacitor C8 as 1000uF/16V however I regret I didn't change it to 220uF bipolar
- because "in ground" is now connected with "ground" connector I didn't soldered it at all, connecting all ground to "ground in"
maybe I should drill out that connection and connect ground in and ground with 10R hum breaking resistor as was suggested in L12-2 thread
-set bias to 8,8mV and check DC offset ( was ca 3mV)
- installed another heatsink ( as seen) - it's plenty of space in that Grundig
- at the end added a blue LED on front panel
How is the sound ?
Nice, but I can compare it only with my upgraded Pioneer SX205 RDS feceiver and the sound is slighltly better only. It is not a night and day difference as I expected.
And there is a hum ( or small brum) coming not from power supply but coming when I connect a aolume plate ( even not a whole preamplifier plate). I was informed by LJM that I should use his P7mini or P8 preamplifier and that could help. Maybe but for the time being at is as it is and I am playing it and enjoying.
Another idea came in my mind - I will order 1pc of L15 amplifier and swap it with L12-2 to see if there is a difference ( I will have L12-2 in one channel and L15 in the other) then I will share my remarks with you guys.
- I have received version 4 of L12-2 as kits so I was able to make some changes:
-didn't soldered C5 coupling capacitors of 33uF but instead added those green ones MKTs 10uF on main board
-added potentiometers to bias adjust as Calvin suggested as well as small 1uF films to almost each big capacitor
- I left feedback capacitor C8 as 1000uF/16V however I regret I didn't change it to 220uF bipolar
- because "in ground" is now connected with "ground" connector I didn't soldered it at all, connecting all ground to "ground in"
maybe I should drill out that connection and connect ground in and ground with 10R hum breaking resistor as was suggested in L12-2 thread
-set bias to 8,8mV and check DC offset ( was ca 3mV)
- installed another heatsink ( as seen) - it's plenty of space in that Grundig
- at the end added a blue LED on front panel
How is the sound ?
Nice, but I can compare it only with my upgraded Pioneer SX205 RDS feceiver and the sound is slighltly better only. It is not a night and day difference as I expected.
And there is a hum ( or small brum) coming not from power supply but coming when I connect a aolume plate ( even not a whole preamplifier plate). I was informed by LJM that I should use his P7mini or P8 preamplifier and that could help. Maybe but for the time being at is as it is and I am playing it and enjoying.
Another idea came in my mind - I will order 1pc of L15 amplifier and swap it with L12-2 to see if there is a difference ( I will have L12-2 in one channel and L15 in the other) then I will share my remarks with you guys.
Attachments
As I promised I installed L-15 amplifier in right channel. Works OK, DC offset is ca 5mV. And the sound ?..............no change at all ( at least to my ears). Even volume level is the same. Will check it again after warm up and with different pair of headphones but don't expect anything different. The hum from preamplifier also exists. As said I will sum up that change later.
Attachments
Warming up gave nothing, I decided to put the L12-2 back to right channel. Having an occasion that my Grundig was disassembled I have changed C8 capacitor from 1000uF/10V no name to 220uF/50V bipolar Nichicon Muse in both channels ( you may see them on picture ( dark green). Now the sound is even better.
