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|previous: Tommy Dale That sounds like the Hybrid-A schem... -- 9/6/2004 7:35 PM||View Thread|
|9/7/2004 5:09 PM|
|Teo||Re: What makes a Dumble sound so good?|
Yes it sounds like the Hybrid-A schematic which leaves you lot of freedom with OD stages cathode and plate resistor, so the degree of "asymmetric distortion" depends a lot on how you choose them.
BTW if you bias a stage in the middle of the available voltage swing the output will be (slightly) asymmetric anyway because of the different sides of the transfer curve.
IMHO Dumble prefers to bias the OD stages the more symmetrically he can in order to reproduce the same kind of distortion that push-pull power amps have. Following this idea yesterday evening I experimented different biasing points by putting a trimmer in place of the cathode resistor (last OD stage) and results are very interesting.
The procedure is as follows:
- attach a voltmeter to measure the cathode voltage
- read the voltage at idle
- play fully distorted and take notice if the voltage goes higher or lower
- adjust the trimmer and repeat until the voltage remains almost stable from idle to full distortion play
This way you should have balanced the output signal from the stage. To me it sounds way better that any usual/unusual cathode/plate resistors combination I ever tried.
Anyway the trimmer let's you fine-tune the most critical OD stage and you can easily adapt it to different tastes.
|Tommy Dale Thank you very much. |