I revisited my 002 clone again after almost 10 years. The clone is a modified version of the original hand-drawn schematic having a Dumbleator loop instead of Reverb. I also revised the circuit over the years to reflect most of the errors which became known. Yet the amp always was much too bright for my tastest, almost brutally bright and harsh.
Once I tried my Double SSS preamp (see other thread) into my 002 clone (into the Return stage of the built-in Dumbleator of my 002 to be exact) I was suprised by the difference between the 004/004 circuit and the 002 preamp.
The 002 preamp was much much brighter than either 004 or 005 (which are much closer sounding to each other). Bear in mind that the 002 preamp in my clone of course goes through the Send section of the built-in Dumbleator thus some minor differences can be expected (I need to built a separate Dumbleator again to make this comparison identical as possible
). So I wondered why the 002 preamp was so much brigther than e.g. 004 (which has a comparable Filter circuit). After searching the Ampgarage I found an interesting post about the lack of a grid stopper on the tube following the filter in 002 compared to 004 and 005. This post (I need to find it to post a link) also discussed the possibility of blocking distortion due to the lack of a grid stopper in 002. So I installed a 220k grid stopper in my 002 and this improved the harsh brightness nicely. Now the high filter is much more usable.Another thing I found is that the Filters as in the hand-drawn schematic are quite usable if you are willing to set the tone controls a bit more extremely. For example the mid control is mainly responsible for the harsh high frequency and dialing that back gives the high filters more room. Then there is the "wrong" postition of the 0.0033 cap in the hand-drwan schematic leading to an extreme high cut (as testified by the Dumbleland demo on Youtube) which works quite nicely if you use the Jazz mode and bright switch (120pf in my case). In summary I think with the 220k grid stopper and a new approach to setting the controls depending on the settings of the filter revealed a very useable tweakability of the hand-drawn (of course minus the blatant mistakes) schematic.
Coming back to the 220k grid stopper: I assume that the person drawing the schematic might have simply overlooked that resistor which most likely is under the PCB in the original amp directly on the tube socket. Maybe the person drawing the schematic mostly measured the values in the amp and there is no easy way to measure that if the resistor is below the PCB. Anyhow, all assumptions from my side. I would invite anyone the test a 220k or larger grid stopper one the tube grid after the filters.
BTW: the Pentode preamp into the 002 Power amp (via 002s in-built Dumbleator Return section) was quite nice and a bit more open and airy than the 004/005 SSS preamps.
Much rambling, looking forward to comments.
Best Regards,
Electron
) to build an external Dumbleator for the Double SSS. Yet the Pentode preamp is comparable in brightness to 002 going into the 002 power amp (same setup as with thw 004/005 Double preamp= into the internal Dumbleator Return of the 002 amp). 