differences with the clipping section between the TS-808 and the Maxon OD 820

[mordechai]

I was just looking over the schematic for the OD 820:



It looks like the major differences here are:

1. that the series resistor has been lowered from 4.7K in the TS 808 to 2.2K, for more gain I presume.

2. the cap following the 2.2K resistor has been upped to .1uF -- is this to maintain a similar corner frequency to compensate for the lowered resistor?

3. the smoothing cap across the diodes is a 100pF rather than the 51pF in the TS 808.  Would this be because the increased gain from the lowered resistor leads to more jagged high end in the signal through the clipping diodes, so a bigger value smoothing cap is required?

4. the pot controlling drive has been lowered from 500K to 250K.  I am not sure what the effect of this change would be...does it focus the usable sweep of grain across the range of the pot?

[Quackzed]

1. that the series resistor has been lowered from 4.7K in the TS 808 to 2.2K, for more gain I presume.

2. the cap following the 2.2K resistor has been upped to .1uF -- is this to maintain a similar corner frequency to compensate for the lowered resistor?

3. the smoothing cap across the diodes is a 100pF rather than the 51pF in the TS 808.  Would this be because the increased gain from the lowered resistor leads to more jagged high end in the signal through the clipping diodes, so a bigger value smoothing cap is required?

4. the pot controlling drive has been lowered from 500K to 250K.  I am not sure what the effect of this change would be...does it focus the usable sweep of grain across the range of the pot?

1,2,+4 : the resistor has been halved, the cap doubled : yes this maintains the corner freq... also because the resistor is half, in order to compensate the gain pot to have the same gain it is halved as well (500k to 250k) so really 1 2 + 4 are all changes but the net result is no change to the corner frequency or to the gain...

3... this will roll off just a hair more high end, not much of a difference but you can always lift one end of that cap with the gain up and see...should sound a bit 'smoother' with it in...

[Quackzed]

check out r.g.'s "technology of the tubescreamer" at geofex for an in depth look at what does what.
http://www.geofex.com/article_folders/tstech/tsxtech.htm