Bassman AB165 To AA864 Revisited

[Amp Kat]

Ok, had to put this one down for a bit but am back on it and wanted some feedback from you guys. After changing the AB165 to the AA165 I hated it and it sounded like crap (Regis and Bruce were right on ) so I'm switching to AA864 and have it almost done but came to the filter section and theres a little difference. The AB165 has the 27k dropper and extra filter cap and it's topology is a little different around V1B and 2A. How did you do it ? Did you leave the last cap in and remove the 27k or just or remove both ? I was thinking just remove the 27k and leave that extra 20uf cap for additional filtering. What do you think ? Oh one more thing (edit) what are your thoughts on the bypass caps for the 100k plate resistors ?

[Rick Erickson]

I wouldn't stack the filter caps in the preamp. There's little to gain and potential to add mud to the tone. If you are cloning an AA864 then do it like they did. There's nothing wrong with pulling the resistor and the cap. The bypass resistors, at least in the Normal Channel were a necessary evil to control oscillation which occured due to the poor layout design of the AB165 circuit. If you can remove them and not have HF oscillation then there's no reason to have them in there - other than to remove some HF content

RE

[Amp Kat]

Funny that you mentioned the HF Rick because there is some and disconnecting the NF made it better which I thought would be the opposite. It also causes the amp to do a little high pitched whine like a flyback tranny would do at startup so I left it disconnected. I'll remove the resistor/cap network and do somemore pondering. Thanks Rick.

[Regis]

I don't think I changed the filter cap setup, and I've always like the tone. If you do change it let me know how it turns out, I might do it too.

I agree with Rick, I would pull the bypass caps on the plate resistors.

I was playing one of my Bassmans last night through a 2x12 cab with a couple of Warehouse Guitar speakers in it, it sounded great.

[Amp Kat]

I think I will try it Regis and do some comparison test. I was using a 4x12 orange cabinet and it sounded good but as Rick pointed out it did have a tad of mud and it's probably from the stacked caps increasing the capacitance of that node. Another thing Regis is the voltage drop of that 27k puts the plate voltage at around 140 where without the resistor it goes up to 265 which adds some gain and really creates a distortion channel on the instrument side when cranked past 3 or 4 and alot of that is also due to the 5881's I have in there so theres a good difference between the two channels instead of two close channels and if I put in that extra 1/2 of triode that Bruce was talking about man that fricking thing would be in the Soldano column. I'll let you know tomorrow Regis what the cap job sounds like.

[georgewilson]

I m thinking to buy new one but wait for my first paycheck!!I wish to learn lot about music composing from you guys.THANKS!!Graphic Design Baton Rouge