The Secret Society of Lathe Trolls

Amp Doc · Joined: 21 Jun 2007 Posts: 108 Location: UK

Does anyone have any experiance with how much feedback to use with he grampian type D??? The head paperwork says 20db and cutoff at 500hz. +20db seem alot and it cuts well without feedback and with a small amount of feedback cuts spot on. So I just want to know how much feedback other people use and what frequency you cut of at . When I get this amp spot on I will put a link to the schematic for people who need a amp and enjoy using a soldering iron. I know motorino has good results with the riaa circuit I use and I know how hard it is to find schematics for simple cutter amps . So any info helps.
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motorino · Joined: 24 Aug 2005 Posts: 164

Hi amp doc

The new circuits are in the insolator...when finish and test i post here

For the mixer and the recording curve use burr-brown op amps, for the lo-pass feedback filter coils and condensators... now i believe stand in the good way Very Happy

Amp Doc · Joined: 21 Jun 2007 Posts: 108 Location: UK

You have been working hard on this I see. what kind of filter are you using on the feedback? I am using a butterworth -36db after 500 Hz using condensers and resistors. Could you email me the schematic for the filter you use I would like to do a comparison between the two I have and the one you use and pick the best one. the problem I have is the phase shift in the filter network above the cut offf frequency goes up could cause 180 phase shift at high frequencys as you cannot remove all the high frequencys causing ossilation and head destruction.....
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!Work or Bang Time!