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Blog » AFD Stage 1 Engineering Complete!

Posted 06.08.10 by Marshall Amplification 129 comments

Over the past few weeks we've been concentrating on developing the fully working, cosmetically correct AFD100 prototype after Slash tested the first handmade prototype in both the studio and on tour. Matthew has been busy putting together all the mechanical drawings and Jenni has been finalising panel artworks. Meanwhile Santiago has been concentrating on drawing the schematics, laying out PCB's which were then soldered by hand to ensure all the electronic parts were properly positioned and everything was correct. The remaining parts were collected to complete and test three working prototypes, two of which were given to Slash to have on the road and one for ourselves as a workbench.

An additional task was to program the amplifier control firmware. We haven’t disclosed it yet but this amplifier features an auto-biasing function which works together with the output power control. We’ve been working on it for more than a year now as it may well appear in some other projects, but we have decided to include it in this amplifier as well. The power control allows the user to obtain power amp distortion at volumes as low as 0.1W going to full 100W with the simple twist of a knob. With a trimmer pot located on the rear panel, the player selects the desired biasing current. When triggered by the user, the amplifier performs a complete biasing job by itself. This feature can be seen as having a little man inside the amp rotating the bias pots and measuring the current for us. Lets highlight too that the biasing is not only limited to the full power control but is performed in all the power range ensuring proper operating conditions at every output power setting. For convenience four LEDs on the rear panel show us if there was any biasing failure. Apart from the obvious easier maintenance, mixing output valve types can also be done without any problems, just plug the valves and let the amp bias them. The self biasing feature was praised as a 'gift from Heaven' by Chet, Slash's guitar tech when first introduced. No more need to get the multimeter, open the amp and tweak the trimmers !

Once the prototypes were assembled the moment of truth came. We met Slash with the working amps in Hong Kong on the 29th July before his first show on the current Asian tour. As his first impression was very positive he decided to use them straight away for the show and perform a real test in a live situation with the band. Feedback was quite good and just a small tweak was needed. Slash wanted the amp a little less aggressive, in his own words he simply wanted to make it perfect! Back to the sound room, a couple of valve changes and immediately we followed the tour down to Singapore. As usual Slash tested the amp during sound check and with a smile on his face he said: 'It is really good, I think we got it' plus some other words and praises that would be impolite to write here!

The rest of the story can be told easily quoting his Twitter entries. After Singapore: 'We've been tweaking the AFD amp & I think we finally have it dialled in. Could be one of the best sounding Marshalls ever.'
After Jakarta: 'Btw, used the latest prototype of the AFD Marshall last couple of shows, its ready for production. It really kicks ass!'

If any of you is attending the Asian tour, you will be hearing the 'real' AFD100 as it is now sitting in his rack as his lead tone amplifier. So now that stage 1 and the design is coming to an end, it's time to transfer the design package to Production Engineering, Purchasing and Manufacturing departments to do their work on it. There is still a way to go until having the amplifiers leave the factory but we will keep you updated in the progress.

The photos below show the final working prototype and Slash's current rig that he is now using on tour.

129 CommentsComment on this post

Posted 1 year ago by masken I really need to have one..