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Old 26th October 2010, 04:33 PM   #1
Diogrus is offline Diogrus  Brazil
diyAudio Member
Join Date: Nov 2007
Location: Campo Grande, Brazil
Default British HiGain Design (from the scratch) - need backup!

Hey folks!

It taked more time that expected - specially cause some trouble$$$ happened - but now, I decided to re-start the design of my amp, from the scratch... however, definitely, I'll need some backup here!!!

From the beginning... my intent was to build an british hot rodded amplifier, single channel... the starting point was the ULTIMATE JCM800 (Tone Lizard)... althought the schematic had already been finished, my idea for the amplifier changed a bit in this hiatus (that about a year)... I'm still looking for a more modern and agressive british tone, which keeps the character of the guitar used and clarity of the notes, but will really appreciate if the amp could presents some new features, like:
- a clean (or semi-clean) channel
- a tight and organic british tone channel (maybe with just the traditional approuch: 3 gain stages + CF)
- (maybe) a tube boost in the gain channel, if this one can't go really higain (the idea here is doesn't use a external pedal to boost the drive)
- separate tonestacks for the clean channel and the gain channel
- footswitchable alltube FX loop
- footswitchable solo master

For now, I think that is interesting just talk about the preamp...

Initially, the idea was to use the two EL34 for the (standard) poweramp and four 12AX7 (two for the preamp itself, one for the loop, and one for the PI)... now, as I'll need some more gain stages in the preamp for the boost and for the clean, needed to look at the PT specs:
HT Secondary: 0-340Vac/300mA
BIAS Secondary: 0-50Vac/35mA
Heater Secondary: 0-6,3Vac/5A
Switching Secondary: 0-6Vac/1,2A

As the Heater Secondary was developed to hold until 5A, it can be seen that it already have some room to add tubes (0,8A specifically)... so, the ideas are:
- or add until two more 12AX7 (+600mA) and build a bassman clean with three of the stages and using the one that will be left to boost the gain channel;
- or add one 12AX7 (+300mA) for the tweaks in the gain stage and one EF86 (+200mA) for the semi-clean stage...

I have two good references to my "new" gain channel:
- the second channel in the PT-100 (especially in 6:53) - YouTube - Suhr/CAA PT100 amplifier demo
- the Iced Earth tone
If I can reach this kind of drive with the gain boost ON, pretty awesome! It seems that the "stock" gain channel could be more like a heavy crunch, good for rhythm, and will clean a bit with the guitar volume!

Well... I really don't know... I'm still f'ing lost... here is the idea that I'm thought about for the gain channel:
1st Stage -> 2nd Stage -> 3rd Stage -> Cathode Follower
Switchable Gain Boost Stage between 1st and 2nd Gain Stages

That's all folks! I think that it's enough for extend the preamp's discussion for a while!!

(and sorry for my brazilian's English)
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Old 2nd December 2010, 10:48 PM   #2
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Join Date: Sep 2008
Location: Near Seattle Wa
diogrus, made any progress? Did you put your ideas to paper?, schematic?
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Old 3rd December 2010, 01:31 PM   #3
Diogrus is offline Diogrus  Brazil
diyAudio Member
Join Date: Nov 2007
Location: Campo Grande, Brazil
Firechief, I'm working in it yet (schematic), using the LTSpice... any ideas? Well, when everything is more clear, I'll let you know!

Cheers mate!
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