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FET Boost Drive Block Settings for the EP Booster

jbaumeister

New Member
So, like many here I have been using the EP as a front end to the AX8. It does something that I like better on than off. So I decided to break out the tools and measure what was going on. It turns out that in Unity Gain and Flat EQ mode it is nothing of the sort. What I found was that the EP (knob all the way down) is actually a low pass filter with some gain in the pass band. The actual readings were +2.4dB in the pass band with a cutoff frequency (-3dB) at about 4.8kHz. In the vintage mode (still unity gain knob all the way down) the gain is 2.2 dB with a cutoff of 1.9kHz.

I'm using the FET Boost drive block because I wanted to keep a FET driven preamp and these settings capture the what the EP is doing:

EP with Unity gain, knob off, "flat EQ" mode:
use the FET Boost as is with Output Level = 5.79 and cutoff frequency = 4800 (it rounds to 4799)

EP, Unity gain, Vintage mode:
Output Level = 5.75 cutoff frequency = 1804
I did not adjust the gain as I wanted it to be clean so I tweaked the output level of the Block.

You could probably do this with an EQ but it's so easy this way and you get the FET Boost model to boot. You can also tweak to output level if you normally add gain but these values match up at min gain.

I've now removed the EP from my chain and only have one box between guitar and amp.

P.S. Many have asked, and I can't find in the manual, what the output level should be set to for AX8 unity gain and that is 41% (about 1:00) for the 1/4" outputs.
 

ak301

Experienced
Thanks mate, the EP Booster was my 'secret sauce' in my old 'real' amp/pedalboard days.

Really keen to try these settings
 

lqdsnddist

Axe-Master
Keep in mind the EP3 circuit isn’t just an eq or filter, but there is also some frequency dependent phase shifting going on, which is a large part of the tonal coloration that circuit provides, and why so many guys used to run an EP3 without actually using it for a delay, even though there were lots of boost pedal options.

I notice this most on more distorted tones, like a cranked plexi. I use the Chasetone Secret Preamp, but there are a few builders who do the circuit as well. On/off there is a unique change in the character of the tone, and the overall “kerraaanngg” on an open A chord. It’s not just an eq cut or boost, it’s a slight phasing effect, just like when your mic with 2 mics and move then around, getting that phase shift, not just the blend of two mics.

I’ve been trying to match the pedal for a long time without much luck. I’m thinking that the key might be trying to use a tonematch or convert one into an Ir, then combine that with another Ir and hopefully get some pleasing phasing

Or just keep my Secret Preamp plugged in before the input as that works too. Haven’t tried it yet in the loop
 

jbaumeister

New Member
Keep in mind the EP3 circuit isn’t just an eq or filter, but there is also some frequency dependent phase shifting going on, which is a large part of the tonal coloration that circuit provides, and why so many guys used to run an EP3 without actually using it for a delay, even though there were lots of boost pedal options.

I notice this most on more distorted tones, like a cranked plexi. I use the Chasetone Secret Preamp, but there are a few builders who do the circuit as well. On/off there is a unique change in the character of the tone, and the overall “kerraaanngg” on an open A chord. It’s not just an eq cut or boost, it’s a slight phasing effect, just like when your mic with 2 mics and move then around, getting that phase shift, not just the blend of two mics.

I’ve been trying to match the pedal for a long time without much luck. I’m thinking that the key might be trying to use a tonematch or convert one into an Ir, then combine that with another Ir and hopefully get some pleasing phasing

Or just keep my Secret Preamp plugged in before the input as that works too. Haven’t tried it yet in the loop
I'm not sure the EP booster is a faithful recreation of the EP3 circuit. At any rate, at least for me, A/B'ing the actual pedal with the AX8 settings above matches well enough for me to drop the pedal.

Edit:
I just looked up the EP Booster schematic on Google and it is a very simple circuit. A single FET variable gain stage followed by a passive RC low pass(switchable frequencies) into a single transistor buffer output amp which is exactly what I measured.

I also took a look at the EP3 preamp schematic and the input is a single FET gain stage with virtually no pass band eq. It has an input low pass at 16kHz then direct to the output mixer. This was for the newer models. For the older models the input low pass is 7.2kHz and they added a bypass in the FET bias which would tend to have increasing gain above about 1-2kHz. Then that goes right to the output mixer. I don't see any magic other than a slight boost above 1-2kHz then rolloff above 7.2kHz. Each of those breakpoints introduces a phase shift but without having one I can't tell if that does anything for my sound.

Anyway I wanted to model the EP Booster and the settings noted do that so I'm happy.
 
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jlynnb1

Fractal Fanatic
Not sure. I'm new and it says I can't post links until I hit 10 posts. That being said just add a drive block, set to FET Boost and adjust the two values. Pretty easy. I'll try later to upload.
cool, i'l try it out. don't worry about the block, it's easy enough
 

Rayos

Inspired
Very interesting. Thank you.

I have two EPs. I used one at the beginning of the chain, to kick the KOT clone that kicked the OCD, or straight into the OCD.

The other one was at the end, as a volume boost for solos.

I'm trying this as soon as I plug my AX8 today.

I just miss the OCD and the KOT in my AX8. I can live (very happily) without them, but... Does anybody know how to emulate them?
 

Rayos

Inspired
KOT is based on the Marshall Bluesbreaker pedal = "Blues OD" model.
I know it. Thank you very much.

Buy what I'd really like is it to use it for pushing and OCD, as I used to do in... Real life (just kidding).

BTW, Yek, let me use this post to tell you how grateful I'm for your guides. Things wouldn't be the same without all that info. Things are much easier. And much funnier too.

Thank you!
 
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Mutha Goose

Inspired
Thanks.

I try to use the wiki as the central location:
There are no others, and I have no plans to add any. :)
Even the task of keeping the guides updated proves to be a challenge.

The manuals and wiki already provide loads of info regarding the other blocks.
LOL, I understand. Thank you for what you have done. I appreciate it very much. These guides are VERY helpful!


jbaumeister: sorry for hijacking your thread :)
 
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Davus PG

Inspired
So forgive my ignorance - and I appreciate that ultimately there are no rules, but would using a block that emulates an EP booster replace the Tubescreamer block with zero gain (as per one of Leon's video tutorials) I currently use to push the front of the amp block, or would it be in addition to that?

I guess use your ears is the answer.......
 
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