AMT Legend R2 pedal or schematic?

[Paul.Ruby]

Just built an O2 per the above schematic. It has one less gain stage than B2/C2/E2/K2/M2. The O2 sounds really good and has a very wide range of gain on the gain control and it greatly affects volume at the same time. This is different than the other pedals that have another gain stage. The gain control affects volume much less. A significant amount of distortion comes from the Schottky on the last stage driving tone stack. I'm using my combo pedal to directly compare M2/K2/O2 as it can switch between the drive options by holding the footswitch.

 

[Feral Feline]

@Paul.Ruby — do you happen to know if the S2 has been traced?

Looking for a schematic for the S2...

 

[Paul.Ruby]

@Paul.Ruby — do you happen to know if the S2 has been traced?

Looking for a schematic for the S2...

Yep: https://www.freestompboxes.org/viewtopic.php?t=26365&sid=9bde81fa28b5b1c985e3a1a13ea37c44

 

[Paul.Ruby]

Yep: https://www.freestompboxes.org/viewtopic.php?t=26365&sid=9bde81fa28b5b1c985e3a1a13ea37c44

Here's a more direct link. https://www.freestompboxes.org/download/file.php?id=27302

 

[Paul.Ruby]

Here's a more direct link. https://www.freestompboxes.org/download/file.php?id=27302

By the way, read my posts on page 8 of that thread. There are two mistakes in the schematics in the clean channel (mislabled cap) and the cabsim (mislabeled transistors in the push-pull output section. Also, the for proper frequency response, it needs different component values than are used in real AMT pedals. Finally, note there is an input buffer stage in the clean channel that feeds the drive channel. So, the drive channel schematics do make a complete drive circuit. It need the input buffer stage that is part of the clean channel schematic.

 

[Paul.Ruby]

Just had a practice with the O2. It's fantastic. Not as high gain as most AMT pedals. It's really great sounding. Tight. Clear. Not high gain but would be great with with a preboost pedal added. Really impressed with it. It might end up in the center position of my combo pedal.

 

[lrgaraujo]

Just had a practice with the O2. It's fantastic. Not as high gain as most AMT pedals. It's really great sounding. Tight. Clear. Not high gain but would be great with with a preboost pedal added. Really impressed with it. It might end up in the center position of my combo pedal.

Do you plan to trace it yourself to check if the schematic on FSB is correct? From youtube videos, the O2 might be my favorite

 

[Paul.Ruby]

Do you plan to trace it yourself to check if the schematic on FSB is correct? From youtube videos, the O2 might be my favorite

I don't have the real one in hand yet. This report is from building based on the schematic and using BAT48 for Schottky. But, I will open the real one and trace it to make sure it's accurate. In general, I've found the fewer the gain stages, the more I like the AMT pedals. I don't like anything with more stages than the B2/C2/E2/K2/M2 and now the O2 has one fewer than those. I didn't know there were any with fewer until now.

 

[temol]

For me O2 is ok, but not amazing. Maybe because I connected it only to the audio interface instead of the power amplifier. I'll give it another chance in some time.

Btw - I recommend Crunch channel of the AMT Bulava SS30. Schematic available here

One comment about the diode in O2. Schematic calls for the BAS70 diode. Looks like BAT41 would be a good replacement.
Forward voltage @1mA
BAS70 410mV
BAT41 400mV
BAT48 300mV

 

[Paul.Ruby]

I'll get some BAT41. I've been using BAT48 for all my builds and they all sound really good. I don't like the higher gain pedals like S2 and P2. They sound thrashy/trashy to me. That includes the real pedals, not just my builds.

Practice testing last night was with active pups into my pedal board volume-only TPA3118 amp and a 4x12 cab with G12H30. Also had the AMT cabsim into a DI and to the mixer for the monitors. This is the same setup we use live. At the moment, I'm using an M2 and Joe uses an E2, both my builds into a combo pedal and using BAT48s.

The O2 does not get into metal territory but really nice crunch tone, so would need a boost in front to get to metal zone, but that's exactly how I like a pedal board setup. At the moment I have a prince of tone in the pre-boost of my combo pedal. That gives me 4 settings: Clean; Clean+Prince; M2; M2+Prince. Very good progression for everything we play.

 

[temol]

Some oscilloscope shots from the O2 on a breadboard. Testing different diodes. Cyan trace - second stage output, yellow trace - third stage output.

1kHz sinewave, 200mv p-p


Gain @ max.

Bat41


Bat46


Bat42


Bat48


Bat85


1N4148


Ge diode

 

[temol]

Gain @ noon.

Bat41


Bat46


Bat42


Bat48


Bat85


1N4148


Ge diode

 

[Paul.Ruby]

Nice. Can see the impact on amplitude on the yellow trace. I'll do some ear testing on the O2 when my BAT41s arrive.

 

[lrgaraujo]

Could you guys please share Vp and Idss in your 2sk208-R? I have a few 2sk118-R that I hope will fit in this circuit (I know I can find 2sk208-R to buy, but I'm not ready to deal with Mouser shipping right now )

And if you could share the specs of a 2n5458 that works in this circuit, it would be much appreciated, as well!

 

[Paul.Ruby]

Could you guys please share Vp and Idss in your 2sk208-R? I have a few 2sk118-R that I hope will fit in this circuit (I know I can find 2sk208-R to buy, but I'm not ready to deal with Mouser shipping right now )

And if you could share the specs of a 2n5458 that works in this circuit, it would be much appreciated, as well!

The specs are virtually identical between 2sk208r and 2sk118r. Use them... Don't worry about the 2n4558. If you have real ones that are within spec, they'll be fine.

 

[temol]

Could you guys please share Vp and Idss in your 2sk208-R?

Vp 0.6–0.63V and Idss 0.5–0.52mA

 

[temol]

@Paul.Ruby - do you use a buffer between output of your AMT preamps and next pedal?
Btw - O2 schematic omitts input buffer.

 

[Paul.Ruby]

@Paul.Ruby - do you use a buffer between output of your AMT preamps and next pedal?
Btw - O2 schematic omitts input buffer.

No, but I always have the cabsim in place which has a buffered output. The schematics at freestompboxs has a mistake in the output buffer. They got the push/pull transistor names reversed. I didn't notice that and built a run of PCBs with the mistake. It was easy to use my PCB by changing the output of the cabsim to a source follower. So, this is what I have at the output. In the combo pedals, this feeds directly into the muzzle gate, spark boost and reverb before exiting the pedal.

 

[Paul.Ruby]

@Paul.Ruby - do you use a buffer between output of your AMT preamps and next pedal?
Btw - O2 schematic omitts input buffer.

And, I always have the clean channel in my pedals, so I have the input buffer and a feed to the drive on the PCB plus a feed to other drive channels. The combo pedal has a send/return for alternate drive channels fed by the input buffer and selected with a 3-relay ATtiny board. One of 3 drive options can be selected as the drive channel by holding down the footswitch.

 

[Paul.Ruby]

Here's the full schematic for my PCB shown with O2 stuffing option on the board. The PCB was designed for B2/C2/E2/K2/M2 so it has a bodge wire to bypass a gain stage for O2.This board fits in a 125B but is meant as the center piece of a combo pedal with extra 9V feeds to all the other modules. I run it all at 18V. This board is shared at PCBway and has the schematics for the others posted there. I've no posted the O2 there yet.

B2/C2/E2/K2/M2/O2 Guitar preamp module for combo embedded projects. - Share Project - PCBWay

This has the Fender clean, Marshall Drive (and others options for drive channel) and Cab Sim modules all on one board for an embedded combo pedal project. It's the core of the combo pedal idea. This b...

www.pcbway.com