AMT - Legend Amp Series 2  [traced]

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bajaman
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Post by bajaman »

@Mbas974 - the power supply muting circuit is shown on the top right of this preliminary schematic :wink:
http://www.freestompboxes.org/download/ ... &mode=view
It's purpose is merely to conserve current draw from battery power when NOT using the cabsim recording output socket. When a jack plug is inserted in the cabsim socket a ground connection is made to this small two transistor and two resistor electronic switching circuit that then connects the +9v supply rail to the cabsim circuitry. :)
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Post by bajaman »

IMG_2501.JPG
IMG_2498.JPG
My E2 control board - the jack socket boards are all identical for the Series 2 pedals :wink:
I suspect that all the potentiometer controls are all the same for the series too.
Drive gain = 50kA
Clean gain = 100kA
Master = 500kA
High = 100kB
Middle = 10kB
Bass = 500kA
The two polystyrene capacitors are both 560p
The two electrolytics are 100u 25v
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Post by bajaman »

I have traced the high gain amp stage of the E2 and am surprised to find that it is almost identical to the schematic posted by JOK3RX in the first post of this topic :shock:
The first stage (before the drive gain) has 5k6 drain and 3k source resistors NOT the 6k8 and 2k2 on the schematic :wink:
Not 100% sure about the 250k bass control - could be 500k perhaps, but apart from these the schematic is correct in topology and component values (for the high gain stage only )

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Post by bajaman »

I confirmed the bass potentiometer IS 500k linear (B) in the E2 - I suspect this will be the same value in all the series :wink:
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ps: working on a layout for a through hole version - may be a while though :)
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Post by Ice-9 »

I have just about completed the high gain section of the S2, just need to complete the last fet stage and tone controls to finish it, as Bajaman mentioned about the E2 the high gain stage is almost identical to in topology to the schems Jok3rz posted at the top of the thread, but on the S" lots of values are incorrect this time.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by Ice-9 »

I have drawn out the S" High Gain section, just on paper and it differs a little from the original post. I am not 100% sure of the tone stack values as I did not remove them to measure but the readings I got with a DD seem to fit the tonestack. First draft so if any silly mistake can be spotted please let me know and I will re check.
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s2-high-gain-sch.jpg
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by guiltyspark »

I've owned 3 of these AMT legend pedals, the Recto, 5150 and Bogner. I kept the B2 (Bogner), I like it a lot. I use it for a gainly Marshallish crunch tone. I think the AMT's are built well and are good sounding. If you get one used it's a lot of pedal for the money IMO. I think the "1" series, E1, B1, etc are single channel and if you don't need their clean channel (I don't) they are a bit cheaper.

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Post by bajaman »

Hi ice-9 :)
From your pictures C15 should be 2n2 not 22n, R28 = 680k, R55 should be 10k not 47k.
I suspect very strongly that the potentiometers will be the same for all models in the series. If that is the case then R7 = 50k log, R62 and R65 are both 500k log.
A quick way to check the bass and output master level control values is: set the bass and treble controls to fully clockwise and the volume and middle controls to fully anticlockwise. Now place your digital multimeter probes across the bass pot and you should read around 270k if they are both 500k pots :wink:
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Post by Ice-9 »

Hi Bajaman - Good catch on the missing R28 value and incorrect C15 value :thumbsup
C15 = 2n2
R28 = 680k

R55 is correct at 47k
measuring the pot as you suggest give a reading of 250k on the bass pot so they must be 500k as you say :slap:
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by bajaman »

Hi ice-9
I took another look at the picture - was a bit blurry for R55, but yes i can now see it is indeed 47k and not 10k as I said :oops:
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Post by Ice-9 »

bajaman wrote:Hi ice-9
I took another look at the picture - was a bit blurry for R55, but yes i can now see it is indeed 47k and not 10k as I said :oops:
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It's my camera skills which are lacking, iphones are not the best to get good pcb pics. It is really difficult to read in that picture.

Now we have two of these traced what do you think the best way to draw them up should be, maybe one main schematic which is the same for all the pedals with separate schematics for each model ?

It might be a good idea as well to do the same with any layouts, ie. a main pcb with a plug in amp board. It could be done in the same size enclosure with through hole components if we lose the battery and use that space for circuitry. :thumbsup
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by bajaman »

Hi ice-9
Yes a schematic showing everything except the high gain amplifier section because the clean channel, boost switch, cabsim, footswitch wiring and power supply circuits are identical across the series 2 range.
The connections to the high gain section could be shown as a blank box with in, out, ground and power supply connections as terminals.
I am nearly finished with the through hole PCB layout - all on one board - it will fit perfectly inside a Hammond 1590BB or NSC equivalent enclosure and will have all the jacks and DC socket along the top side. There will be a space for the battery at the bottom front of the enclosure. The PCB will contain all the extra resistor, capacitor, fet and diode spaces to enable any of the models in the range to be built on the same board.

It would probably be a good idea to include all the 0 ohm (link) resistors used in your S2 model ( R4P, R49P, R58P ) on your schematic for clarity as well.
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Post by bajaman »

Hi all
If anyone has any more of these series 2 models - B2, M2, R2, C2 etc and would be willing to supply internal pictures that would be great :thumbsup
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Post by Ice-9 »

bajaman wrote:Hi ice-9
Yes a schematic showing everything except the high gain amplifier section because the clean channel, boost switch, cabsim, footswitch wiring and power supply circuits are identical across the series 2 range.
The connections to the high gain section could be shown as a blank box with in, out, ground and power supply connections as terminals.
I am nearly finished with the through hole PCB layout - all on one board - it will fit perfectly inside a Hammond 1590BB or NSC equivalent enclosure and will have all the jacks and DC socket along the top side. There will be a space for the battery at the bottom front of the enclosure. The PCB will contain all the extra resistor, capacitor, fet and diode spaces to enable any of the models in the range to be built on the same board.

It would probably be a good idea to include all the 0 ohm (link) resistors used in your S2 model ( R4P, R49P, R58P ) on your schematic for clarity as well.
cheers
bajaman

That is fantastic to have 1 pcb with the option to add whatever high gain components needed to make the model required. :applause:
I left out the 0 ohm links just while making initial drawings and will add them to the finished S2 Gain section schematic along with the full connections for the mute switch fet and led indicator.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by bajaman »

IMG_2531s.JPG
IMG_2530s.JPG
Here is the B2 high gain board :wink:
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Post by bajaman »

Here is the high gain section schematic for the LA2 series S2, E2, K2, B2 models :wink:
The jfets are the through hole equivalents for the smd types fitted.
2SK208 (JR) = 2SK30 (R)
MMBFJ177 (6Y) = J177
MMBF5458 (61S) = 2N5458
AMT LA2 high gain sections E2, S2, K2, B2.GIF
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Post by bajaman »

....and the complete schematic :D
AMT LA2 complete.GIF
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Post by bajaman »

I personally found the clean channel a bit harsh, so I added a 680pf capacitor in parallel with R19P and a 1.5nf capacitor in parallel with R39P to roll off the extreme top end just like a 12AX7 tube does. I also removed R29P to fatten the sound up at lower levels of the clean gain control - less ice pick effect :wink:
cheers
bajaman

I would like to thank Mick (Ice-9) for all his valuable observations and help in bringing these schematics to fsb. :hug:

I would also like to add that these AMT LA2 are very nice pedals and react very much like real tube amplifiers that they are modelled on - the designers are to be congratulated for their work :thumbsup
They clean up extremely well when the volume control is rolled back on my guitar and they have marvellous touch sensitivity - i am using my E2 in the effects loop of a Line 6 HD500 and it beats the Line 6 models both in the clean and high gain channels - i have tried for many years in vain to get a good touch response and sparkling clean sound from the HD500 and now at last i have something very close to perfect with the addition of the LA2 E2 pedal. I purchased mine from Russia for US$175 and I feel this is a very low price for such a great pedal!
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Post by bajaman »

Thanks once again to Ice-9 for spotting a mistake on the AMT LA2 complete schematic :thumbsup - the first transistor in the cabsim section should be powered directly from the +9 volt rail and not through the cabsim socket switched power regulated supply. It requires direct power to enable the drive and preamp sockets to work :wink: . Here is the corrected schematic rev1.0
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bajaman
AMT LA2 complete.GIF
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Post by apollomusicservice »

Nice job guys. I just finished my PCB boards ready for assembly.
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