My flagship amp is up and running, *basically* done

[nandrewjackson]

https://drive.google.com/open?id=1R6--WteNBnQW_4s-Jgrff_O_kKxFYPgZ

https://drive.google.com/open?id=1HECvI2ZzaxjVsQHH5sZtkN2GSTMdG0EL
https://drive.google.com/open?id=1achKz5c3ICXfuWiR4q3KSQxAhiLVnBFm
https://drive.google.com/open?id=1bys2y-89hAMEbz2KMQ3BSgU1ptUuAp1r
https://drive.google.com/open?id=1ptJQGjys2DIkmhTYwIoXI1x4XVcnpMRI

https://drive.google.com/open?id=1DSGo-u7q2xEzEA6-7xA4fbyNy0d3aklz
https://drive.google.com/open?id=1HP_CwREEX0JrFoTqXXdjV0p3KzG1uAwI
https://drive.google.com/open?id=1fXpLseDODCohku4qQCWDbCAnh8rlSPNq
https://drive.google.com/open?id=1HAjf5pPVO9OWGkqgkHfO3W1O4g1tqI0X
https://drive.google.com/open?id=1FHTWEzXisp8b5zvHo6xHc7S5V-fqupK6
https://drive.google.com/open?id=1CkLHWwf2AcKlyn5nViefbNAwTwj__jMW
https://drive.google.com/open?id=14l9vuuyrcAYfe0lE29tpZprHxjXRegJn




 50 Watt 4 channel with 2 Eqs.
Five 12AX7’s and Two 6L6’s, diode rectifier.
The switching is accomplished using two different circuits, one circuit for the 4 different channels, and a different switching controller for the 2 Eqs.

Both switching circuits control LDR/LED pairs that I put together.  .  I used 3mm white LED’s all from the same batch.  I double shrink wrapped them and added teflon tubing to one leg of each to prevent shorting. After a big problem surrounding the 2 Eqs popped up, I used 4 pre-made vactrols around the Eqs.

 
The 4 channel switching circuit uses the following.  4 momentary pushbuttons on the front panel, the pushbuttons go into a 7404 hex inverter, the outputs of the hex inverter go into a 573N octal latch, the outputs of the octal latch go into the inputs of a 2803 darlington driver chip.  The outputs of the darlington driver chip conrol the LDR/LED groups to control the signal swittching.

 
I had this circuit all worked out on a breadboard, then made a PCB version for the amp. It worked for a while, until after 6 or so hours in the amp, the 2803 darlington driver went haywire and did seemingly whatever it wanted to do.  After some google research, I found that for purely resistive loads, the inputs of the darlington driver chip need pull-up resistors to better isolate the input side from the output side.  So I had to make an entirely new PCB that included these pull-up resistors.  Also, there’s a common pin on the 2803 darlington that needs to be connected to the circuit source VDC when driving relay coils, and for purely resistive loads, (LEDs), it doesn’t need connected, and based on various forum posts, may contribute to unexpected behaviour driving resistive loads.  So far, with the rebuilt switching circuit, and maybe almost 20 hours on it, it’s working fine.

 
The 2 EQ switching circuit uses two BJT transistors, one PNP and one NPN, to toggle between the Eqs.  As you can see, the front panel EQ selector is an ON/OFF switch, to toggle the switching circuit.  This is very different from the momentary pushbuttons that control the 4 channel setup.

 
Power for the channel switchers comes from the heater wires.  The heaters branch off to a full-wave bridge with a big ol’ electolytic cap.  The 4 channel switcher is directly off of this, at about 7 VDC.  The 2 channel switcher has a voltage divider to bring it down to about 4.8 VDC.  I don’t know exactly why, but the 2 BJTs have a narrow band of voltage that they prefer to toggle back and forth properly.  I had to use the ground that the full-wave rectifier provides for the ground of all of the switching circuits, including the front panel indicator LEDs.  A bit of a PITA having a 2^nd ground circuit,  since it’s ground is about 2.7 VDC lower than chassis ground due to the full-wave rectifier from the heaters.

 
I’m calling the 4 channels;  Channel 1 Vintage clean.  Channel 2 Modern Clean.  Channel 3 Vintage distortion.  Channel 4 Modern Distortion.  Check the schematics for details.

 
I have the footswitch about ½ way done.  I’m using 8 pin din plugs with 8 conductor cable.  The footswitch won’t have LEDs, would need more conductors/pins to do that.

 
I did dual cathode follower overkill for the effects loop.  Why?  I dunno.  I just did. One cathode follower before the FX loop, and one after, before the 2 Eqs.

 
The 2 Eqs are a “marshall” style, and “fender” style.  I know both brands have used almost both of these EQ values over the years, but in my mind, one is definitely tied more to one brand than the other.

 
It has a fairly standard Long Tail Phase Inverter, with NFB and a global Presence control.

 
The output is again, fairly standard push pull two 6L6 / EL34.

 

[nandrewjackson]

 I’m using the negative VDC bias method.  I’ve got PINS 1 and 8 tied together, with 1 Ohm cathode resistors.

 
I used a 50 K pot to obtain resistance values to bias both types of tubes, then measured each setup, and ordered * unusual * values of resistors to get these bias values and have them be switchable with a SPDT switch for easy tube changes.   
 
 
 For the 6L6 setting, I’m getting about 44mA cathode current @ -44VDC
 For the EL34 setting, I’m getting about 33mA cathode current @ -33VDC
 
 
The cabinet is the Marshall one twelve combo cab from Mojotone.  All stock options.  The chassis is from synapticamps.  I’m using ¼ inch 20, four inch bolts into the top of the cab, through the chassis into cage nuts to attach chassis to cab.  I was very nervous drilling into the top of this beautiful cab, I measured MORE THAN necessary , and viola/ the holes lined up.  Yay.   
 
 
 I’ve got an Eminece Legend 8 Ohm, 200 Watt in the cab.
 
 
 I wired up all three impedence taps on the output.  I’ve got two speaker jacks in parallel for the 2 Ohm tap.  Two speaker jacks in parallel for the 4 Ohm tap, and a single speaker jack for the 8 Ohm tap.
 
 
The transformer set is from Classic Tone.  18107 Power Transformer, I’m using the Lower of the two secondary mains, getting right at 394 VDC after the choke.
 
 
 The output transformer is 18105.  *40 Watt 4K primary.
 
 
 I honestly don’t remember which choke I ordered. LOL  It seems like its the 4H Fender style.
 
 
 Most components are from Mouser.  Some Jameco.  Most Caps are Illinois.  There are some discount Ebay components in there.
 
 
My Voltage readings at the power rail are:  398 pre-choke – 394 post choke – 10KOhms – 301VDC – 10KOhms – 232VDC - 10KOhms – 208VDC, with all tubes installed. 
 
 
 I’m really trying to cover all the bases here, feel free to ask questions though.
 
 
 Aside from the switching circuit PCB debacle, of course, I initially had the OT primaries reversed and upon initial powerup had THE SQUEAL.  Easy fix.
 
 
 
 
 In the pictures, The purple wires are signal wires.  The white wires control the LED side of the LDR/LED combos.  The 16ga bare is main ground buss.  The 22ga bare wire is LED power.  There’s generally at least ¾ inch between any LED control wires and signal wires, pots, other components.  Red is HighVDC.
 
 
 Granted, it’s a Point-to-Point nightmare, but believe it or not, theres not much noise.  I’ve built much more noisy circuits in the past that didn’t have any switching capabilities.  The 2 clean channels are dead quiet, and the 2 distortion channels are about what you’d expect, as quiet as they can be without using a noise gate.
 
 

[nandrewjackson]

 My video camera has WEIRD sound.  The hiss at the beginning IS NOT the amp.  This little Kodak video camera compresses audio so much. The room is SILENT, and the hiss at the beginning IS NOT the amp. And actually, the amp is playing rather loud, louder than I would play at night around here, due to neighbors and thin walls.  The camera takes a lot of the character out of the amp, but it gets the idea across.  The hiss during the “modern distortion” channel is, indeed, the amp.  No getting around that one.  LOL
 Also, on the clean parts, it sounds like I’m slaughtering the strings with a rusty piece of meteorite.  I’m using a standard Dunlop heavy, it’s that dang camera microphone.
 
 
 I’m using a Jackson Kelly with EMG 89s with coil tapping.  For the clean sounds, I’m using neck pickup in coil tapped mode.  For the vintage distortion I use both the neck humbucker and bridge humbucker.  For the modern distortion I use the bridge humbucker.
 I’m playing guitar straight into the amp, nothing in the FX loop, although I usually have a pedalboard in front and another pedal board in the FX loop.
 
 
 Lower left channel is “vintage clean”  Upper left channel is “Modern Clean”
 Lower right channel is “vintage distortion”  Upper right channel is “Modern distortion”
 
 
 Each channel has, left to right, pushbutton , LED , gain , volume.
 
 
 The bottom EQ is “Fender” with 100K curve resistor, 220p , 0.1uF, 0.047uF
 The top EQ is “Marshall” with 33K curve resistor , 475p, 0.02uF, 0.02uF
 
 
 I had a weird problem with phantom background “harmony” notes being heard.  After hours of tracking it down, it was specifically to do with the LDRs attached to the 2 Eqs.  They are the same LDRs used throughout the amp, the ones I rolled myself, so I don’t know why only the ones around the Eqs were causing trouble.  I found a handfull of premade vactrols in my parts bins, so I installed them attached to the Eqs and the phantom “harmony” notes disappeared. I then had to change the 2 EQ indicator LEDs, because the 3MM white ones I used in all other places wouldn’t light up anymore due to different LEDs inside the premade vactrols. Luckily I had other LEDs laying around that matched the specs enough to light up.
 
 
 That’s about all I can think of right now.
 
 
 Thanks to so many members of the forum, this place has been a great reference and support community to me for, dang, almost ten years now I guess.
 
 
 I’m really proud of this amp.  I included all of my favorite features into one ball-of-twine point to point build ! I toyed with the idea of adding a tubescreamer circuit inside the amp at the input, and having it switchable, but the footswitch i’m building for this already has five buttons.  Maybe on my next build.
 
 

[silverfox]

Congratulations. That was a lot of work and practical experience.
I don't have a google. Can you post the final schematic as an image?
silverfox.

[nandrewjackson]

Ok, I'll try to get the files somewhere other than Google. 

[nandrewjackson]

youtube video link

[nandrewjackson]

preamp schematic

[nandrewjackson]

switching circuit

[nandrewjackson]

two EQ switching circuit

[nandrewjackson]

amp in cab

[nandrewjackson]

early in the build gut shot

[nandrewjackson]

up and running gut shot

[nandrewjackson]

drilled holes in top of cab for bolts

[nandrewjackson]

closeup of preamp

[nandrewjackson]

closeup of switching circuits

[shooter]

Nice!  I'm busting out my digital geek box tomorrow 

I like the modular design, keep refining it and plexi the "gut shot" side, you might have a good shot at an Art show.  check out "functional art"

[pdf64]

The 'picket fence' arrangement of terminal strips around each preamp tube socket is a great idea, leading to quick, uncompromised ptp builds