Just Getting Some Amp Building Ideas Out Of My Head

Discussion in 'Other Amps' started by printer, May 16, 2018.

  1. printer

    printer Member

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    I have almost abandoned the electronic side of the guitar world and kind of miss the smell of rosin wafting up in the room. I get the Fender world of amp design until Leo left the company, still think he took a wrong turn leaving the Tweed Bassman behind. I figured I would dip my toe into these waters to get an idea where that iconic design has gone. I saw a thread on changing from a Plexi to a 2203/4 preamp and rearranged things till I thought I had a good compromise given a single toggle switch to change states (a four pole switch mind you). The two pole three position switch on the tone stack is my take on some functionality with the standard Marshall response, the 56k Lead response and for kicks the Blackface scouped Fender curve.

    [​IMG]

    But one thing that was mentioned was getting the 2203/4 flavor but not needing to switch input jacks to get the Plexi vib. So I took that as there wasn't a real need for two holes to plug into, well there is jumpering channels but let's put that aside for now. So with what really amounts to an amp with a normal and lead channel I started rearranging things. It made sense to have a drive and individual volume knobs for the clean and dirty channel, standard fair now days. So while not the 2204/Plexi as stated in the schematic it does have them in its roots. Ignore the IC, the idea might be to go to a Class D amp, maybe even this in a pedal format. At the moment just a design exercise.

    [​IMG]

    I duck here now as the popcorn boxes come flying at me.
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    I did the same thing, with a slightly different plan, but switching between Plexi and 2204 preamp gave me a lot of tonal variations.

    I added stuff to reduce hum and hiss....I used a swing choke instead of the usual smoother choke. I used DC filaments.
    I ran triode instead of Pentode.
    Now I'm adding a Metro effects loop.
     
  3. printer

    printer Member

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    That is an odd thing to use in a guitar amp, the swing choke. I thought we were all about compression and sag rather than trying to keep the supply as stiff as possible. Maybe for the scooped drop D crowd.


    I have already had thoughts about the schematic. The 33k in front of the dirty channel triode can go. Using a volume control after the tone stack kind of negates driving the PI section hard. Maybe a master for the gain channel after the IC? I also think the diodes after the PI should go after the coupling caps. They are suppose to mimic the output tubes clamping the signal voltage from the PI. So I need to move two volume pots and see if they have a three pole footswitch.

    I
     
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  4. printer

    printer Member

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    A little more conventional.

    [​IMG]
     
  5. printer

    printer Member

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    Well I have to see if I can make this. I found a box that should fit the stuff sort of, the tubes will be hanging out and protected by the old standby cabinet handles. I managed to make a bracket to hold the tube sockets, I still have to bend it to be riveted to the aluminum anodized plate. So top row of knobs with gain and volume of the normal channel and gain and volume for the lead channel. Switched by a foot switch, The second row with treble, mid, bass and reverb. The reverb is hopefully a dsp chip from Spin, If I can find it in my parts pile. A second foot switch for the reverb. The high voltage module naturally goes in the case, powered from the 19V laptop supply. Or I might go 24V which should give me 30W instead of 20W with the 19V supply. That is for 8 ohm speakers, if I go four ohms about double that depending on the current capacity of the laptop brick. I might just go two positions on the tone stack with the 33k resistor and the Fender Blackface response. I would use a push pull switch on either the bass or the mid control for that. No presence as shown but I have some ideas still for the Class D module but I have some experimenting to do befor I know if it is feasable. I want a clipping circuit to keep the Class D amp from clipping. A lot of work to do but at least I am off and running.

    [​IMG]
     
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  6. printer

    printer Member

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    Latest iteration. S1 before the gain/cathode follower stage and after the IC selects which channel and associated Master gain pot. S4 bridges the two channels, same tone but the ability to use one of the Master volumes as a gain boost. SW4 selects from the 33k regular tone stack, center position a Fender Blackface scooped sound, or a 56k Lead response. SW3, where the fun begins. A four pole switch that changes the first two triodes to act as a JTM 2203 preamp with the indicated switch position. In the opposite position more or less the early JTM preamp. With SW4 open either channel is selectable. Hope I didn't made a mistake somewhere, a fresh set of eyes appreciated.

    [​IMG]
     
  7. ricksconnected

    ricksconnected Well-Known Member

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  8. tschrama

    tschrama Well-Known Member

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    cool power amp emulator. But why to dont you apply a little feedback around the PI from the opamp.. to emulate the PA closer?
     
  9. printer

    printer Member

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    I thought of that but I need to get this all built and then scope a real amp and compare it to this mess to see if it will actually function in this small chassis. I even thought of making a small companion block which had a pair of 6AK6's and a transformer on it that mates with this box. Electrically it could work but size wise I think things would be a little tight. Am also thinking of putting some current feedback around the amplifier and am not sure how far back I want to bring the loop. Too many ideas to chase, not enough time.
     
  10. ampmadscientist

    ampmadscientist Well-Known Member

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    220444.png
     
  11. printer

    printer Member

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  12. printer

    printer Member

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    The pedal is on hold a while, a good winter project. Been doing some woodworking. Rounded off the edges, the 4x10 is for me, the 1x10 is an amp for a relative. I picked up a Hammond tone cabinet with nine 10" speakers, looking at them I would guess they are 5-10W speakers. I probably could get more output with one of my 12's but I am curious as to the sound rather than the loudness with four speakers in an enclosure. A 59 Bassman sized cabinet.

    [​IMG]

    Speaking of Bassman, I also scored a crappy tube organ, mind you it had a 6V6 amplifier in it. The output transformer along with a 12" alnico 15W speaker out of a Yamaha organ (my trailer was being put to use, swapped out the 12" and donated the organ to Sally Ann) got me to thinking. I have always wanted to build a 6V6 Bassman, you kids play too loud for me with your Marshalls. But as much as I try I end up throwing a little extra into an amp, hey since I am here...

    Just a working drawing, I like Bassmans but also a Blackface sound as well as an early Tweed. The Blackface is really just scooped mids, I found that I could get that as well as the typical Marshall stack with a three position switch. Marshall, Blackface center position, the last is close to flat response. That is to give a Tweed raw sound. But then I decided to switch out the second gain stage and tone stack to go straight into the phase inverter giving me a Tweed type amplifier. But way go part way, this same switch changes the Long Tail Pair into a Tweed era Paraphase PI. A Tweed tone control complements it on one of the channels. With the Bassman config it can act as the treble bypass cap. And the last thing the bias and power supply. Some Tweed amps were kind of loose, think the 5E3 Deluxe with a cathode biased output stage and lower filtering. The final four pole switch makes the PS less stiff and converts the amp to cathode bias. So two switches on the front with the PS one in the back and a tone knob will give this amp an expanded palette of sound. Or so the theory goes. I cut the wood for the combo and just need to glue it together. Then find the time to build it in between my guitar projects.

    [​IMG]
     
    Last edited: Aug 26, 2018
  13. Heph333

    Heph333 New Member

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    Is that supposed to be a TL072? I'm actually kinda interested in trying the preamp version. never thought to use an opamp to sum the PI output. Most just take the signal from a single tube...or omit the PI alltogether, maybe substituting another triode gain stage.


     
    Last edited: Aug 16, 2019
  14. johan.b

    johan.b Well-Known Member

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  15. john hammond

    john hammond Well-Known Member

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    this i find interesting.
    I have several of these amps, several bassmans , a Super reverb, a bandmaster.
    In my experience at volume levels before say..4 or 5 they do sound somewhat ( but not mesa awful) scooped.
    But when you get to 6, it levels out and the more you turn it up, the more mids appear. If your neighbours can tolerate a super Reverb at vol..8? with tube rec left in ( and those ' remove v1 and disconnect tremolo wire from pot mods) then you will behold a heavily mid laden tone beast.
    same as aa864 and aa165 bassmans.
    Interestingly, one of the aa864 bassmans I have here i added an internal presence pot, (just used a bit of silicon to mount the pot to the inside of the chassis and left it on 7.5) and disconnected one end of the bright cap ( all easily removable and no holes drilled) , anyway..that thing has mids almost to a fault ( basically its now a 6g6? style amp)
    there is a lot of tone in these old blackface bangers, you just gotta dial them up ( or do some very mild tweaking) to get the mid love.
    I know you were making a general reference, im simply adding my experience and hope it may be of value to someone.
     

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