Crate V18: Mods and Conversions

Discussion in 'Amps and Cabs' started by steeve_a, Nov 15, 2008.


  1. steeve_a

    steeve_a Member

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    Apr 8, 2007
    Looks great! I still have one unmodded V18 and your mod may be just what the doctor ordered (my conversion mods can be a real PITB!) Only one cut trace... cool! I've been using a small grinding tip on my Dremel to cut traces and to remove the coating for good solder joints.

    Your mod has one less gain stage than the stock V18 so if your overall volume has decreased you make up for it by increasing the value of R25 (which is 12k stock.) R25 sets the gain of IC1b which feeds the phase inverter. You can boost it to 18k or 22k for a stronger signal going to the output section which could be useful with very low gain settings for a clean sound. I was thinking of wiring it up to a "boost" pot: wire up a 10k pot as a variable resistor in series with a 15k fixed resistor and use that as a replacement for R25.

    Thanks for your contribution here!

    Steve Ahola
     
  2. Nick Blue

    Nick Blue Member

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    Dec 1, 2013
    Steeve, thanks for checking out my mod. I'm not completely satisfied yet with the full on distorted tone, needs more definition. The cleans are great and the guitar volume knob response is very cool. I might even have too much gain as the biggest change I made from the JCM was adding a cap around R5 for brightness and some gain in the high freqs. When I was going over Marshall schematics I was surprised that the old Plexis and JTMs just had 2 gain stages. I see what you're saying about R25, the op amp is set up as a small boost, I thought the op amps in the signal path would just be buffers as this is a tube amp. I wouldn't want to overdrive the op amp but a small boost to the PI might be interesting.

    I had built a lot of effects and a basic little tube amp and I was thinking about building a Trainwreck express with 6v6s or EL84s, but for $159 I couldn't pass up the V18. I can mod the heck out of it without caring if I bugger it up! With 18 watts it's just right for my band, so I can crank it and get the EL84s cooking!
     
  3. Nick Blue

    Nick Blue Member

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    Dec 1, 2013
    More changes. Out went the cap around R5, too bright. And the 12AT7 for the PI, it didn't sound good.

    I did some reverb changes similar to Steeve's and it sounds really good. Next I scraped off the mid tone trace making it a divider and it so sweet sounding now!

    Been getting some nice touch sensitivity when the MV is up past 8. I have some concern that the reverb circuit is adding some clipping since it has 15v pp right in the signal path.

    I've got an idea to put a switch in to by-pass the entire reverb circuit from the MV to the PI. Maybe even by-pass the MV too. Anyone try something like that?
     
  4. Nick Blue

    Nick Blue Member

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    Dec 1, 2013
    Update

    After doing an LTSpice analysis of the entire signal path, I found that sometimes at very high MV levels that IC1-B will clip the signal. Probably accounting for the buzzy distortion sometimes I got. The IC yeilds about 3x gain. I clipped a jumper around R25 turning it into a buffer. This resulted in a more natural sound and even more sensitivity! So I think Steve's idea of by-passing IC1-B and those diodes, D1+2 before it would be the way to go to avoid silicon clipping and keep the reverb! If more gain is needed I can lower R62.
     
  5. jimijam

    jimijam Member

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    Jan 28, 2006
    Location:
    Texas
    Wow, amazing someone is still modding these amps.
    I have one that is unmodded and this JCM 2204 mod looks about what I was looking for...
    any updates on the schematic Nick? I am trying to follow the mods your talking about now and will give it a shot based on that schematic you posted.
     
  6. Nick Blue

    Nick Blue Member

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    Dec 1, 2013
    Even more changes including:

    Switchable by-pass around V1B for more old school lower gain "Plexi".

    Throwing out the 10k cold clipper on V1B, for a 1.5k warm bias. So not like the 2204 anymore

    By-passing the filtering before the gain pot.

    Adding a 100 ohm sag resistor to the B+

    Getting closer to what I want!
     
  7. Chip

    Chip Member

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    Jun 4, 2014
    i know i kinda missed the boat on this thread, but i finally got around to doing pretty much all the soldano mods around v1a and v1b...have a 12av7 in v1 , 12ax7 in v2, and 12at7 in v3...even with the 12av7 in v1, this amp still has an incredible amount of gain...these mods seem to leave the gain intact and take most of the mud out of it...i am finally getting some fender type clean sounds from this amp at useful volumes...many thanks to Steve Aloha for posting his mods here...

    i also picked up a crate club 30 on the cheap...all it needed was some electrical contact cleaner on the switches, pedal, and effects loop jacks...i like these older crate tube amps...
     
  8. GuitarCat33511

    GuitarCat33511 Member

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    129
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    Dec 28, 2012
    Just had all my modes done
    Not the Soldano one but most came from here

    I went over them with Bruce from Diversified audio, Tampa
    And a week later what a friggin awesome amp !
    Clips and vids coming soo as I find the charger for my camera
     
  9. Ricktoberfest

    Ricktoberfest Member

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    Feb 16, 2014
    I've been thinking about modding mine more and more lately. Although I like it stock (it's the 212) I'm getting bored with it lately and looking for a change. Any videos/sound samples would be great to hear the differences


    Sent from my iPhone using Tapatalk
     
  10. GuitarCat33511

    GuitarCat33511 Member

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    129
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    Dec 28, 2012
    I only have one 'before' video shot 2008-2009-ish ?
    I changed teh speaker 2010 to a celestion
    No video or audio there
    Mods done august 2014
    I'll setup a camera and a mic and do something soon
    definitely cleaned up everything and works like I think it should

    :JAM
     

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