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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    July 26, 2012 NOTE: With the number of posts in this thread reaching 812 :)eeks) I thought I better add some notes to the initial post here. There have been a lot of really good suggestions and fine-tuning tweaks on how to improve the Soldano mod scattered throughout all 55 pages and I plan to consolidate them all (with the generous help of some of the contributors- a big thanks to all of you!) If you are planning to do the Soldano mod before I get that written up let me know (post, PM or email) so that I can pass on some of those suggestions.

    I came up with the basic architecture of the mod and plugged in the basic values from the SLO schematic without doing a whole lot of fine-tuning. Some of the people here who tried out those basic values did more experimenting than me and have posted their recommendations here. Scattered among the 55 pages of posts... :cool:


    I have 3 of the V18-112 amps (5 as of 01-15-09) that I'm screwing around with. I'm finishing up the fine-tuning tweaks on the first one, which started out with the conversion to the Clean Channel of the V33. By "conversion" I mean reconfiguring the basic architecture of the amp rather than just replacing individual components or adding specific features (which I would consider to be "mods"). The main change was eliminating the second stage by pulling resistors and capacitors, and adding jumpers as needed. I'll post the full details of that conversion as soon as I finish it up.


    For now I thought I'd post something I drew up the other night- a completely untested conversion of the preamp to the specs of the Soldano SLO OD channel. (There are so many similarities in the architectures of the two amps that I wonder if it is more than a coincidence... :)) It will presumably need some fine-tuning tweaks since the SLO is a high gain circuit susceptible to feedback, etc. So without further ado...

    Converting a Crate V18 to the OD channel of a Soldano SLO:

    R1 220k
    R2 1k8
    C6 1uF
    C1 .02uF
    R6 remove
    C2 jumper
    C3 .002uF
    CW1 500kA* [EDIT I reverted to stock 250kA pot]
    R4 remove
    R65 470k
    C10 remove
    R3 100k
    R11 stock 100k but bypass it with 0.001uF cap
    R5 1k8 plus 1uF cap
    R61 470k
    R13 39k
    R16 1k8
    C13 1uF
    R15 use 100k (stock) up to 150k
    R18 47k
    R22/C16 jumper out [EDIT I removed jumper]
    (CW2 1M A) optional [EDIT I reverted to stock 250kA pot]

    The following are optional:
    R43 & R44 2k2
    R45 & R46 220k (reroute leads per layout drawing)
    add 120pF "snubber" cap between two terminals on C21 and C22 coupling caps that are closest to the top panel controls (this can help control any unwanted oscillations- add it if necessary)

    * The regular SLO uses a 0.001uF bright cap across the pre gain volume pot but it is removed for the Warren Haynes mod. You might want to wire this up to a switch.


    Steve Ahola

    P.S. There are many errors in the factory schematics for the Crate V18 so be sure to download the corrected ones from my site:

    http://www.blueguitar.org/new/schem/misc_amp/crate_v18_corrected_drawings_v2.pdf

    Enjoy!
     
    Last edited: Jul 26, 2012
  2. steeve_a

    steeve_a Member

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    I just drew this up for the Soldano conversion...

    http://www.blueguitar.org/new/schem/misc_amp/crate_v18_soldano_conversion-layout.gif

    Enjoy!

    Steve Ahola

    EDIT It just occurred to me that this mod might also work in a V33 (with the Clean Channel bypassing the 2nd gain stage). Just a thought for me to research...

    MORE EDIT There have been a few changes to the design since I made that drawing. You can leave R15 at its stock value of 100k or up it to 120k. However the value shown of 330k is way too high. I also ended up going back to the stock Gain and Volume pots (after trying 500k and 1M). I also added a conjunctive filter of 10k 5W & 2200pF 1kv to the terminals going to the OT primaries (look for a post dated 12/13/08 for more details). BTW this amp conversion is a real monster! Highly recommended...
     
    Last edited: Dec 14, 2008
  3. Feral Tone

    Feral Tone Member

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    Killer idea! I received my 212 V18 today, so I’m just starting to experiment with some of the basic bass and gain correction mods found on http://www.thegearpage.net/board/showthread.php?t=448629 as well as some of the reverb mods on http://music-electronics-forum.com/showthread.php?t=9691 Now I’m thinking of ordering a 112 when they’re available again to try out your SLO idea. BTW--Thank you Steve for your hard work and willingness to share—in particular the schematic corrections and PCB layout color coding. I’ve built a couple PTP single-enders, but this is my first real entry into the PCB world and modding, and you’re already making my life easier.

    Now, if anyone is able/willing to help . . .
    I’m getting more and more interested in the switching power supply. Am I correct in assuming that the 6.3 volt filament tap and the + and – 14.7 volt taps are DC? If I yank out the reverb circuitry, the + and – 14.7 volt taps that once powered the reverb are now free. Is there anything that would prevent me from using these 14.7v taps to power any other internal effects circuits? Basically, I think it’d be cool to take an effects pedal circuit and throw it into the amp. I’m assuming I would just need to add enough resistance to bring the voltage down to about 9v to power your typical effect circuit, no? Could I leave the reverb there and still power another 9v effect circuit?

    There’s a ton of room left on this chassis, so I’m also kicking around the idea of adding a dual triode, a reverb tranny, and tossing in a Fender-type tube reverb. Can anyone think of any reason adding a tube-driven reverb stage wouldn’t work with this amp? At what stage would you recommend adding it?
     
  4. zombiwoof

    zombiwoof Supporting Member

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    If you want a 1-12 you better get it from one of the stores that still have them, I hear they are discontinued.

    Al
     
  5. dimperdoo

    dimperdoo Member

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    I was wrapping tape around one of my reverb spings in my V18 palomino and the spring broke loose at the contact. I imagine it's possible to fix the tank (why? - I would probably go w/ accutronics @ this point)

    But, I wonder if the open circuit could now be used to internalize some effects? Any hows in that direction would be appreciated by me as well.
     
  6. steeve_a

    steeve_a Member

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    Adding resistance would not provide a very stable voltage because of Ohm's law: the voltage drop would be equal to the resistance times the load. So as the load changes so would the voltage. Assuming that the 14.7 volt taps can handle the current you could use a voltage regulator to provide a stable 9 volts. Or just use a zener.

    Back in the 1967 I was *sure* that someone had put a stomp box inside Steve Miller's Twin Reverb but I later decided that an amp tech must have modded his amp. I change pedals like some people change their hair extensions so I don't think I'd want to permanently install a stomp box in my guitar amp. Also, I use several different amps depending on the size of the venue.

    However I think it would be really slick if you had a 9 volt jack on your amp to power your pedals. (The new line of Workhorse amps from Visual Sound have that feature!)

    I have no idea how much filament current is delivered by the switching power supply in the V18- each additional preamp tube would require additional current from the filament supply.

    You might want to look at the schematics for the V16 Palomino to see an alternate method of hooking up the solid state reverb (you could use the same configuration for a tube driven reverb):

    http://www.blueguitar.org/new/schem/misc_amp/crate_v16_palomino.pdf

    Speaking of which, if someone wanted (or needed) to scrap the switching power supply board they could order a replacement power transformer for the V16 Palomino, which will supply the same voltages.

    HTH

    Steve Ahola

    http://www.blueguitar.org
     
  7. steeve_a

    steeve_a Member

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    So is that a V16 Palomino or a V18? You might want to check with Crate parts department- their prices are usually very reasonable.

    I was just comparing the V18 and V33 schematics and it looks like the V18 used the wrong feedback resistor (R38) on the reverb recovery circuit which is one reason the reverb gets so loud so fast. Replacing the 220k resistor with a 100k resistor helps that immensely.

    The reverb drive is excessive, especially when you crank up the amp, so I'd also replace the 1M resistor used for R37 with 470k.

    (The signal going to the reverb springs passes through a 470pF capacitor- that is a *treble* cap so it will have a lot of trebles...)

    The V18 does have a Preamp line out which could be used as an FX send. I suspect that the IC before the phase inverter could be used for an FX return but I would need to see a V33 schematic that includes the FX return (the one I have doesn't show it.)

    Steve Ahola

    P.S. If you go with an Accutronics tank you do need to match the input and output impedances- I have no idea what they would be for the Crate... :(
     
  8. Feral Tone

    Feral Tone Member

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    For those who haven't come across some of the basic v18 fixes in other threads, I did the following, and this amp is now ridiculously tasty:

    Changed the speaker to an old Wharfdale I had laying around. The stock speaks are completely doped, so they sound like plastic. Strange choice by Crate. I tried a number of tube swaps, and frankly, nothing made enough of a difference to keep me from throwing the stock Sovteks back in. Folks love to diss Sovtek, but I've had good luck. BTW--those new "Mullard Reissues" and most of your fancy $50 matched EL84 GT pairs probably came from the Russian Sovtek factory. Scrape the sovtek name off if it bugs you that much. That's what Groove Tubes does before they charge you 3x what they paid for something they didn't make (though I hear they're slowly changing their business model and may even produce their own brand domestically someday!?!?!?!?)

    For the excessive bass issue, I subbed C13 w/ a .68uf 50 volt. It's about the right level of bass, but I may play with a 1uf as well. All I had laying around was a mustard cap, so the thing looks pretty funny in there right now.

    I swtiched R4 and R10 to get the gain under control (careful when removing R4 since there's an 1/8w resistor and a ceramic cap right on it. Just desolder this from the top--maybe even just snip the lead of the original resistor since its 1/8watt neighbor's going to be pretty sensitive to the amount of heat needed to completely and properly desolder the thing. FWIW

    In conjunction with the r4/r10 switch, I changed r18 to 100k, and now I'm getting some very useable cleans and very useable gain that cleans up nicely with a rollback on the guitar volume. Very musical and responsive gain stage now. I was thinking about moving the level post-phase, but the darn thing sounds perfect to me without fussing with that.

    I've tried a number of reverb tweaks--the dwell Steve mentions as well as simply paralleling a 680r with r36, but I just don't like the transistor-based reverb. The spring has nothing to do with it. Just a personal taste thing here.
     
  9. Feral Tone

    Feral Tone Member

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    Thanks Steve. I'll play around a little more with the voltage regulator idea. There's a single 6.3v tap from the power supply that's powering the filaments. Not used to what I'm used to seeing, but 6.3v should be enough to throw in an extra triode. I'll have to see how they have the filaments wired with a single 6.3v tap.
     
  10. steeve_a

    steeve_a Member

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    The 12AX7 family of fine tubes uses two 6.3v filaments in series so they can be connected to either a 6.3v or 12.6v filament supply. The two filaments are connected to pins 4 and 9, and pins 9 and 5.

    For a 6.3v filament supply you would jumper pins 4 & 5 and connect one lead to them, while the other lead would be connected to pin 9. For a 12.6v filament supply you would connect nothing to pin 9 and connect the two leads to pins 4 and 5 (obviously not jumpered in this application).

    If the specs of the power transformer or power supply are not known, you can watch for a voltage drop in the filament supply as you add additional 12AX7's (which is a sign that you have exceeded its capacity). If necessary you can always add a separate filament transformer to power the added tubes.

    For an example of a single tube reverb circuit check out the schematic for the Mesa Boogie Maverick.

    HTH

    Steve Ahola
     
  11. jhucx!

    jhucx! Member

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    I'm about to pull the trigger on buying one of these things...and I can't seem to determine how difficult it would be to get the PCB out for soldering/desoldering. Looks like there are a few screws that would need to come out, but I can't tell if the wire lengths are long enough to take the board out without desoldering those.

    Have any of you folks written out a guide and/or tips on removing the board?
     
  12. dvnator

    dvnator Member

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    Conversions...hmmm...
    Have you ever seen the schematic for the OD channel of the Bogner Ecstacy? Just wonderin'...
     
  13. dimperdoo

    dimperdoo Member

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    Yes, it IS the V16 - sorry, so much discussion w/ the newer V18 that I got a little mixed:messedup

    Obeid references an accutronics replacement for the 32 in another thread - I wonder if that would be the right value for the V16...

    Thanks BTW
     
  14. steeve_a

    steeve_a Member

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    I have found Crate parts and technical support to be very helpful- they should be able to tell you if the V-16 uses the same tank as the V-18, in which case the recommended Accutronics replacement would probably be the 4EB2C1B (you might want to recheck that number!)

    Don't feel left out- the V-16 looks like a much better design than the V-18, and one of the mods I'm considering for the V-18 would basically revert it back to a V-16...

    Steve
     
  15. steeve_a

    steeve_a Member

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    Funny you should ask- I have drawings of the output section and the power supply, but the file for the OD channel was corrupted.. :(

    I just spent the last two evenings wiring up V-18 #2 to the specs of a very famous 18 watt boutique amp and it sounds absolutely killer all of the way from clean to downright nasty! I think I'll keep it...

    Steve
     
  16. steeve_a

    steeve_a Member

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    I just wrote up a lot of tips on working on these over at ppwatt.com (at the 18watt.com site) but they are moving to a new ISP so the site is down right now. :(

    The V18 is very easy to work on. If you want to remove the board completely then you can desolder the shielded cable going to Preamp Out jack- you might as well leave it off until you are satisfied with your mods. With my first V18 I made the mistake of siliconing the ferrite ring on the blue and orange wires to the chassis (to eliminate one of the many rattles) so I was never able to remove the board completely- which was a bit of a hassle. Moral of the story: wait until you are completely down before siliconing anything to the chassis!

    More tips:

    - use wooden clothespins to help pry out the knobs without marking up the chassis (if they are really stubborn they sell a $4 brake tool at Harbor Freight).

    - the controls use a 10mm nutdriver, the input jack 1/2", but just use a large crescent wrench for the black nylon nuts on the back (they measure like 0.6" across!). Nutdrivers leave fewer marks on the nuts and on the chassis, and are easier to use than deep sockets.

    - use curved hemeostats to hold the screws that secure the board to the chassis

    - use blue masking tape to hold things down or in place. In particular, be sure to secure the wire holders for the EL84's or they will get bent out of shape very badly.


    - I just ran across a desolder tool which is made exactly like the one that has been working day in and day out for many, many years- while other desolder tools (like the famed SolderPullIt from Edsyn) have long since bitten the dust. I think I got the old one from Radio Shack- there are no markings on it- but the new one is from Hakko (made in Italy) and the stock number is 2000/P. They call it a Desolder Pump and it cost $12.99.

    Steve

    P.S. Someone should know a little about electronics and have a decent soldering iron as basic requirements. I just saw a temperature controlled solder station sold by Velleman for $19.99 (stock number VTSS5U)... damn, a decent soldering station used to set you back $100! FWIW Velleman also makes a 3-in-1 bench tool kit for about $150 that includes the soldering station, a DMM and a power supply (LAB1U). Probably not that useful for tube amps because the power supply only goes from 3 to 12vdc. :(

    But yes you should also have a DMM for checking all of your joints, etc.
     
    Last edited: Nov 22, 2008
  17. jhucx!

    jhucx! Member

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    Thanks for the info! Super helpful.
     
  18. steeve_a

    steeve_a Member

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    ... and the results are absolutely killer! Endless sustain- you can hit a note, go out for a cup of coffee and when you get back the note is still sustaining! :love:

    Not exactly my cup of tea- I prefer the more vintage and raunchy guitar amp sounds but the Soldano SLO is such a classic how can I say "No"??? This one is a keeper.

    It seems to me that Fender, Peavey and Crate have all been trying to get that SLO sound from the OD channel in their amps and with them being unable to license the technology, their attempts don't even come close. Its usually more like the buzzy sound of hornets in a tin can... :dunno

    Here is a link to the annotated layout drawing:

    http://www.blueguitar.org/new/schem/misc_mod/crate_v18_soldano_conversion-layout.gif

    And you do want to refer to the corrected drawings for the V-18:

    http://www.blueguitar.org/new/schem/misc_amp/crate_v18_corrected_drawings_v2.pdf


    Did I already tell you about my V-18 #2? I call that the MJ Conversion and it is also a really nice design. Less gain than the Soldano but it has that vintage raunchiness. Sound clips to follow...

    http://www.blueguitar.org/new/schem/misc_mod/crate_v18_mj_conversion-layout.jpg

    http://www.blueguitar.org/new/schem/misc_mod/crate_v18_mj_conversion-preamp-draft.jpg

    http://www.blueguitar.org/new/schem/misc_mod/crate_v18_mj_conversion-power_amp-draft.jpg

    Going for a Trifecta, here is the first V18 conversion I did, originally intended to duplicate the Clean Channel of the V33 but I tweaked the design a lot.

    http://www.blueguitar.org/new/schem/misc_mod/crate_v18_clean_channel_conversion-preamp_schematic.jpg

    That should keep y'all busy for at least a few days!

    Steve Ahola

    EDIT Well, the MJ Conversion is no more... R.I.P.
    I decided that the lower gain settings were incurably muddy, and the high gain distortion a bit boring after doing the Soldano SLO Conversion to V18 #3. So I morphed the MJ design into the Trainwreck Rocket that I was planning to do in the first place... go figure!

    MORE EDIT I would have liked to keep the MJ (and will probably build another one later!) because it was really cool. I did not want to post the name of the designer and the amp publicly so I decided to just call it the MJ Conversion. If someone wants to know the real name send me a PM, but please keep the real name of the boards here. Thanks!
     
    Last edited: Dec 14, 2008
  19. steeve_a

    steeve_a Member

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  20. Feral Tone

    Feral Tone Member

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    You weren't kidding about the sustain on that thing. I'm still on my first V18:D.

    As I mentioned earlier in the thread, I want to throw in some tube reverb in this thing and maybe even a tube tremolo at some point. After some experimenting, I won't have enough amps from the filament taps to throw in 2-3 extra tubes.

    But, I've got a Hammond 370EX power transformer laying around that should have enough beef to run the extra tube filaments (4a for 6.3 taps). It is spec'd at 275-0-275 @125ma for the high voltage tap, and it's also got a 5v 3a tap for a tube rectfier available.

    I've had it with this switching power supply, and I can't make sense of the thing. It looks like the rectifier is on the switching supply itself, and then from there I get lost. Most of the filaments are powered by a single 6.3v tap (I'm used to seeing two), and then there's v2a, which powers its filament with a -12.6 v tap??? If I'm not mistaken, since it's DC, there's both + and - for both the 6.3 and the 12.6???? I've had it--I don't get it, and I don't want to. I want to yank this supply out, throw in the Hammond, and just re-wire my filaments the old-fashioned way--with a twisted pair of 6.3 AC.

    I'm a total noob when it comes to power supply design, so please bear with me. How do I design the power supply to accomodate the Hammond? I know I need to add a rectifier, so I'd like to utilize the 5v tap to use a tube to rectify. Which tube should I use? Also, the Hammond appears to be overspec'd for this cicruit. How do I calculate the proper values for the capacitors and resistors in the power section to ensure this thing runs at correct voltage?

    Also, I've never really understood how power transformer specs work. In other words, the Hammond's spec'd at 275-0-275, but I know the amp I had it in before read 301V AC before the diode rectifier and the 366 B+ just after (before any filtering or resistance). Huh? I know I should know this, but, well, I don't, so thank you all for the help.

    P.S. Yes, I know I will need to replace the lamp with a 6.3 volter.
    : )
     

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