Crate V18: Mods and Conversions

[steeve_a]

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/...rawings_v2.pdf

Enjoy!

[steeve_a]

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

http://www.blueguitar.org/new/schem/...ion-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...

[Feral Tone]

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?

[zombiwoof]

Originally Posted by Feral Tone

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?

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

[dimperdoo]

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.

[steeve_a]

Originally Posted by dimperdoo

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.

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...

[Feral Tone]

Originally Posted by dimperdoo

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.

We were talking a few days ago about bypassing the reverb and using the + and - 14.7 volt taps to power an onboard FX pedal or a 9 VDC line out. As Steve mentioned, you'd need a voltage regulator to stabilize and lower the voltage, and I came across this handy little site when I was looking at maybe lowering the 14.7 taps to 9v:
http://hyperphysics.phy-astr.gsu.edu...c/zenereg.html

If you don't want to do that, Ted Weber sells an onboard FX power supply kit that looks really sweet https://taweber.powweb.com/store/modkits.htm#eps
(it's the Pedal Pump Effects Power Supply kit). This actually includes a separate transformer that will give you a bunch of 11 and 9 volt AC taps plus 4 identical small circuits that will rectify and regulate down to 9 volts at 300ma each. 500 ma would be more ideal to run some major power suckers (like delays, etc), but 300ma should work for most anything nonetheless.

You can probably even just modify Weber's little Pedal Pump circuit board to remove the rectifier and beef up the regulator to use with your 14.7 volt taps.

Lots of options here.

[steeve_a]

Originally Posted by Feral Tone

...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?

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!)

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?

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/...6_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

[Feral Tone]

Originally Posted by steeve_a

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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.

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/...6_palomino.pdf


http://www.blueguitar.org

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.

[steeve_a]

Originally Posted by Feral Tone

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.

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

[Feral Tone]

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.

[dvnator]

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

[steeve_a]

Originally Posted by dvnator

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

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

[steeve_a]

... 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!

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...

Here is a link to the annotated layout drawing:

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

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

http://www.blueguitar.org/new/schem/...rawings_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/...ion-layout.jpg

http://www.blueguitar.org/new/schem/...eamp-draft.jpg

http://www.blueguitar.org/new/schem/..._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/..._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!

[steeve_a]

I know that everybody wants to hear the dirty sounds first (gain set to 10; volume at 3):

http://www.box.net/shared/static/c5e0gakhhb.mp3

And here are some of the cleaner lower gain sounds:

http://www.box.net/shared/static/bibz8kb2qj.mp3

This is with my PRS SE Singlecut II (Burstbucker 2 at the neck, BB Pro at the bridge). Speaker is Eminence Red, White and Blues.

Steve Ahola