18W with reverb again...

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

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Graydon
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18W with reverb again...

Post by Graydon »

Guys,

I mentioned last week how I used the second channel of an 18W to amplify reverb only and I tihnk it got lost with Gabi's database corruption. Anyway, I have more news...

I tried it again last night with an old Lexicon LXP-1 (Hey Brian, thanks for the jacks - they work great!) and a Marshall Bluesbreaker overdrive pedal. First, the guitar ran into the BB pedal and from there it went to the trem channel high input of my 18W combo. Then I ran a cord from the low input to the input of the LXP-1. The output of the LXP-1 was fed to the low input of the normal channel and levels were adjusted until I had a nice delay and reverb happening along with some really sweet mild overdrive. This was overall at whisper volume levels since it was after midnight and the kids were all asleep upstairs.

The basic guitar tone is fantastic. It is just like running the guitar straight into the amp. The great thing about this setup is that it retains the tone of the amp and guitar without any reverb at all. Yet, the reverb in the second channel is not being compromised either. It is the classic wet/dry setup without the hassle of multiple amps. The only con is that it is not stereo. The sound is fantastic though.

I highly recommend it.
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Marshall 18 watt reverb circuit?

Post by mark0614 »

Dear Graydon

Has anyone heard from Mitch Colby about the original reverb circuit for the 18 watter?

Yours Sincerely

Mark Abbott
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Post by ColinM »

Graydon

Just tried it with similar gear ('Guv'nor' instead of the BB, 'Alex' instead of the MXP1), and sure enough, it works a treat 8)

However, I had to run the straight signal into the normal channel and use the trem channel for the return. For some reason it just doesn't work the other way around...

Looking forward to using this setup on my next gig on Sunday night.

Regards, Colin
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Post by Prophet »

Hey Graydon,

I tried this reverb method on my 18 watt and it is way better and it works on a Vox AC30 & Selmer Zodiac 30 too.

Tonio
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Post by Gabi »

Graydon!

Thanks for the tip!

It worked for me too! I used instead an Alesis Quadraverb for the delay/reverb part. The nice thing about it is that you can have the reverbed (proccessed) signal but in the same time you have the pure dry signal as well.

thank a lot!
gabi.
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Post by zaphod_phil »

If you're doing this with a regular 18W and not a TMB, then the interesting thing is that your dry and reverbed signals are actually out of phase. Going by what you guys are saying, this doesn't seem to be degrading the sound. Probably the amount of time delay in the reverbed signal is over-riding the phase change.
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Post by Graydon »

Hey,

This is great! I am glad to hear that you guys are also having good success with this technique. I don't know why I didn't explore this a long time ago. I did try something similar. I made an amp with an "effects loop" once and so I tried taking the effects send and running that through a Lexicon and returning that back to the normal channel input. That worked OK for some effects but delays quickly degenerated into mush since each successive delay was sent through the Lexicon in a feedback loop. If I turned it up too high it went into feedback (as could be expected. With the parallel routine, the signal doesn't actually get into a feedback loop so the sound remains pure. The only downside of this is that the reverbed signal is clean as a whistle even if the amp is beginning to overdrive.

Phil,

You are absolutely correct - the two channels are out of phase on a tremolo amp however since we are only concerned with a very low level signal which is probably phase shifted from the original due to the effects device, it doesn't seem to be noticeable. I tried it on my 36W head (which is a TMB) last night as well and it worked great. Wow, that amp is loud!

Colin, your input jacks may have a different schemo than ours. Is that on the red "Colin" 18W amp? I only plugged my guitar into the trem channel so that I could also have tremolo as an optional effect.
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Post by BrianH »

Glad the jacks worked, Graydon!
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Post by Graydon »

BrianH wrote:Glad the jacks worked, Graydon!
Brian, They worked perfectly. They had some extra pins for additional switching circuits so I just cut them off. Then they soldered in perfectly.

I think that old Lexicon LXP-1 is the best deal going for a good quality reverb/delay unit. It is approaching studio quality yet it is small and portable. It has a great sound and it is very quiet. I bought mine for less than $100 and it sounds great. I also have an MPX-100 which is a full rack space but also typically available for around $100 and I have a PCM-81 which is the big dog and it certainly sounds great but the little guys sound nearly as good for less than a tenth of the cost.
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Post by bubba2 »

Tried this idea on my standard 18watt and it worked great.
Graydon your a genius, opens up a padoras box of possibilities
for experimenting. Only wish there were more hours in a day.
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Post by Graydon »

bubba2 wrote:Tried this idea on my standard 18watt and it worked great.
Graydon your a genius, opens up a padoras box of possibilities
for experimenting. Only wish there were more hours in a day.
Bubba,

Glad you like how that works. What effects box did you use?

Speaking of Pandora's box, anyone tried a Korg Pandora?

There are so many very inexpensive little effects boxes out there, it should be easy to get really nice sounding effects on the 18W using this technique.

Oh yeah, Bubba, you're also a great judge of character. 8)

j/k
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Post by bubba2 »

Alas only a boss reverb stompbox thus far but I have plans to try a gt5
next time the wife goes out and I'm home alone. :twisted:
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Post by zenin »

I'm definitely going to be trying this out for myself. I'm curious as to what you guys set the mix control on the delay unit to(Lexicon or whatever). It seems that if you used anything less than 100% wet output, you would begin to get phase cancellation. I like to use analog delay and am going to try this out with an old EH Deluxe Memory Man.
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Post by Graydon »

zenin wrote:I'm definitely going to be trying this out for myself. I'm curious as to what you guys set the mix control on the delay unit to(Lexicon or whatever). It seems that if you used anything less than 100% wet output, you would begin to get phase cancellation. I like to use analog delay and am going to try this out with an old EH Deluxe Memory Man.
I like just a splash of effects, mostly reverb and a touch of delay. Sometimes just delay. So, the proportionate levels of main guitar signal compared to effect signal are highly biased toward the main signal. Therefore, the phase cancellations are unnoticable. I used the low input on the effects side to get a cleaner tone, and the volume still ends up being very low. The effects device is indeed set to 100% wet.

Let us know how well it works with your EH Memory Man.
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Post by pete_skelton »

Sorry guys I've missed something. What exactly are you doing here?

peter
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Post by Graydon »

Peter,

Read my first post in this thread. It explains what I did. Maybe we could persuade Gabi or one of the guys who are good with graphics to make a layout showing how this is done.

Basically, you run the guitar signal through an outboard reverb device and into the 18W channel that you are not using. The 18W is a PA-style amp, so the two channels are operated independently. So, you can treat the second channel as a reverb return like you would on any PA mixing board.
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Robal

Post by Robal »

What would be involved in modifying the regular 18 watt circuit so that the trem channel and normal channel are in phase, not out of phase? Can this be done in a way that does not change the favorable sound characteristics of the amp? I am not a technical guy so I am not really sure how much is involved. I do note that several amp makers with two channel 18 watt amps have in phase channels that are blendable.
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Post by zaphod_phil »

Robal wrote:What would be involved in modifying the regular 18 watt circuit so that the trem channel and normal channel are in phase, not out of phase?
Well with the Richie/JA, the channels are in phase, as there is one more preamp gain stage in it's Plexi/TMB channel. If you wanted to mod a regular 18W, you would need to cascade the two triodes in the Normal channel, rather than have them paralleled, like they are now. This would give a massive increase in gain, which would need to be tamed down somehow, maybe with a resistive divider. So it wouldn't be a trivial mod.
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Post by pete_skelton »

Sorry Graydon it was 11 o'clock when I read that so I was not in the best mental state for picturing gear setups :) I get it now, sounds like an interesting solution to getting reverb. Having said that, I'm not a special fan of reverb on a Marshall tone, but when I get round to building my 18W I will have to try it out of curiosity

Thanks
Peter
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Post by KingCrimson »

Graydon wrote: Speaking of Pandora's box, anyone tried a Korg Pandora?
I have two Pandora's Boxes, one for bass and one for guitar. They are quite incredible. I recorded all my demos direct injection using these devices, and for being able to record in an apartment without bothering neighbors or the wife, they are priceless. Yes, they are fake digital, but for demo purposes, can't beat it.

I recorded this demo with the Pandora's on bass and guitar....used fake drums of course:
http://home.earthlink.net/~tmtetlow/sit ... ration.mp3
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