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PostPosted: Mon Apr 09, 2018 4:03 am 
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Kramer Kingpin
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Wow, Jarrod :headbang . This thing sounds damn good. From cleans to breakup to crunch to rock to full metal. Warm sounding tones with a lot of juice and warm character :not .

Me likey mucho, bro :thumbs .

:yourock

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PostPosted: Mon Apr 09, 2018 7:15 am 
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:thumbs

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PostPosted: Mon Apr 09, 2018 9:01 am 
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KickstartMyHeart wrote:
Wow, Jarrod :headbang . This thing sounds damn good. From cleans to breakup to crunch to rock to full metal. Warm sounding tones with a lot of juice and warm character :not .

Me likey mucho, bro :thumbs .

:yourock


I really want to draw up a pcp for this thing and maybe get a couple of preamp modules built, with all the switches and everything! I've had a few people over the past few months ask me to build them one of these, but I honestly just don't have the time nor money to do so at the moment; but pcp boards that people can populate on their own and match with another amp, I may be able to do.

The magic of this little amp is that I've configured a couple of things within the amp, such as a fake PI stage that breaks up pretty early in order to try and get that 'power tube' breakup sound at quiet volumes. However, the power amp is by no means clean, and cranking that itself can get some JUICEY tones.

What I didn't have a chance to record in the video is the 'crunch' channel with the master cranked; which is probably my favorite sound from this amp. It truly is that classic Marshall sound with a bit more push, crunch, and clarity.

I can't wait to try this thing with a real Greenback because I'm sure that'll REALLY draw out the sound I'm looking for.

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PostPosted: Mon Apr 09, 2018 9:06 am 
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Kramer Kommander
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Small PCB suppliers will do batches beginning at 10 pcs, so that might be an option. Usually not very expensive either. Free software like Eagle can be used for that, if there are not too many parts involved (free version is limited regarding the parts count).

https://www.autodesk.com/products/eagle/free-download


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PostPosted: Tue Apr 10, 2018 7:00 am 
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I for one am interested Jarrod if you decide to do a batch and wish to sell a PCB with a schematic. That way the onus is on those interested to get off their a$$ and do some building. Who knows, maybe your the next Jim Marshall!

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PostPosted: Tue Apr 10, 2018 7:41 am 
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Great job.
Amps are NOT in my skill set.
I just buy the ones I like.
I did make 1 amp, (kind of).
I had an old USA made Rocktron Chameleon collecting dust.
A blown up Marshall MG 100dfx combo that was FREE!, and in new condition. I just bought a used $80.00, Marshall Valve state 40+40 power amp. A new celestion V30 12" speaker. Through it all in the MG cab.
A franken amp was born.
It is my ROCK-ALL MARS-TRON amp. LOL.

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PostPosted: Tue Apr 10, 2018 10:40 am 
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Kramer Maniac
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SWANTECH wrote:
Great job.
Amps are NOT in my skill set.
I just buy the ones I like.
I did make 1 amp, (kind of).
I had an old USA made Rocktron Chameleon collecting dust.
A blown up Marshall MG 100dfx combo that was FREE!, and in new condition. I just bought a used $80.00, Marshall Valve state 40+40 power amp. A new celestion V30 12" speaker. Through it all in the MG cab.
A franken amp was born.
It is my ROCK-ALL MARS-TRON amp. LOL.


Hahah thats funny dude! I've actually been wanting to do that with my ADA Mp1 and the marshall 9001 power amp I have; just throw em in like a modular cab or something. Would be a cool little setup for sure!

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PostPosted: Tue Apr 10, 2018 10:44 am 
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Kramer Maniac
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kremark wrote:
I for one am interested Jarrod if you decide to do a batch and wish to sell a PCB with a schematic. That way the onus is on those interested to get off their a$$ and do some building. Who knows, maybe your the next Jim Marshall!


Being that all Im doing is copying older circuits and making them differ-... Wait... Maybe I could be the next Jim Marshall :roll

Ill defiantly give this some further considerations! My only problem may be with actually drawing out the boards.

Actually used to use a version of that autocad program at one of my former jobs to design small circuit boards; but they were usually a bit on the messy side!

Another concern with doing a preamp board however would be power supply and filtering...

Honestly it may just make more sense to build a full amp at that point as ill still need a power tranny and OT for the preamp module... UNLESS thats something I leave up to the builders? Like; here is the preamp; put it in whatever you want and power it on your own? :roll

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Check out my Soundcloud:
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Or Youtube channel:
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PostPosted: Tue Apr 10, 2018 11:06 pm 
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Kramer Maniac
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Absolutely, it can be up to them. Beware of burns, electric shock, and or death. Can the signal be totally nullified in the power section? Youbetcha. :jump

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PostPosted: Sat May 26, 2018 3:16 am 
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So I havn't made any progress as of yet in regards to building a schematic, as I'm still constantly tweaking it (even thought I tell myself to stop!). This amp is quickly becoming and actual frankenstein monster here with all the switches and knobs and other mods going on under the chassis.

Anywho, I've posted another little crap quality youtube video of the amp as it is currently; I still want to do a real recording of this amp through a mic setup and all that but I've been too darned lazy to set it all up :roll

Here is the video:


Because I ramble in the video, and honestly forget what I've done to the amp, I'll post its specs in written form:

The amp is basically schematically a JCM800 with a ton of mods, as well as a single ended power amp.

The biggest mod to this amp as of late was removing the el84 noval socket, which never got use as of late, and replaced it with a octal socket. There are now two octal sockets; one biased with a 250ohm resistor on the cathode, and the other with about 450ohms.

With this setup you can do a few things here: Run a big bottle tube in the hotter socket (such as an el34 as that socket has a bridged cathode to plate 1 connection, allowing the full use of it), or another 6v6. However, you can also run one big bottle tube, and one 6v6 in parallel for some really cool tonal variations. I feel it'd be a bad idea to run an el34 and 6v6 together as an el34 draws a lot of current, so when I parallel the tubes, I usually only do two 6v6s, or a 6v6 and a 5881.

Being able to mix and match wildly different power tubes gives a whole new dimension to this amp and really makes it come alive. My favorite combo is the 6v6 and 5881: for some loud clean bass, and for some gritty crunch (as well as the added bonus of some extra volume!). Two 6v6s are really cool too; especially with a JJ 6v6 in the 'hot' socket, and a vintage one in the 'cool' one. Very interesting. Fairly loud :headbang . Defiantly get some awesome cleans with the two tubes!

Aside from the power section, there are a couple of tweaks to the preamp circuit; mainly just resistor tweaks to get a little more gain out of the circuit. Also changed the 2nd triode's cathode bias switch back to 1.5k with a 10uf cap, 10k, and 10k with a .1uf cap. When using the clean channel, as like a JCM800 the first stage triode is bypassed. In order to get enough volume to drive the power amp well, the NEW 1st stage (so the second triode) needs to have a higher gain and thus a lower cathode bypass cap (as 10k has nearly no gain; just clipping).

The clean channel then becomes a 1.5k 10uf stage running into an 820ohm stage that can have either no bypass cap, or the choice between .47uf and 10uf for some extra gain-y goodness. This then runs through a cathode follower, some signal reduction/impedance matching, and then out to the effects pedals.

the return of the effects loop also functions as a "fake Phase inverter", or really just another weak gain stage in which negative feedback from the amps speaker out can be utilized. This stage is biased at 1.5k, which limits additional clipping.

This "fake PI" stage receives NFB from the speaker outs and runs through selectable resistors for different NFB responses: 22k, 75k, and around 140k. Each setting has its own advantages, but I prefer the 22k as it lets the most NFB through; tightening up the bass and the whole guitar sound as a whole. The other two settings give you more harmonic content though, and the 140k resistor sounds pretty cool with the JCM800 'mode' engaged: very raw.

There is also a new resonance control, which honestly doesn't do too much: I currently have an extra hole on the front of the amp and it needs to be filled with SOMETHING of use, and I had run all out of ideas!! So resonance knob it is... unfortunately, with the type of amp this is (Single ended) not a ton of low bass is really generated or passed through the Output Transformer, so any benefit I'd get from the Resonance control is near non-existent unless you REALLY crank the master volume; and then even so its only really noticeable on the clean channel.

The "modified Marshall" channel follows the same chain as above, however its an extra triode stage in front of the other triodes mentioned above, biased at 2.7k with a .68uf cap. It also has a 220k plate resistor which leads to more compression and distortion/gain being generated in the stage. The output of this stage leads to a coupling cap that can be switched from .022uf to .0047uf; stock 'fatter' tone, and modified 'thinner' tone. Really changes the feeling of the amp.

In this "modified Marshall" channel, the real magic comes from the second stage; 10k = JCM800, 10k + .1uf = S.I.R #34 (with 3rd stage cathode @ .47uf aswell), 1.5k = Over the top Modded cascaded marshall (Along the lines of Randy Rhoads perhaps?). Bright caps and everything else is tweak-able to taste, but as I have shown in my videos, I have a few generalized "settings/channels" that match schematics/ general values used in other famous circuits such as the #34 or the Mod 5.

It's hard to get much more flexable than this amp without going digital! It's also hard to turn this amp up much louder then 1/4 on the master because oo boy, for 5-12 watts she sure is one loud son of a gun. It's become almost a joke with my bandmates as every-time they hear it, it seems to have gotten louder (first time they heard it, biases were wrong and caps were dead; second time they heard it, it was just running a 6v6, third time a 6v6 and el84... and now, they've heard it with a 5881 and 6v6 paralleled).

I can't wait to get my hands on a greenback and toss her on in there!


FINALLY to end this wall of text, I finally fixed up the Reaper Pacer! Could never get the neck to straighten out, so before I went to buy a new one I decided to just see what would happen if I over tightened the truss rod; and somehow that fixed not only the twist, but the hump towards the end of the neck near the pocket. Who would have thunk it? :roll :roll

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I am the definition of tired

Check out my Soundcloud:
https://soundcloud.com/jarrod-beauchemin
Or Youtube channel:
https://www.youtube.com/user/javamony


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