JCM 800 mod ideas......

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jcmtone1

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Looking to try some new ideas to a JCM 800 circuit in the pre amp section. Any suggestions? At the moment I added a fourth pre amp tube for extra gain.
 
Boost the preamp voltage. Nope Harry Kolbe did that in the 80`s. None of this nonsense is new get it?Play your guitar
 
It doesn't have to be a new idea.....I am just looking for other stuff to do to the amp. I play my guitar, but I like messing around with amps. That is the reason why I bought an amp to just mod and play around with and learn.
 
change the very first coupling cap to a .05 ,it has had some positive results in SOME marshalls i've done,will add to your tone even boost alittle more gain,some though,didnt sound so good with it ,but it's worth a try
 
What do you hope to gain from modding it? If you cant answer this question directly and confidently, then dont bother.
 
First thing I am looking to gain is more knowledge on amps. In terms of tone, looking to remove some bass but not make the tone sound brittle. I have been playing around with the amp for a while. Its just a hobby outside of work. I bought the amp to just play around with. It would be helpful to understand the way the components work with regard to changing the tone.
 
jcmtone1":kr9l6yp3 said:
First thing I am looking to gain is more knowledge on amps. In terms of tone, looking to remove some bass but not make the tone sound brittle. I have been playing around with the amp for a while. Its just a hobby outside of work. I bought the amp to just play around with. It would be helpful to understand the way the components work with regard to changing the tone.
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you're fighting an uphill battle, shotgunning a circuit to get a result is not proper technique.

i suggest you do some research on books and learn to read schematics.

shotgunning to get a result will lead you nowhere and could potentially cause more issues in which you would need to resolve - some even in lead dress - like RF suseptibility and circuit oscillations in frequencies in the Mhz causing pre-mature damage to the powertubes or sacrificing headroom.

i have a ton of answers for you, but you are asking a million dollar question. and is partially the reason why amplifiers cost what they do ;)
 
I know for a fact Mark Cameron is the so-called shot gunning King. Do what you want with the amp. Not much to any amp if you know electronics.
 
Start with opamp or transistor based overdrive pedals. The principles and tone shaping are exactly the same and if you screw it up its a $100 investment. The lesson learned will be worth far more than the risk of loss. :yes:

Learn buffers, RC filters, gain, biasing, power filtering, and tone shaping, and then move onto amps and learn tubes and transformers.
 
Pickup":15080fow said:
I know for a fact Mark Cameron is the so-called shot gunning King. Do what you want with the amp. Not much to any amp if you know electronics.
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exactly! all the great innovators shoot from the hip :rock: :thumbsup: :rock:
 
Is it stock at the moment?
If so, try bypassing the 10k on the V1B with a cap. Maybe like a .22uf. That will boost frequencies starting at around 72 hz. You can also bypass the V2A (the 820ohm resistor) with like a .68uf or something. That boosts the mids and highs. Outside of that you can do a ton of other things. You can remove the Cathode Follower and convert it to a gain stage. All depends on how much work you want to do and how much gain you want from the amp.
 
Vrad":1nlnojo2 said:
Is it stock at the moment?
If so, try bypassing the 10k on the V1B with a cap. Maybe like a .22uf. That will boost frequencies starting at around 72 hz. You can also bypass the V2A (the 820ohm resistor) with like a .68uf or something. That boosts the mids and highs. Outside of that you can do a ton of other things. You can remove the Cathode Follower and convert it to a gain stage. All depends on how much work you want to do and how much gain you want from the amp.
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your avatar is genius bro :m17:
 
kirk":q02ipvbz said:
Vrad":q02ipvbz said:
Is it stock at the moment?
If so, try bypassing the 10k on the V1B with a cap. Maybe like a .22uf. That will boost frequencies starting at around 72 hz. You can also bypass the V2A (the 820ohm resistor) with like a .68uf or something. That boosts the mids and highs. Outside of that you can do a ton of other things. You can remove the Cathode Follower and convert it to a gain stage. All depends on how much work you want to do and how much gain you want from the amp.
Click to expand...
your avatar is genius bro :m17:
Click to expand...

Thank you kind sir...
 
I once changed out the midrange pot in a JMP 2204 I had (similar to a the JCM? ). I either changed a 25k pot to a 250k, or the other way around. I can't remember now. An easy mod, and very easy to un-do if you don't like it. I got the idea from the Torres Engineering tube amp book (Inside Tube Amps, I think), so it's not like I was going crazy trying random things. That book actually has quite a few interesting ideas for the marshall master volume circuit.

$.02
 
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