Having trouble dialing in my JCM800...?

[JakeAC5253]

I have a 1980s JCM800 2203 with brand new tubes and new caps and whatnot, but I'm having difficulty dialing it in :| It seems like it's pretty easy to get a bad sound out of actually, which is surprising to me, and I wouldn't be surprised if it pointed to something else that was wrong, like maybe a bad speaker in the cab or something like that. The amp just doesn't get that greasy midrange smoothness to it that you expect from a Marshall. At low/med gain settings it sounds too clean to work for modern stuff even with a boost, but when you cross the line to higher gain settings, it either sounds way fizzy or depending on the volume settings, it can get a bit of a fuzzy digital distortion thing going on where the gain is kind of squared off. This square distortion thing I would normally attribute to being speaker distortion due to the nature of it, but this can happen at seemingly average volumes where one might not expect this 8{

I've tried a whole gamut of settings including plugging into the high and low inputs, widely varying treb/pres settings, a wide range of volume and gain balances. Problem is every tone is alright, but it's neither here nor there, it never sounds perfect. I have both a Mesa OS 4x12 w/V30s and a Splawn 4x12 with T75s, but lately I'm trying to dial it into the Mesa because I'm trying to record with it, but it's very easy to sound bad through this cab for some reason. I've tried a slew of OD/distortion pedals including Maxon OD808, Maxon OD820, GT-OD, RAT pedal, HM-2 Metal, SD-1.

Oh and another thing, people say they love these amps LOUD, but to me? It just doesn't sound good loud. Anything past 3 on the master through the high input just gets this nasty quality about it and you lose clarity and quickly get too muddy. The low input can handle a bit more volume on the master, but still it plays against the tendency for that dull fuzzy distortion that I want to avoid. It definitely isn't the case where the higher you go the better it is, and that's just not what I expect my experience with a vintage Marshall to be 8|

 

[Anonymous]

Might be time for a recap

Edit: Check the tubes first, obviously

Edit 2: ^ Idiotic post of the day ^

 

[Tone Monster]

Tl;dr

 

[snowdog]

I have a 1980s JCM800 2203 with brand new tubes and new caps and whatnot.....

Might be time for a recap Edit: Check the tubes first, obviously

Wow, amazing advice based on the thread title I guess...even reading the first line is too much work for one of our resident know-it-alls.

 

[Anonymous]

I have a 1980s JCM800 2203 with brand new tubes and new caps and whatnot.....

Might be time for a recap Edit: Check the tubes first, obviously

Wow, amazing advice based on the thread title I guess...even reading the first line is too much work for one of our resident know-it-alls.

lol...didnt even see it had to display it to read it!... have some of these guys on this site muted...it makes reading MUCH easier since i've done that. business is one of them.

 

[H3000]

Check the easy things first ....

try a marshall cab , the Boogie cab may well be the culprit or the splawn cab
the boogie cab will definitely not have the same bass or mid range as a Marshall 1960a and the splawn cab will not sound the exactly same as a marshall 1960a ,I was playing a splawn 4x12 loaded with G12 65 wih 2 JCM800 2203 just last weekend and directly compared it side by side to my own marshall cab loaded with G12 65 and the splawn cab sounded quite different to my marshall cab even though both cabs had the same speakers

other things to check...
I note your comment about new tubes but that certainly does not rule out the possibility that you have a bad tube so if you can find a preamp tube that is known to be working then try and tube swap all your preamp tubes one by one and you may even have more than one tube that is bad even though they are all new and a bad 9th gen in V1 can definitely cause fuzziness ..

next thing the low sensitivity input on the an old 2203 can cause all sorts of problems. if the low input has been unused for years it gets a build up of dirt and when a jack is inserted and removed the input contacts do not close properly and it will cause all sorts of weirdness so cleaning that might help.
what power tubes are you running ? are they biased correctly also check the grid load resistors are actually the right ones for the tubes you are running because if it was originally set up for 6550 and some genius just slapped in el34 without setting the amp up correctly for the the tube change or vice versa then that can sometimes sound a bit weird.

other things that might be causing problems you describe could be pickups or speakers or a combination of both or boosting the amp too hard.
High output ceramic pickups always sound muddy to my ears with a 2203 and so do tone zone in a LP
also V30 speakers can sound bassy and muddy and fizzy all at the same time with a 2203 and so can G12T75 so try another speaker type if possible.
also dirty or worn pots can be problematical and setting the preamp gain above 7 can sometimes introduce a muddy sound.

A 2203 will not have much gain even with a boost upfront and sometimes setting the boost pedal for as much gain as possible to compensate for the lack of gain will make a 2203 sound muddy or sound like the signal is going square similar to how a fuzz pedal can sound when maxed out. different 2203 will respond better than others to how hard the front end is boosted that is just the way they are , they are VERY inconsistent from one amp to the next

if none of those things work then it could also be possible that there is a component drifted out of spec or the amp has been tweaked or modded . check to see if the bright cap has been clipped or removed or if the value has been altered also the treble peaking circuit is a common place for diy modders to tinker with on a 2203 so it might be worth looking at that.
bear in mind that the problem you describe could be caused by just one of the things mentioned or a combination of these things or something else altogether.

 

[Anonymous]

I have a 1980s JCM800 2203 with brand new tubes and new caps and whatnot.....

Might be time for a recap Edit: Check the tubes first, obviously

Wow, amazing advice based on the thread title I guess...even reading the first line is too much work for one of our resident know-it-alls.

That's what happens with diagonal reading

You're still an ass BTW

 

[rcm78]

Try a cabinet with Greenbacks or Greenback style speakers. Where in Jersey are you? I have a 2X12 with Skumback M75's in it. If you're not too far you can demo it.

If you're sure the amp isnt right I'd suggest taking it to Jimmy Somma in Gladstone NJ...

 

[Racerxrated]

With new tubes and caps I'm sure the bias has been checked right? Sometimes if it's biased too hot or cold the amp can sound much different. And V30s with 800s can be harsh. 75s, unless they're really old like from the 80s just plain suck IMO. So a greenback type like G12 65s or as the previous poster mentioned, Scumbacks will probably give you a different take on your amp. Also 800s can be tube sensitive as well. A low gain 12ax7 in the pi spot, like an Amperex or nos Mullard and chinese 12ax7 Bs in the other 2 are the ticket for me. Winged Cs for power..

 

[jamme61]

I have a 1980s JCM800 2203 with brand new tubes and new caps and whatnot, but I'm having difficulty dialing it in :| It seems like it's pretty easy to get a bad sound out of actually, which is surprising to me, and I wouldn't be surprised if it pointed to something else that was wrong, like maybe a bad speaker in the cab or something like that. The amp just doesn't get that greasy midrange smoothness to it that you expect from a Marshall. At low/med gain settings it sounds too clean to work for modern stuff even with a boost, but when you cross the line to higher gain settings, it either sounds way fizzy or depending on the volume settings, it can get a bit of a fuzzy digital distortion thing going on where the gain is kind of squared off. This square distortion thing I would normally attribute to being speaker distortion due to the nature of it, but this can happen at seemingly average volumes where one might not expect this 8{

I've tried a whole gamut of settings including plugging into the high and low inputs, widely varying treb/pres settings, a wide range of volume and gain balances. Problem is every tone is alright, but it's neither here nor there, it never sounds perfect. I have both a Mesa OS 4x12 w/V30s and a Splawn 4x12 with T75s, but lately I'm trying to dial it into the Mesa because I'm trying to record with it, but it's very easy to sound bad through this cab for some reason. I've tried a slew of OD/distortion pedals including Maxon OD808, Maxon OD820, GT-OD, RAT pedal, HM-2 Metal, SD-1.

Oh and another thing, people say they love these amps LOUD, but to me? It just doesn't sound good loud. Anything past 3 on the master through the high input just gets this nasty quality about it and you lose clarity and quickly get too muddy. The low input can handle a bit more volume on the master, but still it plays against the tendency for that dull fuzzy distortion that I want to avoid. It definitely isn't the case where the higher you go the better it is, and that's just not what I expect my experience with a vintage Marshall to be 8|

sounds like someone may have cut out the bright cap? there should be a 4700pf across the gain pots two lugs (middle lug to outside lug) There should also be a 500k in parallel with a 470pf cap- running from the input jack to the gain pot. If you can pull the chassis out (warning high voltage can kill you- have a tech do this if not sure) and look at the gain pot to see if there where changes made. Hope this helps

 

[Kapo_Polenton]

treble peaking circuits might have been tweaked on the amp?

- Check the treble peaker mentioned above: 500k/470pf off the input jack. Sometimes people change the values here to tame the brightness and detail. I dropped the value of the resistor on mine. Some people drop it way too much and end up with 68k on it's own and that can darken the amp.

- Check bright cap.. what you have described doesn't sound like it though

- Check the middle pot. The combos had another 4700 pf cap here to tame the highs. Some people don't like this as it takes some of the bite away from the amp as well and darkens it.

Sounds like as the volume goes up and preamp goes up, you are ending up with a lack of detail. Usually these amps are brighter at lower volume and as you open them up, they smooth out. this is because all that treble serves it's purpose at higher volumes as the power tubes start to work and you get that sag. I personally don't like the stock JCM800's at low volumes. they have to be cranked. Yours was probably modded to sound better at lower volumes. Generally speaking, my preamp vol does not exceed 7 or 8. As the volume goes up, it can mush out in a hurry.

 

[EVHpickdust]

Try a cabinet with Greenbacks or Greenback style speakers. Where in Jersey are you? I have a 2X12 with Skumback M75's in it. If you're not too far you can demo it.

If you're sure the amp isnt right I'd suggest taking it to Jimmy Somma in Gladstone NJ...

^^^ This.

I've got a 1982 2203 and running it thru a 4x12 with Greenbacks or better yet Scumback M75s really tames the shit out of it.

 

[Schaf]

I have a 1980s JCM800 2203 with brand new tubes and new caps and whatnot, but I'm having difficulty dialing it in :| It seems like it's pretty easy to get a bad sound out of actually, which is surprising to me, and I wouldn't be surprised if it pointed to something else that was wrong, like maybe a bad speaker in the cab or something like that. The amp just doesn't get that greasy midrange smoothness to it that you expect from a Marshall. At low/med gain settings it sounds too clean to work for modern stuff even with a boost, but when you cross the line to higher gain settings, it either sounds way fizzy or depending on the volume settings, it can get a bit of a fuzzy digital distortion thing going on where the gain is kind of squared off. This square distortion thing I would normally attribute to being speaker distortion due to the nature of it, but this can happen at seemingly average volumes where one might not expect this 8{

I've tried a whole gamut of settings including plugging into the high and low inputs, widely varying treb/pres settings, a wide range of volume and gain balances. Problem is every tone is alright, but it's neither here nor there, it never sounds perfect. I have both a Mesa OS 4x12 w/V30s and a Splawn 4x12 with T75s, but lately I'm trying to dial it into the Mesa because I'm trying to record with it, but it's very easy to sound bad through this cab for some reason. I've tried a slew of OD/distortion pedals including Maxon OD808, Maxon OD820, GT-OD, RAT pedal, HM-2 Metal, SD-1.

Oh and another thing, people say they love these amps LOUD, but to me? It just doesn't sound good loud. Anything past 3 on the master through the high input just gets this nasty quality about it and you lose clarity and quickly get too muddy. The low input can handle a bit more volume on the master, but still it plays against the tendency for that dull fuzzy distortion that I want to avoid. It definitely isn't the case where the higher you go the better it is, and that's just not what I expect my experience with a vintage Marshall to be 8|

Most 800's with the gain up will rip your head off with the master on 3. Extremely loud. And, it should not lose any clarity that loud. As a matter of fact, the highs tend to smooth at higher volumes and the amp sounds warmer.

They are probably the easiest amp on earth to dial in. There's probably something wrong with it. Although I will say they are sensitive to speakers. I personally hate V30's with them. But I also love a good broken in quad of t75's with it too. Not a real popular speaker around hear.

 

[JakeAC5253]

Check the easy things first ....

try a marshall cab , the Boogie cab may well be the culprit or the splawn cab
the boogie cab will definitely not have the same bass or mid range as a Marshall 1960a and the splawn cab will not sound the exactly same as a marshall 1960a ,I was playing a splawn 4x12 loaded with G12 65 wih 2 JCM800 2203 just last weekend and directly compared it side by side to my own marshall cab loaded with G12 65 and the splawn cab sounded quite different to my marshall cab even though both cabs had the same speakers

other things to check...
I note your comment about new tubes but that certainly does not rule out the possibility that you have a bad tube so if you can find a preamp tube that is known to be working then try and tube swap all your preamp tubes one by one and you may even have more than one tube that is bad even though they are all new and a bad 9th gen in V1 can definitely cause fuzziness ..

next thing the low sensitivity input on the an old 2203 can cause all sorts of problems. if the low input has been unused for years it gets a build up of dirt and when a jack is inserted and removed the input contacts do not close properly and it will cause all sorts of weirdness so cleaning that might help.
what power tubes are you running ? are they biased correctly also check the grid load resistors are actually the right ones for the tubes you are running because if it was originally set up for 6550 and some genius just slapped in el34 without setting the amp up correctly for the the tube change or vice versa then that can sometimes sound a bit weird.

other things that might be causing problems you describe could be pickups or speakers or a combination of both or boosting the amp too hard.
High output ceramic pickups always sound muddy to my ears with a 2203 and so do tone zone in a LP
also V30 speakers can sound bassy and muddy and fizzy all at the same time with a 2203 and so can G12T75 so try another speaker type if possible.
also dirty or worn pots can be problematical and setting the preamp gain above 7 can sometimes introduce a muddy sound.

A 2203 will not have much gain even with a boost upfront and sometimes setting the boost pedal for as much gain as possible to compensate for the lack of gain will make a 2203 sound muddy or sound like the signal is going square similar to how a fuzz pedal can sound when maxed out. different 2203 will respond better than others to how hard the front end is boosted that is just the way they are , they are VERY inconsistent from one amp to the next

if none of those things work then it could also be possible that there is a component drifted out of spec or the amp has been tweaked or modded . check to see if the bright cap has been clipped or removed or if the value has been altered also the treble peaking circuit is a common place for diy modders to tinker with on a 2203 so it might be worth looking at that.
bear in mind that the problem you describe could be caused by just one of the things mentioned or a combination of these things or something else altogether.

Haha, it's funny you should mention "some genius" forgetting to mod the amp from 6550 to EL34s when that's exactly what happened. Said genius forgot to do that part of the work when he replaced the caps for me, so I did the rest of the job myself and changed the grid bleed resistors to 220k and the bias range resistor as well. The power section is now biased at about 33mA and I've got Winged C EL34s in there. Although that's not related to the problem now because that's already been fixed.

Yeah the input tube seems to be giving me some strangeness, I think the tube itself is fine, but it may have been modified as the amp did come to me modified but that's been reverted. On some ODs I have to be careful with how much volume boost I use because the input stage seems to react badly to too much volume. Going through the low input seems to negate this, so I think this particular micro-problem points to an issue with the input stage. I did check over the circuit quickly for some of the more common mods and it checked out at the time, but maybe I'll have to check it again and look closer.

Try a cabinet with Greenbacks or Greenback style speakers. Where in Jersey are you? I have a 2X12 with Skumback M75's in it. If you're not too far you can demo it.

If you're sure the amp isnt right I'd suggest taking it to Jimmy Somma in Gladstone NJ...

I'm located in Southampton near Medford. I'll have to look up that tech as I wasn't really happy with the guy I took it to last time, had to finish the work my damn self 8{

With new tubes and caps I'm sure the bias has been checked right? Sometimes if it's biased too hot or cold the amp can sound much different. And V30s with 800s can be harsh. 75s, unless they're really old like from the 80s just plain suck IMO. So a greenback type like G12 65s or as the previous poster mentioned, Scumbacks will probably give you a different take on your amp. Also 800s can be tube sensitive as well. A low gain 12ax7 in the pi spot, like an Amperex or nos Mullard and chinese 12ax7 Bs in the other 2 are the ticket for me. Winged Cs for power..

Yeah the power section has Winged C EL34s and it's sitting at about 33mA.

 

[lespaul6]

I suspect the previously modded portions of the amp to be the culprit... I was just playing mine on 4 (master volume) and it sounds great, punchy, clear, awesome. Something is wrong with your amp... what mods were done to it?

 

[JakeAC5253]

I suspect the previously modded portions of the amp to be the culprit... I was just playing mine on 4 (master volume) and it sounds great, punchy, clear, awesome. Something is wrong with your amp... what mods were done to it?

It came to me with KT88s in the power section and modded for a PPIMV. I had the power section biased for EL34s and the PPIMV removed supposedly. The guy screwed up the job of rebiasing the power section so who is to say he didn't screw up the job of the PPIMV to stock conversion too? Does that sound like it describes my issue if the PPIMV is still there?