Marshall JCM800 2203x Service - COLD BIAS & CROSSOVER DISTORTION!!
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- เผยแพร่เมื่อ 28 มิ.ย. 2024
- A 2004 2203x reissue has come in for a service, it's sounding pretty thin and has a nasty distortion which is quite evident when playing softly. This clip details the full procedure on the bench to identify and rectify, along with some time on the oscilloscope to discover what cold and warm bias settings do to your power section.
0:00 Play in - post service
1:06 Intro
3:25 Cold vs. warm bias. A/B tone test.
4:35 At the bench
15:33 On the scope
19:37 Outro
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Hell yeah I knew this would be good when I heard the intro song
Again...another valuable and well-explained lesson. Enlightening stuff mate cheers Jas.
I learn something new every video. I love it. Thank you so much for sharing. I have a 2013 2203x it’ll be needing a loop someday, so I’ll be grabbing that from ya bro. Cheers
Great explanation, and man you can really hear it! Thanks!
Thanks Jason, this Marshall information is very much appreciated and valuable
My pleasure!
Sublime tones as always Jason. 👌👍🤘🤘
Thanks!
Your videos are superb!!! Keep positing, you're a great teacher!
Thank you so much!
Great video mate
Thanks!
I don't think the cold bias example sounded terrible. just different. the way you set it up warm though was much more preferable to my ears. but you can hear that cross over distortion/choppy breakup decay on some classic rock records. so some people must like it. or they didnt have a good amp tech! and its funny now that the modelling has gotten so good that it can simulate that with digital bias settings.
really enjoy learning from this channel, thanks
Great vid as always. Would love for you to have a look at euge valovirta's 1984 2203 'bad boy' to find out why it sounds so freaking good.
Aaah, my man! playing Wild Flower! One of my fave ever songs
I have one, and yeah the bias comes coooooold.
Hey Jason, really interesting to see the effect of bias on a scope! Amp sounds fantastic when biased properly btw. I had that recently when an amp was cold biased and there was that cut off like you said. I also had a scenario where the amp was massively hot biased as well (in fact the SLO that I built). The sound of the amp was basically breaking down like there was way too much gain going through it, What is the effect of that on an tubes when that happens and how does that show up on the scope? I can imagine that the power tubes will be overworked and have a very short life! Lol! Watching your videos I am getting so tempted to build an 800! Haha! MCII first though - Nik should be sending me the chassis and transformers in the next week or two 😊🙏🏽🤟🏽 Have an amazing day dude!
The Best, ACDC riff's Excelent.
I might be going deaf at 54 but the cold bias wasn't bad at all.
The warm did seem fuller and warmer.
Don't put delay on the amp in demos.
I personally preferred the cold bias, sounded more gritty and "nasty" in a good way to my ears.
Wow, I'm surprised that it sounded not that bad with 23% dissipation! Generally, on my fixed bias amps, I like 70-75% dissipation.
Brilliant. But the cold bias didn't sound particularly bad, and that sound might fit into a heavy rhythm mix even better. The cold bias also sounded dynamically more even, whereas the hot bias introduced a certain "choking" effect that might fit the 80's style but not the 2000's style, so to speak. Then again, Mesa has defined Nu Metal as a genre, and it's fixed cold bias.
Agree! The cold bias becomes more noticeable when dialling back the guitar vol and playing quietly I find.
When my amp was biased too cold I thought it sounded good for some types of music, but thin. Like It was lacking something. It reminded a bit of a solid state amp. I like it in between.
Nice comparison! Cold bias looses midrange compared to hot bias.
Thank you for this video. My 2204 clone bias has been out of range too low since the initial power up. I’m going to try to find your 2204 video that you referenced here. I have a 47k resistor attached to the bias trim pot and only got max 28mv (through the resistor to ground on the tube). The metro amp instructions state to increase the resistor value to increase the bias range. I put in 56k and was at 0-8mv. I made a 32k resistor with a 27k + 5k and was then at 90mv. Hope the tubes weren’t damaged. Can’t wait to solve this, since this video tells me I have not heard the amps full potential yet. Thank you for the info!
Ps did you find anything with the preamp vol pot that was only coming on around 6-7?
Great vid. A lot of techs just use the scope when setting bias to eliminate the Xover notch and leave it at that without even checking what the plate current is. I’ve often wondered at what % of max plate dissipation is the xover notch eliminated in a 2203/4 .
I believe that varies.
It depends more on tube matching that amp itself. When You put not matched tubes, one will work at optimum bias and another will be pushed hotter too get good results.
Hi. Where have you connected the oscilloscope probe so that you can check the sine wave?
Thanks for your videos.
Greetings
He says at the speaker jack with an 8 ohm load. I imagine he's splitting the signal (can use a 1/4" mono 1-to-2). Then using a dummy load on 1 leg and the oscope probe in parallel on the other leg. Scope probe typically 1Meg impedance and won't add any additional load.
Key here is ALWAYS keep your amp under load. Never turn it on without one!
Hi again. How could a 1959 Marshall be turned a 2203?
Thanks
Great video Jason. Ive got a 05 Marshall tsl100 with the SIR #39 mod. Marshall claims the bias should be 90mv per side. Do you think that is too hot? The opinions are everywhere with people who own this amp. What would you recommend? Thanks man i enjoy the channel!
Do you know the plate voltage on that amp? That would be 90mA for 2 tubes...are they el34's?
@@HeadfirstAmps yes Jason. 4 el34s. I dont know my exact plate voltage, but from what I've read, it should be around 480 or so.
@@jamescarpenter4777 at 480 plate voltage and at 70% bias each tube should be around 36 mv.
Studio tour coming when?
Is that wild flower by the Cult at 3' 30'' ? I thought cold bias was around 50/55% :D
when you replace resistors or caps, do you prefer a certain brand or type? there seems to be much debate on type and tone in old marshalls
For coupling caps, the Mallory 150's are a good choice I find. Freely available and not stupidly expensive.
I have a 2203X made in about 2204 also. On mine I can only get the bias up to 31 mA per tube. Maybe soldering in another resistor in parallel with the stock one at R28 would help. A question: when the effects loop is not being used, is it out of the circuit? Or does it still have an effect on the sound of the amp? I never use mine.
Year 2204 - do you have a time machine 🙂
Hey Jason,in your rig with the amp going into the AxeFXIII,how are you monitoring it,thru your studio monitors or a guitar cab??….Just curious….
Hey Scott, mainly through the studio monitors but I so have a guitar cab in here too that I use from time to time. I should do that setup run down video shouldn't I!
@@HeadfirstAmps I am the same way…I run everything through my AxeFXIII,and I have gotten so used to the “polished “sound of my amp through monitors…..That said,it’s nice to dust off the 4x12 every now and then and push some air….Living in an apartment,I can’t do that as much as I would like….I have modeled my rig after yours ,with the amp/load box/AxeFXIII setup…..I was using the Power Station,but just got the Fractal X-Load….it sounds amazing….I was just curious how you monitored yours…
I have a 2203X made in 2002. It seems I can never get the tubes out of crossover distortion. As when the bias pot is maxed out and I can only get about 30 mA on the EL34. My question is: did Marshall do this on purpose? Did they want the tubes to run cold?
That's normally because your amp was built for 6550's or your matched set of EL34's are very low. Either way it's a simple job for a tech to get you into an adjustable range. 30mA by the way is not that cold, it's just a little under par.
Will the JEL mod work the same on the 2203X amp (ST1 board) as it does with the older 2203 amps? Thank you
Yes, the 2203x is pretty much identical to the older 2203s
Quick question. I have a schematic with voltage notes of the 2204, 2008, vertical input re-issue from "Mark Huss", and the voltages on there are waaay higher than the 'sweet spot' voltages you have on here. Why is that? Which voltages should I strive for if I'm to build a 2204 clone?
That scheme, based on that version of the 2203/2204's only has 1 x 10k dropping resistor between the screen and PI supply. You want 2 x 10k to get the voltages I prefer.
See my 2204 restoration clip for more details
@@HeadfirstAmps Thanks, I see now. The clone I was about to build has only one, suppose they sound better with the 2x 10K resistors between Screen and PI, thus lower voltages on pre-amp?
Exactly. Try it both ways and see which you prefer.
Hey Jason had a question having a biasing issue with 2203x I’ve went through 3 diff sets of power tubes I requested hotter from dealer that I could only get to 65% percent all the bias resistors seem correct 47k and two 220k for the El34s the only thing that’s off is plate voltage is 420v
The 15k resistor and bias pot itself are part of too, if either have drifted in value it will impact your adjustable range
R24 R25 and R28 the same at 35.7 but r29 is 47.1 should all these be equal or is this normal ? Thank you appreciate you getting back to me !
Mind you this amp is a 2023 model
All these were negative readings
Many of those won’t be able to be read accurately in circuit
What is the correct bias value for an JCM 800?
I like ~65% plate dissipation
Careful with DC riffs bro, can you say…. demonitized??? 🤣
They don't seem to care...must be because Phil Rudd is a now a Kiwi, so he gives me a free pass.