2205 2210 Mods Thread!

[RickyLee]

Does anyone want to get this thread going? Or should I say, does anyone have any info to share on mods they have done to their Split-Channel amps?

Early versions or later versions and all in between.

I have a question on something that is also common with the Jubilee amps. Has anyone bypassed/removed and put a jumper in place of the .047uF cap directly after the front input jack? And what is the purpose of this cap in the first place? Is this cap there to attenuate some low end/bass frequencies to make the first gain stage a bit tighter/less farty bass?

I know that adding a bypass cap on the last gain stage of the later versions is a good thing. I did not go that drastic though, as I only used a 6.8uF there.

 

[BDozer]

I'm interested in reading those!
You RickyLee are the master of 2210, I'm always following your experiences
The only thing I did in my 2205 was resolder the C1 leg that the original owner had snipped.

 

[NewReligion]

Ricky, in my quest to learn and better understand the operation of the preamp functions of the 2203/2204 I have came across some interesting Mods for the 2205/2210's from verious resources that I have not tried on my Split Channels "yet". Most are from Vintage Amp Forum. My 2203 is now sounding the way I have only imagined a Tube Amp could sound due to help from this forum, and about 40 hours of reading so far and 20 hours of practical.

That being said I am willing to PM the information on the 2205/2210 to you but would rather not publish them because I can not validate the results. Perhaps in time but I dig those amps stock.

Just let me know.

David

 

[RickyLee]

Thanks for that David. I would appreciate if you can P.M. the info.

I am going to tinker with my 2205 some more today. I did put an additional master volume pot on the back in the vacant hole of the D.I. circuit that I had removed. I can not say that this additonal master volume pot is effective from a tonal aspect, but it does work none the less. It is just a normal 1MEG pot as a voltage divider circuit - same type of master volume found on a 2203/2204, except it is after/downstream from the very last gain stage V4A and the C25 coupling cap of course. To anyone attempting this type of circuit mod: You have to have a basic understanding of the gain stage(s) topology and their associated components. I would not advise using an audio potentiometer on any high voltage leg or branch circuit. I had to install an additional coupling cap after V4A plate pin1 (used a .1uF 630V), then put this new master volume pot then it continues on to the coupling cap C25 and on to the phase inverter.

I am going to try changing out my phase inverter to power tube coupling caps C32 & C34 to a higher value .047uF today. I actually temp'ed additional .022uF's in parallel last night to C32 & C34 and liked the effect. Gave it just a touch more bottom end which helped for the low volume playing. The biggest impact so far was adding the resonance control though.

I still would like to try the PPIMV as well.

Can not decide which type to try. Maybe we will hear from someone on this thread on that?

 

[RickyLee]

I'm interested in reading those!
You RickyLee are the master of 2210, I'm always following your experiences
The only thing I did in my 2205 was resolder the C1 leg that the original owner had snipped.

This is the info I am looking for. Is your 2205 a later version?

So I am figuring that you like having that .047uF in series with the input jack and the V1A pin2/grid?

When you say you re-soldered the cap leg, was there a jumper wire in place of the cap before that?

And what was the effect without the cap in the circuit?

The Jubilee's have this same .047uF cap between the front input jack and the first gain stage as well.

 

[RickyLee]

I am also wondering if anyone has tried running both the Clean and Boost channel TOGETHER - as in jumpering the channels?

I tried this on my '83 4210 a long time ago. But the early version amps two channels are out of phase with each other. Should work on the later versions as they have the same number of gain stages. Or am I missing something that still makes them out of phase with each other? Like the diode clipping circuit?

I am pulling the amp back out right now. I am going to also try to solve this slight channel bleed I have.

 

[BDozer]

This is the info I am looking for. Is your 2205 a later version?

So I am figuring that you like having that .047uF in series with the input jack and the V1A pin2/grid?

When you say you re-soldered the cap leg, was there a jumper wire in place of the cap before that?

And what was the effect without the cap in the circuit?

The Jubilee's have this same .047uF cap between the front input jack and the first gain stage as well.

Yes, it's a later version. It's a late 1986 amp, and I' ve tried the preamp tube removal test.
Oh my mistake above - that wasn' t C1, it was the D1 that was snipped.
Here it is:

I think the previous owner was trying to get rid of the SS boost - and I don't even know if he was trying the right way. What I've found after I've resoldered that is the amp now is as loud as expected, tighter and with a lot of gain on tap. I think everything else might be stock.

 

[RickyLee]

Well I found a cure for half of the Channel Bleed solution. I was able to cure my '88 2205's Clean channel from bleeding into the Boost channel by increasing the capacitance of C40. The stock value is .22uF and I just grabbed what was close on hand - a 100uF - and it took all the bleed away.

But I can not cure the bleed of the Boost channel bleeding into the Clean channel. I tacked another 100uF onto the bottom of the PCB of C12 which is .22uF also, and it did nothing for the bleed. I even have two more caps on the bottom of my PCB that I just clipped this extra cap onto as well and it did nothing. I am quite sure it should be C12 that controls this - taking the Boost channel signal into the IC chip.




Anyone else have any ideas??

 

[RickyLee]

OK. I forgot to mention that C40 is on the bottom of the PCB on my amp. And those other two caps I have underneath would be C41 & C42 after a little investigating.

I am going to try and just replace C12 altogether. Could it be that this needs to be a polarized cap to be effective? I have the small white lego block style cap for C12, and I am figuring those are not polarized.

 

[RickyLee]

Has anyone tried lowering the value of their tone stack slope resistor on the Boost channel yet? I lowered mine to 43K , then I tried 33K as well and could not hear a difference - maybe just slightly.

Maybe I did not have the amp up loud enough to notice it?



And I replaced C12 with a 100uF cap and it made no change in the Boost channel bleeding into the Clean channel.

 

[RickyLee]

Another thing of interest maybe to some. Anyone know why Marshall split the reverb tube assignment up between two different tubes - V3B & V4B - to run the reverb circuit on these amps (later versions)? Is it better than just using one tube and it's two triodes for the reverb drive and recovery? This is for the later version Split Channels. The earlier versions used the same tube - V4 - for the reverb drive and recovery.

 

[pluto]

Hi BDozer, RickyLee, and all users,

I have very similar amp (but 4210 combo version), I posted some questions here:

http://www.marshallforum.com/workbench/26140-jcm800-4210-1986-remove-all-mods.html

I can see that all your clean channel pot covers are connected with wire which goes to "Bk" (which is ground) on the PCB.
My amp does not have this, and my pot covers are not connected to Bk (I checked with multimeter),
but I think it does not matter, because they are grounded through chasis anyway
(only the outer gain pot cover must be separately grounded, and it is).

Futhermore I can see BDozer has this awkward connection between the "D5" and "Link" with resistor and cap... my amp has the same, so it seems this might be factory.

Maybe you have some more high-res photos of your PCB, if yes, I would be very interested, it would help me to revive my amp to original.

Do you possibly have some photos of the bottom (the other side) of the PCB ?
I have some connections there, which I think are mods, in particular the C40, which RickyLee have mentioned in one of the previous posts. The PCB of BDozer has the C38 instead, which in my amp was removed (see my thread with the link above).

Yes, it's a later version. It's a late 1986 amp, and I' ve tried the preamp tube removal test.
Oh my mistake above - that wasn' t C1, it was the D1 that was snipped.
Here it is:

I think the previous owner was trying to get rid of the SS boost - and I don't even know if he was trying the right way. What I've found after I've resoldered that is the amp now is as loud as expected, tighter and with a lot of gain on tap. I think everything else might be stock.

 

[cruisemates]

Hi...

I am VERY interested in MODs for the 2205. I have not done any yet. I have a later version with the IC switching. I do get channel bleed but it is not noticable unless you go looking for it.
If you set the amp up with the master volume higher so the channel volumes are lower they do not bleed as much.

I have found using different tubes changes a LOT on this amp. I do have NOS Mullards in V1 and V3. The one in V1 changed a lot. I just happened to have two NOS tubes and decided to go with V3 since the gain channel is the one I am really trying to optimize. You only need the one in V1, really.

I would like to be able to change the tone stacks somehow. I just think that if I could find a higher frequency for the mid control I would be much better off. My highs are harsh on this amp, even with very smooth speakers (G12-65). I would like to be able to tame that high harshnes down, but it isn't in either the mid or the high control - its somewhere in between.

My amp has the resistor mod to accommodate EL34 biasing. I found the GrooveTube EL34M to be a nice tube for these amps if you want gain. You can specify how gainy you want them with a number system GrooveTube uses. I have a set of 2s (very gainy) and a set of 6s - much smoother. I am using the 2s.

Nothing has been done to my diode clipping. That is contained in a little black bridge rectifier that says W005F on it. On the scematic is shows 4 diodes, but that isn't what is there in reality.

I will be watching this thread - looking for people who have done magical things to these amps.

 

[RickyLee]

Figured I should revive this old thread. I had put some info on the conservative mods thread. But then, this hacking I did on my '88 2205's PCB yesterday was anything but conservative LOL.

So yesterday I did some more experimenting on my 2205. I put a 10uF bypass cap on V2A and a 330uF on V2B. My Normal channel now sounds more Fenderish than ever. I am digging it. No huge added hum either, so that is cool. But remember, I am running an Electro Harmonix 12AY7 in V2 as well.

As for the Boost channel, I did quite a few experiments. I removed the clamping/cathode bypass diode on V1B. I tried a few different capacitors in its place and settled on .68uF. I then removed the huge 22uF bypass cap on V3A and added a huge 100uF bypass cap on V4A. All this changed the character of the Boost channel and removing that diode on V1B is the main player in that change. BUT .... be forewarned that this change takes away the Split Channel edge and bite that we all know and love. That diode not only gives a massive frequency boost, but it has a very interesting biasing characteristic to the the tube/gain stage that I can't explain. Maybe Mickey or Damien would like to explain that one as they put it in laymans terms so well for all of us to grasp.

The low end on my 2205 is still a bit abrasive and distorted. But a bit less flabby and overbearing. The overall feel of the amp seems percussive and chewy, a slight sponginess in a good way I guess is a good way to describe it. It also seems more colorful, as in the upper mids and highs are a bit more clear.

But then, the last time I got excited about my 4210 having a much more defined distortion voicing, I came back the next day to play it and was not happy - I then undid most of the mods LOL.

We will see on this one. At least I still have my other all stock '88 2205 to compare to this modified '88 2205. I had planned on taking my 2555 to the gig this weekend as I dialed it in for a sweet Blues/Country/Classic Rock tone. But now I might just take the modified 2205 along to compare . . . .

 

[ricksteruk]

I hope the new mods work out! Glad you've revived this thread. I think I am going to be in the mood for tinkering with my amp till I'm happy with it.

I'm wondering about the "factory mod" with the resistor piggybacked on the cap going from D5 to BK.. Does yours have this one Ricky? Or did they fix this on later PCBs? My 84 does not have this. What does it do? Should I install it?

 

[RickyLee]

OK. I am getting frustrated and and really think I need to quit making changes on this 2205. I am starting to wonder if there is something going on inside my brain, and Musical Soul for that matter, that has me hearing something 180 degrees off within a matter of a few days.



Take all those preamp changes I made a few days ago with a grain of salt. I just plugged into the amp and did not like anything I heard. Of course, those settings I had are all changed around as I just could not dial out the loose and distorted/fizz in the bottom end. I was disgusted with the amp. And the stock 2205 did not do anything for me either. So I grabbed the 2555 and I heard only a slightly better tone. So part of it is the room I was just playing in. I tweaked the 2205 a few days ago in a different part of my house. And maybe being tired and burned out after work today is contributing, as I also just thought my guitar playing was a POS.

But anyway, I am hearing a texture in the low mids/lows that I am just not digging. And the part of this that bugs me possibly the most is that I used to love the tone of this amp . . . .

 

[RickyLee]

I did forget to mention that the Normal channel actually sounds awesome. A big improvement there for sure.

 

[RickyLee]

I hope the new mods work out! Glad you've revived this thread. I think I am going to be in the mood for tinkering with my amp till I'm happy with it.

I'm wondering about the "factory mod" with the resistor piggybacked on the cap going from D5 to BK.. Does yours have this one Ricky? Or did they fix this on later PCBs? My 84 does not have this. What does it do? Should I install it?

I am not familiar with this. Where did you hear about this one? I am looking at the schem and I am confused on this one. I see a D5 in the switching circuit, but no cap across it. C10 and C45 are connected at one end though.

 

[RickyLee]

I was thinking that part of my problem is my extremely hot bridge humbucker. My pickup does have a good amount of lows as well. The amp still sounds awesome for playing lead. But I just can't get that defined crunchy rhythm out of it. Single coils would probably jive with it.

 

[Mosher Zone]

Is there an FX loop mod for the 2205/2210 to put it before the master volume?