Tube Amps / Music Electronics
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|4/7/2000 9:21 PM|
||Difference JCM800 2203/pre JCM800 2203|
Are there many significant differences between a JCM800 2203 and a Pre JCM800? I have an '80 model 2203 that I would like to convert to PtP and I need an accurate schematic. The one in "The History of Marshall" is kind of hard to read, and the only other ones I can find that are legible are JCM800. Any input here is greatly appreciated.
|4/8/2000 9:25 AM|
The early JCM800 is exactly the same as the pre JCM800. There is a legible schematic in the Doyle book somewhere.
I'm not sure PtP actually makes much difference, but I know a few people who think it helps the tone.
|4/8/2000 11:33 AM|
I just redrew the schem from page 207(dated 1976) which matches up with the 77' MK2 100w Master Lead I just picked up. I found a couple of differences from the later 2203.
No 100pf across the first preamp tube.
500pf in the tone stack instead of the later 470p.
No 47pf across the driver tube
150K instead of 220k bias splitter resistors
1.5K grid stoppers on the el-34's
That's what I'm remembering--I can't say for sure that's what Marshall used. I haven't double checked it against my amp.
|4/9/2000 9:28 AM|
At the risk of stepping into the fire (ha,ha) I really don't think you'll hear a difference if you go to point to point verses the PCB that's in there now. (for what it's worth)
I've seen several JCM800's without this although the schematic shows it should be there.
This was very popular with the pre-80's 2203's. I've also seen 82K's here as well as 100K's.
I've seen some 80's and 81's where there were no grid stoppers at all but at the same time the plate voltage was around 385V.
That's all I can think of off the top of my head
|4/9/2000 1:43 PM|
I think the reason that many people feel that P-T-P boards sound better is because that the quality of parts on P-T-P boards are usually better. The resistors and caps on a P-T-P boards on an early Marshall are better than the lower quality parts used today. Also, when someone goes to the trouble of putting together a P-T-P board (like www.hoffmanamps.com for example), they are usually using better parts. I suspect that if those same higher quality resistors and caps were used on a PCB, there would be little or no difference in sound.
I do agree that it is much easier to tweak the sound of the amp by changing out parts on a P-T-P board.
|4/9/2000 4:01 PM|
This is true. It's a lot of work to pull out the PCB and wire up a PTP amp. It's fun, don't get me worng but most of the time the difference you hear in tone typically doesn't off set the amount of work that went into the project. (for what ever it's worth)
|4/12/2000 12:00 AM|
That's not true. Todays components have much tighter tolerences than what was used on the old PTP amps. Maybe you have it backwards, maybe people prefer the sound of PTP because of the bad quality of parts
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