1987x - old one vs. new series vs. metro board

philip · Post by **philip** » Tue Nov 13, 2007 7:29 pm

ok, I have a problem. (what else is new)

so I have this '91 1987x that sounded like shit when I got it. Replaced the filter caps and installed a metro board. It sounds nice now, but not great. In a rehearsal situation i.e. almost dimed I find it to have too much of the high mids. And I do miss one thing that I really really loved about a brand spanking new 1987x (the one with the fx loop):
it was soooo easy to get nice musical feedback from it! You could really ride a note forever....
My amp just won't do that.

Now I wonder why? Are the new reissues different in any way from the older ones? Does the metro board have something to do with that?
(it's not the tubes; I tried 2 different sets of preamp tubes incl. NOS Brimar, and 3 sets of power tubes. It's not the cab or guitar either)

Has anyone else experienced this?

Please, I'm real desperate here : P So desperate that I shot one new 1987x on ebay (for rather cheap) to test side by side with mine and keep the one I like best. Crazy? Yeah, well... *shrug*

NY Chief · Post by **NY Chief** » Wed Nov 14, 2007 3:36 pm

Did you change out the stock OT?

as5431 · Post by **as5431** » Wed Nov 14, 2007 3:42 pm

do the bright cap values differ?

philip · Post by **philip** » Wed Nov 14, 2007 4:30 pm

no I did not change the OT... I bought it used, so I don't know for sure if it's the stock trannie... but it looks like it.

Would the OT have such a big effect on the feedback?

bright cap: it's a 500pF... but I tried it without one as well.

philip · Post by **philip** » Wed Nov 14, 2007 4:34 pm

regarding the bright cap: if I understood it's purpose right, it allows higher frequencies to bypass the Vol pot. So: the higher my Vol setting, the less the effect of the bright cap, right?

as5431 · Post by **as5431** » Wed Nov 14, 2007 5:58 pm

the 1987x stock value is 4700pf.

when you mention "musical feedback", are you also referring to easy to obtain feedback? like on demand whenever you want it? if so, try a 4700pf bright cap. that's what brought back my screamin' feedback.

philip · Post by **philip** » Wed Nov 14, 2007 6:07 pm

as5431 wrote:when you mention "musical feedback", are you also referring to easy to obtain feedback? like on demand whenever you want it?

yes, exactly!

I'll check my bright cap. Chances are I mixed up some values. I was pretty sure it was the stock value....

[edit] I just checked the attached schematic and it says it was a 500pF...

as5431 · Post by **as5431** » Wed Nov 14, 2007 9:41 pm

that's a '70 schematic.
the bright cap values increased chronologically.
1987x(x being reissue) is 4700pf.
try to find a '72 schematic.
or, better yet, a 1987x schematic.

Post by **Scumback Speakers** » Wed Nov 14, 2007 9:58 pm

What speakers are you using with it?

philip · Post by **philip** » Thu Nov 15, 2007 4:30 am

Southbay Ampworks wrote:What speakers are you using with it?

I'm using a slant cab of a Hendrix Jtm 45/100 stack and whatever speakers are in there.... G12M Heritage I believe?

But I played the new 1987x *with* the nice feedback through the exact same cab. That's why I ruled out the cab as a factor.

as5431: oh, that's news to me. Thanks! I'll try to find one.

toner · Post by **toner** » Thu Nov 15, 2007 5:16 pm

Here's a 1987x schematic from 1994. It shows a 4n7 (4700pF) bright cap.

http://www.drtube.com/schematics/marsha ... 0-02-1.gif

philip · Post by **philip** » Sat Nov 17, 2007 6:10 am

ok, my new 1987x arrived and I like it better than my metro'ed '91...
(even if that's flame bait... oh dear...)

it *does* have the feedback on tap, all the shimmering highs you'd want and overall just feels much more alive. (with the same tubes I had in my '91 before)

I wouldn't have thought this possible. Really.

Also I don't think it's the metro board, so it must be the Trannies, right?
Does anyone know if they changed them in any way between 1991 and 2007?

I'm kind of tempted to swap boards for a check, but honestly I shy away from the work involved.

Now what do I do... I kind of bonded with my old one, with all the work and tweaking I put into it. And I tried to like it more; it looks so much cooler inside =)

Any thoughts?

PS: on the chassis there's these little stickers, right? And on my new one it says "Tested by Philip" ...maybe that's an omen?

neikeel · Post by **neikeel** » Mon Nov 19, 2007 8:47 am

I think that if you cross check your two set ups first. What spec. Metro board did you end up with, plexi or metal panel, lead or bass spec.

The trannies on the 87X is not supposed to be that bad (I have a spare lying around from 99 which is pretty average!).

If all the component values and tubes are the same with the negative feedback wired the same then one must implicate the trannies. Have you measured the B+ and checked the bias is in the same ballpark?

Sorry to ask basic questions which you have probably excluded long ago but I am intrigued why two similar amps sound very different.

Any way, looking on the bright side you will end up with a nice two amp set up, one dry and one 'wet' with your effects loop

philip · Post by **philip** » Mon Nov 19, 2007 9:42 am

hey Neil, came to earn your fourth pint, have ya? =)

I haven't got around to compare all components yet, but I plan to mod the metro'ed plexi duplicating the reissue's setup.
If it comes alive then, including the feedback, then I may sell the new one.
Else it has to go...

Right now I have a EH holy grail in the FX loop which is nice for cleaner SRV type Strat tones. And being able to bypass the loop completely for gainier and Les Paul tones is really great.

The weird thing is that since I have the metro board in there, I tried a 47k and a 100k NFB resistor, NFB to 8 and 4 Ohm tap, .022 and .0022

NY Chief · Post by **NY Chief** » Mon Nov 19, 2007 11:00 am

Hey, fil. That a Rory Strat I see in the pic?

Metropoulos Forum

1987x - old one vs. new series vs. metro board

1987x - old one vs. new series vs. metro board

are my ears broken???