Join me on a magical journey: Metro Plexi Superlead Build

[stephen sawall]

The no midrange thing is not my experience with that kind of amp ..... I have noticed the sound smooths out a lot when I get a amp that was recently built. But I believe they all had a burn-in before I ever saw them.

 

[novosibir]

It's not too much the still missing burn-in IMO, it's because he hasn't cranked over 11:00 yet.
Especially the High-Treble channel with that low Volume setting is ice-picky and must be set at least at 1:00 or 2:00 to sound 'right'!

Larry

 

[FourT6and2]

It's not too much the still missing burn-in IMO, it's because he hasn't cranked over 11:00 yet.
Especially the High-Treble channel with that low Volume setting is ice-picky and must be set at least at 1:00 or 2:00 to sound 'right'!

Larry

That's what I thought. I'll crank it soon!

For what it's worth, the tone I'm after is Adam Jones' sound on the album "Undertow." I know what mods he has in his amp. And I know his EQ settings and speaker-type (yeah, I'm a little obsessed...

Presence: 11:00
Bass: off
Mids: maxed
Treble: 9:30
Bright Channel Volume: 10:30
Normal Channel Volume: 1:00-2:00
Channels jumped with a cable into Marshall 4x12 with Greenbacks

Superbass modified to lead spec. with 0.68 V1a/V2a cathode caps, 0.022 plate bypass caps, phase inverter coupling caps are .022, 100k NFB on the 4ohm tap.

That seems to get a really raunchy, aggressive and mid-heavy sound with plenty of gain. It could also be my speaker cab. I have a mesa 2x12 with V30's. Not the best choice for this type of amp.

 

[FourT6and2]

I found the missing mids!

Caps came in today. Threw the 0.68 cathode cap in V2a and replaced the 0.1 presence cap with another 0.68. Sounds good, now! Still a lot of treble on Channel II, but the V2a cathode cap added a good bit of mids to even it out. Haven't removed the bright cap, yet. But I'll try that and see how it goes. After that, it's PPIMV.

 

[FourT6and2]

Anybody know anything about the Lar/Mar PPIMV? I installed one but I'm getting a loud hum when I flick the standby. Installed it, checked my wiring a few times, went to bias the amp and BAM, crazy noise.

Here's some pics of the install, if anyone wants to check my wiring. No clue what the cause of the noise/oscillation is. Sounds like a low-frequency howl.

 

[johnnyjellybean]

So, I have a few issues:




3. I got a 100k metal oxide resistor to replace the 47k in the feedback section of the board (along with placing the negative feedback wire on the 4ohm tap). This will bring the amp closer to mid-late 70's JMP. The only thing is, after I installed on the board and was checking continuity, I noticed the resistor is measuring 4.5k and NOT the 100k it's supposed to be. The color code is: brown, black, yellow, red. This is what a 100k (2%) value should be.

I don't understand why you would raise the value of the nfb resistor to get less nfb and then put it on the 4 ohm tap which will give you more nfb. You'd be better off leaving the 47K and pulling the nfb off the 16ohm tap .

 

[novosibir]

I don't understand why you would raise the value of the nfb resistor to get less nfb and then put it on the 4 ohm tap which will give you more nfb. You'd be better off leaving the 47K and pulling the nfb off the 16ohm tap .

Back to school and some more lessons in physics!

At the 4 ohms tap there's half the voltage than at the 16 ohms tap - what lessens the nfb

Larry

 

[novosibir]

Obviously nobody has an idea?
On the photos all's looking ok, but there must be a bug, because all LarMar PPIMV's are working fine, when done properly.

So go and start troubleshooting!

Have you verified with Power on, but the amp still at Standby, whether you have negative bias voltage on every lug of the PPIMV pot? Is there also negative bias voltage on all pin 5' of the output tubes?

Another test: Switch the amp off and measure between the shields and the conductors of the shielded cables of the PPIMV, whether there's continuity! Sometimes it happens by soldering too hot and/or too long, that the hot shield insinde the outer insulating is melting the inner conductor's insulation - and then the conductor is shorted to the shield. Maybe this has happened to you?

Larry

 

[FourT6and2]

Thanks, Larry. Will check and report back.

I don't understand why you would raise the value of the nfb resistor to get less nfb and then put it on the 4 ohm tap which will give you more nfb. You'd be better off leaving the 47K and pulling the nfb off the 16ohm tap .

Other than the fact that's how late 70's JMP's were wired (and that's the sound I'm trying to recreate), read what Larry said...

 

[FourT6and2]

Typical disclaimer: I suck, yadda yadda, webcam shit quality, etc...

Sounds a little fizzy here since the PPIMV is at 9:00. after about noon it opens up and sounds great. But it clips my webcam, so I have to record at a lower volume.

LP into DD-3 into BF-2 into amp. Channels jumped.

 

[LP Freak]

Sounds great. Isn't it cool to have a pile of parts show up and a week later you're making music with it?

 

[FourT6and2]

Sounds great. Isn't it cool to have a pile of parts show up and a week later you're making music with it?

Absolutely!

 

[stephen sawall]

That is very cool.

 

[peterc52]

Because of you I am seriously considering ordering a kit from Metrokit! :-D

Btw. what camera are you using, the pictures are great?

 

[FourT6and2]

Because of you I am seriously considering ordering a kit from Metrokit! :-D

Btw. what camera are you using, the pictures are great?

Go for it! Metro is a great resource.

I shoot with a Nikon D700. But I'm a decent photographer, so that helps. Tone is in the fingers!

 

[glassjaw7]

Awesome pics!!! That your fam?

 

[FourT6and2]

Awesome pics!!! That your fam?

no....

 

[Mr. Willy]

Sounds killer! No fizz that I could hear. Great job man!

 

[FourT6and2]

Oh shit, this thing sounds so goooood! Cranked through a Bogner 4x12 with Greenbacks. I never thought a guitar could sound so amazing. Every time I play it, it gets better. The caps are starting to slowly break in and everyone who's heard it in person says it's like a Marshall Plexi mixed with a later JMP... but just... more aggressive and mare balls. There's no fizz. There's no piercing/harsh high-end. It's all mids and a good amount of low-end. But the amp isn't overbearing in any one area. It's just mean. The master is fairly useful. At lower volumes (like TV volumes) it gets a little fizzy. But as you open it up, the amp breaths fire. I can't imagine needing more gain than this thing has.

Still haven't played a real Plexi or JMP. But if they sound like this, I don't understand why people get them modded. With the channels jumped and the volumes at about 10-11:00 the amp has that AC/DC, classic rock sound. With the bright volume at 2-3:00 and the normal volume at noon, the amp is great for 90's metal. Maybe the over-sized Mercury Magnetics transformers are part of it? I don't know. All I do know, however, is this amp is close to perfect.

Compared to my Diezel, it's pretty close to channel 2 on the VH4 with the mids and gain maxed. Only way less compression and fizz.

Picking up a Bogner 4x12 by the end of the week.

 

[stephen sawall]

For me the these style amps are a perfect fit. It was the stuff that I grew up playing and what I always end up going back too ....Killer to hear you are liking the results.