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#1
Troubleshooting Problems / Re: Loud pop/click when changi...
Last post by RobinL - Today at 06:42:36 AM
Yeah, i agree with the tube stage, but i am not sure if the board is to blame... on monday, the holidays here started, schools are closed for the next 6 weeks and my two kids and wife constantly draw me away from caring about my poor mp-1    :dunno:

So I´ll inch my way forward trying to circle the problem. I started scoping the signal through the tube path. It enters healthy at the grid of v1, still healthy at grid 7 of v1, but on v2, pin 2, the sine wave is really blurry. The Dist voicing is fine at this point, but of course the distorted sine wave is much stronger, so i might not see it. So maybe section H, OD2 is the bad guy.

Stay tuned on what i can report next time, after some more minutes in the workshop. Of course the mp-1 decided to misbehave once it gets busy at home  :lol:
#2
MP-2 / Mullard Long Pates vs origiona...
Last post by rnolan - Today at 03:48:05 AM
I'm posting this here as it is MP-2 specific (as opposed to tube talk in general), and there are a bunch of posts about it in the Tube threads.  But this wasn't a subtle difference, it was a big difference.

So I changed out the original tubes (Chinese ADA) from my NOS (well it's now getting used allot more) MP-2 the other night.
Some history, I started using the Mullard LPs years ago and fell in love with them (in my MP-2) any long time members will maybe remember the journey?.
I'd been enjoying this NOS MP-2 (which is now my live preamp), but the top end was quite brittle (and way more presence(y) frequencies), allot of edginess (2-6khz). Initially I thought it may be the brand new Lorantz speakers (happy to report that it isn't BTW).
So obviously this is extremely subjective, but the Mullard LPs just sounded so beautiful, all the harsh edges were gone, smooth distortion, warm, 3D, balanced freq response (low, mid, Hi)

12AX7s all sound different.  The new sensor Mullard LPs are the best I've used in a MP-2 by a country mile.

I started using the Mullard LPs a long time ago after trying Boogie SPAX7s (most likely JJs rebadged) as my first ever swap. And I'd forgotten how "big" a difference they make.
#3
MP-2 / Re: MP-2 S/N 501251 from eBay ...
Last post by rnolan - Today at 02:49:33 AM
Hey Gregg, no worries, PMs and emails sent to connect you and I also included MJMP.  Also I'll try to bing Laurence (my friend) up to some understanding of the "why" (what's it all about Alfie), he's not a muso but he likes assembler.
#4
Troubleshooting Problems / Re: Loud pop/click when changi...
Last post by rnolan - Today at 02:35:24 AM
Hey Robin, the hum shouldn't be there, sure, high gain brings some noise as does old age of caps etc., but the MDRT should reduce noise albeit it opens up the dynamic range of the MP-1. So my take is something isn't quite right in the tube stage (so not  Maybe it´s just the nature of the beast? ) .

The pop is another question, it also shouldn't happen.  Maybe the 2 issues are related? but I don't think so.

So do you always get a pop when switching? As I said previously, I get it with my MP-2 but only in particular circumstances (i.e. going from distortion patch to fairly heavily compressed/chorused clean patch too quickly).

Anyway, hang in there, MJMP will help get you sorted :thumb-up: .  Maybe it's time for a new tube board??
#5
Troubleshooting Problems / Re: Loud pop/click when changi...
Last post by RobinL - July 17, 2024, 11:21:49 PM
No. The hum is in the tube voicings only. Solidstate is fine.


What i tested in the meantime:

The hum is indeed on both tube voicings. Same thing with the Dist as in the clean -> The hum gets really loud when the Master Gain is above 7.5. The Gain 1&2 settings make no difference. Changing tubes makes no difference. Turning both trimpots concerning the tube board make no difference. Changing the EQ settings alters the sound of the hum.

Shorting Point F on the mainboard cuts the hum. Removing the tube board cable F and injecting a signal directly to Mainboard Point F produces a good clean signal, without any strange noises at all. Connecting the tube board out (cable F) to a clean and silent power amp carries the hum with the guitar signal over to the new poweramp.

So i think that the hum creeps into the guitar signal somewhere in the tube signal path. The Master gain section (u13) is clean, as is the guitar signal in the solid state path. I need to test the output of U4, but I can turn up the Solidstate Mastergain to 10.0 without the annoying hum.

Maybe it´s just the nature of the beast? After installing the MDRT i had to turn both OD trimpots all the way down and just barely got it within the factory specs. Maybe there is just a lot of gain in the tube circuit now, which results in a louder base hum level, which gets annoying with a loud Master gain?

All parts i checked in the meantime are good. I don´t know about the C -Ref and E-Drive section and especially the parts on the mainboard belonging to that section. What does this part do?

And still,  all of this doesn´t cure the popping when switching  :facepalm:

Really thankful for your help
#6
MP-2 / Re: MP-2 S/N 501251 from eBay ...
Last post by Gregg - July 17, 2024, 11:45:41 AM
My plan was to write some code to exercise the RTM MIDI functions and anything else I couldn't find open source for. There are some libraries out there already that should make it easy to write a test suite for Linux / a Raspberry Pi from what I saw.

Please connect your firmware friend with me.  I have done some preliminary reverse engineering work / notes that he probably doesn't want to have to figure out from the schematics.  I haven't made any tangible progress reverse engineering the firmware mostly due to lack of time, but have a memory map derived from the schematics.

Gregg
#7
Troubleshooting Problems / Re: Loud pop/click when changi...
Last post by MarshallJMP - July 17, 2024, 10:46:19 AM
Do you have hum on the SS clean ?
#8
MP-2 / Re: MP-2 S/N 501251 from eBay ...
Last post by rnolan - July 17, 2024, 06:37:31 AM
Hey Gregg, I thought you may have read the manual :thumb-up: .
The hardest part to test is the RTM stuff since you don't have a midi controller.  A cheap way is to pick up a Behringer FCB1010 (https://www.behringer.com/product.html?modelCode=0715-AAA).  They are not particularly expensive and have all the things (and more) you'd need to exercise the RTM functions.  Alternatively (albeit maybe a bigger rabbit hole) is to use some recording software that lets you record and edit midi (a midi track).

Then again, this is way more testing than I've ever seen anyone bother with (not that you shouldn't BTW).  Generally, if it makes a (reasonable) sound and the outputs work, they say it's good to go.  Moreover, of all the MP-2s I've picked up over the years, they have never had any issues with the RTM side of things.

But hey, you are an engineer, the requirements are in the manual, so lets develop a proper test plan (happy to help BTW).

An interesting (potentially) aside, I gave a friend (who likes assembler etc.) a copy of the 1.31 and 1.41 hex tonight and he's started to reverse engineer it (I suspect from his initial look that adding additional patches wouldn't be difficult).  I also sent him some schematics so it makes more sense.  Who knows, maybe we can optimise the firmware (not sure what I'd want to change), but it would be nice to develop a pseudo code algorithm.  Who knows, maybe we could develop a delay + reverb mod to include :dunno: .
#9
Troubleshooting Problems / Re: Loud pop/click when changi...
Last post by rnolan - July 17, 2024, 05:54:25 AM
But i would think you could use the whole master gain range. 

Yes you should be able to.
#10
Troubleshooting Problems / Re: Loud pop/click when changi...
Last post by RobinL - July 16, 2024, 02:01:23 PM
Yes. The hum is present when i short the Input to ground, it does hum when i short the tube board input to ground.

The hum does stop when when i ground pin 7 of v2. Yet all the usual tests i know when troubleshooting tube amps are fine, no dc or ac in the wrong places, no leaky caps or open resistors. The fets in v1 cathode are working as they should, all grounds are where they should be.

Maybe my settings are a bad coincidence? Gain 1 & 2 make no difference at all to this hum.  But when i raise the master gain above 7.0 it is really loud. Below that it is acceptable. But i would think you could use the whole master gain range.

I test and double check some more and will post my results.