Mysterious Mesa amp(s) problem, I'd appreciate some help

[BassmanPaul]

On 07/01/2024 at 19:15, agedhorse said:

Try the valve before screwing with anything else. 

 

Good advice from an expert!  

[BassmanPaul]

On 06/01/2024 at 10:10, sandy_r said:

 

Both valves listed as 12AX7 (a standard valve ...but genuine parts preferred!) 🤔

 

Or ECC83 even 7025 which is a low noise version of the 12AX7..

Edited January 9, 2024 by BassmanPaul

[sandy_r]

4 minutes ago, BassmanPaul said:

 

Good advice from an expert!  

 

It doesn't take an expert to discern that the discussion about the footswitch has nothing to do with the discussion about the gain/valve issue

 

Edited January 9, 2024 by sandy_r

[BassmanPaul]

Which is why I quoted what I did!

 

[sandy_r]

44 minutes ago, BassmanPaul said:

Which is why I quoted what I did!

 

 

clarification is always welcome 👍

 

Edited January 9, 2024 by sandy_r

[peteb]

I'm afraid that I haven't read the whole thread, but I am a long time mpulse user.

 

When I have had any problems with the mpulse, it was when I have changed the preamp valve. It doesn't seem to like anything other than a standard JJ 12ax7 for some reason. Good luck in sorting it out. 

 

[No lust in Jazz]

13 hours ago, agedhorse said:

The values of the components had nothing to do with your problem, it’s not a Marshall amp. 
 

The fix was just a lucky byproduct of the “repair”.

Wow.

[agedhorse]

15 hours ago, No lust in Jazz said:

Wow.

Yeah, sometimes it happens that way. Maybe a bad solder joint, maybe it was simply a bad connection that was corrected as a byproduct of the repair. 

 

Since there were thousands (6227 to be exact) amps built with those values without a problem, it should be obvious that it wasn't a problem. They don't have to be the same values as Marshall used, why would the?

[Beedster]

So, the Boogie is back in my studio and as Russ indicated, it certainly wasn't a well amplifier, it sounded really quite unwell and gut feel was that the problem was a lot more substantial than a pre-amp tube.

 

But, start simple and small and move towards large and more complex is the rule, so that's what I did. Luckily there's a pretty substantial collection of tubes here and as a few people suggested above, the pre-amp tube was the obvious starting point and bingo, it was also the culprit. So it's all fixed now.

 

I have also recognised that fate has decreed that I shall always own at least two pieces of Mesa Boogie amplification  

 

Russ/@binky_bass, many thanks for your patience throughout mate, as it turns out it was after all quite a simple fix although we weren't to know that from the symptoms, and also as I said above, it really did feel like something so much more problematic than the pre-amp tube. 

 

Gonna need to buy some more electric basses again now  

 

[Beedster]

On 09/01/2024 at 08:24, sandy_r said:

 

Thats a B-Link 1A - 5 switches (adding Tuner Mute) - your amp version only supports 4 switches (The B-Link F/S)

 

...if you, or a Techie friend, are confident with checking wire continuity and making a plug-type mod, you could swap out the existing 7-pin DIN on the cable (at the Mesa end) for the relevant 5-pin plug needed by your amp, and you'd be able to use the 4 switches as expected by your amp (Solo, Compression, Loop & EQ)

 

Or, you could make a complete new cable similarly (ie. 7-pin to 5-pin, 5-wire shielded cable?) and keep the original cable unmodded, in case you ever sell the footswitch on

(personally, i'd prefer this option)

 

 

Now it's back and working, anyone got any idea where I might be able to source a 7-pin to 5-pin DIN?

 

[pete.young]

This any good?   https://www.designacable.com/7-pin-to-5-pin-din-midi-cable-1.html

[BassmanPaul]

@Beedster did you try the old saw of linking the Send and Return of the Effects Loop with a signal cable to see if that helps?

 

[TheGreek]

9 hours ago, Beedster said:

So, the Boogie is back in my studio and as Russ indicated, it certainly wasn't a well amplifier, it sounded really quite unwell and gut feel was that the problem was a lot more substantial than a pre-amp tube.

 

But, start simple and small and move towards large and more complex is the rule, so that's what I did. Luckily there's a pretty substantial collection of tubes here and as a few people suggested above, the pre-amp tube was the obvious starting point and bingo, it was also the culprit. So it's all fixed now.

 

I have also recognised that fate has decreed that I shall always own at least two pieces of Mesa Boogie amplification  

 

Russ/@binky_bass, many thanks for your patience throughout mate, as it turns out it was after all quite a simple fix although we weren't to know that from the symptoms, and also as I said above, it really did feel like something so much more problematic than the pre-amp tube. 

 

Gonna need to buy some more electric basses again now  

 

 

Glad that this was resolved amicably.

Good to know that at least the members here can sort things out without recriminations.

Great bunch of people. 

[binky_bass]

Just now, TheGreek said:

 

Glad that this was resolved amicably.

Good to know that at least the members here can sort things out without recriminations.

Great bunch of people. 

We did have a 7 hour bare knuckle fight followed by a battle with Rhodesian fighting sticks. But in the end, all was settled!

[Beedster]

15 minutes ago, binky_bass said:

We did have a 7 hour bare knuckle fight followed by a battle with Rhodesian fighting sticks. But in the end, all was settled!

 

Scene in Russ's studio last Thursday....

 

[Beedster]

7 hours ago, pete.young said:

This any good?   https://www.designacable.com/7-pin-to-5-pin-din-midi-cable-1.html

Thanks Pete, I'm not sure, I guess it depends on how it's connected, @agedhorse @sandy_r any thoughts? 

[agedhorse]

3 hours ago, Beedster said:

Thanks Pete, I'm not sure, I guess it depends on how it's connected, @agedhorse @sandy_r any thoughts? 

 

There is one pin that's connected to circuit ground and 4 pins that are pull-down pins connected to the opto-isolators for each function. The footswitch circuit works by connecting each of the function pins to ground which will switch the function. A QUALIFIED tech will be able to identify the correct pins and not damage anything.

[Beedster]

7 hours ago, agedhorse said:

 

There is one pin that's connected to circuit ground and 4 pins that are pull-down pins connected to the opto-isolators for each function. The footswitch circuit works by connecting each of the function pins to ground which will switch the function. A QUALIFIED tech will be able to identify the correct pins and not damage anything.

Thanks @agedhorse, I assume an off the shelf 7-pin to 5-pin cable's not going to do the job then?

[pete.young]

14 hours ago, binky_bass said:

We did have a 7 hour bare knuckle fight followed by a battle with Rhodesian fighting sticks. But in the end, all was settled!

Must have looked like the Star Wars bar fight scene!

[BassmanPaul]

I just watched all of the Star Wars movies, not at one sitting I should add!! LOL

 

[agedhorse]

On 15/02/2024 at 00:43, Beedster said:

Thanks @agedhorse, I assume an off the shelf 7-pin to 5-pin cable's not going to do the job then?

I kind of doubt it. I don't know which pins are dropped as to how the adapter is wired. Since I can't find any docs on the original 7 pin wiring diagram, I would be just guessing and there's no need to guess wrong here.

 

All I can find is this information on the 4 button footswitch and 5 pin DIN wiring:

 

 

[Beedster]

4 hours ago, agedhorse said:

I kind of doubt it. I don't know which pins are dropped as to how the adapter is wired. Since I can't find any docs on the original 7 pin wiring diagram, I would be just guessing and there's no need to guess wrong here.

 

All I can find is this information on the 4 button footswitch and 5 pin DIN wiring:

 

 

 

Many thanks @agedhorse, is this the sort of thing that if I get wrong I've wasted some cash, or if I get wrong I've damaged the amplifier?

[BassmanPaul]

8 hours ago, Beedster said:

 

Many thanks @agedhorse, is this the sort of thing that if I get wrong I've wasted some cash, or if I get wrong I've damaged the amplifier?

With the greatest of respect @Beedster that schematic  is about as simple as one could be.  I could almost build that blindfolded!!

 

[binky_bass]

2 hours ago, BassmanPaul said:

With the greatest of respect @Beedster that schematic  is about as simple as one could be.  I could almost build that blindfolded!!

 

That's like saying a language simple if you already speak it. That diagram means nothing to me! 

[BassmanPaul]

For anyone who plans on working on an amplifier it behooves them to at least learn the basics of electronics. Would you work on a car's engine without learning a bit about it before you start?