LSC/LSS owners; are you happy with channel2?Want to fix it?

[simonich]

He used a sort of jumper that connected to the caps. Almost like you would drain a tub of water. I didn't watch the whole process. Maybe someone could chime in that knows what they are doing on the technical side.

The caps store a lot of electrical energy, or "charge". They charge up when the AC is applied. When the amp is turned off, the circuit is broken so they stay charged.

They are dangerous because of the very high voltage, >=450V depending on the amp. As mentioned previously that's more than enough to get current running across your heart, which will stop it.

So... What needs to happen to make is safe is to discharge the caps before work begins. The only way to do that is complete a circuit. The easiest way to do this is mock up a resistor with clips soldered to its leads and connect that resistor across the terminals of the capacitor. The voltage will cause current to flow through the resistor and be dissipated as heat.

The problem is you have to size the resistor right. It will want to dissipate power equal to the voltage squared divided by the resistance. If you assume there is 400 volts, that's 400 * 400 / R. If the resistor is a 10K resistor, the power will want to be 1.6W, so you'd need a 2W resistor. If you can't find one that big (2W), then use a 100K and a standard 1/4 W resistor will do.

The time constant of this circuit will be RC. So if there is 400uF of capacitance in there, the time constant is 40s. After 1 time constant you'll bleed off about 2/3 the voltage. So just strap it on there for a few min and let it bleed off. Then check the voltage across the caps when you come back.

BTW, in no way am i suggesting people that don't know what they are doing dive in and try this. This is just an informational post. Hope it helps.

 

[Monsta-Tone]

I'm going to try this mod tonight. If it works, I will definitely report back ( :lol: like I wouldn't report back if it sucked :lol: ).


As for the caps.
It is not a good habit to reach into your chassis when:
It is plugged in, no matter where the power switch is
When the caps have not been discharged. Period.

Just because you don't touch the caps does not mean that you won't accidentally touch somewhere else in the circuit that is attached to the caps.

And, just for the record, it fucking hurts when you get careless. It only took me once to learn this.


I use a test jumper with a 1k 5 watt resistor soldered in the middle so that the stored energy goes through a load and not directly to the ground (chassis). Otherwise you will get sparks.

I also turn the Standby Switch to the ON position, like it would be when playing. This allows the 1st Cap stage to discharge also, otherwise, it will be sitting there just waiting for you to touch it.


I place 1 end of the jumper on the Ground
I place the other end on the POSITIVE side of any of the large filter caps.

Then, I place a meter (set to DC VOLTS) from ground to the capacitors. It should take only a matter of seconds before they drain, and it is well worth the effort.

 

[Monsta-Tone]

OK, so I did the mod.

The cleans on Channel 2 are vastly improved. The Drive seems about the same, but I will have to play with it some more.

There are definitely different model numbers stamped on the pots, but they measure almost exactly the same.

This has got to have something to do with the taper of the pots. I don't think that it has much to do with the fact that Mesa didn't want to have the channels sound the same. Look at the DR's. They have channel cloning.


I bet that somebody just thought it sounded better to them and that is why they send them out that way.

I'll leave it like this for a few days and see how I like it.

 

[sbalderrama]

I bet that somebody just thought it sounded better to them and that is why they send them out that way.

Mesa has always advertized that C2 sounds like C1 "with an added touch of roots level gain", which seems to mean not that channel 2 sans Drive actually has more gain than C1, but that when the pots are in the same position because of the taper C2 has more gain dialed in.

 

[ja22y]

I bet that somebody just thought it sounded better to them and that is why they send them out that way.

Mesa has always advertized that C2 sounds like C1 "with an added touch of roots level gain", which seems to mean not that channel 2 sans Drive actually has more gain than C1, but that when the pots are in the same position because of the taper C2 has more gain dialed in.

That somebody at Mesa must have the same thought as mine. Typically I like the 2nd channel to be of higher gain than the 1st. I never have the need for 2 identical channels. So with the same gain pot position, ch2 naturally has just the right amount more gain for me.

 

[BobL]

After about 3 weeks of testing and live play I have converted both my Lonestars back to the original position. What I did find is that when in the circuit the pots read the same regardless of which pot is used, and it is the taper which is not the same. Unfortunately I wrote down the info and threw the paper away by mistake. My ears, with my equipment, likes the sound of the second channel better as shipped from the factory. And you should also be aware that this change / mod alters the gain structure more than it alters the tone.

Mesa's are well known for their interactive gain structure, i.e. the effect each control has on each other. What I really disliked was the channel 2 drive after the change was made. I lost the subtle grind that was so pleasant to listen to and found my self reaching for more and more gain to acheive the same effect. Unfortunately by the time I found the same feel in the guitar the tone was nowhere close to usable for me. I also found that the bridge pickups in all of my guitars were to bright with this change and compared the tone to more of a Rect-O-Verb tone. A little to harsh. I wouldn't mind posting some recordings but unfortunately this cheap site makes you find your own host, something I don't care to do.

If I get time I'll take a look at the circuit as a whole and find the correct way to alter the tone without effecting the gain structure. Have fun.

 

[plan-x]

After about 3 weeks of testing and live play I have converted both my Lonestars back to the original position. What I did find is that when in the circuit the pots read the same regardless of which pot is used, and it is the taper which is not the same. Unfortunately I wrote down the info and threw the paper away by mistake. My ears, with my equipment, likes the sound of the second channel better as shipped from the factory. And you should also be aware that this change / mod alters the gain structure more than it alters the tone.

Mesa's are well known for their interactive gain structure, i.e. the effect each control has on each other. What I really disliked was the channel 2 drive after the change was made. I lost the subtle grind that was so pleasant to listen to and found my self reaching for more and more gain to acheive the same effect. Unfortunately by the time I found the same feel in the guitar the tone was nowhere close to usable for me. I also found that the bridge pickups in all of my guitars were to bright with this change and compared the tone to more of a Rect-O-Verb tone. A little to harsh. I wouldn't mind posting some recordings but unfortunately this cheap site makes you find your own host, something I don't care to do.

If I get time I'll take a look at the circuit as a whole and find the correct way to alter the tone without effecting the gain structure. Have fun.

Interesting! I'll look forward to that.

 

[djw]

After about 3 weeks of testing and live play I have converted both my Lonestars back to the original position. What I did find is that when in the circuit the pots read the same regardless of which pot is used, and it is the taper which is not the same. Unfortunately I wrote down the info and threw the paper away by mistake. My ears, with my equipment, likes the sound of the second channel better as shipped from the factory. And you should also be aware that this change / mod alters the gain structure more than it alters the tone.

Mesa's are well known for their interactive gain structure, i.e. the effect each control has on each other. What I really disliked was the channel 2 drive after the change was made. I lost the subtle grind that was so pleasant to listen to and found my self reaching for more and more gain to acheive the same effect. Unfortunately by the time I found the same feel in the guitar the tone was nowhere close to usable for me. I also found that the bridge pickups in all of my guitars were to bright with this change and compared the tone to more of a Rect-O-Verb tone. A little to harsh. I wouldn't mind posting some recordings but unfortunately this cheap site makes you find your own host, something I don't care to do.

If I get time I'll take a look at the circuit as a whole and find the correct way to alter the tone without effecting the gain structure. Have fun.

Fascinating. I'm also eager to see what you have to share about your findings. We could be one more mod away from The Perfect Amp.

I agree that the gain structure is more affected by the mod, but my experience in terms of aesthetics is completely different. My ears are pleased, pleased, pleased at what I get with the mod -- nothing harsh, and with more gain than I ever use still on tap. Brighter, yes, but the breakup is in a range that's more to my liking, and for me the brightness is sweet, not glaring.

So I'm happy as a clam, but I'm also fascinated at the variety of reactions the mod receives. I'm curious to know more about your config, BobL -- you obviously use quality axes, but what about tubes? Speakers? Which models are your LSCs?

 

[sbalderrama]

If I get time I'll take a look at the circuit as a whole and find the correct way to alter the tone without effecting the gain structure. Have fun.

If the schematics on the web are correct, and you don't use the drive or voicing switches, it appears to me that the two channels are electrically identical, aside from a couple of switches in the path. So I think the entire effect of the mod can be attributed to the pot tapers effect on the gain structure. It's possible that something about the way the pots are manufactured causes some other electrical difference when they are in different parts of their range as well I suppose to make the sound more open; but its definately true that C2 opens up as the gain control is dialed down, so I suspect that the fact that the mod gives finer control over the lower gain range of the pot is the main benefit of the mod to those who don't use alot of gain on the channel.

I want the compression effect of gain on C2 for my lead tone, so I tend the run the gain up high and so I suspect that I probably prefer the level of control I get over the higher ranges in the gain with the standard pot layout. I might do the mod at some point just to see if I like it any better though.

 

[BobL]

I have just taken a look at the schematic for the lonestar and it's apparent now why the pot swap effects the tone and gain structure of channel #2. Without getting into the amp with a scope or taking any measurments it's plain to see that the tone circuits for channel 1 and 2 are NOT the same.

Both channels share the same input, 1/2 of V1, V1B. When switched to channel 1 the tone circuit follows V1B directly to V2B and then to V2A. The reverb shares this circuit and taps the circuit between V2B and V1B.

When switched to channel #2 the same path is followed through V1B, the first gain stage, however, the second half of V1, V1A is placed between V1B and and V2B adding another gain stage. When the additional gain stage is not used V1A is bypassed using relay DC-A.

HOWEVER, and even though at first glance it may appear that the TREBLE, MID, and BASS tone circuits are identical for both channels. they are not.

Channel #2 has additional components in the tone circuit and they are the resitors and capacitors that make up the settings for the thicker, thick, normal switch.

We have been, or at least I have been, led to believe that this function is only active when the additonal gain stage is engaged. This couldn't be further from the truth and a good look tells you that these components are always in the circuit regardless if the drive is on or if it is bypassed.

There is no exception here and my theory is this. The pots are both 1M pots, but they are not both linear taper. I am assuming (not good) that the resistance when applied through the GAIN pot in this portion of the tone circuit is electricaly high enough to force the signal around this portion of the channel #2 tone circuit.

Remember this is only theory but I think it's fairly sound. Now here's my thought.

The thick, thicker, normal switch has no connection in the normal position. My thought is that without changing the pots at all, a jumper could run from the center post on the switch, currently not used, to the point where the 100K resistor in the TREBLE, MID, BASS circuit connects to the bypass relay. That removes the thick, thicker, normal components from the circuit and truly makes the 2nd channel "normal".

I am not able to work this mod for perhaps another 2 weeks or so, but if you would like to give it a shot here is the schematic for reference and the portion of the schematic I'm speaking about is on page 3 of 6.

Have fun and good luck.

http://www.schematicheaven.com/boogieamps/boogie_lonestar.pdf

 

[sbalderrama]

That portion of the schematic with the voicing switch seems a little unclear to me. I was assuming ( as you said, bad) that if the switch is in normal, that both the thick and thicker paths are also broken, although the schematic diagram seems difficult to tell that. Are you saying that isn't the case? If not, what is that part of the schematic showing the switch operation to be?

It is interesting that the voicing circuit seems to be in parallel with the tone controls and the gain control. Looks like if any of the voicing paths are engaged, that the amount of current going through them is going to be dependent on the gain control. I'd guess that the more the gain is dialed in, the less effect the voicing controls would have.

 

[Monsta-Tone]

It's an old trick. The switch just changes the level of mids and the resonant frequency of the mids. The more capacitance in the Treble cap, the more higher mids will be present. This switch merely switches more capacitance in parrallel with the original cap. Caps are opposite from Resistors, in the sense that the more caps you have in parrallel, the more capacitance you will have.


There is a 10 Meg Ohm resistor in series with each of these added capacitors so that there will be no noise when switching them in or out. Without the resistors, there would be a horrendous pop noise.


The Resistors are so large that almost no, or no signal at all will pass through them. The signal will take the path of least resistance.


When the switch is in the Normal position, the capacitors are switched out of the circuit and you will notice little if any difference if they were not there at all.

 

[sbalderrama]

Ok, so tell me if I'm reading this right then in the schematic. The high resistances electrically are "switching" the capacitors out of the circuit. In the normal position, both capacitances are actually in circuit, but due to the high resistance should be nearly completely ineffective. When the voicing switch is switched, it looks like it probably bypasses one or the other of the resistors in the voicing circuit, bringing that capacitor full online in parallel with the treble control.

So technically, there is always a path or two through that network, but the high resistances should keep the vast majority of signal from passing through them in "normal" mode. The question is whether enough of that signal gets through to make an audible difference.

 

[Monsta-Tone]

I don't think any signal will pass through the 10 Meg Ohm resistors. There is just too little resistance through the Treble Cap and Pot and the 100 K resistor that feeds the Bass & Mid caps.

It's a lot like a river. If you see it split and the water only goes one way, it's most likely because the other way is too hard for the water to flow through unless there is a flood.

Electrons will always take the path of least resistance.

 

[sbalderrama]

Makes sense. Now I'm thinking that BobL's idea of a bypass though would actually end up completely bypassing the tone stack, rather than just eliminating the voicing network.

 

[BobL]

Makes sense. Now I'm thinking that BobL's idea of a bypass though would actually end up completely bypassing the tone stack, rather than just eliminating the voicing network.

That's possible, and I'll need more time which I don't have right now. Fact is that the balance between the gain pot and that portion of the circuit are what makes the difference in tone and that is determined by the pots taper.

 

[Monsta-Tone]

I have to agree with that, but be careful. The part of the circuit that you are talking about is directly after the tube, and before the coupling cap, so you are talking about 155 volts DC according to the drawing. Not much, but it won't make you happy if something frys or you get shocked.

 

[BobL]

I have to agree with that, but be careful. The part of the circuit that you are talking about is directly after the tube, and before the coupling cap, so you are talking about 155 volts DC according to the drawing. Not much, but it won't make you happy if something frys or you get shocked.

Thanks for the concern. Actually there is 203V on that circuit and I'll take it for granted that you and I are both saying;

Don't try this modification if you are not fully capable of working with electronics and high voltage circuits of this nature. I do not endorse or do I suggest that anyone reading this undertake this change unless they do so at their own risk.

In a few weeks I'll run this mod, after I run a few tests with a scope on the circuit to see if it is possible without effecting the amps performance. That will also include a call to my contacts at Mesa.

 

[simonich]

Mostly true. But some amount of current will flow through any resistor that has voltage applied. Yes, clearly most of the signal will go through a path of lower resistance path, just not all.

 

[gregit]

Just do what I did...cut your losses and go with another amp. I couldn't get my LSS to sound like I wanted it to. I also had a matching 410 cab which helped a bit. Anyway, I traded my rig + a few bucks for a '06 Bogner Shiva. Oh yeah.... Guess I'm outta the Mesa club?