Mesa Mark 1 versus SOB

[mark1406]

I have mentioned this before, but I can’t get over how different my SOB sounds to my original Mark 1 amp that I owned years ago.

My Mark 1 amp was a sixty watt model with the stock Eminence speaker, and reverb. It wasn’t particularly bright sounding though it could get a lot of different timbres. If I had the first volume at “10” the second volume at “2” with the brightness on. I got a faux Marshall sound from it. If I had the first and second volume on “7” it sounded like Santana. On the lower gain input it sounded very Fender like.

By comparison SOB is 60 watt amp with a Mark 1 reissue P.I. stage as the TCR508 went bad. I liked the sound of the reissue P.I. but I find if I try settings that were effective on my Mark 1, I get a similar sound coming out of the SOB regardless of where the volume controls are set. The SOB does appear to have more gain than my old Mark 1 which is good, though I wonder if this because the Mark 1 had reverb. I miss the various tones I could get out of the Mark 1 amp. I wonder why I’m not getting the same results from the same preamp.

Any thoughts?

Regards

Mark

 

[MK IIB]

I also have a SOB 60 watt (Non reverb)..I've never played an original Mark 1 but have heard lots of clips and my SOB sounds a lot more aggresive and lacks the smooth Boogie lead sound on input 1..

I've read that adding a presence pot makes it a lot smoother as the the lack of one means it's like having the presence on 10 all the time but somene else said the addition of a presence pot will only make it brighter and not reduce high end?

The presence on my Mark 2B makes a huge difference and makes the lead channel really smooth..I'd love this style of presence to be added to the SOB if possible?My amp is far too bright for my tastes as it is and I have to have the treble around 3 but even then the lead "channel" (Input 1) i still too fizzy/bright..I would love to have it converted to as close to a Mark 1 as possible..Input 2 is excellent but input 1 too bright for me so I used an overdrive pedal for lead sounds.

I also have to have both volume 1 and 2 up almost full to have any real amount of gain to acheive the sustainy "Boogie" lead sound.

 

[mark1406]

There is a reason that your SOB is bright. The cathode bypass caps on the preamp valves aren’t the same value as the Mark 1 amp.

The Mark 1 amp has all 22uF@25V caps, the SOB uses quite small value cathode bypass caps on V1 (first 12AX7 near the inputs). The gain stage has a 0.47uF cathode bypass cap (which is smaller than a Marshall’s 0.68uF cap), I made this cap 2.2uF in my amp instead of 22uF as I wanted a tighter bass response. The input 2 stage has a 3.3uF cathode bypass cap across it, this cap should be 22uF to sound more like the Mark 1.

In the picture you can see the cap I replaced and the node I added to the power supply as per the Mark 1 amp. I added the extra power supply node as I seem to remember there was some oscillation in the amp and the extra node killed that off.

SOB circuit 1

SOB circuit 2

Regards

Mark

 

[MK IIB]

Interesting..I wasn't aware there were so many differences as apparently the SOB was a Mark 1 preamp?

The only reason I can think of why your amp wouldn't sound the same especially having converted it to exact Mark 1 specs is possibly becuase the Original Mark 1 had some tone shaping going on in the power amp if I'm not mistaken?

Are the voltages the same in both the original mark 1 and the SOB do you know?

I'm seriously thinking about having mines converted to original Mark 1 specs too but wasn't exactly sure of the differences (except for the limit circuit)

Does yours have a presence control?

P.s I've never noticed any oscillation going on in mines.

 

[mark1406]

Interesting..I wasn't aware there were so many differences as apparently the SOB was a Mark 1 preamp?

The only reason I can think of why your amp wouldn't sound the same especially having converted it to exact Mark 1 specs is possibly becuase the Original Mark 1 had some tone shaping going on in the power amp if I'm not mistaken?

Are the voltages the same in both the original mark 1 and the SOB do you know?

I'm seriously thinking about having mines converted to original Mark 1 specs too but wasn't exactly sure of the differences (except for the limit circuit)

Does yours have a presence control?

P.s I've never noticed any oscillation going on in mines.

There are a couple of circuits for the Mark 1 amp. The preamp is pretty much the same but the P. I. stage is different. One variation uses a tweed Bassman P. I. stage which has that Marshall like tone, the grid leak resistors have been reduced to 330K to reduce gain in the P. I.
In later amps the Blackface P. I. stage was adopted.

My amp originally had a limit control but the TCR508 was blown so I had to go down the path of a different P. I. stage.

I experienced oscillation when I changed the caps in the preamp.

Regards

Mark

 

[James]

I’m not familiar with the circuit differences, but they don’t sound that similar to me. I was pretty surprised by the amount of drive the SOB has. Far more aggressive and less midrange too. Almost reminds me of a Soldano type sound

It’s not a bad sounding amp, but I’ve considered having it modified. I might try the presence control and see how that sounds. Supposedly it’s already setup for one, but not connected. The early ones did include one.

https://music-electronics-forum.com...od-how-to-add-a-real-presence-control?t=40273

 

[mark1406]

Hi James

I put this on the site so it doesn’t get lost.

https://boogieforum.com/threads/mesa-boogie-sob-mod.87143/
SOB limit control

SOB presence control





The 1M pot needs to be replaced with a 250K pot and wired to the secondary of the output transformer. The constant current diode needs to be earthed where the pot is/was, you need a 3nF (3000pF or 0.003uF) presence cap attached to pin 7 on the valve, the other side goes to the presence pot. The pot is wired as a variable resistor, I think when the pot is on “10” you want maximum resistance.

Regards

Mark

 

[trenken]

I saw this post a few years ago. Thank you for reposting James! I went ahead and did this mod back then to the best of my ability. My SOB is a 1982 and the limit control on the front panel is labeled presence, although yes, it was a limit control. The mod vastly improved the SOB. I soon after sent it into Mesa Boogie to have it re-capped. Mike B. did the work and I asked if he would check the work on the presence control mod. He gave it the greenlight, so yes this is a good mod. I primarily use Channel 2 as a clean pedal platform. It came stock with an EVM 12. However, it is a very bright amp where the presence control comes into play. Takes the edge off. Still interested in ways to take some of the harshness out. Really do like this amp a lot.

 

[DavidMenke]

I have mentioned this before, but I can’t get over how different my SOB sounds to my original Mark 1 amp that I owned years ago.

My Mark 1 amp was a sixty watt model with the stock Eminence speaker, and reverb. It wasn’t particularly bright sounding though it could get a lot of different timbres. If I had the first volume at “10” the second volume at “2” with the brightness on. I got a faux Marshall sound from it. If I had the first and second volume on “7” it sounded like Santana. On the lower gain input it sounded very Fender like.

By comparison SOB is 60 watt amp with a Mark 1 reissue P.I. stage as the TCR508 went bad. I liked the sound of the reissue P.I. but I find if I try settings that were effective on my Mark 1, I get a similar sound coming out of the SOB regardless of where the volume controls are set. The SOB does appear to have more gain than my old Mark 1 which is good, though I wonder if this because the Mark 1 had reverb. I miss the various tones I could get out of the Mark 1 amp. I wonder why I’m not getting the same results from the same preamp.

Any thoughts?

Regards

Mark

Here is some information from the original catalog:

 

[DavidMenke]

I saw this post a few years ago. Thank you for reposting James! I went ahead and did this mod back then to the best of my ability. My SOB is a 1982 and the limit control on the front panel is labeled presence, although yes, it was a limit control. The mod vastly improved the SOB. I soon after sent it into Mesa Boogie to have it re-capped. Mike B. did the work and I asked if he would check the work on the presence control mod. He gave it the greenlight, so yes this is a good mod. I primarily use Channel 2 as a clean pedal platform. It came stock with an EVM 12. However, it is a very bright amp where the presence control comes into play. Takes the edge off. Still interested in ways to take some of the harshness out. Really do like this amp a lot.

Do you turn up the presence to take away the harshness? What settings 1-10 typically works?

 

[trenken]

Do you turn up the presence to take away the harshness? What settings 1-10 typically works?

Yes. On the presence control… 10 is the brightest, so I back it to around 6 1/2. It takes the bright edge off. I typically run my treble around 6 1/2 as well. Any higher is just too bright and any less is a bit dull. Took me a while to understand the cascading EQ thing down. I don’t really go by the list they suggest, I have to go by ear. Set the bass around 7 in the mid around 6.

 

[MK IIB]

Yes. On the presence control… 10 is the brightest, so I back it to around 6 1/2. It takes the bright edge off. I typically run my treble around 6 1/2 as well. Any higher is just too bright and any less is a bit dull. Took me a while to understand the cascading EQ thing down. I don’t really go by the list they suggest, I have to go by ear. Set the bass around 7 in the mid around 6.

Can you confirm something for me please?
This presence mod is something I'd be interested in having done to tame the harshness and smooth out the lead channel (Input 1)
A fellow user though said that by adding a presensce control it will only accentuate the highs even further..Ie presence on 0 is like the amp was without it and turning it up makes it even brighter?
I'm looking to reduce highs as with my treble even at 4-5 it's still too bright for lead work (for me)
Can you confirm if you were able to reduce the highs by adding a presence control?

 

[trenken]

Can you confirm something for me please?
This presence mod is something I'd be interested in having done to tame the harshness and smooth out the lead channel (Input 1)
A fellow user though said that by adding a presensce control it will only accentuate the highs even further..Ie presence on 0 is like the amp was without it and turning it up makes it even brighter?
I'm looking to reduce highs as with my treble even at 4-5 it's still too bright for lead work (for me)
Can you confirm if you were able to reduce the highs by adding a presence control?

Hey MK IIB, yes, I was able to reduce the highs by adding a presence. I did the MOD that James had posted, but can’t speak for any other mod and how they work. I can turn my treble up to 9, and then dial the presence control down to zero and it will cut the highs severely, if I turn, the presence control up to 10, it will accentuate the highs. I hope that helps to explain.

I read this on a forum recently and it seems to explain best the way this mod performs:

“The presence control takes care of the overall treble response of the amp from the power section. This means once you’ve dialed in your tone, you can increase the overall brightness of the entire tone with the presence control.
If you turn the presence down, you get a sound with a noticeable cut in top end. This is ideal if you are using a particularly bright set of pickups or finding your tone too harsh overall.”

Will try to post some pictures sometime this weekend of the inside where the mod was performed and the cap value etc. I’m no electrician but felt comfortable enough to try this mod. To me, it was worth the time.

 

[trenken]

Here's a few pics of the limit to presence control mod. I used a 250 audio taper pot, and also had an orange drop in at first, then thought to try a paper in oil cap. From what has been debated is the PIO doesn't really effect the tone much when used in a guitar pot nearly as much as in an amplifier circuit, so though to try it there. Actually seems a bit smoother to my ear, but could be placebo. Anyway, have read some interesting posts here regarding adding an effects loop, as it would be nice to use the lead channel 1 with delay rather than being limited to use drive pedals w/delay through Channel 2. Also Mark 1406 mentioned "The input 2 stage has a 3.3uF cathode bypass cap across it, this cap should be 22uF to sound more like the Mark 1." I've never played a Mark 1, so how does that effect the sound? Thanks.

 

[mark1406]

Hi Trenken, thanks for your reply and pictures. One thing I have found with my amp is the ceramic caps sound better than silver mica caps. I have taken silver mica caps out of my amp and reverted to ceramic caps as it diffused the treble somewhat.

Regards

Mark

 

[James]

Anyway, have read some interesting posts here regarding adding an effects loop, as it would be nice to use the lead channel 1 with delay rather than being limited to use drive pedals w/delay through Channel 2.

I assume it would be like the tube driven version that was offered for the original MK I and IIA. The master on the front becomes a send level, and the added volume on the back is a return level. They both function even when nothing is connected though (unlike the MK 1 reissue)

I'm not sure if that's what the SOB with factory loop mod in the other thread has. I think the added control was for reverb.

 

[mark1406]

I assume it would be like the tube driven version that was offered for the original MK I and IIA. The master on the front becomes a send level, and the added volume on the back is a return level. They both function even when nothing is connected though (unlike the MK 1 reissue)

I'm not sure if that's what the SOB with factory loop mod in the other thread has. I think the added control was for reverb.

The Mark 1 amps never came with an effects loop. The only Mark 1 I know of with an effects loop is the reissue, and the Kingsnake, as far as I can tell the loop is the same in the reissue and the Kingsnake.

I probably would go with something like the Valve Wizard effects loop.

Regards

Mark

 

[James]

The Mark 1 amps never came with an effects loop. The only Mark 1 I know of with an effects loop is the reissue, and the Kingsnake, as far as I can tell the loop is the same in the reissue and the Kingsnake.

I probably would go with something like the Valve Wizard effects loop.

Regards

Mark

Yes that's correct - I was referring to the one Mike B could add as a modification. I don't think it was an option until sometime in the 80s. When I asked him about it a few years ago, he seemed a bit hesitant to modify the originals at this point.

 

[mark1406]

Yes that's correct - I was referring to the one Mike B could add as a modification. I don't think it was an option until sometime in the 80s. When I asked him about it a few years ago, he seemed a bit hesitant to modify the originals at this point.

I asked Mike B about the effects loop he fitted to Mark 1 amps but he referred me to the circuits in the reissue and the Kingsnake. The circuit that he did to amps back in the day is very different to the effects loop that is in the Mark 1 reissue amps. The master volume preceded the effects loop and he added an entire 12AX7.

Completely aside, I find the SOB tends to like the ceramic picofarad value caps instead of the silver mica caps which are generally regarded as superior to the ceramic caps. My original Mark 1 amp came with ceramic caps.

Regards

Mark