NAD - Mesa Mark III Green Stripe
Posted: Mon Dec 18, 2017 4:51 pm
I'm in Tokyo periodically and usually spend some time wandering around the guitar shop districts looking for cool stuff. I wasn't disappointed on this trip, spotting this mint Mark III green stripe sitting under a pile of other amps in a corner of a basement shop room.
This amp was full featured. Long head (all controls on the front except presence), reverb, simul-class power amp, graphical EQ. Loaded with 6L6 and 5881 power tubes.
Had a quick play in the shop to confirm it was healthy and bought it. Came with a flight case that sealed the deal.
While in the shop I also weighed the thing. Came to 29kg, scraping under the 32kg upper limit for AirNZ baggage allowances.
So it could go on the plane home. Just had to drag it back to my apartment then later to the airport. Lugging 29kg of huge amp crate through Tokyo on the trains and stations etc was a fucking mission that I dont want to repeat in a long time... I think my arms have been permanently stretched.
Regular rests were in order.
Out she comes at AKL
So I got her home safe in the end. Next there were a couple of thing to sort out.
1. First was the mains voltage. Being from Japan it was configured to run on 100V mains.
2. The master volume control on these amps is known to be a shite configuration offering nothing between barely audible and full blast. It's 2017 and we aint got time for dat anymore
3. Get rid of stupid ideas Boogie had in the 80s
4. The Rhythm 2 channel no volume control, making the R1, R2 and lead channels nearly impossible to balance.
5. Try out the Boogie factory mods
I should preface the following by mentioning I have 25 years in amp building ad modding experience. So, don't try this at home or whatever.
First was to change the mains input voltage. Marks were sold with either US power transformers which only accepted 110V mains, or the "Export" transformer which has taps for the various international mains voltages.
Here's the guts. Overall, in really good condition. I can only see one coupling cap replacement, the rest looks factory.
I did a quick test of all the tubes and power supply caps. Everything was healthy.
Measuring the inductance of the transformer taps to find the 240V winding. Easy to find and switched it over. Now the amp runs on 240V, except the internal fan which is 100V, so I left that running in the 100V tap.
Wiring insulated and tidied up again
Next thing to do was rewire the master volume control. The factory setup has the master potentiometer wired as a rheostat. Ive changed this to a more conventional potentiometer wiring. Now the volume control works smoothly from nothing to max as it should!
Next was to remove what are known as the "Death caps". Lots of amp manufacturers did this back in the day - installed a capacitor from the mains wiring to the chassis. The idea is to couple noise from the mains to earth. However, 30 years later we know that if/when these capacitors fail, they connect the mains to the chassis and blow things up and potentially kill someone. So in the bin it goes. They dont do anything 99% of the time, and if they do, there are much better solutions to filter mains noise.
This amp has two death caps, the green one and the orange on this switch
Now binned. Amp safe.
The next thing to do was install a volume control for the R2 channel so the three channels can be properly balanced. This amp is a "long head", meaning there was a useful empty space on the back panel where the reverb control goes if there is no room on the front. My amp has the reverb control on the front so the rear location is blanked off. The mod involved replacing a fixed resistor R130 with a pot. R130 gets pulled out and the pot put into it's place. Full control of the R2 volume now.
I even found a sorta matching knob for the pot
Next thing to try was the Mark III+ factory mods Boogie did. These are, essentially, the presence cap (1nF to 5nF), the c30 + high frequency shunt capacitor for the lead channel, and the clean channel coupling cap.
Because this amp is a green stripe, it is the last rendition of the Mark III before the Mark IV came out. Hence, these amps contain some of the factory mods Boogie did to the earlier (black and red stripe) models.
First, the presence cap is already 5nF, choice. That's it there, C516
Second, the clean channel coupling cap is 20pF, instead of 10pF. I think i'll leave that. That's it at C27
Last, the 2C+ lead channel mod. C30 on this amp is empty. The C30 cap position filters high frequencies on the lead channel. This is why the blue and green stripe Mark IIIs sound angrier than other models. And why the 2C+ sounds a little darker or more vintage or raw. Insert superlatives here.
Empty C30
1nF WIMA cap installed into the C30 position.
After some testing, I have decided I sometimes like the amp with C30 and sometimes without it. Solution: put C30 on a switch. So that's what Ive done, the R2 volume control on the back is now has a push-pull switch to engage C30 and 2C+ tones, or not. Best of both worlds.
And here she is all buttoned up.
At some stage I'll put in an adjustable bias control into the power amp, but I wont bother until it's time for new tubes.
Overall, a mission to get it home and sorted out. But now that's all done, what a great amp!
This amp was full featured. Long head (all controls on the front except presence), reverb, simul-class power amp, graphical EQ. Loaded with 6L6 and 5881 power tubes.
Had a quick play in the shop to confirm it was healthy and bought it. Came with a flight case that sealed the deal.
While in the shop I also weighed the thing. Came to 29kg, scraping under the 32kg upper limit for AirNZ baggage allowances.
So it could go on the plane home. Just had to drag it back to my apartment then later to the airport. Lugging 29kg of huge amp crate through Tokyo on the trains and stations etc was a fucking mission that I dont want to repeat in a long time... I think my arms have been permanently stretched.
Regular rests were in order.
Out she comes at AKL
So I got her home safe in the end. Next there were a couple of thing to sort out.
1. First was the mains voltage. Being from Japan it was configured to run on 100V mains.
2. The master volume control on these amps is known to be a shite configuration offering nothing between barely audible and full blast. It's 2017 and we aint got time for dat anymore
3. Get rid of stupid ideas Boogie had in the 80s
4. The Rhythm 2 channel no volume control, making the R1, R2 and lead channels nearly impossible to balance.
5. Try out the Boogie factory mods
I should preface the following by mentioning I have 25 years in amp building ad modding experience. So, don't try this at home or whatever.
First was to change the mains input voltage. Marks were sold with either US power transformers which only accepted 110V mains, or the "Export" transformer which has taps for the various international mains voltages.
Here's the guts. Overall, in really good condition. I can only see one coupling cap replacement, the rest looks factory.
I did a quick test of all the tubes and power supply caps. Everything was healthy.
Measuring the inductance of the transformer taps to find the 240V winding. Easy to find and switched it over. Now the amp runs on 240V, except the internal fan which is 100V, so I left that running in the 100V tap.
Wiring insulated and tidied up again
Next thing to do was rewire the master volume control. The factory setup has the master potentiometer wired as a rheostat. Ive changed this to a more conventional potentiometer wiring. Now the volume control works smoothly from nothing to max as it should!
Next was to remove what are known as the "Death caps". Lots of amp manufacturers did this back in the day - installed a capacitor from the mains wiring to the chassis. The idea is to couple noise from the mains to earth. However, 30 years later we know that if/when these capacitors fail, they connect the mains to the chassis and blow things up and potentially kill someone. So in the bin it goes. They dont do anything 99% of the time, and if they do, there are much better solutions to filter mains noise.
This amp has two death caps, the green one and the orange on this switch
Now binned. Amp safe.
The next thing to do was install a volume control for the R2 channel so the three channels can be properly balanced. This amp is a "long head", meaning there was a useful empty space on the back panel where the reverb control goes if there is no room on the front. My amp has the reverb control on the front so the rear location is blanked off. The mod involved replacing a fixed resistor R130 with a pot. R130 gets pulled out and the pot put into it's place. Full control of the R2 volume now.
I even found a sorta matching knob for the pot
Next thing to try was the Mark III+ factory mods Boogie did. These are, essentially, the presence cap (1nF to 5nF), the c30 + high frequency shunt capacitor for the lead channel, and the clean channel coupling cap.
Because this amp is a green stripe, it is the last rendition of the Mark III before the Mark IV came out. Hence, these amps contain some of the factory mods Boogie did to the earlier (black and red stripe) models.
First, the presence cap is already 5nF, choice. That's it there, C516
Second, the clean channel coupling cap is 20pF, instead of 10pF. I think i'll leave that. That's it at C27
Last, the 2C+ lead channel mod. C30 on this amp is empty. The C30 cap position filters high frequencies on the lead channel. This is why the blue and green stripe Mark IIIs sound angrier than other models. And why the 2C+ sounds a little darker or more vintage or raw. Insert superlatives here.
Empty C30
1nF WIMA cap installed into the C30 position.
After some testing, I have decided I sometimes like the amp with C30 and sometimes without it. Solution: put C30 on a switch. So that's what Ive done, the R2 volume control on the back is now has a push-pull switch to engage C30 and 2C+ tones, or not. Best of both worlds.
And here she is all buttoned up.
At some stage I'll put in an adjustable bias control into the power amp, but I wont bother until it's time for new tubes.
Overall, a mission to get it home and sorted out. But now that's all done, what a great amp!
