Grateful Dead Music Forum

I'm a bit worried that there's something wrong with my new-to-me MC50, but I don't have enough experience with these to know how much volume I can reasonably expect. If you run a MC50 or MC250 and a SMS CTP, how much preamp level, output padding, and amplifier volume do you need for a decent sound level?

More background:
I recently tracked down a freshly restored MC50 on eBay, which I'm using in conjunction with a SMS CTP and a pair of older Celestion/Ampeg Pro Series 10's. These are 8 ohm speakers wired in parallel for a nominal 4 ohm load; actual load as measured with my multimeter is 5.25 ohms at the jack. I'm using the MC50's 4 ohm speaker output.

The problem is that in order to get any sort of decent volume from the MC50 I need to have the SMS CTP's output padding knob cranked to around 3 o'clock, and the MC50's volume knob cranked to almost full. The CTP's level control is set to 11 o'clock or so. With the output level this hot I get a decent volume (think "loud-ish band practice level", not "play a venue" volume) but also I think there is some clipping of the input signal by the MC50. I can obviously play quieter without clipping, but I'm surprised that I can't play at this volume level.

For comparison, I have also tried the same CTP and speakers with both a Mesa 50/50 and a MV-962 (both in single channel mode), and with a similar level setting on the CTP I need much less output padding (approx. 9 o'clock) and *far* less level on the amplifiers. The CTP sounds great with those amps, but doesn't sound as good or as loud with the MC50 (or at least not as good/loud as I expected it to).

I played my iPod through this setup, and it also seems quieter that I would expect for a 50 watt amp, but this was without a preamp.

Any thoughts or suggestions would be very much appreciated - before I take it in to have it looked at I need to know if my expectations are reasonable or if it's working as it should.

Thanks!

Definitely sounds like something isn't right with the MC50, OR you simply are looking for a bigger, louder sound. With a Mac, the SMS Classic should always have its rear knob wide open, but the preamp's gain should be a click below noon for the Jerry thing. From my experience, you should likely have the Mac's knob around half way as well, and at that point I'd expect you to be able to drive the Mac into clipping.

With this setup, the preamp will be clean and the input stage the to the Mac will be clean, but the power section of the Mac is what will distort first. If you're hearing clipping, it's most likely happening in the Mac's power section. It is possible that the Mac just isn't loud enough for you. If the Mac is healthy, it should be delivering anywhere from about 60 to 75 watts or so. This will be a quieter and less ballsy sound than an 80 watt Twin driven to full power. It would be good to have the Mac bench tested to see what it's really doing, power-wise, and then go from there to trouble shoot.


B

SarnoMusicSolutions wrote:Definitely sounds like something isn't right with the MC50, OR you simply are looking for a bigger, louder sound. With a Mac, the SMS Classic should always have its rear knob wide open, but the preamp's gain should be a click below noon for the Jerry thing. From my experience, you should likely have the Mac's knob around half way as well, and at that point I'd expect you to be able to drive the Mac into clipping.

With this setup, the preamp will be clean and the input stage the to the Mac will be clean, but the power section of the Mac is what will distort first. If you're hearing clipping, it's most likely happening in the Mac's power section. It is possible that the Mac just isn't loud enough for you. If the Mac is healthy, it should be delivering anywhere from about 60 to 75 watts or so. This will be a quieter and less ballsy sound than an 80 watt Twin driven to full power. It would be good to have the Mac bench tested to see what it's really doing, power-wise, and then go from there to trouble shoot.


B

Brad,

First -- I really love your preamp!

This is exactly what I was looking for: With a Mac, the SMS Classic should always have its rear knob wide open, but the preamp's gain should be a click below noon for the Jerry thing.

I'll give that a try tomorrow and see what I get. I wasn't using the full amount of output padding from the SMS Classic, but I did have the Mac's volume knob pretty much dimed. If I hear clipping when I have it setup as you suggest I'll take it in to have it tested.

Thanks!

PS: I revised my OP for clarity.

I run the same set-up MC50+SMS+2x12 cab and it's plenty loud for my needs. I'm thinking somethings up with your Mac. I have my rig set just as Brad described with Mac set around Noon and it rips. With you having your Mac almost wide open and it still not being that loud seems a bit fishy. Good luck.

I was running basically the same setup and found it capable of really lots of volume and dynamic punch. I rarely had to turn the Mac volume to half way to get ample stage volume (indoors small venue) and my band tends to get loud.

Thanks for the feedback, guys, it really helps. I won't have a chance to test it again until I get home tonight, but I'll crank it up as per Brad's instructions and see if I get anything more. If not, I suppose it's off to the shop

Thanks!

I'd run the CTP full up on the trim pot on the back and the gain knob on the front about 1 or 2 o'clock. You shouldn't have to crank the MC50 past 1 o'clock either to be plenty loud. Mine used to distort past 2 o'clock. It also depends on how much signal your guitar is feeding the preamp. With a buffer and 25K volume pot on the guitar, I usually only play 1/2 to 3/4 up. Never full blast on the guitar.

Thanks, everyone -- I tried it with the CTP's rear trim pot at full and the level between 11:00 and noon and those changes made a big difference -- the sound is much louder and not distorted like it was. It sounds much better.

I'm still hearing something odd occasionally within the first 5-10 minutes of use, like a transient level drop of about 25% with a little distortion/loss of tone thrown in. It lasts for a second or two at a time when it happens. It sounds a little like a blown speaker, but I know it isn't that as I only hear it when I use the Mac as the power amp, not with the Mesa 50/50 or the MV-962 (at higher volume levels). It may be either the Mac or the CTP is still warming up? It does seem to go away after 10 minutes, so I don't know if this is something to be concerned about or just an artifact of the amp and CTP warming up. BTW, the CTP is still very new, with less than 3 hours use, so there may be some break-in related noises with it as well? I know Brad recommended allowing the CTP to run for 30 or more hours continuously to aid with break in, and I still need to do that. I'm going to keep it on for a few days beginning tonight and really let it burn in, so it's possible that may resolve that issue.

I don't have a lot of time yet with either the Mac or the CTP, so I am still getting to know this gear and this setup. As you can tell, I am still getting my head around the right way to use this equipment. I'm loving the tones I'm hearing, but I'm climbing the learning curve on what works/doesn't work.

Another factor may be my guitar signal. At this point my guitar signal is unbuffered and passive, but I have a TPC1 on order and will be incorporating that, new 25k ohm volume pots, and probably an OBEL as well. I had been wanting to make some changes to my guitar for a while, and this site has really helped me crystalize my thoughts and come up with a plan. I think I'm going to be very happy once the dust settles, but in the mean time it's still very much a work in progress.

Anyway, sorry if this rambles a bit, but I greatly appreciate the suggestions you've given me. I was hesitant to run the CTP's rear trim pot at full volume as I assumed the signal I was sending to the Mac was already too hot, but that's clearly what the Mac needs to work as a guitar amp. Before making these corrections I may have been hearing the some output distortion from the Mac, not the input clipping as I had originally thought.

I'm really looking forward to getting this gear sorted out -- this setup is going to produce a very sweet tone once I get these kinks worked out.