A few quick quesitons before I start a project...

[mills]

Hi everyone...  just started poking around here today, but it looks like lots of good info is around.

So, where I'm at is, I have a 30W solid state marshall that I rarely use but I think I'd get almost nothing if I sold it.  I was hoping someone could help answer a couple quick questions before I spend a ton of time researching a project that probably won't work.  

What I was thinking about doing was tweaking the preamp a bit, and hopefully changing things around to get a bit more clean volume out of it.  I don't expect to be able to turn it into a monster, but just a bit more would help.  I understand that its probably cheaper/easier to give this away and buy a bigger amp... this just souds like more fun.  I also expect that I'll have some serious reading to do about wiring something that connects to mains power, and making sure I don't die in the process.

That said, here's what I was thinking and the questions that came up...

1) I'd like more clean volume from it.  Its 30W right now (and I think just a chip for the power amp), and I think that if I could get it to 60W the rule of thumb says I'd get about 3dB more?  So Ideally I'd like to get it to the 60-100W ballbark.  After a quick skim on here, I think thats doable with 1-2 LM3886's.  I think I'd need a new power transformer, changes/replacements to the power supply, and probably bigger heatsinks.  Is this a reasonable goal, or is that just crazy talk?

2)Speakers.  What's a reasonable 10 or 12 inch speaker to handle that?  They have to exist, but I always see 25 and 30W ratings on guitar speakers, but I thought a distorted tube amp tended to put out significantly more than its rated power and still use these, so what kind of options do I have?    What do you guys use, or do you just drive more than 1 speaker when the wattage comes up?  If I'm replacing the speaker would I be better off going for something with a higher sensitivity and not bothering with other mods?  I'm open to a neo speaker to drop some of the weight that the heatsinks and transformer might add.  I would just like to be able to use most of the wattage the combo puts out, with a decent sensitivity, and not sound terrible.

2b) bonus speaker question... With an open back cab, is there less consideration to cab size/etc, or am I looking for trouble if I don't really check speaker parameters the way I'd need to for a sealed/ported design?

3) The preamp.  I'd like to maybe tweak the dirty channel, and probably make sure that the clean channel either clips more smoothly than it does now, or not at all...  I assume that some improvement could be made, but I'd have to try and sort out if the clipping I get now is the pre or power stage.  This is less key because I figure that if I can get through swapping the power amp and supply around without hurting myself, I can probably mess around in the preamp with less risk.

Thanks for taking the time to read, and any help or guidance that can be offered.  I don't mind doing my reading, but an initial push to see if my goals are too lofty, or I'm even asking the right questions is appreciated.

PS.  Sorry about any typos, my screen is jumping around while I type and I can't really see everything....
 

[bry melvin]

I've never played a SS Marshall but:

30 Watts? should be enough to power a reasonably efficient 4 or 2 12" cabinet... (or 10s)

That should give you that few extra DB

assuming the 30 Watts is output and not power consumption.

I know they are  different...but have played outdoor concerts with a 50 Watt tube marshal (JCM 800) stack

Also does your marshall have a "DI" or Line out  or effects send and return JacK?

If so you could just build/get yourself an external power amp and Speakers.

Simple solutions.


As far as neo speakers...the ones I'm familiar with need too much power for this amp.

Might consider something like Jensen Mod 10-35 speakers.

[mills]

Thanks for the comments.

I guess I should say that I'd like to keep it a combo... that I'm not really looking to get a bigger cab, or haul around a power amp/etc.  I'm more a bassist, and just use this to jam with friends now and then, but it'd be nice to have a little more volume when I do (and I think it'd be an entertaining project). 

I thought it output 30W, but I could well be wrong...  I also thought that the "tube watts" thing came from the tubes putting out more than the specified 50W because they could be pushed past it without sounding harsh and terrible. So that plus the speaker area should give you lots of potential to be loud.  This little combo is a long way from a stack, and I'd never expect to get that kind of volume out of it.  I just figure that I should be able to squeeze a few more "clean" dB's out of it one way or another.

[bry melvin]

Well "watts" is often used more as hype than reality IMHO. Some companies rate their amps more conservatively than others. If Marshall is still as conservative with today's SS amps as they were in years past with their tubes. (I'm still using 1982 JCMs) Your amp might very well power external speakers adequately...After all the famed Fender Super Reverb 4X10 was only rated at 40 watts.

Seen plenty of club bands with 25watt Rages (Peavey) feeding a 4x12

The solid state amps I use roughly compare with the Tube amps I use...Gotta remember MOST tube amps favor the midrange...where our hearing does best, so to make a fair comparison you might need to set the mids higher than bass and treble. Probably why Abbot and others had preferences for SS for scooped mids metal sound. Drop the mids to 0 on a JCM for example and it gets weak.

Generally a sealed cabinet takes more power to drive similar to Acoustic suspension Hi Fi speakers. Have to compress that air. It also has different tone emphasizing lows more usually. Although it sounds counter-intuitive however stuffing a sealed cabinet at least 50% with fiberglass insulation can make it behave like a much larger cabinet so that isn't written in stone.

I don't know what speaker is in your amp. If for example it has a 16 ohm celestion and the amp is rated at 30 watts at 4 or 8 ohms just changing the speaker to the lower impedance can make a big difference. Changing to a more efficient speaker of the same rating can make an improvement.

Changing a power amp would be quite doable if there are separate circuit boards for the pre and power amp. Adding a power amp to a line out won't necessarily make it not a combo...Chip amps can be quite small and there may be room to shoehorn one into the cabinet or chassis WITHOUT removing anything. I've tucked 2u worth of Rack equipment into a combo before! (Processor and EQ). Leaving nothing plugged into the original speaker connection shouldn't bother an SS amp.There may even be room OUTSIDE  your chassis above the speaker... I've done that before ...adding electronics and covering everything (except the heat sink) with a modified cap pan from an old Fender

[mills]

Good thoughts, thanks again!

I should double check the speaker, but thats a good point about checking the load the speaker is providing.  I'd more thought of looking at sensitivity... I unfortunately don't have the cab in front of me, but I think it says 4 ohms (which I assume is just the lowest load I should attempt to drive).  No idea what the speaker is at, but the datasheet on whatever chip is in there now should give me some ideas what I can use without wrecking things.

I also like the line out to an attatched power amp suggestion.  I hadn't even considered that.

[J M Fahey]

You can leave your amp stock and built  powered speaker cabinet., driven from your line out.
One LM3886 can supply 50W RMS into a good sounding, cheap, and very efficient Jensen MOD 12-70 .
Your extension cabinet will be the size of your 30W combo, and very LOUD.

[mills]

Well, some more thought, and I think I have a plan.

Going to swap the power amp as discussed and upgrade the speaker to something appropriately rated and sensitive.  I expect that'll probably be enough to do what I need. 
But depending on how much room there is, I might think about dropping a powered line out in there as suggested.  For that, I'd imagine that a stereo chip amp kit with one power supply is sufficient? 

Anyway, thanks for the thoughts and guidance... I'm sure I'll be back with questions once I can get started though!

[bry melvin]

   

I think you already have a "line out."  (DI) Direct injection.?? Most marshalls 've seen do.

If you add in another stereo power amp and use the Direct out make sure that it IS stereo out I don;t think it is. Not on any Marshall I've seen.

For one speaker you need a mono power amp anyway. Not stereo.

There are pcb kits useable for LM 1875 or tda20X0 L M3886 amp chips
the most current TDA is 2050 nominally a max of 32 watts.power is dependent on voltage
That level isn't going to make a significant difference UNLESS you add an external speaker for the new amp. In which case the suggestion to add a powered speaker..(new amp in the new speaker box) makes the most sense.
Using a stereo setup is probably not a great idea.You will need TWO speakers for the new power amp There are kits available for either.

Adding one INSIDe your amp you would need something like a 3886 mono amp. This would make significant improvement. Remember hearing is logarithmic not linear. You need to approximately double sound level to make a significant difference. anything smaller than a 3886 near its max voltage supply isn't going to do the job.


One time and money saving thought: using DI if you are "jamming" where there is a PA/mixer  all you really need is a patch cord.

[mills]

All good points.  My amp does have a line out, but its a rare day when we have a PA around.  I'm still probably not going to pack an extra cab around, we just occasionally have an extra cab or two (passive) that we can use.  And, really if I was looking to save time/money I'd just buy a bigger amp.   

I think after looking at some speakers, it might be smarter to just load the combo with an 8 ohm speaker and add another plug for a passive cab and only use it with other 8 ohm cabs.  Should have thought of that in the first place.