Thanks for the responses.

I can tell you that I don't like eggs because I have tried/been forced to eat them. I can tell you that I like steak (if you count filet mignon steak) because I have enjoyed them. But I can't tell you that I like or dislike a food that I have never tried.

And that's the point here. I've zero experience with Marshall amps. I've 2 now, but have owned them less 10 days! I am also a beginner guitar player.

So... what do I like sound-wise? I don't know. And that's all I'm asking: help me discover tonal options. If we all already know exactly what we like/dislike, won't life be boring like hell?

If I can improve the Marshall-tone on my Marshall amps, I would love to. I just don't want to spend $$ and turn a Marshall into a Fender because I've already enough Fenders.

Anyway, I've been fiddling with the MG15CDR and plans for this weekend are:
1. Swap out the power supply caps to solve the bang/spark noise when I switch off the amp. That mod worked for 2 Fenders. May yet work on a Marshall...
2. Swap in an audio taper pot for the drive channel volume control to have more adjustability. Yes, I continue to struggle with overly loud amps.
3. Swap in a bigger value pot for the clean channel volume control, again to have more adjustability.
4. Maybe do a LED/germanium diode mod like what I did with the Pathfinder

Celestion has an 8" Eight 15 speaker that claims to "upgrade your bedroom blaster with an authentic British tone" (whatever that is, heh?) and that may be a mod down the line. Of course, I won't know whether I'd like that mod until I try it out 

Quote from: nikkram17 on April 27, 2014, 01:04:52 PM
i just want want an amp that has a volume control and a tmb knobs,coz i have a zoom multi effects and can ran into a 4x12 cab,. and specially its non complex and simple as the noisy cricket to built?

Your set up is similar to what I started off with, except that I had a Joyo American Sound to do the tone control.

Why don't you use the Tonemender circuit (http://www.runoffgroove.com/tonemender.html) for TMB, then a plain Smokey Amp circuit for the power amp?

Or you may be able to skip the second op-amp in the Tonemender circuit if the LM386 has enough gain.

Actually, I don't like eggs. Long story of being force fed eggs as a kid.

But let me rephrase the question since there are no stupid questions. Just misunderstood ones.

For Fender amps, I see generally and that's probably just my observation (via Google) and interpretation of search results, a recommendation for "American" sounding speakers. Something bright with great cleans to match what Fender amps are good at. At least their SS amps.

On the other hand, I am completely unfamiliar with Marshall amps and what it means by "Marshall" sound.

So would "British" sounding speakers be the natural swap ins to keep or enhance the "Marshall" sound in Marshall amps? Or would an Eminence Ragin Cajun be more appropriate for my MG30CFX?

Or you can tell me that there is no such thing as a "Marshall" sound. And that is as good an answer as any.

If you are trying to replace the MPF102 on the Noisy Cricket, use the whole 741 op-amp section of the schematic.

The point of the op-amp in the schematic is to create some grit/distortion/overdrive.

I don't think gain with the LM386 is a problem. If you look at the Smokey Amp design, it didn't even have a pre-amp stage.

For my first DIY guitar amp, I used an overdrive pedal (Joyo Vintage) feeding into a TDA7052A audio amp kit. I didn't bother to use a pre-amp stage since (a) the TDA7052A has enough gain to deal with guitar-level signals and (b) the overdrive pedal took care of the "sounding like a guitar amp" feature...

What's the best speaker upgrade for a Marshall (e.g. MG15CDR and/or MG30CFX)? Celestions? British sound?

I think I've a pretty good handle on Fender amp speaker upgrades but am totally new to Marshalls.

Thanks.

Quick update here on the Fender Reverb Amp aka first generation Mexican-made Frontman 15R.

I bought a couple of 2200uF 35V capacitors off Eb*y, swapped them in and that effectively cured the amp of any residue buzzing (noise you hear with all controls set to zero). It looks like the original power caps were faulty.

The capacitor swap also cured the amp of the cackle and spark noise coming from the speaker when I switched it off. Which was the other annoyance.

Woohoo!

I took the opportunity while the amp was disassembled to do some A/B testing of various op-amps I have lying around.

For U1, which is the clean channel input stage and originally a BA4560, I tried an NJM4580DD, TLE2072 and NE5532. The one I liked least was the TLE2072. It sounded colder/harsher. I ended up using the NE5532. The end result was a very chimey clean channel (even without the reverb) when used with my Squier CVVB.

For U2, which is the overdrive channel and originally a TL072, I tried out the OPA2132 and OPA2134. Interestingly, the OPA2134 sounded better. The OPA2132 sounded harsher and colder.

All this is subjective, obviously, with the additional caveat that I'm an inexperienced guitar player.

Other mods I did:
1. Swapped out the resistors in the input circuit around U1A for 1% metal film just because I could...
2. Reduced the power amp feedback resistor to 33kohm from 100kohm
3. Jensen C8R speaker. This last mod is one reason for the resistor change in #2 as I only had the 4ohm version of the speaker and the original was an 8ohm. The TDA20x0 family devices tend to be able to double the power output when moving from an 8ohm load to a 4ohm and I'm certain that the power transformer can't follow...

The volume controls have the same problem as all the other amps I have (other than the Vox Pathfinder 10 now) in that the living room-usable range of volume is limited. So I may yet pull the amp apart and put in a voltage divider network at the input of the power amp.

These are clipping diodes. The schematic has a note about what they are.

You can google for "diode clipping guitar" which gives you a ton of articles on what they are and options e.g. types of diodes to use.

I have bookmarked articles such as the following:
http://krooshof.home.xs4all.nl/instrumenten/fuzzing.html
http://www.diystompboxes.com/cnews/mods.html

Diodes.

Probably used for clipping?

And... Eureka!

One of the things that folks don't like about the Vox Pathfinder is the usability of the drive "channel". Turn it on and you more distortion than overdrive. To the point where, if Google is fact, the "LED mod" is the most popular mod on Pathfinders: where the LEDs that are used to clip or distort the signal, are removed.

I don't like the default distortion effect and have been looking for a middle ground: to have more adjustment in the gain control between high gain clean, crunch, and distortion.

I think I have found my middle ground. YMMV.

The combination is the following:
1. Swap the volume control for an audio taper pot, replacing the factory linear taper. "Part is Parts" has the right one that will fit the factory chicken head knob.
2. Solder a 1M resistor in parallel with R7 to reduce the gain in the second stage pre-amp. This gives more adjustability to the gain pot.
3. Increase the clipping voltage of the LED pair.

For #3, LEDs apparently clip at 1.6V or more (I've not managed to measure myself, but if Google is fact...). So the trick there, if you want to have more adjustability in the gain control and therefore more headroom, is to add more diodes in series with the LEDs to increase the clipping voltage.

My choice was a pair of germanium diodes which I got from Frys (part number NTE110MP). They had about 230+mV (measured) in clipping voltage. So putting them in series would increase the clipping voltage by that much. For even more headroom, one could use another set of diodes in series or a silicon diode.

Anyway, in addition to the germanium diodes, I added in a 220pF cap in parallel. This is, in theory, supposed to removed some of the high frequency fuzz. Not really noticeable, to my old ears, but the 220pF value was chosen because I thought the original 100pF I used didn't work that well.

Finally, I added a 100ohm resistor in series with the LED+diodes+cap. This is supposed to mellow the effect.

The outcome of all these changes is a much more usable drive mode. More crunch and a very marked reduction in fuzz and fizz.

Pics of the mod are attached.

IMHO, this is better than removing the LEDs all together as you still have an option to go all out in metal distortion mode.

I'll be putting everything back together again and using this over the next few days.

EDIT: Put in lower res pics

I've confirmed (2 years of woodworking classes) zero woodworking skills. So a 10" speaker is out of question.

But good point. I'll try the amp with my 1x12 cab to see how the sound changes.

Perhaps a speaker-out socket will be in order.

I have an MG30CFX which I like a lot. That's DSP-based tho' and no schematic so far. So no modding.

I started looking at my new/used Marshall MG15CDR last night.

Nothing wrong with it. So I haven't quite figured out what to do with it. Perhaps socket the op-amps and do some swapping.

Picture of the innards attached. The schematics can be found at amparchives.

The thing at the bottom below the PCB is the reverb unit. It looks rather fragile: hanging from some springs.

The power amp is different from the one on the schematic. This one's an LM1875 which I guess is an equivalent. I like the big heatsink.

I'm taking suggestions for mods/not-mods/experiments

I managed to "finish" up the mods that I wanted to do on the Vox Pathfinder. It helped that the parts I ordered arrived.

Although not exactly the right parts: the audio taper pot was solid shaft instead of split/knurled. So I have to get a chicken head knob with a set screw in order to use the pot. The other option was to get the "right" pot from Eb*y with an unpredictable ETA.

The other new parts were a bunch of different op-amps. Woohoo!

So changes I made included:
1. Swap out the linear taper volume control for the audio taper. I instantly had a better, more usable volume range. Otherwise, usable volume = first mark on the dial.
2. Soldered a 1M resistor across R7 to half the effective resistance hence reducing the gain with Drive. The theory was to have Gain control with more usable crunch range before fuzz. Result: not really effective.
3. Desoldered the 4558DD op-amps and put in sockets. For newbies considering modding their amps: desoldering wick is your friend
4. I replaced U1 with an OPA2164 and U2 with an NE5532. The latter because U2A was just a post-tone pre-amp so low-noise and clean was important. The former because I'd used the same chip to replace a TL072 on the Fender 15R and I got a "better" crunch from that swap.

I don't have an experience enough ear to really tell the benefits of the op-amp swap. At least, the differences weren't as obvious and I didn't spend any time doing A/B testing before I put everything back together again. But the swap didn't hurt.

I'll use the amp over the next week to see how much more I like it.

Finally put back together the Pathfinder.

Mods include:
1. Green LED (see pic).
2. Jensen MOD 6-15 8ohm speaker

It was fun to play my usual power chord sequence while watching the LEDs. The green seems to clip earlier than the red: my interpretation from seeing the green LED come on earlier and brighter than the red. I can't speak to the improvement or lack-thereof from the LED change as I didn't spend that much time playing on the un-modded amp.

On the other hand, the Jensen speaker is a nice upgrade. Better, richer sound, and very nice chimey cleans. I can tell the difference from my Fender FM 65R.

I still don't like the following:
1. Jump in volume when switching from clean to drive
2. Usable volume when in drive is at the first notch. Yes, the volume control IS a linear taper pot. I measured it as suggested by Roly. An audio taper is on order

In drive mode, gain is good for crunch until 9am. After which it's fuzz overdrive. It's pretty similar to the FM 65R (dry crunch until 4, then fuzz overdrive...).

I'll be using the Pathfinder over the next week to see if the noise level is acceptable. It's definitely better than the Fender 15R (in the other thread): you really don't hear any hiss until you switch to the drive mode. If I don't like the noise level, I'll have questions about op-amp swap 

I used a bunch of aluminum foil and shielded the reverb unit. Pic attached.

Also added a ground wire from the heatsink (which is apparently the common ground point) to the foil.

All that manipulation eliminated the reverb buzz when all the controls are set to zero.

That still doesn't eliminate buzz when I turn up the reverb.

All in all, the amp is noisy. Very noticeable background hiss (without the amp, all controls to 0).

Otherwise, it plays very nicely. Especially through the G12C/S speaker on my 1x12 cab. But as I said earlier, there's some cheating there because the cab includes an L-Pad that cuts down the noise level.

I'm going to put this aside and look at the Champion 110 next. Same basic circuitry, same buzz and noise. I'll probably replace the reverb unit on that one.

So I dug into the Frontman Reverb Amp (Frontman 15R).

It has the "newer" circuit board with a TDA2050 power amp instead of the now-obsolete uPC1188H.

Touched up some of the solder joints, replaced a cap. Then found out that the buzzing came on only when I connected the reverb wires. Without the reverb wires connected, there was hiss, but no buzz.

This is with the volume/gain/all controls turned to zero with no guitar connected.

One thing I found out during all this experimentation was that connecting a speaker cab through an attenuator (L-PAD) will actually cut off some of the noise. Presumably because the overall signal from the amp is reduced, hence the noise as well.

As a reference, I tried out the Champion 110 that was delivered today (yes, NAD again) and heard the same thing: hiss and some reverb buzz. That is probably also normal because the Champion 110 shares a lot of the same circuit as the 15R.

I see a noise-reduction project in my future. Question is: which amp should I work on first?