I have mentioned my Marshall Haze 40 in the “For Sale” section in the past.

I bought this amplifier (Serial code I-2010-05-….-E) because I thought my Marshall G15RCD solid state (my first new amp ever) was rather lacking in oomph. (This was before I had any knowledge of amplifiers, and had limited knowledge about guitars, despite being a player (that’s a lie) for about 14 or so years.) Apparently the G15 is a bottom-feeding pond scum type practice amp, but, hey, with spring reverb? I thought I needed more power. I wanted valves, so - Mistake. The Haze 40 was way too loud, the Haze 15 might have been a better choice, many other valve amps might have been ideal.

The claim is that 40 Watt is not much louder than 15 Watt (just over 3 dB louder?), but there is no way I can even open up the Haze volume to 5 (1-10 scale) for “indoor” playing with the Ibanez. Max seem to be at around 2½ - 3, which must be very few Watts, with the guitar volume at about 2. This is still loud. Being a bedroom player, I put it up for sale. No takers.

Since joining this Forum, I have gained a lot of Internet knowledge about electric guitars and amplifiers. Seems that “HAZE 40” is not words used in polite conversation. Early production problems. Seems that “Marshall” and “Haze” should be mutually exclusive terms as well. But, for every nay-sayer, there is a happy yay-sayer. The internet has lots of information on modifying the Haze series to resemble a Marshall amplifier. Seeing as nobody was interested in buying this almost-new amplifier, I decided to try and use it anyway.

Since advertising the amp, I have moved into a bigger room. That should help. Apart from being too loud, once I reached “maximum bedroom level” (too loud) my ears experienced the amplifier as “harsh” and unpleasant. Too much horrible high frequency on the Normal channel. A jarring, not-nice tone, to my ears. Ah, yes, the “treble” control to the rescue? No. The amp sounded bad. The “Overdrive” channel is darker, and I ended up playing on the OD channel, with Gain down low, allowing me to turn the Treble control up from zero. Which made me think a Master Volume on the clean channel might have helped too.

I resisted the suggestions to fit an attenuater, but have come to accept that as a way to open up the Volume to drive the understressed valves past “idle”, and into sweet-spot valve-sounds territory at “bedroom” volumes. Dissipate about half the wattage going to the speaker as extra waste heat. What would another 5 Watts waste heat matter? I hope to test this soon, and hope that, at low volumes, the attenuator will not impact the tone too much. Of course, at low volumes the speaker is understressed as well.

An aside: This is a budget amp – low-cost material. Removing the chipboard self-tappers that help to hold the back panel on is a quick way to damage the holes in the soft frame. The screws do not go back quite the way they came out, I had to re-drill some holes, and I can see that the solution will be glueing some threaded studs into the framework, for normal machine screws, like the ones going into the metal chassis at the top. I lowered the value of a sought-after amp by cutting the one-piece back into a top and bottom pair, so I can work on the electronics without having to remove the whole back, and leave the “speaker cabinet” closed while working and testing.

Split back. Will fit two more screws to the bottom panel.

Cool post. Be careful in there. Loaded caps can kill people. Learn how to discharge these.

Fyi. 5w valve amps will also be too loud for bedroom. My JP never gets past 2. Even at garage days.

An increase in vol only works the power tubes. The gain typically pushes the preamp valves. Either way.. i like to set a valve amp on the cusp of break up on the clean. Liberally blend the gain and clean until it get there. Then either a boost to push the valves to saturation.. or in the case of 2 channel amp.. set the dirty the way you like it. Admittedly.. i know nothing about these Haze amps. Nothing about bass mids and treble sensitivity.

I had similar tonal issues with my laney. Very harsh. Very trebly. I subsequently learnt.. it wasnt the laney. It was me. Part of me was chasing what the interwebz was saying.. and i wasnt using my logic. A fellow forumite who took it off my hands made it sound sublime

I know it wont help with modding.. but maybe it helps with setting it up.

Also.. volume control on the guitar rolled back 2 3rds also takes the edge off a gainy sound. Then for gain.. just wind er up. I heard a feller with some crazy good chops playing through a Haze40, it sounded bloody great.. fwiw. Good luck.

I forgot to warn readers about the dangers of splitting rhe back, bandsaws are notorious for removing fingers. Unfortunately much of the work on amps require full Voltages to measure. Caps charged. I live with optimism.

Guido
If you have not posted how the Laney became a sublime amp, please do.

While looking for a solution to the excessive volume, and harsh, overly-treble-high-frequency unpleasant problems, I researched speaker choices. At that stage, the Celestion “A” Type was a new choice, and the frequency response curve looked like just what I needed to cut off the higher frequencies. It did take some time (in years) to fit that speaker, but I did, eventualy.

A Type graph, off Celestion site. Sharp cut-off at 5 kHz. Small peak at 2 – 4 kHz. Slow low-frequency roll-off. No mid-range dip.

Much hated PCB layout. Stock speaker. Apparently not too bad once broken in, my amplifier did not improve in sound quality. Which leaves a problem – If I do manage to “tune” the amp, will the stock speaker be OK after all?

The new “A” type.

They say these valves are too close to the speaker, and have a hard, short life. No closer than many other amps, much better than a lot of Fender-type builds.

This is a 40 Watt valve amp, and this here speaker is only 50 Watt? I do not plan to ever send more than 10 or 20 Watt to the speaker, even if I do get to play in a larger room. The speaker should be safe for a very long time.
The “A” Type speaker does help, the harsh high-frequency jarring, unpleasant sound is gone, replaced by a smoother, fuller, mellower sound (with the Humbucker guitar). The Normal channel is now OK with volume at 3 (loud…, guitar only at 2 or 3), but this speaker emphasizes the “dark” (Internet says “muddy”) character of the overdrive channel. The OD is not of much use now at low volume, I have to open up the treble a lot, which skews the tone again.

If I have to be honest, this might not be the ultimate solution. The amplifier is better for my use, but it lacks “sparkle” with this guitar. It is not dead, just, well, not quite there. Not that it is lacking in treble, I can still hurt my ears. I shall test with the single-coil guitar as well. Apparently a Celestion Creamback (65 Watt) might work - some internet posters say it does. Expensive upgrade, maybe later. First, some easy amplifier mods.

modulator alas.. it didnt become sublime in my hands.. i just heard it being sublime in said forumites hands.

It was largely tweaking the controls as above. I was treating it like i would a SS amp. It was its own very different animal though. Also always tried winding it to hit the sweet spots.. it didnt need it.

That amp had a celestion 70/80 speaker. It did sound bassier through a 2x12 with jensen c12q.

I only learnt about the preamp and power amp blends from sitting with said forumite

Onward with my quest. My research indicated that all valve amplifiers are not alike. They differ in sound character due to design, components, and, of course, valve type. Who knew? I did not. Adding amps to my collection, my ears seem to like 6V6 power valves in simple low-Watt amplifiers, driven by low-output single coil Stratty guitars, with a bright, responsive speaker without ice-pick treble emphasis. With valve amplifiers, modifications (money, expertise) can change any valve amplifier into another type of amp. I have read up on mods for the HAZE series: Most are aimed at increasing gain to get to the legendary Marshall sound (which is?), and to add brightness to the overdrive channel (yes please, within reason). No mods to “tame” the clean channel, though – all to add more gain/grit (?). There is one sensible mod, add a Master Volume for the clean channel. Sure. There may be many more mods, but I really do not understand what the people are talking about, what this and that capacitance and resistance do to the whatever circuit giving that and such tone. Most of these mods are done to add gain and punch and volume and such. Not what I need. A re-design (re-voicing) is what I need, without all the IC junk, on a turret board. Any volunteers?

Seeing as I know nothing about the working/design of amplifiers, sorting out suitable modifications by myself is not going to happen (soon). I shall have to study Rob Robinette’s pages in detail. Being a PCB design, swapping around components will not be fun either. One could snip a capacitor leg here and there, but to re-soldering will be a hassle. I shall only do that when I have the relevant “try this one” replacement, with a new original value component in hand, long legs, to fit/re-fit. Snip the old component at the body, leaving some leads for soldering on another one.

They tell me valve amps have to be “biased”. I always took this to be something calculated at design stage, testing the bias and fine-tuning relevant resistors after assembly, to be done again when changing valves. More importantly, only to be done by valve amp experts and magicians. I was lead to believe that this is an art only handed down from father to son, in secret. Could well be. Many ways to test, maybe only one correct way. How do you do it?

This amplifier has two small trimpots (“VR1” and “VR2” on the circuit diagram, which I could find thanks to that modern marvel called “Internet”). The amplifier also has a “CON3” block on the PCB, looking like it requires a three-pin socket to go there. I would think the factory tech has just such a fitting to do the bias. The circuit diagram says “BIAS PIN 1, 3 39mV” above this “CON3” thing. The centre pin splits through two 1 Ohm resistors to the power valve cathodes. Now, posters on the net use mA as well as mV (both 39) for this setting, some sayning you need to bias for maximum 70% of plate dissipation, hence 39 mA, etc. Of course, the owner’s manual does not mention this rather important detail (“no user servicable parts inside”). And so, I would have destroyed my valves (if not damaged already) by doing just what the amp was built for – playing it.

Easy-to-locate “CON3” .

Conveniently placed VR1 and VR2. After initial adjustment to 35.4 mV. Schematic specifies 39 mV.

I started by checking the bias. This should be correct from the factory, yes? Many internet posters tell horror stories. I concur. I clipped some alligator clip leads to the three pins, centre pin lead clipped to the earth probe of the multimeter, so all I had to do was clamp the positive probe alternatively into the leads from Pin 1 and Pin 2 as I go along, far away from the circuit itself. Less Stress.

Leads clipped to the pins. Just enough space. This is a photo mock-up, no power.

I was amazed to measure 75 mV for VR1 (Valve 5) and 48 mV for VR2 (Valve 4). The valves were being cooked in a bad way. Harsh sound indeed.
Setting the bias is an “adjust VR1, adjust VR2, adjust VR1, adjust VR2” procedure. I set both close to 35.4 mV for a start. Too cool?

(Must check HT and filament supplies as well. The circuit diagram shows the filament supply to Valve 1 to be separate from the rest, taken off the 12.6 VAC tap. Why? All three pre-amp tubes are ECC83-A? Oh, wait, I see. Pre-amp Valve 1 has DC filament voltage. Cute. Still is a noisy amp.)

Does it sound better? Maybe. How would one be able to tell at my low volume? I can say, when it is warmed up well, it does appear to be “smoother”, and I perceive it to have less bass/more treble. (But, my ears seem to get more treble-sensitive as I go along. Or is it really the amp “opening up” as it gets warm? I find this to be true with my valve Hi-Fi as well.) Is this a result of cool bias resulting in “thin” tone? But, here’s the thing, turning the speaker away from me, opening the Normal volume to 5, with the OD channel set at Gain 5 and Master Volume 8 to match, with the guitar volume at 5 – 6 (Ibanez, linear pot?), covering my ears, the system reveals some interesting and exiting dynamics, which sounds like fun, and encourages me to keep on making noise. It did not have that character, before. Fun as it may be,
1. it is beyond way too loud, and besides,
2. I cannot play well enough to exploit this newfound tone.

I really do need to explore this, if an attenuator does not work, I see myself in the market for a smaller Marshall (DSL 1, 5 or 15? Other, better options?), suitably speakered and modded. (Rob Robinette has a 1 Watt JCM 800 (and 22 Watt) circuit on his site, but after the 5F1 build, I am not feeling in the mood to go that route. Would be fun, though.)

I am still amazed by this amp’s volume. I have a 15 Watt Ibanez TSA15H, which Internet posters agree is weak in volume (it is), and the small (ha) 5F1 build, which gets to window rattling volumes, but this Marshall Haze 40 is, well, very loud when I plug the Ibanez into it.

hi

I would suggest you get hold of JP Le Roux at lerouxampworks with a view to buying one of his great little amp designs. He will happily supply to suit the speaker of your choice and probably have some good advise re valve amps generally.

JGP, such an amp may well cost more than my entire collection, I would not be able to go audition it, and the final speaker choice would only be possible after completion and testing with a known speaker. I would like to look through his designs though, someday. As for advice, still waiting...

guido, I wonder if a 1 Watt amp would be good - not enough headroom maybe. (OK, the speaker sensitivity measured at 1 Watt thing aside - different guitars, different environment, tone perception, etc. Hey, everybody keeps on telling everybody else 3 dB is almost not noticeable, but they also recommend a 97 db speaker over a 95 dB speaker for more volume and more headroom and less distortion...) Seems like one requires a bit of volume to have fun anyway, unless the amplifier design would allow the sweet tone at low volumes. Including cleans and overdrive. Looking for that one. 5 Watt can be pretty loud, yeah. You should really poke a dB meter at it, and report back with details such as speaker sensitivity, estimated (measured?) amp output to speaker, guitar pickups, and so on.