Need advice on Marshall Haze 40

[Ernie]

I have this combo and have used it in the studio for less than 10 hours.

The other day, when playing, the boost channel fizzled - just died. It makes strange popping sounds and sometimes sounds like bacon frying. The normal channel is working just fine.

Is there a simple solution? I have used Marshalls since 1988 and have never had one problem until now. I'm totally perplexed.

I have emailed this problem to Marshall directly, but they have failed to respond. Please help, if possible.

Ern

 

[jcmjmp]

Try new tubes? Personally, I'd bring it back.

 

[Ernie]

I hope it only tubes; but why would one channel work fine and the other die? Are there different tubes for each channel?

I ordered this from American Musical Supply. After contacting them, they referred me to Marshall, who haven't returned the call/email.

 

[pacAir]

I hope it only tubes; but why would one channel work fine and the other die? Are there different tubes for each channel?

Different designs do different things with the tubes. The ECC83/12AX7 tubes have 2 sections, essentially 2 Triode tubes in one common glass envelope and with a common heater.

Since there is a single input on the Haze 40, it makes sense that the first half of Tube #1 is used as the input stage and both "channels" would share this (this is the tube with the metal shield around it). The second half of tube #1 is probably used for the Clean channel preamp. Since you still have a working clean channel, this tube seems to be working fine.

The second tube probably has the first half used for the Boost channel preamp (where the distortion is generated) and the second half to return the signals back to normal levels after the passive tone controls. Since you still have clean signal AND tone controls, it appears your failure is in the area of the Boost preamp half of this tube.

This is not to say it definitely is a tube failure though. If swapping tubes 1 & 2 (or 2 & 3) don't change anything then it is not a tube but some other failure that will have to be fixed by a technician or the factory.

The last tube is the phase-splitter which drives the output tubes. In other amps/preamps, a fourth (or fifth) 12AX7 or similar tube could be used in a tube-driven effects loop or for Reverb or vibrato/tremolo. Since none of these things exist in the Haze there is no need for a fourth or fifth tube in the preamp section.


Steve

 

[Ernie]

Steve,

Thanks for the valuable info. I haven't turned a screw on the amp since it is so new. But, checking the tubes as you mentioned (swapping them around) would not void the warranty, would it?

 

[(war)thrash5150]

wow, there seems to be so many problems with these amps

 

[pacAir]

If the back of the amp is removed carefully so the screws do not show any abuse and the tube swap is done carefully and correctly there probably wouldn't be a problem in my opinion. However, if you are not well versed in this stuff you can have problems changing tubes you cannot see (it must be done by touch unless you remove the chassis from the cabinet).

If there is any doubt, take it back and don't chance it.

These amps have seemed to have their fair share of teething problems. However, their basic design and construction seems sound, Since I rebuilt mine after massive shipping damage and fixed a factory mistake (wrong resistor value affecting the footswitching circuitry) I have had few problems. I have properly tightened all hardware and rebiased the output tubes as well.

I don't like the fact that the combo doesn't have auto output transformer tap switching on the 8-ohm jack (necessitating the use of a custom "speaker Y-cable" or a two-jack extension cab and a manual change in speaker jack used).

I also noticed an odd problem using the Standby and On/Off switches. I was checking out the amp at home just prior to taking it out for its first gig and was in a hurry. I mistakenly turned the Standby and On/Off switches to the OFF position together. About and hour later when I set up my amp at the gig I turned on the amp (with the Standby switch in the Standby position) and noticed that the power indicator did NOT light up and the effects button indicator lit up then faded out. I tried this several times and the same thing resulted. Next, while the amp was OFF I switched the Standby switch to ON for a moment, then off. This time when the amp was turned ON with the power switch, the amp came up normally. Apparently high voltage stored in the High voltage filter cap(s) was leaking (back-biasing?) into other circuitry and preventing the amp from turning on. Discharging the cap by taking the amp out of standby must have bled-off this voltage and the amp resumed normal operation.

I wish Marshall would post the schematic of this amp. I hate taking educated guesses on technical matters that SHOULD be published in the public domain for service purposes.


Steve

 

[Ernie]

I spoke with an authorized Marshall technician today who told me these amps are experiencing a "bad batch run" of caps (capacitors) and that may likely be my issue; howver, he has to open it to determine the actual causes. Anyway, I am taking it over to him tomorrow (11-17) and will post back here whatever I learn from this. Hopefully others having similar problems can be helped from this aggravating experience.

Check back in a few days (or a week?) and maybe there will be new insight.
And, thanks again, for your insight, too. I'm learning as I go...

Ernie

 

[Jonathan Wilder]

Different designs do different things with the tubes. The ECC83/12AX7 tubes have 2 sections, essentially 2 Triode tubes in one common glass envelope and with a common heater.

Since there is a single input on the Haze 40, it makes sense that the first half of Tube #1 is used as the input stage and both "channels" would share this (this is the tube with the metal shield around it). The second half of tube #1 is probably used for the Clean channel preamp. Since you still have a working clean channel, this tube seems to be working fine.

The second tube probably has the first half used for the Boost channel preamp (where the distortion is generated) and the second half to return the signals back to normal levels after the passive tone controls. Since you still have clean signal AND tone controls, it appears your failure is in the area of the Boost preamp half of this tube.

This is not to say it definitely is a tube failure though. If swapping tubes 1 & 2 (or 2 & 3) don't change anything then it is not a tube but some other failure that will have to be fixed by a technician or the factory.

The last tube is the phase-splitter which drives the output tubes. In other amps/preamps, a fourth (or fifth) 12AX7 or similar tube could be used in a tube-driven effects loop or for Reverb or vibrato/tremolo. Since none of these things exist in the Haze there is no need for a fourth or fifth tube in the preamp section.


Steve

This is incorrect. Most multichannel amps use different preamp valves for different channels. However, they get two gain stages out of each valve so both stages of the same valve are used in the channel that a particular valve socket is wired to. In other words, both stages of one valve would do the clean channel while both stages of another preamp valve (or more) would do the dirty channel. This explains how one channel can work fine while the other could be dead if you were to loose a preamp valve. But since one channel is working, the problem is definitely somewhere in the preamp circuitry and the power amp is fine.

In amps where the channel outputs are "mixed" (such as in the Super Leads) one 1/2 of the valve is Channel I while the other 1/2 is Channel II. The outputs of these channels are mixed together via "mixer resistors" and fed into the input of V2. But this is not the case with this amp.

Also, they do not have a common heater. They have individual heaters connected in series, with pin 9 being where the heaters connect together. Pin 4/9 is one heater while pin 5/9 is the other. You can either run the heaters in parallel by bridging pins 4 and 5 and applying the heater voltage to pins 4/5 and 9, which only requires 6 volts heater voltage (most common configuration) or you can use them in series by omitting the pin 9 connection and applying 12 volts to pins 4 and 5, hence the "12" in 12AX7(in US valve numbering schemes, the first 1 or 2 digits in the valve number indicates required heater voltage).

 

[MKB]

I just yesterday received a "defective" Haze 40 from an ebay auction, turns out the only issue with the amp (so far) is the most microphonic preamp tube in V1 I've ever seen. When you handle it it sounds like an egg shaker; the only other tube I've seen that rattled this bad was some very old worn out EL34's. Replacing it seemed to cure that problem at least. But I only got to play it for a few minutes, will wring it out more tonight.

 

[MKB]

Well, I was able to work with the Haze 40 a bit more, and found out some interesting things about it.

First, anyone trying it out should play it briefly plugged into a 4X12 Greenback cab. It starts sounding like a real Marshall then. The Marquee speaker is a bit mellow on the high end, and a brighter speaker may help it a bit. I'm hoping the Marquee will sound better after it breaks in.

This amp seems to be extremely sensitive to microphonic tubes in V1. As I said in my previous post, the stock tube in V1 (looks to be a Chinese 12AX7, branded as Marshall, with yellow paint on the tip) rattled very badly. This was the only problem I've been able to find with the amp. I installed a Telefunken ECC83, and the rattle went away, but I really don't like those in V1 in a Marshall. So I installed a RCA 7025 (which is a bright tube and this particular one is known to be microphonic), and when switched to overdrive the amp went into crazy screming oscillation that changed frequency whenever you changed gain controls or tapped the cab. So I pulled that one out and installed a NOS GE ECC83, and it was dead quiet again. So if your Haze starts screaming on the overdrive channel, replace V1!!!

The Bright switch works on both the clean and overdrive channels, so switch it on and leave it on. Otherwise it is too dark/dull sounding with humbuckers. However, when you get the overdrive channel sounding good, the clean channel is a bit bright. It sounds like the design rolls off the treble in the overdrive channel too much. When I get a schematic I will definitely be clipping some caps.

It's not a really high gain amp, and the boost switch on the overdrive channel changes the tone quite a bit (mellows it out too). The best overdrive tone I've gotten with it is with the boost switch off, bright switch on, and boost the heck out of the input with a clean boost. It starts to get tasty then, reacts similar to a 2204 as the preamp has similar gain with the boost off. There are some real Marshall tones in there, but might take a tweak or two to get them out. I can't wait to get a schematic for this thing...

The amp seems to be well built. Marshall gets a plus for the 1% metal film resistors in the signal path, less noise. But the particle board cab is a definite negative. The top of mine cracked in shipping and will have to be eventually glued back together. Other than the cab, the construction looks very good. Those worrying about poor workmanship from India should stop worrying, it's top notch. I'm certain the particle board cab was a design decision made in England.

 

[Jonathan Wilder]

Marshall gets a plus for the 1% metal film resistors in the signal path, less noise. But the particle board cab is a definite negative. The top of mine cracked in shipping and will have to be eventually glued back together. Other than the cab, the construction looks very good. Those worrying about poor workmanship from India should stop worrying, it's top notch. I'm certain the particle board cab was a design decision made in England.

Define "top notch". Lots of players prefer the tonal coloration provided by components that are considered to be "inferior" by today's engineering standards, such as paper wound transformers, carbon comp resistors, high ESR film caps, etc etc. It seems to me that these days lots of production amps are designed with the same methods as "hi-fi" amps and think that because we use 1% precision components that our product is better, when lots of times nothing could be further from the truth.

 

[GibsonMarshall]

I spoke with an authorized Marshall technician today who told me these amps are experiencing a "bad batch run" of caps (capacitors) and that may likely be my issue;

Is there any indication as to which specific Haze 40 amps (by serial number or series or something) are experiencing this problem? I've tested these out a couple of times, liked them a lot, and decided to get one. So I was going to buy the floor model at my local music store this week. If there is a bad batch, I'd like to try to see if the one they have is a "bad one" or not.

Thanks,
Jim

 

[MKB]

Define "top notch". Lots of players prefer the tonal coloration provided by components that are considered to be "inferior" by today's engineering standards, such as paper wound transformers, carbon comp resistors, high ESR film caps, etc etc. It seems to me that these days lots of production amps are designed with the same methods as "hi-fi" amps and think that because we use 1% precision components that our product is better, when lots of times nothing could be further from the truth.

By top notch (in respect to the construction, not specifically the parts used in the design), I meant the quality of wire dress, the fit of the tolex and grill cloth, board assembly quality, and the general quality of the build was very good. This is in response to those that say that since it's from India, it can't be assembled well. That simply isn't the case.

BTW, my day job now is primarily working as a manufacturing engineer with a contract manufacturer in the US to get my company's products built. My daytime job depends on monitoring the quality of another company's work in assembling electronic devices I help design. And I say the Haze is very well built from a manufacturing perspective.

The majority of the problems I've read about with the Haze is due to design decisions, and it is highly likely those decisions were made by engineers in England. It doesn't matter where the amp was built, the same problems would probably occur if they are design issues.

Now the components used in the design are another issue. The metal film resistors are a good choice for consistency's sake. The tonal effects (other than noise) are probably minimal. But I would never use metal film resistors in a tube stereo due to their tone (that's another long story).

If someone wants an amp with tone carried to the extreme, using paper in oil or teflon signal caps, polypropylene filter caps, Allen Bradley 1 watt carbon comp resistors (or even better Mills noninductive wirewound units), silver solid conductor Teflon insulated wire, and maybe even a Audio Note silver wire primary output transformer, they probably shouldn't look at the Haze. It's a simple grab and go amp for the gigging musician.

 

[pacAir]

This is incorrect. Most multichannel amps use different preamp valves for different channels. However, they get two gain stages out of each valve so both stages of the same valve are used in the channel that a particular valve socket is wired to. In other words, both stages of one valve would do the clean channel while both stages of another preamp valve (or more) would do the dirty channel....

Oh? I have not found this to be universally true at all. The Haze is not a true multichannel amp (as is traditionally defined) but a single-input switched-channel amp. For example, a Fender Twin Reverb (or most blackface models) have different input jacks for each channel and separate tubes for each channel's electronics. Both channels can be used simultaneously by different instruments if desired. These channels are then summed somewhere prior to the P.I. stage.

Many single-input tube amplifiers (only one input jack) with switched-channels I have worked on use a common tube stage or two as the input buffer and the "gain channel" is actually a separate section that is switched in and out of the signal chain but sharing that same common input tube stage.

I have the schematics for several single-input amplifiers that show this topology quite clearly (Vox AC50CP2 / Vox AC100CPH / Marshall JVM / Peavey Classic 30/50). These same amps also have the Clean & Dirty stages sharing separate sections of the same tube. You can do this on a single-input amp because you cannot drive both "channels" at the same time (this is enforced by the switching logic) as you can with a "true" multichannel amplifier. A small distinction but an important one to appreciate.

Also, there are amps such as the Carvin Nomad & Belair that drive both sections of V1 (in parallel) from the common single input jack with V1a as the first section of the clean channel and V1b as the first stage of the Dirty channel! This clearly and definitively illustrates the use of a shared halves topology.

Without a schematic for the Haze (or tracing it out yourself) it is hard to know exactly what single-input tube topology that Marshall employed. With only two tubes in the preamp, it is even more likely that tube halves are shared or a common input stage is employed.

Never say Never!


Steve

 

[MKB]

Oh? I have not found this to be universally true at all. The Haze is not a true multichannel amp (as is traditionally defined) but a single-input switched-channel amp. For example, a Fender Twin Reverb (or most blackface models) have different input jacks for each channel and separate tubes for each channel's electronics. Both channels can be used simultaneously by different instruments if desired. These channels are then summed somewhere prior to the P.I. stage.

Many single-input tube amplifiers (only one input jack) with switched-channels I have worked on use a common tube stage or two as the input buffer and the "gain channel" is actually a separate section that is switched in and out of the signal chain but sharing that same common input tube stage.

I have the schematics for several single-input amplifiers that show this topology quite clearly (Vox AC50CP2 / Vox AC100CPH / Marshall JVM / Peavey Classic 30/50). These same amps also have the Clean & Dirty stages sharing separate sections of the same tube. You can do this on a single-input amp because you cannot drive both "channels" at the same time (this is enforced by the switching logic) as you can with a "true" multichannel amplifier. A small distinction but an important one to appreciate.

Also, there are amps such as the Carvin Nomad & Belair that drive both sections of V1 (in parallel) from the common single input jack with V1a as the first section of the clean channel and V1b as the first stage of the Dirty channel! This clearly and definitively illustrates the use of a shared halves topology.

Without a schematic for the Haze (or tracing it out yourself) it is hard to know exactly what single-input tube topology that Marshall employed. With only two tubes in the preamp, it is even more likely that tube halves are shared or a common input stage is employed.

Never say Never!


Steve

A quick look at the Haze circuit board will reveal a lot about the circuit. You can see that V2 is configured as a cathode follower like V2 in most classic Marshalls. You can also trace enough of the circuit to see that V3 is the classic phase inverter. That, along with the promise from the designer that no solid state amplification stages are used, means the amp has to have one basic channel with a gain stage switched in for the overdrive section.

The overdrive channel, with the boost switch off, sounds and reacts almost exactly like the 2204 head preamp I used to own. It also reacts the same using certain overdrives. So I am certain the preamp is basically the Marshall Master Volume (2203/2204) topology, with the second stage of V1 configured with higher gain. You can take the second stage of V1 in a standard Master Volume amp and get a LOT more gain out of it by changing the 10k cathode resistor to a smaller value bypassed with a capacitor.

Another thing you see with the Haze is it has a bunch of relays that chatter away when switching channels. They could be reconfiguring a lot of circuitry with that many relays. Marshall has been making some mighty complicated switching circuitry lately, and the Haze is no exception.

 

[pacAir]

Haze 40 Footswitching

Yes, the switching has become a lot more complicated!

I wasn't trying to say that the Haze conformed to the same topology as those other amps. I was simply defending my previous topology choices as "customary" and normal in many other designs. Without an open Haze or the schematics you cannot tell simply by looking at the knobs!

Speaking of switching, I am about to try an experiment based on nothing but (once again) observations without schematics! It seems that no one in recent history has had the PEDL-10049 Marhall Haze 40 4-button footswitch in stock and the retailers all claim it will be available sometime after Christmas! I have no idea who screwed the pooch at Marshal or Korg, but having a nice little amp like this and no supply of footswitches to feed the demand (for many months!) while it is a hot topic is an extremely DUMB move on someone's part!

I have never seen this footswitch in the flesh and know of no one who actually has one! I also regularly check eBay and while a number of different people sell the amps no one sells the footswitch! While repairing a Marshall JVM I noticed that the 4-button JVM footswitch used on the 2-channel JVMs looks remarkably like the sole picture Marshall has released of the Haze foot switch. Also, the footswitch interface is the same... through a standard guitar cable and not some DIN plug derivative.

This means the Haze 4-button will most likely have to "talk" to the Haze 40's switching processor in a fashion similar to that used in the JVM (overlooking the "programmability" aspect of the JVM footswitch for now). Since Marshal patented this technology it makes sense to use it in new designs!

I was able to pick up a 4-button JVM footswitch on eBay cheaper than buying the Haze FS (which is currently unobtainable). I intend on experimenting a bit to see if I can get the pair to talk or work without modification (or with simple "programming" using a friend's JVM combo). It would make sense for Marshall to use the same or similar footswitch circuit & technology so it may be possible to adapt the JVM footswitch to the Haze 40.

What I would give for a Haze schematic to evaluate some of this stuff! I have all the JVM schematics and the story they tell is fascinating (and absolutely required for repair). Why aren't the Haze schematics available?

If the 4-button JVM footswitch can be made to work, what might be done with the JVM 6-button? Perhaps anything that can be switched with the front panel controls could be assigned to the footswitches like the JVM (either hardwired internally or programmed). Only the footswitch firmware knows for sure!

Interesting possibilities... sorry if I hijacked the thread!


Steve

 

[pacAir]

JVM Footswitch to control Hze 40

I have moved the JVM footswitch discussion to its own thread here:

JVM Footswitch for Haze 40 Thread

Steve

 

[Raymond R.]

Does anyone know where I can find a new or used input jack attached to the printed circuit card for a Haze 40? Thanks?

 

[Raymond R.]

For a Haze 40.