Volcom1720
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So do the new DSL401's still overheat? A lot of people complain there's do. Any sound difference between the older and newer versions?
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Before 2003 models can have issues with overheating, but as long as they haven't been pushed really hard just keep a fan blowing on the back of the combo and the power tubes and you'll be problem free.
From an earlier post, some input by Thrawn86. Apparently the overheating issue was on models built prior to 2003.
thrawn86
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drriff is correct. IIRC, starting in 2003, they changed a few things around with the resistors and lowered the bias value to around 550mV.......before that (like on my 401) the bias is called for at 1300-1400mv (or 1.3 to 1.4 V). Dr. Tube has the schematic to back this info up. They still get hot, but if you put a small fan behind the amp, to push air through and out, it will remedy the heat.
bxt403
New Member
I have the older 401 (2002) and have only seen the 2002 version of the schematic:
I think Marshall decided that it'd be much simpler/easier (from a business standpoint) to bias the amp colder and swap-out components than to add more or redesign the amp to keep running at the original bias voltage.
I added three PC fans to the rear grill that run from 12VDC power (to make sure there's no stray power or motor noise going to the speaker compared to having gone with an AC powered fan). Plus the PC fans have a lower octave operating noise and the speed is adjustable via DC wall-wart. There's plenty of circulation since one fan is facing opposite the other two (so one sucks all the hot air out by the power trafo and two blow the cold air toward the EL84s). After the fans- the area that has "JCM 2000 -" that's above the Overdrive EQ controls got hot to the touch (versus the whole front panel being scolding without any mods)...after the BR mod the "JCM 2000 -" is almost as warm as the rest of the front (after an hour or two of playing on it).
But if the older and newer 401's have the bridge rectifier installed the same, the "JCM 2000 -" area should be hot to the touch.
FYI the BR is meant to be used with a heatsink, as it has a hole in the centre of it (and the datasheet also shows that the hole's for a No. 6 screw). But if my 2002 didn't have a heatsink, I'm thinking the later ones didn't either. I suspect Marshall never factored in the size of cabinet and the resulting excess heat build-up when it was designed. A two resistor fix is only a few cents and doesn't change the way it's built. It cost me $2.60 for a new BR and heatsink and $50 for a Universal DC wall-wart and 3 PC fans from a local electronics supplier. Just adding a heatsink is going to compound into the manufacturing process- if one factors in the manpower hours of people having to flip the board over- and make sure there's space between the circuit board and the BR (and also installing the heatsink to it beforehand).
I've read a lot of posts from ppl who've tried both versions of the 401, saying that the earlier ones had more mojo. Even though I haven't tried the later 401's, I'm extremely happy with the sound of my 2002 DSL401. My biggest constraint was not effecting the mojo while minimizing the heat build-up. It's clear that Marshall's only issue was reducing the heat build-up for the lowest cost possible (hence the colder bias with a few cents worth of resistors). The compromise for me keeping the original bias & resistor values, on the other hand, is that even though there's shortened tube life; I get a tone I'm happy with.
I think Marshall decided that it'd be much simpler/easier (from a business standpoint) to bias the amp colder and swap-out components than to add more or redesign the amp to keep running at the original bias voltage.
I added three PC fans to the rear grill that run from 12VDC power (to make sure there's no stray power or motor noise going to the speaker compared to having gone with an AC powered fan). Plus the PC fans have a lower octave operating noise and the speed is adjustable via DC wall-wart. There's plenty of circulation since one fan is facing opposite the other two (so one sucks all the hot air out by the power trafo and two blow the cold air toward the EL84s). After the fans- the area that has "JCM 2000 -" that's above the Overdrive EQ controls got hot to the touch (versus the whole front panel being scolding without any mods)...after the BR mod the "JCM 2000 -" is almost as warm as the rest of the front (after an hour or two of playing on it).
But if the older and newer 401's have the bridge rectifier installed the same, the "JCM 2000 -" area should be hot to the touch.
FYI the BR is meant to be used with a heatsink, as it has a hole in the centre of it (and the datasheet also shows that the hole's for a No. 6 screw). But if my 2002 didn't have a heatsink, I'm thinking the later ones didn't either. I suspect Marshall never factored in the size of cabinet and the resulting excess heat build-up when it was designed. A two resistor fix is only a few cents and doesn't change the way it's built. It cost me $2.60 for a new BR and heatsink and $50 for a Universal DC wall-wart and 3 PC fans from a local electronics supplier. Just adding a heatsink is going to compound into the manufacturing process- if one factors in the manpower hours of people having to flip the board over- and make sure there's space between the circuit board and the BR (and also installing the heatsink to it beforehand).
I've read a lot of posts from ppl who've tried both versions of the 401, saying that the earlier ones had more mojo. Even though I haven't tried the later 401's, I'm extremely happy with the sound of my 2002 DSL401. My biggest constraint was not effecting the mojo while minimizing the heat build-up. It's clear that Marshall's only issue was reducing the heat build-up for the lowest cost possible (hence the colder bias with a few cents worth of resistors). The compromise for me keeping the original bias & resistor values, on the other hand, is that even though there's shortened tube life; I get a tone I'm happy with.
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JohnH
Well-Known Member
My 2005 model got hotter than I liked it, although it never failed. ie, after a half hour, it got so hot that youd burn your finger on the front panel. It was biased at 550mV. Now I dont have experience to say if that was normal (my first tube amp), but I was not happy with it, based on everything I know from many years as an electronics tinkerer.
I added a heat sink to the BR and internal mains powered fans (in series, they run very quietly on half their design voltage each), but no circuit mods. Then I put the bias back up a bit to about 750mV (sounded better).
It sounds great, has been totally reliable, runs quietly, has no extra trailing wall warts or outside fans needed, and just gets slightly warm on the front panel.
Its a keeper, I dont know if I needed to do what I did, but Im more relaxed having done it.
John
I added a heat sink to the BR and internal mains powered fans (in series, they run very quietly on half their design voltage each), but no circuit mods. Then I put the bias back up a bit to about 750mV (sounded better).
It sounds great, has been totally reliable, runs quietly, has no extra trailing wall warts or outside fans needed, and just gets slightly warm on the front panel.
Its a keeper, I dont know if I needed to do what I did, but Im more relaxed having done it.
John
LpPepper
New Member
I find everyone beeing worried about the overheating issues on this amp quite funny.
I have had a 401 for a year , its a 2000 model . So its meant to have "overheating issues" . I had it re-valved and biased at 1.1V . Sure it gets hot but these are valve amps guys
I had it on for 6 hours at a gig and the closer to the end of the gig it got it sount much better , there meant to get hot . The hotter the better
I have had a 401 for a year , its a 2000 model . So its meant to have "overheating issues" . I had it re-valved and biased at 1.1V . Sure it gets hot but these are valve amps guys
I had it on for 6 hours at a gig and the closer to the end of the gig it got it sount much better , there meant to get hot . The hotter the better
bxt403
New Member
I find that the DC wall wart is the most elegant solution that can be easily undone- which is important if you want to to quickly open the amp up. Since the 2.1mm female jack (and the entire fan circuit) is on the upper vent, I just have to unplug the DC adaptor and can disassemble amp as I normally would.
After the heat mods I've had the amp run for around six hours (playing FM radio with the Master turned to 5 and the FX return set to 2)- and with the DC supply set 7.5 volts- the panel gets only slightly warm. Remember that mine is still biased to the original 1.3 to 1.4 V spec.
But I have this "special" IEC power cable that came with a used monitor that allows two devices to be plugged into one outlet (and the DC and IEC cables are the same length) so the cabling is very clean and I'm happy with the results.
And running the amp "hotter the better" is not really the case (at least with pre-2003 models)- the problem being the excess heat build up of the EL84, BR, and the power trafo in such a tiny enclosure. Yes- having the EL84's run hot is prime- however the power trafo is mounted upside down and the BR is located very close to the EL84's and power trafo: this is how cold solder joints are cropping up (along with other problems); as the circuit board is absorbing all the EXCESS heat. The panel still gets warm with mine (right around the Master controls- which is where the EL84 section is)- that is what we want (and I haven't changed how hot they're running). The rectifier is solid state- so the only thing the heatsink does is reduce the amount of heat transferred to the circuit board (which helps prevent cold solder joints from cropping up). The fans are just circulating the air so that there's no heat build up (and aren't cooling the EL84s as much as making sure that the heat below isn't transferred to the circuit board above).
After the heat mods I've had the amp run for around six hours (playing FM radio with the Master turned to 5 and the FX return set to 2)- and with the DC supply set 7.5 volts- the panel gets only slightly warm. Remember that mine is still biased to the original 1.3 to 1.4 V spec.
But I have this "special" IEC power cable that came with a used monitor that allows two devices to be plugged into one outlet (and the DC and IEC cables are the same length) so the cabling is very clean and I'm happy with the results.
And running the amp "hotter the better" is not really the case (at least with pre-2003 models)- the problem being the excess heat build up of the EL84, BR, and the power trafo in such a tiny enclosure. Yes- having the EL84's run hot is prime- however the power trafo is mounted upside down and the BR is located very close to the EL84's and power trafo: this is how cold solder joints are cropping up (along with other problems); as the circuit board is absorbing all the EXCESS heat. The panel still gets warm with mine (right around the Master controls- which is where the EL84 section is)- that is what we want (and I haven't changed how hot they're running). The rectifier is solid state- so the only thing the heatsink does is reduce the amount of heat transferred to the circuit board (which helps prevent cold solder joints from cropping up). The fans are just circulating the air so that there's no heat build up (and aren't cooling the EL84s as much as making sure that the heat below isn't transferred to the circuit board above).
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bxt403
New Member
I think the fan setups you guys use is cool. I went in a different direction:
$6 at Walmart. Takes 10 seconds to install. Pushes lots of air. Front panel is no more than slightly warm.
It looks like you chopped the top of the cab and installed the head backwards (my fan grill is your front grill!).
I thought your enclosure was painted ivory white...and it still looks cool in blue. IMHO-the white colour was more exotic for some reason (reminded me of the colour of a sports car) .
That's a cool rig you got there! However, I'm not jealous of you (seeing as how I'm happy with my red 401).
Much respect.
I'm new here but, i saw a post asking about the new DSL100MLB's and how they sound. They sounds fantastic! I just got one, hopefuly it doesn't have the combustible carbon film resistors found in pre 2005 DSL/TSL's though. I can say it sounds WORLDS better tonaly in EVERY setting that my TSL60 ever did. tighter bottom end,clearer and all the tones are useable so in that regaurd it's more versatile as well. I run mine the a 4x12 with V30's. I didn't get the package, i bought the head off a guy that got carpel tunnel really bad so i need the footswitch as well but, it's brand new. He hadn't even burned in the tubes yet. It also doesn't get that frying an egg on heat on the control pannel like alot of the others do.
thrawn86
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There's a discrepancy between the EL34-based 50/100w heads and the EL84-based 20/40w combos.......I haven't really heard of the bigger heads having this problem....it's exclusive to the combos. It doesn't suprise me that noone with a 50/100 has an overheating problem.
