Eden WT400 Bass Amp

[bsco]

Have an Eden WT400 Bass Head which somebody has worked on before. Can't find a schematic for this... Somebody replaced 2 of the high wattage power resistors(there are supposed to be 4 of them), that are located on the far right side of the preamp board...they rigged up a handful of resistors of various values in place of these two resistors. I believe they are 5 watt ones. Trying to find out what the correct value of these resistors are supposed to be so I can remove all this junk that was installed. Anybody out there have a schematic or know what the proper resistor values are???
Cheers,
Bernie

[Billy R aka DynaFreak]

the ones I've worked on were .5 ohm on the schematic, I used .47 which is a more common std value.

[Enzo]

Did you search this foprum for the WT400? Seems to me we have posted those drawings.

[bsco]

Thank you Billy R....these are the ones with the red plastic spacer which keeps the resistor from the board surface?? I didn't realize the schematic was posted here Enzo....I'll see if I can find it...Thank you both for your replies.
Cheers,
Bernie

[bsco]

Hi Enzo. Just went in and had a look around. Found a partial schematic...Looks like the resistors are R74 and R79....rated at 500 ohms at 5 watts and there are a total of four of them. Is this correct?? Looks like it is in the positive and negative 15 volt supply rails.(two resistors in series with each voltage rail)...If this is correct, I'll pick up some tomorrow and install.
Cheers,
Bernie

[Enzo]

Looks like each of those "resistors" is a pair of resistors in series.. Looks like two 500 ohm for a 1k total, in each position. I see this sometimes, they wire them in series with the free ends down to the board, and the junction between them up in the air. This allows the resistors to snug to the board for stability, yet still stick up into free air for cooling. Or so it seems to me. Note the drawing has pairs of resistor symbols end to end.



I just posted on another thread about similarly placed resistors. If pairs of 5 watters doesn;t do it for you, then get a couple 1k aluminum extruded wirewounds from Mouser and bolt them to the chassis amd run wires to the circuit board from them. 10-15-20 watt aluminum resistors are not really very large and are in the $2.50-$3.00 range each.

[bsco]

Thanks Enzo...There is one of each of these resistors still there but most of the lettering in gone and a bunch of other resistors of various values and wattage ratings are wired up to them. I'll have to pick up some of these resistors at the local parts shop if in stock and let you know how I make out. Thanks for all your hep...
Bernie

[bsco]

Hi Enzo. Just checking my meger parts supply and found some 470 ohm 5 watt resistore and if I remember correctly I had to repair one of these amps before and had to swap out the originals which were 470.....so these should work fine... I have a bunch of them so I can measure them all and pick the best four matches to 500 ohms...
Cheers,
Bernie

[bsco]

Hi Enzo.. Installed the 470's this afternoon...works great.....looks a lot neater and professional as well...I did notice that there was a mod done to this amp some time ago...by whom I don't know...There are wires ran from different parts of the pre-amp board underneath and a few components are also added...such as .01uf/100v caps across some of the 100uf electrolytics, and other various resistors and disc ceramic caps as well....Was there any specific mods that were available for these amps and if so what was their purpose?? The guy who owns this has told me the only mod he is aware of is to get the fan to continiously run as soon as power is applied. Outside of that, he has no idea...I also noticed that there is an EQ clip led which is always on as soon as power is applied. Whne tracing the led back I noticed that a couple of these mod wores that I mentioned run right to this led....I don't want to remove anything in case the unit fails to work or causes some damage...The amp is working great right now...but I can't see all the wires under the preamp board for a fan mod... You and other people here on this form have vast amounts of experience with all kinds of gear so I figured I'd mention it here to see if anybody is familiar with mods to this particular amp.
Thanks,
Bernie

[MarkusBass]

The wires that ran from different parts of the pre-amp board underneath are the original design of the amp . It's an old design and it was disigned in kind of a hurry. Eden had to apply all these modifications at the factory.
The modification for the fan is not on the preamp board. As far as I remember the fan is connected through a thermal switch and one or two resistors. So most probably this thermal switch is shorted so the fan is on all the time.
Only the clip LED may be incorrectly connected. I don't have a schematic for this preamp but I think that the LED is on an output of a comparator that checks the level of the input signal. So maybe the inputs of this IC are incorrectly connected, or the IC has failed. A schematic and a photo of the preamp could help.

Mark

[bsco]

Thanks Mark. I didn't think the pre amp board had anything to do with the fan mod....but when I saw all these wires I didn't know what was on the go. This is only the second one of these that I have had the pleasure of working on. THe EQ clip led is indeed connected to the output of a comparator but I changed the Ic chip..... it is a TL072 and I just swapped it out as I had a spare one...still the same thing so I installed the original one in another location on the preamp board and then took that IC chip and installed it in location U4...same thing. Because some of these white wires connect directly to the led, I thought that they might have something to do with it...but I guess not....I only have a partial schematic that I got here from an Eden WT400 thread...and it is not entirely complete but most of it is there.....I am going to have another go at it later tonight and see what I can come up with....Thanks for the help.
Cheers,
Bernie

[MarkusBass]

If you know that the LED is connected to an output of a comparator, and the LED does not work correctly, it is usually a good idea to measure the input voltages of the comparator. You will often find that there is nothing wrong with LED, nor with the comparator, only one of the input voltages are incorrect.

Mark

[bsco]

Hi Mark.... Just checked out a few things and I have come to the conclusion that the replacement IC at U4 was bad and so was the original one. I measured voltages for the power to the ic and they didn't seem right. The double power resistors, R74 and R79 were down from the normal voltage of around 50 volts to something like 39.....and they were very hot to the touch....when I pulled the ic the voltages returned to normal.I also noticed that the eq clip light would light up with different brightness levels depending on which ic I installed in the socket....I had 2 spares but was not sure if they were good...it turns out that they were not(although they are supposed to be new).....If I removed the ic completely, I would get sound from the amp and the resistors did not overheat....when I installed the ic chip, there would be backround electronic noise when the master was turned up but no audio when advancing the gain control with a guitar plugged in and the resistors would overheat very very quickly....I have to pick up some parts tomorrow so I'll get another dozen of these TL072 chips.....Once I put in a new one I'll let you know how it turned out.....Thanks to everybody for all their help so far....Much appreciated.....
Cheers,
Bernie

[bsco]

Hello there MarkusBass...I picked up some op amps and installed one in the amp and same problem....So I started to probe around and when I installed the previous op amps, the 470 ohm, 5 watt resistors used to get very hot....If i removed the chip, then things would return to normal or so I was thinking... anyway, was looking over the schematic again as I had printed it off...not a very good copy...somebody had replaced the two 15 volt zener diodes with rectifier diodes BYV95C...these are just regular diodes used in power supplies for rectification. Now this explains why the 470 ohm resistors were removed and a bunch of resistors of various values and power ratings were connected into the circuit to drop the voltage down to where it was supposed to be....plus and minus 15 volts...instead these voltage rails were at plus and minus 37 volts... I orded a dozen op amps so when I replace the diodes with the correct ones, I am going to swap out all the op amps as well....TL072's there are six of them in total. I am not used to seeing these kinds of modifications done to people's equipment and use whatever is on hand just to get it in and out and make a quick buck. But I think this is what has happened here. Then again, if I had been paying more attention to what was happening, I would have picked up on it earlier...so I guess I am partly to blame....I am going to replace the diodes with the proper ones, replace the op amps and then see what the outcome will be...Thanks everybody for all your help so far and hopefully this will finally solve the problems with this amp...and the next time I see this kind of shabby work I'll know right away to suspect something out of the ordinary.I'll let you know how I make out with this....

[doctor]

Hello there MarkusBass...I picked up some op amps and installed one in the amp and same problem....So I started to probe around and when I installed the previous op amps, the 470 ohm, 5 watt resistors used to get very hot....If i removed the chip, then things would return to normal or so I was thinking... anyway, was looking over the schematic again as I had printed it off...not a very good copy...somebody had replaced the two 15 volt zener diodes with rectifier diodes BYV95C...these are just regular diodes used in power supplies for rectification. Now this explains why the 470 ohm resistors were removed and a bunch of resistors of various values and power ratings were connected into the circuit to drop the voltage down to where it was supposed to be....plus and minus 15 volts...instead these voltage rails were at plus and minus 37 volts... I orded a dozen op amps so when I replace the diodes with the correct ones, I am going to swap out all the op amps as well....TL072's there are six of them in total. I am not used to seeing these kinds of modifications done to people's equipment and use whatever is on hand just to get it in and out and make a quick buck. But I think this is what has happened here. Then again, if I had been paying more attention to what was happening, I would have picked up on it earlier...so I guess I am partly to blame....I am going to replace the diodes with the proper ones, replace the op amps and then see what the outcome will be...Thanks everybody for all your help so far and hopefully this will finally solve the problems with this amp...and the next time I see this kind of shabby work I'll know right away to suspect something out of the ordinary.I'll let you know how I make out with this....

I hope schematics can help.

There are two options for the power amp: PM400 and PM600

Good luck