Eden Metro schematics? Pre-2000 power supply.

[msaudio]

Hi, folks

Anybody have access to early Eden amp schematics or BOMs? Pre-2000. Current US distributor (US Music) where I have a field service contract only has schematics for post-2003. This one's very different. Normal web search came up empty. I need to identify an LED on the power supply board.

Background:
An Eden Metro came into the shop with a problem with no output even though line current draw was normal. Turns out there's a control voltage which mutes the power amp until it's up and stable. Something like -12VDC needs to be on pin 5 of the header of the power amp board. As received, there was nada, zip on that pin. No negative voltage, no sound. Simple as that.

Cause:
An LED in series with the mute voltage circuit, located next to the bank of filter caps on the power supply board was open. Without a good LED, there was no de-mute voltage on Power Amp pin 5. It was a very small LED with a slightly pink lens. Since it was open, there's no way to determine the proper forward voltage. And, of course, LEDs don't sport part numbers.

Temporary fix:
I assumed the function of the LED was to drop the control voltage to a safer value and to act somewhat as an onrush current limiter during charging of the muting circuit. . (the de-mute voltage appears on the gate of a J112 N-ch FET on the power amp which, in the absence of a gate voltage, would shunt all input signal to ground. I wasn't sure of the correct forward voltage of the LED so I chose one with a pretty high FV: A big-ass blue one. Amp works now.

Nagging problem:
I'm just not sure if I used the correct LED. It glows really bright blue. Could the original have been an IR unit, which can withstand higher currents, but having a lower FV? I'm just not sure and the 2003 power supply board (for which I have schematics) doesn't have an LED in the mute circuit.

Humerous aside:
This is sort of funny. The location on the circuit board shows a standard LED symbol...cathode, anode and zig zag arrow coming out. There's also a "+" symbol on one of the terminals. The "+" symbol on an LED usually denotes the anode, but it was on the terminal which was shown to be the CATHODE according to the silkscreened LED symbol. HAH! Which one was right? I went with my gut and followed the "+" indication and not the LED symbol. Voila, the amp works, but I'm STILL not convinced I used the right LED.

Why did the LED fail?
I'm not sure. The amp seems to be fine, but the LED is on the opposite side of the PCB from a pair of big 10W resistors serving the fan & protection circuit. The resistor is flown RIGHT over the solder side of the LED (cushioned by a little glob of RTV. I'm guessing repeated heating of the resistor baked the LED. No wonder they discontinued this power supply board!

Bragging rights goes to anybody who knows what kind of LED this should be! It's small with a slightly pink lens.

Thanks!!!

[mozwell]

not sure if this is the correct one, Eden nemesis amp has red led LED2 (location D3) in mute circuit, its called out as red.

schematics for posterity. i hope they help someone repair an amp
nemesis RS700 (NA650)
WT800
PM400 (WT400)
E300T (WTB300V)
WTX260 pre
WT330, 390, 405
WT500, 600, 800

[msaudio]

Thanks for the schematics! The LED in question, however, is actually on the power supply board and not in the preamp as you indicate. The Metro's power supply is completely different from the Nemesis.

From looking at the other schematics, it looks like the WT800 power supply board (page 4 of the WT800 file) is the one used on the c.2000 Metro (but I won't know for sure until I get back to the shop tomorrow). On the WT800 power supply, the LED is simply marked LED1, smack dab in the middle of the schematic, right above the +15V regulator IC.

At least the schematic confirms the LED's polarity (the "+" on the actual board is correct and not the LED symbol), but, there's still no mention of the color which would give a hint to the FV of the LED. However, Page 11 of the WT500,600,800 diagram shows a voltage range of -12 to -15 for the de-mute line, and that's nearly as good.

THANKS!!!!

--Mike

not sure if this is the correct one, Eden nemesis amp has red led LED2 (location D3) in mute circuit, its called out as red.

schematics for posterity. i hope they help someone repair an amp
nemesis RS700 (NA650)
WT800
PM400 (WT400)
E300T (WTB300V)
WTX260 pre
WT330, 390, 405
WT500, 600, 800

[msaudio]

Now that I have a chance to see the thing, it's not even the WT800's power supply. The de-mute circuit is fairly similar, but the rest of the PS board is way different. No 15V regulators nor even zeners (???) (The bulk of the +/-15V supply must be on the preamp board). The PS board is dated 8/93, but no other part number.

Still a mystery, but the amp does work now, and even though I can't identify the LED, I'm apt to just do some extended load testing and call it good.

The 10W resistors on the solder side of the board supplying the fan do get VERY warm when the fan is running. I may want to move them to the heatsink or maybe the chassis floor, using those cute hi wattage Dale surface-mounted power resistors.

Thanks for the schematics! The LED in question, however, is actually on the power supply board and not in the preamp as you indicate. The Metro's power supply is completely different from the Nemesis.

From looking at the other schematics, it looks like the WT800 power supply board (page 4 of the WT800 file) is the one used on the c.2000 Metro (but I won't know for sure until I get back to the shop tomorrow). On the WT800 power supply, the LED is simply marked LED1, smack dab in the middle of the schematic, right above the +15V regulator IC.

At least the schematic confirms the LED's polarity (the "+" on the actual board is correct and not the LED symbol), but, there's still no mention of the color which would give a hint to the FV of the LED. However, Page 11 of the WT500,600,800 diagram shows a voltage range of -12 to -15 for the de-mute line, and that's nearly as good.

THANKS!!!!

--Mike

[mozwell]

If the led is used anything like LED1 in the power supply of WT800, its no wonder it failed. Also C7 is shown in the wrong polarity i think.
C7 looks to charge up negative via R3 & LED1. The problem is, the reverse voltage across the led.

A little known fact, led's are only rated for approx 5VDC across them in reverse. Dont take my word for it, check the attached data sheet, page 4 which shows max 5V reverse voltage
If you use an LED on AC volts as an indicator, you need an antiparallel diode.
That wont work on this case unfortunately as the led is being used as a rectifier.

A better solution would be to just replace LED1 with a 1N4007, and run the led in series with R4, so that the led only ever sees forward voltage.

[msaudio]

Hah! C7 is definitely drawn wrong. There's about -15V on the anode of the LED. I would have thought the cap's purpose would be to provide a modicum of time delay for the de-mute voltage, but the RC constant as drawn is only about 2msec, and I think it's about 5x that on the '93 version on my bench (I'll confirm tomorrow when I can see it). Either way, that's not much of a delay, but it might protect against a quick switching transient.

Also, the LED isn't really acting as a rectifier; on the 800 drawing, it's anode is connected to the negative leg of the full wave bridge, and a half-wave on the actual Metro. (Again, the drawing is WAY different from the '93 Metro PS). Either way, I think both the drawing and the actual amp are biased correctly (cathode is at a higher-magnitude negative potential than the anode). I'm still thinking it's supposed to reduce the demute voltage by the FV of the LED. (1.7-2.5v, depending on the type of LED). Why they didn't use a (much cheaper) zener is still a mystery.

Also it wasn't exactly an immediate failure. The amp was perhaps 12 years old. I'm thinking it was a cumulative heat issue...the huge 10W dropping resistors were RIGHT over the foil side of the LED connection. I'm definitely replacing them with a pair of heat-sinkable ones asap.

Dangit, I wish I had the actual prints to the PS board in use.

[Andrea Filippig]

Hi Mozwell,

BTW, do you happen to have the electric diagram (schematics) for the Eden The Metro DC210XLT 2X10 Bass Amp?

I would really appreciate this...

Thank you so much, any help would be welcome.