Eden Electronics VT-.40 Bass Amp Schematic Search

[duff2]

Hi,

I am searching for schematic diagrams or the service manual for my 1992 vintage Eden Electronics VT-.40 bass amp. This is the 1st generation Eden bass amp with a preamp designed by James Demeter. Designwise it is a totally different beast from their current line of amps.

My amplifier needs servicing and my local amp tech said he can't help me without having the schematics to refer to. I have contacted Eden Electronics and Demeter Amps but they longer have these documents on file as the amp is no longer produced.

Would anyone here have the documents I am searching for?

Thanks,
Duff2

[Amp Kat]

I doubt it seriously because EDEN doesn't give out their schematics or give support to any technicians. They will gladly fix it for you for a nice price but won't give you any support which is why I don't recommend their products and even reject them . After repairing several Eden's they all usually have the same problem and it's in the power supply. They all work the same way so basic amp troubleshooting goes a long way for any experienced tech. The power supply voltages are probably missing somewhere either positive or negative and once you get them back, it will work fine. Doesn't that amp have a 12AX7 preamp tube in it ?

[duff2]

Hi Amp Kat,

My amp is quite different from the current generation of Eden amps. The WT series have a single 12AX7 tube and have a preamp designed by Russ Allee. The amp for which I am seeking schematics predates the WT series. It has two 12AX7 tubes and it's preamp was designed by James Demeter. Here's some pictures of my amp....







In their defence, Eden has been as helpful as possible in this instance. In the past when I have requested schematics for other Eden amplifiers (I used to own a WT-400), they have been more than happy to send them to me.

I hope this helps clarify things.

Thanks for your reply.

Cheers,
Duff2

[Enzo]

But you haven't mentioned what is wrong with the unit. What are you trying to fix?

[Amp Kat]

Ok maybe I just had a bad rap with them but anyway I agree with Enzo and what is wrong with it ? I have done one exactly like that one and the power supply caps were bad. Also on that board to the left of the power supply you will see two zener diodes sticking up. These are the op-amp regulators and make sure they are zenering about 16 volts +/-. Also check the rails on the output transistors. Is the tube lighting ? That was one of the problems with the one I did. I actually emailed Enzo about this amp for schematics about 3 years ago and he didn't have them but he worked it thru and we figured it out without them so I feel you can do it too.

[duff2]

The problem I have is with the level of background hum produced by the amp. It is much louder than I observed with my other Eden amp (WT-400). I had both amps in my possession at one point so I compared them plugged into the same outlet and speaker cabinets using the same cables. My amp tech told me he wanted to see a schematic to determine if the hum is related to the design of the amp or due to something else.

The other reason I'm looking for these documents was based on the desire to be able to have my amp restored to factory specs in the event something goes seriously wrong in the future (likely given the age of this amp). I am a novice when in the area of electronics, so forgive me if my assumptions are completely wrong relating to schematics as a necessity for this purpose.

Thanks a lot for your enthusiastic level of interest, and your efforts to help me out.

Cheers,
Duff2

[Enzo]

I can appreciate your tech not wanting to open a can of worms, on the other hand, I venture into these things every day without drawings.

As to getting it "back to factory specs" in most cases all there is is a schematic. So other than identifying components and their values, there is not a lot left. Amps all tend to adjust the same way.

Excess hum? There is so much we can do. First isolate the problem. Is the hum still there with ALL controls at zero? Does ANY control affect the sound of the hum in ANY way? (Tone, amount, whatever) ANy tech can identify the power supplies in an amp. We need to determine if they are all present, up to voltage, and clean. Both the high voltage supplies for the power amp, and the low voltage ones for the preamp. And in this case, the extra supplies for the tubes.

We can substitute known good tubes for the ones in there.

We can verify the amp is not drawing excess power and is biased properly. Improper bias in a power amp can cause hum.

One can also check the solder under the cable connectors - those Molex headers that send the white wires board to board.

All of this we can easily do without schematics.

[duff2]

Thanks Enzo. I'll pass along your feedback when I talk to my amp guy again.

For the record, the amount of hum is not affected by any of the control settings nor is it affected by the identity of the tubes in the preamp. If I turn on my amp without connecting speakers, I can hear (in a quiet room) the same humming frequncy albeit at a much lower level. All of the screws are present and tightened, all the components of my amp (including the transformer) are secure and not loose. Based on this I'm guessing the origin of the annoying hum is electrical and not vibrational in nature.

Assuming that the hum is from the transformer, is it possible to install some sort of hum cancelling choke wire to rectify the problem? Would a schematic be required for this?

Cheers,
Duff2

[Enzo]

The hum you hear from the speaker sounds the same as the sound coming from the transformer mechanically because everything is operating on the same 60Hz mains current, not because the transformer is causing it.

Your hum is electrical in nature, and is coming from a ground issue somewhere, or a filter issue, or an imbalance or something.

And comparing this model to a different model is not a fair comparison. it is possible this amount of hum is normal for this amp.

[duff2]

Before I purchased the amplifier, a respected techician went through it, replaced some parts and gave it a clean bill of health. So perhaps the level of hum is inherent in the amp design, assuming something didn't get knocked around during shipping.

Just out of curiosity...

I have seen later versions of this series of Eden amps that have toroidal transformers instead of the block style transformer that's in mine. Assuming everything else is OK, would installation of a toroidal tranformer reduce the background hum? Or stated differently, is there any advantage to uses of a toroidal transformer over a block style other than weight reduction?

Thanks again for your input. I'll post an update here after the amp comes back from it's service visit.

Cheers,
Duff2

[Amp Kat]

I would be shocked if your transformer is bad causing the hum and a Toroidal will not necessarily reduce the amount of hum as far as % wise or the signal to noise ratio. There are many factors that would decide that. IME with this exact amp and the other Edens it's been the power supply caps and I think that's your problem with this amp. While that power board is out I would change all of the E-caps on that board. These amps sound very good when working right and have almost no decernible hum so thinking they are not designed right is not the case in my opinion and would not have let them go out like that if they were. That amp you have is much better than any of the new ones as they went to single sided cheap PCB borads that are very fragile yet cost more.If the problem is anything other than that Power supply I'll be as shocked as if the transformer is humming.

[duff2]

KB,

Thanks for your reply to my question regarding the transformer. With regards to the E-caps, they have not been changed since the amp was built in 1992, so they may be the source of my problem.

As I said before, I used to own an Eden WT-400 and I was very happy with the way it sounded. The only trouble I ever had was with one of the resistors on the preamp board...an easy fix. Tonewise, the VT-.40 sounds better to my ears. Unlike most of the other amps I have owned, it sounds as good at high volume as it does on lower settings. It also doesn't get too "grindy" at higher volumes.

Cheers,
Duff2

[stratomaster]

I am having a problem with this amp. I can't get the tubes to light up. So far I've replaced all the caps in the power amp section, checked for shorts, replaced wirewound resistors, and checked solder joints. There's a set of 6 pins in the power filtering section that go to the preamp board. They are supposed to be (from left to right) -15V, 18V, Ground, 6V, ground, 235V. They actually measure out to -16.1V, 16.56V, 0v, 1.15V, -1.17V, 173. I suspect whoever worked on the amp before may have reconnected the jumpers incorrectly, but without a schematic I can't really confirm this. I would like to ask if anyone would mind taking a photo of the back side of the power filtering board in their Eden VT-.40 and posting it here. Thank you.

OMJ

[fmeynert]

Hello:
I have an Eden VT.25 with the same tubes not lighting up problem.
My voltage readings are also the same as yours. The tube heater voltage is low.
Did you find the cause of the problem?
Thanks,
Franz