Demeter VTBP-201 Transformer Info help needed

[SneakyT]

Was wondering if any of you guys could help me out. I'm looking for the part number for the Jensen transformer for this unit. I found a picture of the transformer on here before and saved it so I could get one or an equivalent one when I got around to it. I have since got a new computer and apparently that picture didn't make it in the transfer. I've searched for a couple of hours and can't seem to find that picture again. If someone knows the part number or better yet knows the transformer ratio it would really help me out. If any one who has one of the 1.5u models that has the transformer could open it up and take an up close picture of the DI section that would really help as Demeter doesn't like to post his schematics. That would be this area.


I'm really not wanting to send it off to Demeter and paying him to do work that I'm very capable of doing so please don't recommend that.

[SneakyT]

Ok I found the picture of the transformer.

Jensen JT-DB-E

http://www.jensen-transformers.com/datashts/dbe.pdf
http://www.jensen-transformers.com/as/as007.pdf

It is a 12:1 DI transformer. That info will give me a few options for transformers (Lundahl, Cinemag, Edcor, etc). All I need now is to see where they tie into the flat signal for the Flat/Eq Switch. If anyone could take the time to open theirs up I would appreciate seeing the wiring on that switch. Pretty Please.

[SneakyT]

Ok here is what I've found so far for transformers that will work in place of the JT-DB-E.

Apparently these (Including the Jensen) are all based on the Reichenbach RE-DB-E. Jensen and Cinemag are both historically tied to Reichenbach. Should be the exact same transformer:

Reichenbach RE-DB-E
Bauer RE-DB
Cinemag CM-DBX
Lawson RE-DB-E

These are different transformers that should work as well. They have a different ratio though so they will sound a bit different:

Lundahl LL-1530
Sowter 4243 & 8044

Lastly:

Edcor WSM 10k/150 using half of the secondary to up the ratio. Although these are unshielded they are pretty inexpensive and get good reviews.

I'm thinking of going with the Cinemag ($40-$50) myself to keep it as close to oem without paying $70-$90 for the Jensen.

Hopefully this info will help others that are in the same boat.

[dmk]

I have one of these preamps so I'll be able to take pictures if you need. I can get to it in a couple of days.

[Rick Auricchio]

You should be able to buy a Jensen JT-DB-E at mouser.com or digi-key.com.

[BassmanPaul]

I'm a little confused as to what you are trying to accomplish. Do you have a Demeter unit that lacks a DI? Are you wanting to add the DI to another company's product?

Paul

[MR PC]

Originally Posted by SneakyT

Ok here is what I've found so far for transformers that will work in place of the JT-DB-E.

......'guess you've answered your own question!

Ok, I cheaped out when I purchased my Demeter pre, and didn't purchase the built in DI option. OTOH, now we are using the JDI passive box with a Jensen xformer (after the Demeter), and it works great, and has several other features that the built in DI doesn't.

[SneakyT]

Originally Posted by dmk

I have one of these preamps so I'll be able to take pictures if you need. I can get to it in a couple of days.

Thanks I would appreciate seeing the wiring on the switches. I'm pretty sure I've traced down the flat signal but conformation would be awesome. Don't get in a rush. Whenever you can get to it is fine.

Originally Posted by BassmanPaul

I'm a little confused as to what you are trying to accomplish. Do you have a Demeter unit that lacks a DI? Are you wanting to add the DI to another company's product?

Paul

Yes to the first and no to the second question. Lots of these early (1.5u non-s) units had the space for the DI just without the transformer installed. They even have the switches installed just not wired to anything. It was an option on those as the transformer added a lot of cost. These early units w/o the DI can be found for quite a deal on occasion. I, like a lot of others, like the sound of these early units better than the newer ones (probably just due to the tubes and caps used as the circuit is supposedly the same). I thought it would be helpful to other that have the non-DI version to see how I go about installing one. Maybe de-mistify the whole "Jensen Transformer Is magical" deal that a lot of people around here seem to believe in the process.

Originally Posted by MR PC

......'guess you've answered your own question!

Yeah Luckily I had made a backup that had that picture in it. Who said being anal doesn't pay off.

Originally Posted by MR PC

Ok, I cheaped out when I purchased my Demeter pre, and didn't purchase the built in DI option. OTOH, now we are using the JDI passive box with a Jensen xformer (after the Demeter), and it works great, and has several other features that the built in DI doesn't.

That is what I was doing as well when I was using the Demeter in live situations as well. I have decided to decommission it as a gigging pre and rack it up in the studio so having it permanently wired in makes more sense. Some people would also like to have the Flat/EQ option. The external DI is certainly a very valid option for a lot of people though. It can also be used in combination with the one internally set to flat so you can re-amp later. External DI's are always great to have about.

[BassmanPaul]

Are you forgetting that the transformer will need a driver circuit? You can't just wire it across the output jacks.

Paul

[dmk]

Originally Posted by SneakyT

If any one who has one of the 1.5u models that has the transformer could open it up and take an up close picture of the DI section that would really help as Demeter doesn't like to post his schematics.

Let me know if you need a different angle.

[SneakyT]

Originally Posted by dmk

Let me know if you need a different angle.

First I would like to say thank you for your help. I really appreciate it. If you would not mind helping me just a bit more I kinda need to see where this wire goes.

It should just be ground but its hard to see.

Next if you could take pictures of these output jacks it would be helpful.

I'm pretty sure the orange and black from the transformer are just going to ground and the white wire is coming off the tip but verification would be great. Thanks again for taking the time.

[dmk]

PM sent.

[MR PC]

So somebody scavenged the original transformer for this pre amp?

What's going on here......I know there is a guy in the Austin TX area who regularly "borrows" parts from gear, and passes it off on ebay. Very sneaky.

[SneakyT]

Originally Posted by dmk

PM sent.

Thanks again Dale.

I'm gonna copy all of the pictures that you sent me to my photobucket account and post them to try and help everyone who is in the same boat as me.

[SneakyT]

Originally Posted by MR PC

So somebody scavenged the original transformer for this pre amp?

What's going on here......I know there is a guy in the Austin TX area who regularly "borrows" parts from gear, and passes it off on ebay. Very sneaky.

The DI was an option on the early ones as you mentioned. It was not removed. Another guy (DMK) on here has sent me pictures of his to help in wiring in one on mine that did not have one. I thought at first you were trying to say I was trying to pass stuff off so if you read my first reply I apologize.

[SneakyT]

So here are the pictures Dale sent me. You can follow the Jensen direct box schematic and tie into the full range signal off the main outs as shown in the photo. The positive signal goes to the EQ/Flat switch and the brown wire near the effects loop jacks that is hanging free is the flat signal that connects to the other leg of that switch. The ground/lift switch and transformer tie into ground off the main outs as well. It was exactly as I thought it was but a big thanks goes to Dale for taking the time and confirming this. If anyone has any questions on how to do this feel free to ask me.






http://www.jensen-transformers.com/as/as007.pdf

I'll let you guys know how it works when I get done. Think I'm gonna order two transformers and put one in my RPM evoII since the DI on that sucks.

[MR PC]

Originally Posted by SneakyT

I'm really not wanting to send it off to Demeter and paying him to do work that I'm very capable of doing so please don't recommend that.

To each there own, but Demeter took the time to create and market a very nice product, and keep it on the market for 20+ years. They aren't a big company, and they probably depend on the support and loyalty of customers. Going out of the way to solicit photos on their designs seems wrong, IMO. Granted, my ethics in this area could be viewed as old fashioned.

Originally Posted by BassmanPaul

Are you forgetting that the transformer will need a driver circuit? You can't just wire it across the output jacks.Paul

Still waiting to see the answer to this, since you said that you are very capable of doing the work.....I'd think that you'd be eager to "talk tech", and not need any photos asking where each wire goes. That could have made this discussion interesting and educational a well. Lots of us here can handle a soldering iron.

Originally Posted by SneakyT

The DI was an option on the early ones as you mentioned. It was not removed. Another guy (DMK) on here has sent me pictures of his to help in wiring in one on mine that did not have one. I thought at first you were trying to say I was trying to pass stuff off so if you read my first reply I apologize.

Didn't see your reply, and I wasn't trying to say you are that guy.....I was just wondering if this unit was one of his victims.

[SneakyT]

Originally Posted by MR PC

To each there own, but Demeter took the time to create and market a very nice product, and keep it on the market for 20+ years. They aren't a big company, and they probably depend on the support and loyalty of customers.

And I have by buying three of his pre-amps over the years not to mention the on-board pres that a few of the basses I've had. Oh yeah and a compressor too.

Originally Posted by MR PC

Going out of the way to solicit photos on their designs seems wrong, IMO. Granted, my ethics in this area could be viewed as old fashioned.

I disagree completely here. I feel that all manufacturers should include schematics with their product just the way most used to. Most customers will not work on their own pre-amp and will most likely send it back to Demeter to have it worked on which is fine. Forcing them to do so by not sharing schematics is in my opinion the unethical practice (although it is not uncommon one now days). To those that say this is necessary to protect your intellectual property: if someone wants to steal it bad enough, they can reverse engineer the circuit so that is really not an excuse. Not to say that James is a bad guy (he is a damn fine engineer). I just disagree with this stance.

Originally Posted by MR PC

Still waiting to see the answer to this, since you said that you are very capable of doing the work.....I'd think that you'd be eager to "talk tech", and not need any photos asking where each wire goes. That could have made this discussion interesting and educational a well. Lots of us here can handle a soldering iron.

I didn't answer this at the time as I was waiting to have pictures of the circuit so that there would be no unnecessary argument. He is in-fact wrong. That is why they used a DI transformer. The DI transformer was first created (by Ed Reichenbach) so that you could take a line level signal and convert it to a balanced level without adversely affecting the line level to a great degree. No need to have a separate driver circuit. That is why a passive DI works. Of-course in electronics there is always more than one way to skin a pig so I wanted to see how it was done originally. It in-fact pretty much followed the Jensen DI schematic as I had thought. You never know till you look at it though.

Originally Posted by MR PC

Didn't see your reply, and I wasn't trying to say you are that guy.....I was just wondering if this unit was one of his victims.

That's the way it read after re-reading the post so I changed it. Sorry about that again.

[BassmanPaul]

So no driver. Interesting. That mean the inductance of the transformer will be shunting the outgoing signal continuously. Not such a good idea IMHO although if the output impedance is low enough it should be alright.

Paul

[synaesthesia]

Originally Posted by SneakyT

A


I disagree completely here. I feel that all manufacturers should include schematics with their product just the way most used to. Most customers will not work on their own pre-amp and will most likely send it back to Demeter to have it worked on which is fine. Forcing them to do so by not sharing schematics is in my opinion the unethical practice (although it is not uncommon one now days). To those that say this is necessary to protect your intellectual property: if someone wants to steal it bad enough, they can reverse engineer the circuit so that is really not an excuse.

The general idea for doing what you are doing, i.e. fitting a Jensen transformer by tapping the outputs, is attended to by various schematics at the Jensen site.