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Pass/Salas DCB1 Preamp Layout Questions

Zonker92

Zonker92

All shiny and chrome
Bought this transformer for a DIY preamp (DCB1) I'm building. I see the two secondary coils are 15 volts / 1 amp each, as I wanted, but there are two primary coils, which is confusing me. Do I wire them in parallel to the power cord, or what? (The build instructions assume I'm using a battery instead, and I'm having trouble finding a good thread on the DIYAudio forum to post this question.) Thanks!

Product description here: http://www.parts-express.com/avel-y236103-30va-15v-15v-toroidal-transformer--122-605

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The primary can use either 115 volts or 230 volts. If you are in the US and are using this on a 115 volt circuit, wire the two primary coils together in parallel: the blue wire connects to the violet, and the gray wire connects to the brown. This now forms the two primary connections for the incoming 115V AC.

If you are going to run this on 230 volt supply, then wire the two primary coils in series: connect the gray to the violet wire (and tape that splice so it is not exposed). Then the blue and brown wires are now your connections to the 230 VAC.
 
The manufacturers website:
http://avellindberg.com/transformers/tech_notes/tech_notes7.htm

It is preferable to try to obtain the required secondary voltages using separate identical primaries to be used in series or parallel. For example, two identical 115v 50 Hz primaries would be connected in series to obtain 230v 50 Hz, or in parallel to obtain 115v, 50 Hz. This arrangement is the most economical in both price and transformer size. A more versatile arrangement would be 2 identical primaries of, for example, 0-100-115V. This will provide 100, 115, and 230V, covering input voltages for places such as Japan, USA, and Europe.

(The unused taps must then be insulated well, as these will be at their stated voltages above ground and to the other windings when the transformer is in use.)

Another option (which generally requires a larger and more expensive transformer), is a multi-tapped or ladder primary.
 
Zonker92 said:
Bought this transformer for a DIY preamp (DCB1) I'm building. I see the two secondary coils are 15 volts / 1 amp each, as I wanted, but there are two primary coils, which is confusing me. Do I wire them in parallel to the power cord, or what? (The build instructions assume I'm using a battery instead, and I'm having trouble finding a good thread on the DIYAudio forum to post this question.) Thanks!

Product description here: http://www.parts-express.com/avel-y236103-30va-15v-15v-toroidal-transformer--122-605

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Click to expand...

Funny, I just ordered a DCB1 (Mez) board this morning. :yes:

Take heed of the warning in the BOM for this build (applies in your case with 15V trafo):

If you decide to ride over the use of 2x12v Transformer add sinks to IRFP and L7815
Click to expand...



Perhaps you (or someone else) would know. With the transformer wiring, how do you feed it to the board and/or what do you do for grounding? I would have thought you'd use an IEC socket for the cord but if you're twisting two pairs of wiring together, where's the third (ground) wire? Same on the other end (to the PCB), what would the wiring pair to the board be?
 
Thanks. I think my "complete" parts purchase from Tea-Bag includes the heat sinks, but I'll check.

I still haven't really dived into this project as I'm awaiting some more bits, including a 20K Goldpoint attenuator, a Bent Audio remote motor for same, and a power supply for the remote motor. :D

I still haven't checked out the power wiring yet.
 
Next question, if anyone's still checking this thread:

So if I used the layout below, with the ruler where the back of the case would be, the LOMC stage on the far left, the HOMC/MM stage next to it, then the phono stage power supply, then the preamp, then the transformer on the far right:

(1) Do you think the transformer would be far enough from the phono stages to avoid hum?

(2) Is there some sort of metal box I could put around the transformer to mitigate hum, or maybe a wall down the middle of the case, front to back?

If need be, I can put the phono stages in a sepasrate case, but I'm hoping to put everything in one sleek case.

Thanks!

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You know there is no guarantee you won't get hum with the transformer in the same case, it's trial and error, keep the devices with the most gain furthest away.

Why not try this turn the HQMC so the inputs face the left side, then put the HTMCPS parallel to it with it's inputs facing the left side, have the preamp board to the right as you look at your picture close to them. Then have the transformer and the SPS as far right as possible.

There is also a chance you will get some EMI from the transformer but you won't really know until you wire it all up but it should be fine.

If all else fails it can go in a separate case with the SPS.

Hope this helps.

You can also talk to Sachu888 as he and his friends have built many projects similar to yours.
 
Cool; thanks, Phillip!

I was a little worried about putting the preamp close to the phono boards, since its on-board power supply is running off 15 volts AC, but I'm not sure if that's an issue or not.

Is there any easy way to shield the transformer?

And I just remembered, I'm also including a remote control motor for the attenuator, and a 12V power supply for that remote / motor. (Still in transit to me.) Man.

I'll PM Sachu888. I really appreciate the help.
 
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Zonker92 said:
So if I used the layout below, with the ruler where the back of the case would be, the LOMC stage on the far left, the HOMC/MM stage next to it, then the phono stage power supply, then the preamp, then the transformer on the far right
Click to expand...

Nice! The attenuator alone is worth the price of admission.

I've only ever done an inclusive build where everything fed off the same DC power supply. How do you plan to tackle your project? Are you just going to split AC coming into the chassis and have it feed the DCB1 and the SPS?

Take lots of pics of this build (please) as I always love to check out what others do on their builds.
 
Thanks for the interest, dogdog! I will try to remember to take more photos; I tend to forget in the heat of a build. The case is something just in my head right now but I'm hoping it's a real stunner.

As for the power source, I'm feeling a little stupid right now and I just know that if I understood anything about circuit design I could make this much simpler. Here is where I am at the point, looking at three, count 'em, three, separate power supplies and two power cables going into the case:

(1) The Simple Power Supply board: This is currently slated to run off a 12V AC / 1 amp wall wart plugged feeding into the back of the case.

(2) The DCB1 Preamp board with onboard power supply: This is currently slated to run off the dual 15V AC / 1 amp toroidal transformer linked above, connected to an IEC power jack on the back of the case. (Hmmm. Now I think 30VA is too low, darn it! Time to order more parts! :rolleyes:)

(3) The Bent Audio remote control module shown here, which needs about 12V DC and just over 1 amp when the motor is running; it's slated to run off a new power supply board with onboard transformer that I found on eBay, which would be connected to the same 115V AC leads supplying current to the preamp transformer. (I checked with its designer, and it would be too much of a draw to take power from the DCB1 power supply. I could use a battery pack but that feels like a kludge to me.)

So yeah, at this point there would be two cables connected to the back of the preamp; one coming out of the wall and the other coming from the wall wart, unless I decided to hide the wall wart inside the case. Plus three power supplies. Before I commit to this approach, I'll try to solicit some better ideas though ...
 
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What if you changed your transformer to a 12V version. Could you take the output of that and feed all three boards, then skip the wallwart for the SPS?

Don't feel stupid about any of this. 99% of DIY enthusiasts don't really know what they're doing but rely on the experts here and diyaudio for help in their projects. Ask the right questions (or the wrong ones) and you'll get plenty of help (at least that's been my experience).
 
Thanks for the kind words! Yes, for me every project is a major learning experience, but I do feel more confident as I go along.

The problem with using a single 12-volt transformer is that reportedly the preamp board sounds better running with a bit more current: The "hot rod" version that I'm working toward specifies a 15-volt transformer to support that approach. But I will check and/or ask the designer whether I could get away with a 12-volter; it might suffice for one of the lower current "hot rod" configurations; that could be a good solution.
 
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The SPS has voltage regulators it won't hurt to run it off 15vac if that helps.

Also another option is to use the PSU on the preamp to power the HQMCPS.

If it has voltage regulators on it and it's split rail it should be fine.

Do you have a schematic for the preamp?

I couldn't find a schematic but by the look of the PCB it would be easy to wire up the HQMCPS and the HTMCPS to run from it they draw very little current, you could have a switch to run either one and not both at once.
 
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That's huge, Phillip! Thanks so much for keeping an eye on this thread and thinking of that elegant solution. In fact, the preamp board designer has said that I can tap off the board's power supply for small loads, so that might work fine. I would just need to figure out where to tap in.

Here is the board for a version with input switching (the Mesmerize). My board is the Hypnotize, which does not have input switching but is otherwise the same (?).

Basic information here: http://ce-designs.net/index.php/my-projects/pre-amplifiers/salas-hot-rod-dcb1

Build guide here: http://www.audiocircle.com/index.php?topic=85001.0

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Looks like you could skip the SPS and just use the +v/G/-V from the DCB1 board to feed your phono stage(s). Not sure if splitting VAC input would hurt anything or not for your volume pot motor... but probably not.

I purchased a Mezmerize set as liked having the multiple inputs/switches and volume "stuff" on board. I may strip my LSA kit out of my current preamp and feed that to the DCB1. Damn, now you have me thinking. Of course, I should probably build my ACA kits and my Aleph J first. :)
 
That would be really convenient. I just don't know how many volts are on those taps. 15V DC maybe? I thought the LEDs were there to step down the voltage? Dunno. I know I saw that information somewhere, but I can't recall where.

The PITA with the DCB1 is that everything is spread out over many threads, different configurations and even different forums. I have trouble figuring it all out and I'm trying to keep my brain from exploding. :D But basically, I'm just going to follow the build thread I linked above, and use a nice selector switch for the input and the Goldpoint for the attenuator.
 
OK, it looks like the voltage test point eyelets on the DCB1 board supply just over 10 volts DC. If I needed 12 volts, here is what the designer said (I was asking him earlier about the remote control module):

1 amp is too much, better dedicate it a trafo. If on the other hand it does not pull that current and its only a max figure, you could tap off the main filter caps to an LM317 or 7812 of its own (sinked).
Click to expand...
 
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So, looks like you could feed your phono section(s) off the DCB1 and just split the incoming VAC for the DCB1 and remote module. Easy-peasy.
 
That sure would be nice. Would the 10+V eyelet be sufficient? It looks like it comes right "off the main filter caps."
 
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