Custom ESL using quest panels

[Brandon Hartwick]

After much thought as to how I was going to seal up all the key holes that pass through the side and top panels I settled on using 2 part liquid silicone. This was a great solution and it's really easy to apply.

I was running a little low by the time I finished the second box and I likely missed a few spots. I bought another pack of silicone just in case.

 

[18000rpm]

The boards are directly out of the Quest power supply but the transformers are aftermarket.

Can you provide info on the transformers and how did you know the specs or what to use? The reason is I may have a problem with the transformers in one of my Prodigies.

 

[Brandon Hartwick]

Can you provide info on the transformers and how did you know the specs or what to use? The reason is I may have a problem with the transformers in one of my Prodigies.

In the very first post of this thread I have the part numbers and wiring diagram, but the Prodigy will not use the same ratio transformer. I was given the info for these transformers from @Jazzman53, if you shoot him a PM he could probably point you in the right direction. I'm not an expert on picking transformers.

 

[Jazzman53]

Can you provide info on the transformers and how did you know the specs or what to use? The reason is I may have a problem with the transformers in one of my Prodigies.

Here's a link to the transformers I use in my DIY speakers, which requires two per speaker in a tandem arrangement:
https://www.rapidonline.com/vigortr...sformer-230v-single-primary-50va-0-6v-88-5190
But I'm pretty sure Brandon is right:
The tandem toroids could not be plug-N-play replacements for your Prodigy transformers.

Just eyeballing the Prodigy interface, it looks like there are more connections/inputs on the primaries than would be available with the tandem toroids, and their voltages may be different as well.

The only way to use the tandem toroid setup in your Prodigy would be to replace the entire passive crossover/EQ network with a DSP crossover with parametric EQ's for tuning, and put the woofer and panel on separate amp channels. That would be easy to do and give very high-performance but it wouldn't be cheap $$$

 

[18000rpm]

Just eyeballing the Prodigy interface, it looks like there are more connections/inputs on the primaries than would be available with the tandem toroids, and their voltages may be different as well.

I think most of the connections are not actually connected to the transformers. I'll send you a message when I open it up and take some better pictures.

 

[Jazzman53]

I think most of the connections are not actually connected to the transformers. I'll send you a message when I open it up and take some better pictures.

Does anyone know the step-up ratio of the Prodigy transformer(s)?

 

[18000rpm]

Does anyone know the step-up ratio of the Prodigy transformer(s)?

And is the only purpose of the two transformers that are side-by-side in the Prodigy chassis to step up the voltage to energize the panel? What does each do or do they work as one?

 

[Jazzman53]

And is the only purpose of the two transformers that are side-by-side in the Prodigy chassis to step up the voltage to energize the panel? What does each do or do they work as one?

I haven't a clue. I'm thinking they would either have to be identical transformers connected in tandem to double the voltage out (like my dual toroidal setup), or an arrangement where one transformer has a lower ratio driving the treble band and the other a higher ratio driving the mid-bass band. The old Acoustat Medallion speakers used such an arrangement, which they called "Mirror Drive".

Electronics isn't my forte so perhaps someone here who knows something about the Prodigy setup could compare the connections between my tandem toroid setup to those in the Prodigy schematic and figure it out.

My schematic is shown below. It uses two identical transformers (each having 38:1 ratio with its 2 primaries in parallel). Combined, as shown doubles the ratio to 76:1

 

[18000rpm]

I haven't a clue. I'm thinking they would either have to be identical transformers connected in tandem to double the voltage out (like my dual toroidal setup), or an arrangement where one transformer has a lower ratio driving the treble band and the other a higher ratio driving the mid-bass band. The old Acoustat Medallion speakers used such an arrangement, which they called "Mirror Drive".

Electronics isn't my forte so perhaps someone here who knows something about the Prodigy setup could compare the connections between my tandem toroid setup to those in the Prodigy schematic and figure it out.

My schematic is shown below. It uses two identical transformers (each having 38:1 ratio with its 2 primaries in parallel). Combined, as shown doubles the ratio to 76:1

View attachment 24344

BTW I just watched all your ESL build videos, very cool stuff.

 

[Jazzman53]

BTW I just watched all your ESL build videos, very cool stuff.

Yeah I have the mechanical stuff down pretty well after all these years... it's the electronics I struggle with.

 

[Jazzman53]

I admire anyone with the smarts to make passive setups work, as I would be so lost attempting it.

As you can see from the schematic; my setup can be very simple because I don't have a passive crossover and a bunch of EQ filters between the amp and transformers-- just the two outs from the amp into two transformer inputs. Simple as can be, which I about as complex as my mind can handle

All the crossover and EQ'ing is done with a DSP upstream of the power amps, and I can tweak crossover frequencies, slopes, and EQ tuning in real time from my listening spot on the sofa using the DSP's I-pad graphic interface.

It's so much easier with this setup-- I'm completely spoiled now and totally useless for any kind of actual work.

 

[Jazzman53]

I haven't a clue. I'm thinking they would either have to be identical transformers connected in tandem to double the voltage out (like my dual toroidal setup), or an arrangement where one transformer has a lower ratio driving the treble band and the other a higher ratio driving the mid-bass band. The old Acoustat Medallion speakers used such an arrangement, which they called "Mirror Drive".

Electronics isn't my forte so perhaps someone here who knows something about the Prodigy setup could compare the connections between my tandem toroid setup to those in the Prodigy schematic and figure it out.

My schematic is shown below. It uses two identical transformers (each having 38:1 ratio with its 2 primaries in parallel). Combined, as shown doubles the ratio to 76:1

View attachment 24344

I just looked at the Prodigy schematic that someone posted today.
Some one please check behind me on this because I'm petty much a dumb-*** when it comes to figuring out electronics.

If I'm interpreting the schematic correctly; I'm seeing two transformers connected in parallel, and each transformer has a single primary winding and a single secondary winding. Each winding may actually be several interleaved windings connected in series but the schematic depiction showing a single winding would be equivalent.

What caught my eye are the center taps on the primary windings. I'm referring to the [common] brown lead in from the crossover/EQ network, tapping into both primary windings.

We were wondering if the toroidal transformers that I use could be plug-N-play replacements for the Prodigy transformers.

Assuming the the step up ratios are comparable (we don't know that), I'm thinking the center-taps on the primaries are a turd in the punch bowl...

The tandem toroid setup is (2) 230V/2x6V transformers turned around backwards to make the 6V windings the primaries & 230V windings the secondaries. With all (4) primaries in parallel and the (2) secondaries in series, the step-up ratio becomes 76:1, which is what we want.

However; with the primaries in parallel there's no place for the center-taps. We would have to change the primaries' connections from parallel to series, and then tap in between the windings. That's the turd in the punch bowl.

Putting each transformer's primaries in series would cut the step-up ratio in half (from 76:1 to 38:1), which wouldn't drive the stat panels.

 

[Brandon Hartwick]

@18000rpm have you tried getting in touch with Ron over in the service department of ML? He will likely be able to dig up some information on the OEM transformers that could help you narrow down a replacement.

 

[18000rpm]

@18000rpm have you tried getting in touch with Ron over in the service department of ML? He will likely be able to dig up some information on the OEM transformers that could help you narrow down a replacement.

Thanks for the suggestion. I asked Ron yesterday and got a quick reply today. He didn't provide the specs directly but gave me these two schematics. Maybe someone can decipher it?

 

[Jazzman53]

If you could get the manufacturer and part number of those transformers you could probably find a data sheet on the manufacturer's website.

There should be a part number on the transformer somewhere.

 

[Brandon Hartwick]

Unfortunately they don't list the transformer winding ratio on any of those prints. It's probably possible to measure the existing transformers as long as they're not fried, but I'm not experienced enough to say how to go about that.

 

[Leporello]

Just re-read this thread after a long time. Looks like a fun project, Brandon. Must be nice to have that much garage/workshop space.

Measuring the turns ratio of a transformer is relatively easy. You just need to excite one winding with a signal then measure the RMS voltage across each winding. A decent function generator should work fine. Doesn't matter if the transformer loads it down somewhat as long as you measure at the windings. They are essentially linear and reciprocal devices, until you get into saturation. If measuring as a step-up loads down the signal too much just measure it as a step down.

Since the Quest has almost the same panel area as the 15, did you think about just ordering the transformers for the 15? I'd be hesitant about using a transformer designed for 60hz for a wide band application, though you and Jazzman53 seem to be getting good results with them. The better response with the lower turns ratio is exactly why I have fantasized about using a low turns ratio transformer to go between tube plates and ESL stators.

The important panel parameters are area and stator spacing. I wouldn't know how the Quest and 15 compare in that regard. The crossover frequency may have to do with whether or not they are different. If you happened to have both Quest and 15 panels (which of course, you don't) and a capacitance meter, that could give you some idea. Or compare measurements from another ESL/DIY fan.

I'm good with electronics, and have degrees in physics and EE, but know relatively little about transformer design. I have one book that's written primarily for switching power supply applications, otherwise information is hard to come by. Also, I have no idea how toroids are built. With a standard E-core you just wind the windings with a machine (some people use a drill) then slip them onto the core (people re-wind such transformers onto existing cores all the time). So with my current state of knowledge, I would definitely have to have someone custom wind transformers for me, and people who do that specifically for audio applications are also hard to come by. I'm actually a little surprised the DIY ESL community hasn't produced such experts by now.

 

[Leporello]

I just looked at the Prodigy schematic that someone posted today.
Some one please check behind me on this because I'm petty much a dumb-*** when it comes to figuring out electronics.

If I'm interpreting the schematic correctly; I'm seeing two transformers connected in parallel, and each transformer has a single primary winding and a single secondary winding. Each winding may actually be several interleaved windings connected in series but the schematic depiction showing a single winding would be equivalent.

What caught my eye are the center taps on the primary windings. I'm referring to the [common] brown lead in from the crossover/EQ network, tapping into both primary windings.

We were wondering if the toroidal transformers that I use could be plug-N-play replacements for the Prodigy transformers.

Assuming the the step up ratios are comparable (we don't know that), I'm thinking the center-taps on the primaries are a turd in the punch bowl...

The tandem toroid setup is (2) 230V/2x6V transformers turned around backwards to make the 6V windings the primaries & 230V windings the secondaries. With all (4) primaries in parallel and the (2) secondaries in series, the step-up ratio becomes 76:1, which is what we want.

However; with the primaries in parallel there's no place for the center-taps. We would have to change the primaries' connections from parallel to series, and then tap in between the windings. That's the turd in the punch bowl.

Putting each transformer's primaries in series would cut the step-up ratio in half (from 76:1 to 38:1), which wouldn't drive the stat panels.

Just to be clear, you guys are talking about the signal driver transformers, right? Not the bias transformer. You need a center tap on a push-pull panel driver, whether it's a single center tapped transformer or two distinct transformers. Also, I think ML, on some models anyway, used transformers optimized for different bandwidths in parallel, as Acoustat did. I don't know where the "turd in the punch bowl" comes in, one way or another you need a center tap.

 

[Russr]

@Brandon Hartwick - So, after moving in to the new house, etc., etc., etc. .. how did these turn out?

 

[Brandon Hartwick]

@Brandon Hartwick - So, after moving in to the new house, etc., etc., etc. .. how did these turn out?

They haven't changed much since the last updated unfortunately, I've just been very busy with other things and projects around the house.

Another big reason is that my active setup running my Aerius I's is just way too damn good. Even just plunked into the living room with no DSP or anything they are just so good.

I'll get them done on Tuesday (I didn't specify what Tuesday)