Ecoplate amp electronics

dmp · Mar 4, 2020

I picked up a ecoplate electronics housing on ebay a while ago which I want to use for my ecoplate. It's in bad shape so I am going to DIY the electronics.

I have 4 piezo pickups on the plate. Currently I use a direct box followed by a preamp, followed by a Rane 4 ch rack mixer to create a stereo output. It sounds great and 4 pickups sound better than 2, so I want the electronics to handle that.

This is a sketch of the design. Simple opamp circuits using bb2604 with a level / pan circuit. Since the 4 pickups sound different with the phase flipped, I added an option for this. Also a balanced direct out for each pickup.

Any issues or mistakes, particularly in the pan?

dmp · Mar 4, 2020

And this is the L /R amp after the mixer. The transformers are optional

Bo Deadly · Mar 4, 2020

Personally I think I would keep things really simple. Do you really want a bunch of circuitry and controls at the plate which presumably will be in some far-away quiet place?

Alternatively you could just use a mixer with a decent aux send to the plate but put a 600R:4R transformer in the echoplate housing to drive the "speaker" directly from the aux send (assuming the loss isn't too much). Then, make a PCB with phantom powered Schoeps mic amps to drive balanced lines in a snake cable back to mic inputs of the mixer. One potentially important affect of this arragement is that there is no power at the plate which would require a ground and possibly noise that goes with. All signal and power lines "follow" their returns. If you do 1 send and 3 return, you could use literally one single 4-way snake cable for the whole shebang.

Rob Flinn · Mar 4, 2020

Could be wrong but I thought piezo pickups like to see hi Impedance inputs. Looking at your diagram the input to you amp doesn't look to be hi Z. Ecoplate used fet inputs for their reproduce amps I guess because they are hi Z. They are really simple maybe you could just copy them. I have attached a copy of the ecoplate reproduction amp.

dmp · Mar 4, 2020

squarewave said:
Personally I think I would keep things really simple. Do you really want a bunch of circuitry and controls at the plate which presumably will be in some far-away quiet place?

Alternatively you could just use a mixer with a decent aux send to the plate but put a 600R:4R transformer in the echoplate housing to drive the "speaker" directly from the aux send (assuming the loss isn't too much). Then, make a PCB with phantom powered Schoeps mic amps to drive balanced lines in a snake cable back to mic inputs of the mixer. One potentially important affect of this arragement is that there is no power at the plate which would require a ground and possibly noise that goes with. All signal and power lines "follow" their returns. If you do 1 send and 3 return, you could use literally one single 4-way snake cable for the whole shebang.

It's a trade off - I like the simple ease-of-use of having a stereo return on the patch bay that is ready to use in a mix. But I really like the idea of not having AC power (and the power transformer) anywhere near the pickups. If the hum/buzz could be brought down it would be really nice. Not an insignificant amount of hum.

dmp · Mar 4, 2020

Rob Flinn said:
Could be wrong but I thought piezo pickups like to see hi Impedance inputs. Looking at your diagram the input to you amp doesn't look to be hi Z. Ecoplate used fet inputs for their reproduce amps I guess because they are hi Z. They are really simple maybe you could just copy them. I have attached a copy of the ecoplate reproduction amp.

Wow - I had not seen that schematic before. I only have the Ecoplate II schematic. Do you have the rest of the schematics (driver card)?
Thanks very much for posting it.
The circuit boards came with the box I bought but they have some fried components. The 10 ohm resistors and Q3&Q4 all look bad. Also someone modified it to have an EQ trimmer.

The bb2604 is a FET input opamp and I've seen it recommended for piezo pickups. I think you are right though that piezo pickups need a hi impedance input.

I could fix it but I don't want to go from 4 to 2 pickups. The sound is better with 4.

Rob Flinn · Mar 4, 2020

dmp said:
Do you have the rest of the schematics (driver card)?

Rob Flinn · Mar 4, 2020

There is also a driver card diagram, but for some reason the forum won't let me upload it due to some security issue with the file. It uses an MJE3055 & MJE2955 complimentary pair and has some PSU details +&-18v.

dmp · Mar 4, 2020

Rob Flinn said:
There is also a driver card diagram, but for some reason the forum won't let me upload it due to some security issue with the file. It uses an MJE3055 & MJE2955 complimentary pair and has some PSU details +&-18v.

Thanks for the driver schematic.
Can you send the diagram to my email? I'll send a pm.

fazer · Mar 4, 2020

I’ve used the pan circuit which I think came from Jung opamp book Over 40 years ago. It worked great. Single pot may not have perfect sweep but fine for your use. I used it with a 4 track tascam to mix my Guitar tracks and flying around guitars like I would hear on a Hendrix record. Lots of fun.

mjrippe · Mar 4, 2020

Rob Flinn said:
There is also a driver card diagram, but for some reason the forum won't let me upload it due to some security issue with the file. It uses an MJE3055 & MJE2955 complimentary pair and has some PSU details +&-18v.

Often changing the name of the file will fix this.

EDIT: Had the same problem. Only solution was to change the file format (export as PDF).

emrr · Mar 5, 2020

Are those original files not in Tech Docs?

JohnRoberts · Mar 5, 2020

dmp said:
Wow - I had not seen that schematic before. I only have the Ecoplate II schematic. Do you have the rest of the schematics (driver card)?
Thanks very much for posting it.
The circuit boards came with the box I bought but they have some fried components. The 10 ohm resistors and Q3&Q4 all look bad. Also someone modified it to have an EQ trimmer.

The bb2604 is a FET input opamp and I've seen it recommended for piezo pickups. I think you are right though that piezo pickups need a hi impedance input.

I could fix it but I don't want to go from 4 to 2 pickups. The sound is better with 4.

Back in the 80s I made a few phantom powered JFET DI/buffers that fit inside a 1/4" jack barrel. Now with SMD you could make it even smaller, but no need to.

My point is that a mic input with phantom voltage could power a modest discrete JFET buffer, so no need for PS and power transformer at the plate.

JR

dmp · Mar 5, 2020

EmRR said:
Are those original files not in Tech Docs?

No - there are some docs but not what Rob posted (which are nowhere on the internet either). The schematic you posted for a Eco preamp is different, maybe for the ecoplate 3? I have a collection of docs now I can post there. Both the Ecoplate 1 from Rob and the Ecoplate 2.

https://groupdiy.com/index.php?topic=52701.0

dmp · Mar 5, 2020

Now you guys have me thinking of just leaving it as it is.
The phantom powered DI I have now works fine - Stewart Audio ADB-4. I have the preamp and mixer next to the plate but I could bring them into the control room.

I did do some tests last night on the hum and it doesn't seem to be coming from the electronics. Ambient noise from the environment picked up by the plate / pickups.

mjrippe · Mar 5, 2020

dmp said:
No - there are some docs but not what Rob posted (which are nowhere on the internet either). The schematic you posted for a Eco preamp is different, maybe for the ecoplate 3? I have a collection of docs now I can post there. Both the Ecoplate 1 from Rob and the Ecoplate 2.

https://groupdiy.com/index.php?topic=52701.0

Please do! Will add a few from my collection as well.

dmp · Mar 5, 2020

The tech docs section has schematics and other docs now. Thanks mjripp - this place is great.

If you guys like Ecoplates, this is a pic of mine. I got it from Smart Studios when they closed.
B. Vig has said they bought the plate for $500 from a guy in Chicago that was handmaking them (and the studio manager told me it was an Ecoplate).
But it is before the 'production' ones and looks homemade.
It's very light too so I think the frame is aluminum instead of steel. I built the wood box. Without the box it weighs less than 50 lbs I'd say
They had it hanging from the ceiling vertically in the drum iso room and would record it live while tracking.
The driver works but the speaker sounds the same (to me) except for rolling off the very low end.

dmp · Mar 5, 2020

Damper side

abbey road d enfer · Mar 5, 2020

dmp said:
Any issues or mistakes, particularly in the pan?

The opamps need galvanic continuity at the input. Typically a 1Megohm resistor.
The input amps have way too much gain. 100k/100r is 60dB gain. the opamps will run out of open-loop gain, and probably clip like crazy. I would think replace the 100r with 5-10k.
The 100k level pot is not really the right value to drive the pan pot. It should be about 5k.

abbey road d enfer · Mar 5, 2020

dmp said:
And this is the L /R amp after the mixer. The transformers are optional

Same problem, you need a resistor at the input and increase the 100r.

BTW, you don't need an OPA2604 there. An OPA2134 will do equally well and be much cheaper. the only significant difference is the 2604 can be powered with +/-24V rails, which is irrelevant there.

Ecoplate amp electronics

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