ECP Torpedo III [indexed in first post]

I really enjoyed the lcd 2 and even more the lcd 3 on the eddie current balancing act. OTL was not a good choice in my exp. Don't know how the t3 does unfortunately.

 

The T3 does fine with the LCD series, I've tried with the entire line. Hifimans is where it flops over and dies.

 

The Output CCS boards are finally finished. 100 of them! I'm still cleaning them up and then will test them. So they'll go up for sale, maybe late today or sometime tomorrow.

 

Great stuff @TomB! Can't wait to order a set

 

Gentlemen, start yer engines!

 

OK, this is encouraging. 100% test good. They average 8.5 ma, with a high of 8.6 ma and a low of 8.37 ma.

I'll have to prepare a page to show how to install these, so bear with me. Basic installation is to install these vertically, flush to the T3 PCB, with "K" and "A" connected to the resistor pads in each case for R19, R20, R21, and R22. Use a spent resistor lead for "K" and "A," bending it around and down on the other side, and soldering front and back. That adds stability to keep these things vertical. Doug strongly recommends a fillet of Dow Corning 748 at the right angle intersection of the vertical CCS board and the T3 PCB. Just remember that "A" goes toward the heat-sinked transistor for each resistor position. You'll end up with two of the CCS boards facing the front of the amp and two CCS boards facing the rear of the amp.

I'll get some photos to make this clear, but I may go ahead and start selling them tomorrow. I'll have the pics up before any of them get shipped to you.

 

Pics:

 

Marvin does not appear particularly pleased with your progress, @TomB.

 

Nah - that's the look of determination and a task finally whipped!

 

@TomB

Makes sense. Dow Corning 748 is non-corrosive, which is important in this use case - not just at the application site but also from off-gassing. The installation does not sound too janky, but I am curious why not go underneath and flush this time? Could be a space restriction - don't have mine open at the moment.

 

Heat.

 

Any photos of the installation of the output CCS boards?

 

I'll be working on it tonight ...

 

Awesome, are these going up for sale imminently?

 

Yes.

 

I'll document this properly before long, but Doug pointed out that I got it exactly wrong in my post up there (since edited) - "A" goes toward the heat-sinked transistor, not "K."

 

Pardon the intrusion gents, but I wanted to get the opinion of the Torpedo III experts as to whether the circuit would be a good theoretical match with the new Focal Elear headphones. Subjective impressions appear to be limited to nonexistent given the recent launch and shipment delays for the headphones.

The Elear's impedance is rated at 80 ohms, and it has a large impedance bump centered around 50hz: http://www.innerfidelity.com/images/FocalElear.pdf. @OJneg has done some modeling here as well.

From past reading in this thread, it appears that (in layman's terms) the Zo of the T3 is roughly 10 ohms with the switch to the lo Z setting and roughly 20 ohms with the hi Z setting. I assume with a bump that large, the lo Z setting would be more ideal with the Elear to minimize frequency response variation?

cc: @brencho

 

I guess many of us are looking forward to hear the Focal Elear..!

They should be an OK match on the low setting as is.

The 80 ohm impedance give us the option to add resistors in parallel with the ouput to bring down the impedance. This should give you the perfect theoretical match you ask for. For instance 56 ohm in parallel with 80 ohm headphones will result in an ideal 32 ohm load for the transformers and the impedance bump will be limited to less than 50 ohm.

 

Yeah, low Z will give the better impedance matching obviously, and that parallel resistor would probably be OK if you really thought a perfect match was needed. The loss shouldn't be too bad without it though, and you'd dissipate a high percentage of the output power in that resistor. But that might be OK since these Elears are rated at something like 104 dB / mW.

Anyhow, just passing the time here until those output boards appear on Beezar! Looking forward to it!

 

No, not a lot power.

Dsavitsk has mentioned the solution with parallel resistors from time to time during the thread... To match headphones to the trannies...