mwl168

I missed that it's a 4.4mm so not even backwards compatible. Sigh!

Cardas must have coated the individual strand in this wire. They are difficult to solder. And yes, the wire is quite old, I am guessing somewhere between 6 - 10 years old if not older. Here is the FR for HD800 and HD800S included in the HD800 user manual which now comes in a thumb drive. There is also an individual FR included for the particular headphone.

I have fantasized about fabricating some sort of Y splitter to use but ran out of patience.

Re-cabled the HD800 for balanced connection. Cardas Headphone cable, Neutrik 4-pin XLR.

Harvested an old Cardas Headphone cable to make a balanced cable for the HD800. Neutrik 4-pin XLR connectors. The HD800 connectors are from Parts Connecxion and a royal PITA to work with.

Did you try re-inserting the noisy THAT340 to verify if it's a contact problem instead of a defect BJT?

Is this because how Justin chose to implement it with 4 separate front end on GS-X MKII? Looking at the original Dynalo schematic, one single 2SJ109/2SK389 JFET front end is capable of differential and balanced input and output to the next stage?

Yes, you need a quad potentiometer for two channel, balanced inputs.

Thanks Chris for the great summary of the Dynafet information. It does look like more than I can handle at this time. I don't know if CFA or CFP is proper name for it. It's a current feedback amp and the boards stated so as well. But the Gerber file name says "CFP". I'll send you a PM about the CFA boards

Don't understand the rationale of going through the trouble to develop a 5-pin TRS connector when a 5-pin XLR connector would have serve the job better and is readily available. I guess one of the rationale is the pentacon connector can be made to be backward compatible with a typical 3-pin TRS connection.

Thanks for checking Chris. That is a beautiful Dynalo built. What sands does the DynaFET use? Does it use obsolete parts?

I have like 200 of those original Dynalo output resistors in my house - got carried away trying to match the PNP to the NPN sands. Eventually gave up because they are horrendously mismatched. The completed amp works just fine regardless.

Find them Chris!!! My CFP boards for your Dynalo board

I actually have 8 or so 6C33C in my house that I bought like 10 years ago, not yet find an application for them. These things are big and requires ~ 7A filament current. I read getting good tube sockets for these tubes are challenging, most sockets simply deteriorates quickly due to excessive heat. The Menace's simplistic circuit also lands itself well for a point-to-point construction which also makes circuit experimentation easier.

Yes, I've always wanted to build an OTL amp for my dynamic headphones and that's what lead me to this Menace thread. The Menace's simplistic circuit is also very attractive to me. With that said, I do like the idea of the CCS and I have experienced what good CCS can do to with JimL's SRX Plus. My plan is to build a simple Menace OTL as close to Nate's published schematic as possible. Once that's working properly I will be able to experiment and add on more sophistications. That, to me, is a big part of the DIY fun!

To my knowledge the original Dynalo PCB is obsolete. I bought mine from AMB and they ran out of it long time ago. I have never seen a published Gerber file of the original Dynalo. I would love to have another board or two myself if possible.

Thanks! That makes more sense (re: the plate to cathode voltage). Maybe I should sell my NOS BlackGate over at eBay or the other site. I've seen them advertised for silly money... Can you elaborate on what can be done to improve the circuit?

A few more questions: The 6AS7G and 6080 are both recommended output tubes for this amp. They are both rated 250V for max plate voltage. Would applying the 270V B+ direct to the plates of the output tubes as shown on the schematic shorten the life expectancy of these tubes? What other output tubes are recommended to use for this circuit? I have a few 150uf/350VDC rated BlackGate caps on hand. Is it a good idea to use them for PS bypass for this amp?

This looks very nice and intriguing. Where is the connector for outputs?

Thanks Jim and Nate! Did some reading on the motor run caps. Looks like they are often chosen for audio purpose when high capacitance and high voltage are needed in critical positions. They are actually film caps and often oil impregnated polypropylene. No wonder their size.

I have some CFP boards made for my own use - I plan to build a balanced CFA. I have some extras so PM me if you are interested. These are 2mm and 2oz copper boards.They are about 101mm x 94mm. These are the gmt, version 1.09 boards. EDIT: Here is an image of the board. I believe the Gerber file is cfp2gmt. Kevin may have laid out a full balanced board which includes an unbalanced-to-balanced converter on the board that uses THAT340 but I am not certain. I plan to build my balanced CFA using two pairs of boards as I believe that's what congo5 has done.

I recall these 78xx regulators some times overshoot without load. Maybe try putting a load on the output and re-measure?

Resurrecting an old thread because I've always wanted to build an OTL dynamic headphone amp and my Google search brought me full circle back to HC. I have a couple questions reading the amp schematic on page 14: 1. The output capacitors - it shows two 100uf/370vac caps in parallel. Is there a reason other than parts availability/cost to not use a single 200uf caps? Also, what AC potential swing will these output caps see? 2. Any particular reason for the way C4 and C5 are located in the schema? Can C4 be soldered directly on top of C5 like the way C1 and C2 are? Thanks in advance for your help!

Ah, that explains it. Thanks! Looks like the 5 contacts arrangement, instead of 4, is to allow it to be used for both single-ended and balanced amps. I wonder what kind of risk it incurs when plugging and unplugging from an energized headphone amp?

Maybe Sennheiser decided that they rather produce their own "HD650 on steroid" that many have been wanting. The cable plugs on the headphone side look similar to those on the HD650. It would be nice that the aftermarket cables many have invested on can be also used for the new headphone. Why so many rings on the TRS plug shown?