Time to DIY like it's 2009! (hobby has changed, man)

Alright thanks I'll just find a 15k resistor and cut the output v to 20 with the 15va transformer and hopefully I'll be able to fit all of it inside the box okay that one is certainly much smaller.

 

I'm swapping the attenuator I was gonna use for the EHHA. I didn't even realize the new one would be so much smaller, but it was actually an extremely tight fit with the original, which is roughly khozmo quad attenuator sized so I guess that worked out conveniently.

Because this was one of my favorites before I broke a channel messing with nfb I've decided to go the extra mile... upgrading the heatsinks that came in the kits because while they work they get real hot, replacing the xlr sockets from neutrik to a little fancier, going to wire this one a little different so the switch just switches the rca sockets into the circuit and the xlr in will need to be unplugged/will have a direct connection to attenuator instead of going through the switch at all. It's actually all working again and sounds "good" (as far as I could tell with no attenuator, very basic tests). Also I suppose you can include upgrading the chassis in that, originally it was in a super cheap steel instrument box.


From L to R the front outputs are 6.5mm, 4pin xlr, pentacon/4.4mm, 6.5mm, I am only "fancifying" the 4pin xlr and the 2 xlr inputs and outputs on the back. Though it won't be fully "working" for a little bit because I don't have the "upgraded" sockets on hand, creating artificial delays for myself I guess.

Then for this monstrosity....



I need to... tap the heatsinks, holding the current L angle bracket on there with the pretapped holes but 1 is too far off and am just pinning it there with a screw and washers right now. Also thermal paste/isolation pads, bolting the small toroid to the inside of the lid, drilling some 16mm holes on the back panel for outputs (or I could put them on the front I guess) + some wire management.

 

What are you guys using for bushings where the pot extension rod goes through chassis fascia? I'm looking for something uber cheap/free.

 

I got mine a while back not sure I have a little baggie of them...

basically have a couple of these exact sets though I didn't get them here was years ago. You can see the L brackets in the pictures... actually kind of annoying they fit fine for this smaller potentiometer which has smaller threads around the 6mm shaft but for a khozmo or that other one I have on the side in the ehha pic I have to actually file a spot bigger to fit the threads through. Though it does help hold it at a specific vertical height those things are steel and it's a pita to file. If you only care about the bushing though you can just toss that bit or keep it for something else.
https://www.aliexpress.com/item/1005003752633666.html
https://www.ebay.com/itm/154587907409

and they work okay but the one I actually have in that ehha is a different one I can't find a link for, but the shaft in it is steel and permanently in the bushing like it would take some serious force to move it in or out from it's position in the bushing.

 

not sure if that is a before pic with the EHHA heatsinks - those are small for the current that is typically used. You can see the outline on the board where the heatsinks should go - I built mine with off board sinks to really crank up the bias but decent onboard options will work fine.

 

Those are indeed the before pics ;/ the spacing of the holes in this version of the pcb is like not standard heatsink spacing and I have to yank out the pins of the heatsinks first or they won't fit.

 

Thanks, I have a rod and coupler, just need a bushing. Took apart an old pot I have to take that bushing out and use it but the bastard tricked me. The shaft is the 6mm I need....but only the part that sticks out. It's reduced to 5mm inside the bushing so naturally the bushing is only 5mm. Any hard plastic like Derlin will work though so maybe I'll make my own out of bits of material I have laying around. I just refuse to spend money on a damn circle of plastic lol. If it was part of a big order from somewhere sure but not for a single tiny item.

 

Whenever I see price of pentaconn jacks I always think about getting 6.5mm TRS + 4-pin XLR instead.

however I realized that pentaconn is a switching jack and is the one way I can use balanced preamp outputs like other headphone amps

 

I've never found a proper chassis mount or panel mount pentacon socket all the actual sockets I found were pcb mount, this is actually some random chinese female plug I found on aliexpress for around $2 .... I just threaded it into the front panel instead of the shell. The actual sockets were stupid expensive, more than a viborg xlr socket. I am not spending that much on a 4.4mm socket.

 

You’re in luck my friend as I just came across this

https://pentaconnglobal.com/products/NBD1-14-001/54

 

I used something like this though my original listing is gone now, slightly different socket but very similar (to the one I got not the official one) and $1.85 instead of.... apparently $42.50

https://www.aliexpress.com/item/1005001324466794.html (p1057)

 

Well... psu is finished other than I will label the outputs and I'm not sure yet if pi2aes has 2.5 or 2.1mm barrel as I'm still waiting on the hat, but I have both plugs and that will not take any significant time. Otherwise I tested it and it puts out 5.1v & 20.1v, the 5.1v was able to power a rpi4 np. Actually my 5v diode was kind of a dud and only made 4.6v which was out of spec for the diode (& rpi4) but I just upped the gain a little bit to 1.1, easy enough.



Swapped out the heatsinks on the ehhas from the previous dinky ones, hard to see from this angle but theyre 2" tall which is all I could fit.

Removed all the xlr sockets and I discovered that the rear panel was never electrically connected to the rest of the chassis, I thought the 4 corner screws to the sides would have broken the anodization and been enough , it only broke any anodization in the side panel threads and didn't conduct to the anodized countersinking unlike the countersunk holes for everything else that have exposed aluminum. Just going to sand off the anodization in the countersunk holes or attach a g wire from the back to the rest.

Replacing the switches so I can float g for balanced in and switch signal g in for single ended ;/ previously it was only for switching in the L/Rs / +/-. While I'm at it, replacing all the signal paths to chassis G with bronze nuts/bolts/washers. Leaving the black screws & steel nuts etc for the front panel for appearances (/laziness), as se g out the front is actually the center tap of that side's psu and unnecessary for 4pin/4.4mm (4.4mm g is directly threaded into the chassis, good enough for me :/ I don't really have the impression that any headphones with 4.4mm use it or have shielding anyhow)

This attenuator has loudness pads, does anyone know how you're supposed to wire those up to a switch? I could add a 4pst or something to the front panel but I've never actually used a loudness control on a diy amp, I'm not sure how to wire it up, or if I should bother.

 

I have never actually connected one but I thought you had to connect the tab to ground through a series resistor to create a voltage divider ( and add a switch for the loudness component )

I would likely still keep ignoring it

 

It depends on the config, but ones I've seen before you pick a resistor to put in series before the pot, wire your input before it, and then the switch shorts over the resistor when flipped.

 

So from what I'm able to gather it just connects to the "middle" of the pot, and I need to implement my own loudness RC circuit / switch it in & out if I want that, given that I never really had a loudness circuit in mind for this I'm just going to leave it out.

 

So I got all my "fancy" xlr sockets and the only thing holding me up now is... brass flathead screws ;/ actually kind of pita to change them once it's all wired up so I'll just wait a little bit longer. Also considering what to use for the wiring, my options right now for the hook up wiring are 21(.5?) awg cardas copper, 18? awg norse audio stranded copper (it's norne now), 16awg solid core copper?, 21 awg 45% silver 45% copper 10% graphene? Not that it's going to change much but while I'm being crazy anyhow...

 

Now I just need to remember the pinout of this dumb pentacon plug... and which tab is the tip or ring on the 6.35mm plugs ;/ err and I still need to take off some anodization on the screw hole countersinking of the back panel or wire it to the rest. Also need to hook it up to a scope but I've lent it to someone so can't do that for a few days... I left c2/c3 on the new boards just attached on one leg because I put them together like a zombie without thinking. Oops. I will just fully remove them if they turn out to be unnecessary. I did wind up sending the xlr input through the switch, they measured 1 milliohm +- .2 milliohms per contact I am okay with that and this way I don't have to unplug the xlr inputs if I wanted to use an rca input.



Other projects... kinda taking over someone's build of an f5x preamp, he's mailing me his boards and the parts he's collected so far... not sure what all that includes but some matched fets, again not sure if that includes input devices or just the output devices.

I was thinking about putting together and F5-HA ;/ maybe even try to reverse engineer an F5X-HA I have 2 matched octets of 2SK170/SJ774 ... or I could just save them. I actually think the f5x-ha is basically the f5x-pre with different output devices (and everything that goes along with that) I could potentially just try to put a buffer on the pre but I think they've worked out the case layout and everything so there may not be room to do something like that...

and this thing is silly but... I swear the switches will let it be a PI-2XX/2RX/2XR/ CI-2RR when I'm done, not that I really need it, but do I really need anything? Wiring is going to be a little ridiculous but oh well. I was just kind of making sure everything will fit I didn't have proper dimesnions for the inside till I had the chassis.



I'm legitimately thinking of getting a laser engraver/cutter to label things due to this monstrosity... that's a lot of switches but I've measured which of my crappier switches measure the best and those ones will only be on G float switches. I don't really want to try to cut out a slot for dip switches on this weird shaped piece and the top/base are 7mm thick. I have to thread the holes through the top for the switches that won't go through the back, and the transformer mounting holes will just be blind holes/tapped like for the attenuator. Which I suppose isn't in any of those jensen isolation boxes, but it (or the transformers) will be able to be switched out of the circuit.


Gonna use this neoprene sheet + a to220 mounting kit to isolate the transformers from the chassis (besides through white/black wire through g switches... or directly switched to rca g as per CI-2RR schematic.