and now for something completely different part 3

[Helium]

1 hour ago, Satyrnine said:

You don't happen to have dimensions of the bracket do you?

Here they are.

Consider 2-storey layout, where CFA boards are mounted on top with each other and to L-brackets on heatsinks.

This is what I have in mind for my CFA3 project.

 

[audiostar]

With this 19" 3U case the amp will look like a 100w class-A power amp. 

A better idea would be to separate the PSU from the amp.

Also, 100VA toroids aren't giant, I wouldn't be concerned about mounting them with 4 or more bolts. 

4 hours ago, Helium said:

Well, I myself don't like mounting trafos on aluminum plate.

Depends on how thick the plate is. Dissipante panels are only 1.5mm I think, so this makes sense. Wouldn't be concerned though mounting the 100VA to 3-4mm thick panels. But don't use countersink bolts, only buttheads so you do not weaken the hole. Will be on the underside anyway.

Edited April 25, 2023 by audiostar

[Satyrnine]

2 hours ago, audiostar said:

With this 19" 3U case the amp will look like a 100w class-A power amp. 

A better idea would be to separate the PSU from the amp.

Also, 100VA toroids aren't giant, I wouldn't be concerned about mounting them with 4 or more bolts. 

Depends on how thick the plate is. Dissipante panels are only 1.5mm I think, so this makes sense. Wouldn't be concerned though mounting the 100VA to 3-4mm thick panels. But don't use countersink bolts, only buttheads so you do not weaken the hole. Will be on the underside anyway.

I'm going with aluminum panels, so they are 3mm aluminum. The steel are thinner though, obviously. I figure a 3U chassis isn't much bigger than two separate chassis though, no? The extra heatsink on the 3U for speaker use was my thoughts.

The toroid cans are a single bolt, but the edge of the can is flush with the chassis, so any lateral force would be more distributed and less likely to bend the mounting plate, vs a "roundish" toroid without a can/cover. 

2 hours ago, Helium said:

Here they are.

Consider 2-storey layout, where CFA boards are mounted on top with each other and to L-brackets on heatsinks.

This is what I have in mind for my CFA3 project.

 

This is fantastic, thank you! I'll mock up the layout and see if it's feasible. If not, I'll change up the design. Many thanks for this! Edit: Yep, not going to work as I had it drawn. Thanks for saving me a lot of headache!

[Satyrnine]

Alright, here's the new idea. 

[audiostar]

So, you will be running single ended wiring from the back panel's RCA connectors alongside the transformers all the way to the bal/unbal board located at the front panel? 

[audiostar]

On 11/18/2017 at 6:08 PM, mwl168 said:

Plus, it will still have the two holes for the screws exposed on the front panel which is not ideal either. It would be great to have XLR jacks made similar to Justin's Stax socket.

Here an idea for further builds: I am using the Neutrik NC4FAH-0 connector and mount it behind the front panel using blind taped holes, same as with the teflon Stax sockets. The hole is 22mm in diameter and for any panel thicker than 2.7mm a beveled edge on the front is a nice addition. Here the panel cut out and dimensions for the NC4FAH-0. If you do not PCB mount the connector, the NC4FAV-0 would be the vertical pin version where the contacts might be easier to solder wires to. Front design and dimensions are the same. These connectors don't have a locking tab, which is nice as well.

Edited April 25, 2023 by audiostar

[Satyrnine]

4 hours ago, audiostar said:

So, you will be running single ended wiring from the back panel's RCA connectors alongside the transformers all the way to the bal/unbal board located at the front panel? 

I should clarify, because it's not clear, the stacked holes labeled just R and L are speaker jacks, not RCA jack holes. I didn't want them too close to either the inputs or the mains. Thoughts? RCA's would be the labeled SE input further to the sides. I do need to move the inputs further to the sides now that there's room to do so. Good call.

I'm forgoing the bal/unbal board for now. (Had a hard time finding good input jfets, and Dukei suggested I try it without first) But yes, I'd run them around each side to the vol pot first, then off to CFA boards. Was planning well shielded Ag/ptfe for the runs fwiw.

The SE inputs would be parallel to bal inputs. Flipping the switch grounds the neg boards inputs, and then you get SE output only. For the outputs, a 4pdt. Planned on running the speaker leads centered near the top of the chassis, or possibly back around each side of the trafos. Any input welcome! 

4 hours ago, audiostar said:

Here an idea for further builds: I am using the Neutrik NC4FAH-0 connector and mount it behind the front panel using blind taped holes, same as with the teflon Stax sockets. The hole is 22mm in diameter and for any panel thicker than 2.7mm a beveled edge on the front is a nice addition. Here the panel cut out and dimensions for the NC4FAH-0. If you do not PCB mount the connector, the NC4FAV-0 would be the vertical pin version where the contacts might be easier to solder wires to. Front design and dimensions are the same. These connectors don't have a locking tab, which is nice as well.

Wow, I think I'm going to convert to this actually, that's a far better look. Thank You!

I wish they made a female version of this.

[Satyrnine]

Alright, here it is updated with the recessed jack with hidden tapped holes, and the inputs and speaker outs spaced better to fill the space opened up by moving the grlvs.

 

[audiostar]

19 hours ago, Satyrnine said:

The SE inputs would be parallel to bal inputs. Flipping the switch grounds the neg boards inputs, and then you get SE output only. For the outputs, a 4pdt. Planned on running the speaker leads centered near the top of the chassis, or possibly back around each side of the trafos. Any input welcome! 

You might want to consider having only balanced inputs and *if* you need to connect a single ended cable to it, then use external Neutrik NA2 MPMF to convert a chinch cable. Will make things simpler.

The mount-from-inside version for the 3-pin XLR connectors for the inputs on the back would be the Neutrik NC3FBH2-B or the NC3FBV2-B with vertical pins.

For the speaker terminals, personally I would use the Neutrik SpeakOn. Would keep your back plate clean and can be mounted from inside as well into a round hole and are the best speaker wire connectors anyway. NL2MP or NL4MP-ST depending on what kind of connection from the inside you want and bi-wiring (4-pole) or not. 

This will clean up your back panel with only 2 holes on the left and 2 on the right side. In the middle you can have the IEC inlet. Just a thought...

Edited April 26, 2023 by audiostar

[Satyrnine]

3 hours ago, audiostar said:

You might want to consider having only balanced inputs and *if* you need to connect a single ended cable to it, then use external Neutrik NA2 MPMF to convert a chinch cable. Will make things simpler.

The mount-from-inside version for the 3-pin XLR connectors for the inputs on the back would be the Neutrik NC3FBH2-B or the NC3FBV2-B with vertical pins. 

For the speaker terminals, personally I would use the Neutrik SpeakOn. Would keep your back plate clean and can be mounted from inside as well into a round hole and are the best speaker wire connectors anyway. NL2MP or NL4MP-ST depending on what kind of connection from the inside you want and bi-wiring (4-pole) or not. 

This will clean up your back panel with only 2 holes on the left and 2 on the right side. In the middle you can have the IEC inlet. Just a thought...

You're full of good ideas! Thank You! I love the adapter idea, will go that route. For rear panel XLR's, since it's less visible and I already have the jacks, I'm going to stick with they type I have. Will use the new style in the future for sure. For speaker terminals, I may keep the posts, as most of my speaker cables already have them. They aren't exposed metal at least, fully insulated, so less chance of shorting. Thanks again!

One other question. I assume I want to isolate the unbal out jack ground from the chassis, right? The jack I have is a switchcraft metal barrel type. Should be able to isolate it without too much trouble with some kapton tape and fiber washers.

Edited April 27, 2023 by Satyrnine

[Satyrnine]

I'm hoping to mount output transistors flat to heatsink, although I realize this makes tapping mounting holes a rather arduous adventure. If I snap/jam a tap off in the heatsink, I'll have to move where I'm mounting boards, which would suck. I was considering a 1/4" thick by 2" bar of copper that I'd use as an interface. I'd lap both the bar and possibly the heatsink for a good joint and use some CPU thermal grease for a good thermal connection. A few big bolts to secure. Would use forming taps vs cutting taps since it's copper. Thoughts?

[Pars]

Yeah, that could work, though I'm not sure why everyone breaks taps? Are you tapping by hand or using a drill? By hand, do a couple of turns, back out 1/2 turn or so, continue, rinse and repeat. I've never broken a tap, even on blind holes with a bottoming tap.

[Satyrnine]

9 hours ago, Pars said:

Yeah, that could work, though I'm not sure why everyone breaks taps? Are you tapping by hand or using a drill? By hand, do a couple of turns, back out 1/2 turn or so, continue, rinse and repeat. I've never broken a tap, even on blind holes with a bottoming tap.

I haven’t either, just going by other peoples warnings I guess. I have a drill press I can use as a guide too. Maybe I’ll just mount direct if its not such a problem. 

[johnwmclean]

having the amps boards stacked like that you won't be able to bias the lower board if needed. Just ensure there’s adequate space, maybe longer standoffs.

Edited April 27, 2023 by johnwmclean

[Helium]

I would use different layout.

Move transformers and grlvs to the front. Move cfa to the rear. Keep DC protection board where it is at the front. Use extension shaft to mount volume pot at the rear close to inputs.

Side notes: move ac inlet to the left or right, it doesn't have to be on the center, it gives nothing. Stack the upper cfa higher so that transistors are distributed more evenly over heatsinks area. Move inputs closer to center (and to the pot) and move speaker terminals to outer edge of the chassis. Cause your speakers will be placed to the left and right and maybe quite far away from the amp.

Consider stacking transformers on top of each other, you have 120mm clearance if you don't use steel chassis.

That way you will have space to mount grlvs horizontally.

After all I don't think that amp with bjt output transistors is good to drive speakers. I would consider omitting speaker terminals completely.

Edited April 27, 2023 by Helium

[audiostar]

I would not stack anything, at least not horizontally. In addition to what John already said, the upper board will always run hotter and also its transistor will be on the upper part of the heatsink already heated up by the lower row of transistors. 

Stacking boards vertically on the heatsinks is much better, thus the reason for the CFA split boards. 

Make sure you mount transistors to the lower on the sinks as heat moves from bottom to top. 

[Satyrnine]

5 hours ago, johnwmclean said:

having the amps boards stacked like that you won't be able to bias the lower board if needed. Just ensure there’s adequate space, maybe longer standoffs.

I was thinking I could either use a horizontal adjust trimpot or a remote trimpot, but others suggestions might mean a reconfig anyway. Thanks!

4 hours ago, Helium said:

I would use different layout.

Move transformers and grlvs to the front. Move cfa to the rear. Keep DC protection board where it is at the front. Use extension shaft to mount volume pot at the rear close to inputs.

Side notes: move ac inlet to the left or right, it doesn't have to be on the center, it gives nothing. Stack the upper cfa higher so that transistors are distributed more evenly over heatsinks area. Move inputs closer to center (and to the pot) and move speaker terminals to outer edge of the chassis. Cause your speakers will be placed to the left and right and maybe quite far away from the amp.

Consider stacking transformers on top of each other, you have 120mm clearance if you don't use steel chassis.

That way you will have space to mount grlvs horizontally.

After all I don't think that amp with bjt output transistors is good to drive speakers. I would consider omitting speaker terminals completely.

This sounds like a good idea, I'm going to draw it up as you suggest.

I laid it out as is just to minimize distance from IEC to trafos mostly, since I don't have a front power switch, it'd keep it all the mains lines nice and isolated. Unnecessary? The rear mounted pot near inputs also sounds great though, so that probably trumps the mains being isolated/short.

I would only be driving small efficient nearfield desk monitors with this. I recall seeing others review it well for such use, am I off there?

2 hours ago, audiostar said:

I would not stack anything, at least not horizontally. In addition to what John already said, the upper board will always run hotter and also its transistor will be on the upper part of the heatsink already heated up by the lower row of transistors. 

Stacking boards vertically on the heatsinks is much better, thus the reason for the CFA split boards. 

Make sure you mount transistors to the lower on the sinks as heat moves from bottom to top. 

Thanks, will consider all this in new layout. In the last drawing I tried to keep them as close to bottom of sink as possible, but then as you say they are too close. Was hoping that direct-mounting the sand with a thick copper bar would help with the heat soak. I'll see what I can come up with. Thank you!

[Satyrnine]

Alright, here's what I came up with. Any issue with proximity of IEC to CFA board on right, or the grlv to the bal/unbal outputs on front?

[luvdunhill]

Where the wires go into the toroid is probably the place to tweak a bit. Rotate them both towards the shaft if possible. The only other issue might be getting the wires safely to the 4PDT switch.

[Satyrnine]

49 minutes ago, luvdunhill said:

Where the wires go into the toroid is probably the place to tweak a bit. Rotate them both towards the shaft if possible. The only other issue might be getting the wires safely to the 4PDT switch.

Yes, I was thinking mains in the center, and out on each side towards each grlv. As far as the 4pdt, it'd come from the protect board to the 4pdt, and then I was thinking speaker wires tucked along top or bottom edge all the way back to the speaker outs on the same side as the 4pdt. The back panel shows speaker outs on right, but it has to be rotated obv vs the drawing so they'd actually be on the same side of chassis as the 4pdt. I was planning on braid shielding pretty much every wire to chassis as well, unless that's excessive.

Edit: Here's the wiring mockup. Anything look problematic? Also, best solution for rear mounting a pot? First time doing so.

Edited April 28, 2023 by Satyrnine

[Satyrnine]

12 hours ago, audiostar said:

I would not stack anything, at least not horizontally. In addition to what John already said, the upper board will always run hotter and also its transistor will be on the upper part of the heatsink already heated up by the lower row of transistors. 

Stacking boards vertically on the heatsinks is much better, thus the reason for the CFA split boards. 

Make sure you mount transistors to the lower on the sinks as heat moves from bottom to top. 

I'm confused, aren't the split boards long and narrow, and designed to be stacked horizontally? Wouldn't vertical mount exacerbate the heat issue? 

Was thinking a single 3/8" copper plate as an interface between devices and sink would act as a great heat spreader, reducing the heat soak effect of the stack configuration.

Edited April 28, 2023 by Satyrnine

[Satyrnine]

Here's another idea. Mount the grlv sand offboard, and flip is on its side.

Mounting grlvs on top of trafo covers and remote mounting sand to sink.

Edited April 28, 2023 by Satyrnine

[audiostar]

5 hours ago, Satyrnine said:

I'm confused, aren't the split boards long and narrow, and designed to be stacked horizontally? Wouldn't vertical mount exacerbate the heat issue? 

Was thinking a single 3/8" copper plate as an interface between devices and sink would act as a great heat spreader, reducing the heat soak effect of the stack configuration.

Stacking is vertically for proper heat dissipation, bolted directly to the heat sinks (so boards are long and narrow). 
* vertically in terms the boards are parallel to the sinks.

 

Edited April 28, 2023 by audiostar

[johnwmclean]

FWIW with 2 X 100VA the GRLVs are not going to run hot, you can mount them to the base plate.

 

[audiostar]

8 hours ago, Satyrnine said:

Mounting grlvs on top of trafo covers and remote mounting sand to sink.

Not really going to work as there are caps on the GRLV boards. Maybe, with a 5U case 😎

The pass transistors you better mount directly to the bottom plate, like John has shown above. Oriented to center, straight below the Goldpoint stepper.

Edited April 28, 2023 by audiostar