Round 2 for pcbs in the cfa3 - updates to back panel psu board, input connectors & new vertical layout for golden reference regulators also making it easier to wire the star ground

 

19 hours ago, justin said:

Round 2 for pcbs in the cfa3 - updates to back panel psu board, input connectors & new vertical layout for golden reference regulators also making it easier to wire the star ground.

Bravo! Looking excellent! Sure going to be a smaller package than the 2x 2U chassis I'm working on, haha! I'm adding the ubal2baltube input, plus 4x cfa2, but still! 

Edited September 8, 20232 yr by Satyrnine

Just made a crude frequency response measurement of the right channel on my oscilloscope. C1 is OUT+ and C2 is OUT-. At about 1k Hz the amplitude of OUT+ drops by about 1 dB. Anybody know what might cause this? Maybe its because of ZF?

On 9/7/2023 at 9:02 PM, justin said:

Round 2 for pcbs in the cfa3 - updates to back panel psu board, input connectors & new vertical layout for golden reference regulators also making it easier to wire the star ground

 

And now for the Deluxe edition. It adds dual mono Golden Reference regulators and a motor w/ remote for the 47-step attenuator

 

On 11/20/2022 at 11:40 PM, kevin gilmore said:

a pre turkey day new year teaser.

sanken output transistors, in parallel.

with appropriate switching power supplies, capable of about 25 amperes.

can be built with 30v, 35v, 40v power supplies

if you change out the pzta06/pzta56 with bf722/bf723 then you can go up to 60v supplies.

with 40v supplies and big enough heatsinks, 100 watts rms into 8 ohms.

lets see how much joamat can shrink this one.

balanced output impedance, .5 ohm

 

 

I give up, can’t find a way to significantly shrink it.

 

But this one has four pair output transistor each channel. BIAS servo controlled. Flat on Modushop 300mm x 80 mm heat sink. Project name is CFA3 smd something X4.

Edited October 6, 20232 yr by JoaMat

12 hours ago, JoaMat said:

I give up, can’t find a way to significantly shrink it.

Splitboards? Will probably half the real estate on the sinks and reduce width.

Please don't kill me for asking this: Can anyone suggest the best method to connect a subwoofer with SE or speaker-level inputs only to a CFA3? (specifically ubal2baltube boards into 4x cfa2) I imagine the sub inputs grounds are not floating, which obviously presents a problem. Maybe a 15k 1:1 audio transformer tapping signal after volume control? aka a "DI box"? Or maybe something like this paralleled to CFA inputs post-volume?

Am I missing an easier method?

Edited October 28, 20232 yr by Satyrnine

Just wanted to share a sneak peak of the machined panels for my split chassis tube input CFA3. Just got pics from modushop. 10mm thick. Very pleased with how they turned out! Will be 1x 2U Dissipante and 1x 2U Pessante. Gianluca was amazing to work with, top notch customer service.

 

Nice. How much did you pay for them?

1 hour ago, audiostar said:

Nice. How much did you pay for them?

About $650 shipped, with all the customizations and upgraded alum top/rear panels and 10mm front panels. Rear panels are machined and labeled as well. Pricey, but fair I think, I wanted to go all-out. The tube input boards are fantastic sounding.

Edited November 2, 20232 yr by Satyrnine

Normally around Thanksgiving in years past, Modushop has done a sale at something like 20% off. A couple of years ago, they included the customizations in that sale, which is where they get expensive with the machining, anodizing, etc. I did my DynaFET and Salas FSP cases on one of those. Still not cheap, but probably quite a bit cheaper than finding a CNC machine shop, designing your own cases, etc. as Kevin did for the T2's.

I got lucky with them, usually they charge if you don't supply CNC files directly. I made vector drawings to-scale, but don't know solidworks or such, so they definitely had to do some conversion and recreation to some degree, but I didn't get charged for the additional file creation fee. Gianluca and I went back and forth probably 50+ times over a number of months. Definitely great to work with, and like you mentioned, easily cheaper than sourcing locally or taking a risk with aliexpress/etc. 

If anyone with a CFA hasn't tried the ubal2baltube boards, they add just the right amount of "tube" flavor, and still keeps the CFA detail/slam. I splurged on nice Siemens E288CC tubes (not quite the same as a 6922, double heater and plate current) which meant some additional tweaking of the tube boards, but I think it was worth it. Compared to basic EH 6922 they are a clear improvement. They ARE a bit taller than a 6922 though, so they may end up sticking out the top of the chassis, we'll see, ha! Could look pretty neat with some tube cages, and make swapping easier. Like this: 

Chassis Mocked up. Still mostly empty. Definitely will need to trim the lips of the top and bottom plates of the PSU chassis to fit the IEC block's trim, but otherwise extremely happy. Not sure if I've mentioned but this is just a one-off for personal use. Definitely a huge setup, and doesn't come close to the refinement of many of your amazing builds, but for the first headphone amp I've built from scratch, (RIGHT to the deep end, haha!) I'm pretty content so far. haha! 

Not pictured, JAE DC connectors, Neutrik XLR inputs, CMC Rhodium 5-ways.

Suggestion - instead of trimming the lids to get the IEC to fit, why not 3d print a spacer?  Be a shame to risk mangling an otherwise pristine set of cases. Looks like you only need a mm or two.

6 hours ago, n_maher said:

Suggestion - instead of trimming the lids to get the IEC to fit, why not 3d print a spacer?  Be a shame to risk mangling an otherwise pristine set of cases. Looks like you only need a mm or two.

Good idea! I was planning on using a nibbler to just cut a notch in the lips, which should look decent, but a spacer would definitely work too.

Can anyone verify this is the proper way to connect a subwoofer with speaker level inputs to a differential amp like the CFA3:

CFA3       >   SUB
R+           >   R+ SPK LVL IN
L+           >    L+ SPK LVL IN
Chassis  >    R- and L- SPK LVL IN

I'm excited to use the CFA3 with high efficiency monitors, but with "only" 15W/chan will definitely want a small sub. Sub is a small velodyne.

No, chassis (and ground as well) do not touch the signal. You have two halves + and - per channel, from input to output. Speakers connect the same way to the amp as headphones. The only difference is the impedance. 

5 hours ago, audiostar said:

No, chassis (and ground as well) do not touch the signal. You have two halves + and - per channel, from input to output. Speakers connect the same way to the amp as headphones. The only difference is the impedance. 

Sorry if I mis-wrote. The sub is a powered sub, the speaker level inputs are just a way to get signal to it. Said speaker level inputs have an opamp buffer/mixer to combine the L and R signals and feed it to the built-in plate amp of the sub. So the CFA should see no load from the speaker level inputs on the sub. This method is how REL tells customers to connect their powered subs to a differential amp. According to them the only necessary connections are the L+ and R+. They suggest the cfa chassis to sub high level - connection “if there is hum”.

https://rel.net/blog/2015-07-23/how-to/how-to-connect-a-rel-to-a-balanced-amp/

I would think for that application it would be the same as how you would wire an SE headphone jack. L+, R+ and PSU gnd for the - for each channel (L and R). For example, look at how Kerry did it for the SS mini dynalo.

53 minutes ago, Pars said:

I would think for that application it would be the same as how you would wire an SE headphone jack. L+, R+ and PSU gnd for the - for each channel (L and R). For example, look at how Kerry did it for the SS mini dynalo.

Oh, yes, right in this case - the same as how you would wire single-ended headphones, as suggest by Pars. 

1 hour ago, Pars said:

I would think for that application it would be the same as how you would wire an SE headphone jack. L+, R+ and PSU gnd for the - for each channel (L and R). For example, look at how Kerry did it for the SS mini dynalo.

 

49 minutes ago, audiostar said:

Oh, yes, right in this case - the same as how you would wire single-ended headphones, as suggest by Pars. 

Thanks Guys! I’ll give it a shot! 

The only question that remains for me is why wouldn't you want to convert SE headphones to balanced? Just recabling necessary and using 4 instead of 3 wires!? 

2 hours ago, audiostar said:

The only question that remains for me is why wouldn't you want to convert SE headphones to balanced? Just recabling necessary and using 4 instead of 3 wires!? 

I surely am using balanced headphones and balanced speaker outs. The issue just lies in that the speaker level inputs on most subs have negative terminals that are common, which would pop the cfa3 -outs if wired traditionally. Maybe that question was more aimed towards Pars' comment on how Kerry wires SE headphones to a differential amp, and not me specifically, but thought I'd clarify. Thanks!

I think it is just a convenience factor, as all headphones aren't wired for balanced (as well as power amps, etc.). Home audio components still live in a mostly SE world.

Can anyone offer their input on my layout before I start drilling?

Amp: Left or right layout? Input comes in the middle, so figured I'd go right down the middle to the vol pot. DC comes in on each side. Which layout is best?

Power Supply: The center transformer will interfere with the rather deep power switch if I push it back any further. Too close to the GRHV100 board? Is the GRHV too close to IEC input at the rear/bottom? Note the heatsink on the GRHV won't be there, sand will be sinked to bottom plate via a block I think. Flip position of GRHV?

Thanks!