and now for something completely different part 3

[Satyrnine]

Last CFA board has spicy bias. With bias pot all the way down, I get about 150ma across the 1R's. That can't be right. The rest needed to be set around middle to get any idle current at all. Rechecked my P's and N's, and resistor values. Any thoughts? Suspect the middle (bias driver?) 15030? 🤔 

Edit: replaced the middle 15030 with a slightly lower hfe version, dropped minimum bias to 120ma or so, so not the culprit. And then I shorted legs with my probe again like an idiot and popped the "last" 30/31's again. You'd think I would have learned something. I need probes designed for this clearly. 
 

Here's latest chassis face design:

The horizontal lines would be deep machined grooves. 

Edited May 25, 2023 by Satyrnine

[jamesmking]

21 hours ago, Satyrnine said:

Last CFA board has spicy bias. With bias pot all the way down, I get about 150ma across the 1R's. That can't be right. The rest needed to be set around middle to get any idle current at all. Rechecked my P's and N's, and resistor values. Any thoughts? Suspect the middle (bias driver?) 15030? 🤔 

Edit: replaced the middle 15030 with a slightly lower hfe version, dropped minimum bias to 120ma or so, so not the culprit. And then I shorted legs with my probe again like an idiot and popped the "last" 30/31's again. You'd think I would have learned something. I need probes designed for this clearly. 
 

Here's latest chassis face design:

The horizontal lines would be deep machined grooves. 

for smd and transistor probing I highly recommend spring loaded very fine tip probes. I use these

https://probemaster.com/spring-loaded-micro-tip-test-lead-kit/

the tips are replicable and have an assortment of end types and the leads are high quality...

for more hands free measurements I use Sensepeek 4011 PCBite 2x SP10 Probe set

https://telonic.co.uk/product/4012-sensepeek-pcbite-kit-with-2-x-sp10-probes-for-dmm/

they are not high voltage rated because of the exposed metal and relatively thin insulation on the wires but they stay in place. The tips are as sharp and fine as the probe master. They also sell scope probes:

 

 

Edited May 25, 2023 by jamesmking

[Satyrnine]

29 minutes ago, jamesmking said:

for smd and transistor probing I highly recommend spring loaded very fine tip probes. I use these

https://probemaster.com/spring-loaded-micro-tip-test-lead-kit/

the tips are replicable and have an assortment of end types and the leads are high quality...

for more hands free measurements I use Sensepeek 4011 PCBite 2x SP10 Probe set

https://telonic.co.uk/product/4012-sensepeek-pcbite-kit-with-2-x-sp10-probes-for-dmm/

they are not high voltage rated because of the exposed metal and relatively thin insulation on the wires but they stay in place. The tips are as sharp and fine as the probe master. They also sell scope probes:

Oh! Excellent, love both options! My main work is with instrument tube amps which often have a bit more real estate, so my probes are not so small. I think part of my issue is there was no good place to rest my arm/hand to stabilize as I probed, since this is all out on the table in spaghetti form currently. 

[Satyrnine]

On 5/16/2023 at 4:39 PM, audiostar said:

The Amphenol's don't have removable pins, so no crimping possible and also no variable size pins available as well. It only has one 18 AWG pin (and all the others are max 20 AWG wire pins), so not really suited for a high current class A amp.

A much better connector is the AMP CPC shell Size 17, p/n 206043-1, 206044-1 (PSU side), 183040-1, 183039-1 (amp side), as used on the BHSE or the Dark Star. Pins are removable and all sorts of pins for crimping (as well as soldering if you wished) and sizes for 16...26 AWG wire are available for the same size 17 connector. Very nice modular and serviceable system. It is HV rated and the 16-18 AWG pins would be perfect for the beefy GRLVs. Really nice. 

Was going to go with switchcraft due to being less modular and worried about getting the right pins and all, but these are WAY cheaper than switchcraft too. Do you happen to know the right "pins" I'll need? I'd hate to order the wrong thing, and there are TONS of options with this line. Are locking nuts, plug housing, and everything but pins included with the connectors, or do those need to be sourced separately too? Doesn't seem clear. Datasheets show no accessories. Thanks!

 

Also, does anyone have any guesses on what could be causing the spicy bias on the one board? I'd really hate to resort to shotgunning all the sand to try to find the culprit. I have a decent Hakko desoldering gun, but extensive rework sucks if avoidable. I'm going to go through and measure voltages across each resistor and compare to a working board. 

Edited May 26, 2023 by Satyrnine

[Satyrnine]

I built a protector board up for this. When I connect it to one of the grlv set to 30v (also powering 2x CFA boards), it  causes pretty bad high frequency noise on the outputs. Right now in SE mode, grounding negative inputs.

I tried grounding two ways:

1) GRLV ground AND cfa output grounds all connected to protector board. (hf noise was present) 

2) Only GRLV ground connected to protector, cfa output grounds and protector input ground connected to star ground. (hf noise was worse)

When I remove the protector, cfa is dead quiet. I've read these can be used with 30v, but maybe I'm stressing 12v regs too much?

[JoaMat]

14 hours ago, jamesmking said:

for smd and transistor probing I highly recommend spring loaded very fine tip probes. I use these

https://probemaster.com/spring-loaded-micro-tip-test-lead-kit/

Interesting item. I use Pomona model 6341. On my third pair now – after some use it seems that the wire break at the handle edge - else I like them.

Probe Master looks good so I ordered a pair. Can be bought in EU at https://eleshop.eu/probe-master-8150-spring-loaded-micro-tip-test-lead-kit.html and/or https://www.welectron.com/Probe-Master-8150-Spring-Loaded-Micro-Tip-Test-Lead-Kit_1 .

[ang728]

On 5/25/2023 at 5:23 AM, audiostar said:

Those large boards on top look interesting.

yeah that's for ZF/SS switch and protector hat PCB ,but can do better placement on next revision

[migo]

On 5/26/2023 at 3:51 AM, Satyrnine said:

I built a protector board up for this. When I connect it to one of the grlv set to 30v (also powering 2x CFA boards), it  causes pretty bad high frequency noise on the outputs. Right now in SE mode, grounding negative inputs.

I tried grounding two ways:

1) GRLV ground AND cfa output grounds all connected to protector board. (hf noise was present) 

2) Only GRLV ground connected to protector, cfa output grounds and protector input ground connected to star ground. (hf noise was worse)

When I remove the protector, cfa is dead quiet. I've read these can be used with 30v, but maybe I'm stressing 12v regs too much?

When do you disconnect one of CFA3 boards from power is that noise still there while using protector board?

[EL_Ken]

Thanks audiostar for crucial knowledge about grounding.

Added banana jacks to both Amp & PSU chassis for grounding.
When all cables are connected, circuit ground is measured ~3.5ohms to PE and every parts of the two chassis are 0ohm to PE.
Next step is shielding the two DC cables to block out noise.

Also made some PCBs for simplify wiring, reduce half of the cables.
On the RCA/XLR board, XLR (1) & RCA GND connect to chassis through mounting screw of NC3FAAH2.
Relay NC for HOT&COLD, NO for RCA (+) and short (-) to circuit ground.

The larger board is used for switching headphone/speaker output.
R- & L- are bypassed, only switching R+ & L+ between two outputs.
Similar to Kevin's protector, cutoff R+ & L+ when DC occur.
With those hollow areas, I can access the underneath protector much easier.

Input transistors swapped to J109/K389 with 50K attenuator.
Bias set to 150mv and temperature raises from 20°C to 45°C.
Although this temp is ok for transistors but don't want being to hot as a desktop setup.

[audiostar]

5 hours ago, EL_Ken said:

On the RCA/XLR board, XLR (1) & RCA GND connect to chassis through mounting screw of NC3FAAH2.
Relay NC for HOT&COLD, NO for RCA (+) and short (-) to circuit ground.

Hmm, while XLR pin 1 is fine going to chassis as it is basically shield, RCA GND should not go to chassis. This is why the RCA sockets have an insulation ring. It goes to circuit ground and is shorted to - half of the channel when the RCA input is engaged. 

5 hours ago, EL_Ken said:

The larger board is used for switching headphone/speaker output.
R- & L- are bypassed, only switching R+ & L+ between two outputs.

This is a balanced amp, so I would switch all 4 channels (+ and - halves) between the outputs. And I would handle the speakers like balanced headphones, i.e. wire the +/- to the banana plugs and not circuit ground. Especially important when using a balanced source. For when you use the RCA input, the - half would be shorted to circuit ground anyway.

[EL_Ken]

1 hour ago, audiostar said:

Hmm, while XLR pin 1 is fine going to chassis as it is basically shield, RCA GND should not go to chassis. This is why the RCA sockets have an insulation ring. It goes to circuit ground and is shorted to - half of the channel when the RCA input is engaged. 

This is a balanced amp, so I would switch all 4 channels (+ and - halves) between the outputs. And I would handle the speakers like balanced headphones, i.e. wire the +/- to the banana plugs and not circuit ground. Especially important when using a balanced source. For when you use the RCA input, the - half would be shorted to circuit ground anyway.

Will make new PCBs for RCA GND/circuit ground/(-) just as your words, thanks.

I wire the +/- to the banana plugs, not using the circuit ground, same as 4pins XLR headphone out.
R+L+ will cut off from unused output and R-L- remains connected.
No issue with a balance source but not yet try SE source.

There is no complete circuit when only (-)cable connected.
Cut off all 4 channels for preventing noise from cable to amp?

[audiostar]

14 hours ago, EL_Ken said:

R+L+ will cut off from unused output and R-L- remains connected.
No issue with a balance source but not yet try SE source.

There is no complete circuit when only (-)cable connected.
Cut off all 4 channels for preventing noise from cable to amp?

If you mean the Protector3, yes, it cuts off only R+ and L+ to protect the phones. That's enough.

[audiostar]

On 1/11/2023 at 3:20 PM, kevin gilmore said:

here you go

cfp3largeT.ZIP 42.53 kB · 114 downloads

Ready to order BOM here, Mouser ID=43398b8123.

Everything included for a 4ch amp, except for 24x 2sc4886 and 20x 2sa1860, which are double the cost of the items in the bom above and are pretty much nowhere to be found except for some 2sc4886 at Digikey.

Edited June 5, 2023 by audiostar

[Angchuck]

Hi, 

would anyone have links or files to the cfa2/3 gerbers?  I tried the above but does not work 
 

much appreciated! 

[jamesmking]

3 hours ago, Angchuck said:

Hi, 

would anyone have links or files to the cfa2/3 gerbers?  I tried the above but does not work 
 

much appreciated! 

gerbers:

https://drive.google.com/drive/folders/1r3g2TAtBUaBdiMorTWX7yYgeJ7maQbYW

schematics and other things:

https://drive.google.com/drive/folders/0B7egryukiT7_TFlEQlBRejdVdDQ?resourcekey=0-nGWwBYQ_Uivj-ciBLYMeaA

[Angchuck]

4 hours ago, jamesmking said:

gerbers:

https://drive.google.com/drive/folders/1r3g2TAtBUaBdiMorTWX7yYgeJ7maQbYW

schematics and other things:

https://drive.google.com/drive/folders/0B7egryukiT7_TFlEQlBRejdVdDQ?resourcekey=0-nGWwBYQ_Uivj-ciBLYMeaA

Thank you 

[migo]

Anybody here with complete CFA3 split board version Mouser BOM for sharing? Thank you!

[audiostar]

On 11/29/2022 at 5:58 PM, kevin gilmore said:

nope, going to need two boxes. no easy way to stack the front end board onto the heatsinks. the 2 boards will take up much of the bottom.

I think I am going to enlarge the front end board so I can stack it on top of two CFA3LargeT boards and mount them exactly the same way as the split boards are mounted. This leaves me the middle of the case for two stacked GRLVs in the front and a toroid in the back. 

What was the max output a GRLV can be modified to? I think @sorenb did a special power version of it.

Edited June 6, 2023 by audiostar

[sorenb]

1 hour ago, audiostar said:

... I think @sorenb did a special power version of it.

Look at the Uberamp output stage.

[audiostar]

3 hours ago, audiostar said:

I think I am going to enlarge the front end board so I can stack it on top of two CFA3LargeT boards and mount them exactly the same way as the split boards are mounted. This leaves me the middle of the case for two stacked GRLVs in the front and a toroid in the back. 

Something like this:

Both 285.6 x 116.8 mm

Edited June 6, 2023 by audiostar

[audiostar]

On 6/5/2023 at 2:10 AM, audiostar said:

Ready to order BOM here, Mouser ID=43398b8123.

Everything included for a 4ch amp, except for 24x 2sc4886 and 20x 2sa1860, which are double the cost of the items in the bom above and are pretty much nowhere to be found except for some 2sc4886 at Digikey.

Look what UPS just delivered from Digikey...
And of course something is missing (3x 2sa1860)!

[audiostar]

On 4/9/2020 at 12:46 AM, MASantos said:

I plan to use this side panel, it is 10mm thick and is able to cope with a few watts. Should be similar to a bottom panel some others have used I believe. 

Anyone has a source for this type of side panels? They are used by Modushop as well, but unfortunately not selling as spare parts outside of a complete case set! 

[JoaMat]

They do sell as spare parts. You just have to dig deep enough. Click this link and scroll down till you find side panels 1/2/3/4 U and lengths of 170/230/280/350 mm.

[audiostar]

Indeed, you are absolutely right JoaMat. I was looking earlier but couldn't find anything. Thanks again!

[Satyrnine]

I bit the bullet and took measurements of an OK and the "Hot Bias" CFA2 boards. Here is what I found:

Test conditions:
OK board biased to around 120ma, trimpot in middle-ish position.
Hot bias board has trimpot all the way down, which gives about 100ma of bias.
Ran from the same GRLV at 30v.

Clearly the big difference is the output of the servo is showing 10v on OK board, and only .8v on hot bias board. Servos getting proper voltage on each board. I swapped in a known good chip, no difference. The 5k feeders after servo are showing dif drops between boards too.

Can anyone give me some guidance on where to go from here?

Edited June 8, 2023 by Satyrnine