and now for something completely different part 3

[Pars]

Working on a CFP3 for Todd, and had a question as to why a couple of caps aren't populated. This has switching for SS or ZF implemented.

 

It's consistent in all 4 locations on the 2 boards.

[kevin gilmore]

the 47uf caps have to be populated. the 600pf caps are optional, paradoxper decided not to populate them

[Pars]

Thanks. I guess one more thing to do on this thing

Is that (paradoxper) who built this? Or was this one from Dukei?

Edited March 12, 2021 by Pars

[Mirko]

I built that one, Dukei is my handle on hf. 47uF cap is installed on the backside on the smd position.

[Pars]

Got it, thanks. I was trying to not disassemble it that far, so that is good to know.

[starcat]

Ordered as well 2oz boards from the cfp3rssfixedsssw-CADCAM.zip gerbers and will be building one later on. 

[Pars]

Anyone have a CFP3 BOM? Excel spreadsheet preferred, but google or whatever is fine as well. Thanks!

[starcat]

20 hours ago, Pars said:

Anyone have a CFP3 BOM? Excel spreadsheet preferred, but google or whatever is fine as well. Thanks!

Sure, here is the Mouser BOM for the CFP2/CFA2, order two times for the CFP3/CFA3. Here the BOM for the GRLV 30V for it as well. Some of the transistors are currently on back order, if you know of a viable replacement would be great. I've also made the latest CFP3/CFA3 version 2oz boards, so if you need some let me know. This would be the ready made transformer for the CFA2 as well. 

This above is for the non-stat version. For the static CFP3/CFA3 I have it as well together with the BH Mini PSU v1.4. 

@Pars

Edited March 17, 2021 by starcat

[Pars]

Thanks. I already had my own BOM for the CFP2. 2x that is missing the front end section on the CFP3, but should be more or less the same as an SS Dynalo for that portion.

[starcat]

I see, thanks. I guess I haven't checked the boards yet, just ordered the BOM (and will miss some parts then) 👍

[Pars]

I mentioned this in the dynahi thread, but after getting the input wiring fixed (cable jackets were putting too much pressure on the screw down terminals resulting in intermittent channel drop), I ran into another problem with the protect circuit tripping. It turns out that I had broken the ground connection at the pot of one of the wiper to amp cables.

This connection is the only connection between the L and R channel grounds in the amp. The amp uses dual GRLVs, one per channel.

Should I connect the DC grounds of the GRLVs to one another back at the PSUs? I'm thinking Yes.

In this instance, I was seeing a DC offset of what appeared to be 36V, but that was dependent upon which ground was being referenced (which I didn't realize at the time). I found that when I ohmed out the input grounds between boards and it wasn't 0.

Edited March 21, 2021 by Pars

[starcat]

7 hours ago, Pars said:

Should I connect the DC grounds of the GRLVs to one another back at the PSUs? I'm thinking Yes.

I read somewhere a comment especially on this from Kevin saying both grounds must be connected. Can't remember which amp thread this was. 

Are you using a separated PSU chassis? 

[Pars]

This is an amp built by Mirko, that tkam bought from someone on HF I presume. The right channel was flaky, and since the builder is in the EU, he asked me if I'd take a look at it. It is in a single 2U 400mm Modu Pesante case.

This isn't the exact amp, but similar.

[starcat]

What are the two small boards in front of the case left and right used for? 

[Pars]

Like I said, this isn't the exact amp I'm working on. The board on the right is a Gilmore protect board (HIGHLY recommended on one of these). The one on the left in this amp I believe is doing the SS/ZF switching.

[Pars]

@kevin gilmoreFor a CFP3, in SS mode, the gain is set by the 25K / 1.9K resistors? Or is it the 25K / 5K on the input?

What determines gain in ZF mode?

Thanks!

[kevin gilmore]

SS mode its 25k (or 50k) /5k as long as there is enough gain in the front end.

in ZF mode front end is a voltage to current converter.

So 10k in parallel with whatever you pick for the ZF resistor. Much easier to do in spice.

[Pars]

Thanks Kevin. The ZF resistor is the one shown as 1.9K in the schematic and on the board (section marked Gain)?

Edited March 24, 2021 by Pars

[kevin gilmore]

paradoxper settled on 50k feedback resistors and 4.2k ZF resistors. to increase the gain.

both have to match so there is no volume difference between modes

[starcat]

Guys, where can I get some more information on the implementation of the SS/ZF switching board? Appreciated all the great work you are putting in. 

[Pars]

Dukei (Mirko here) uses something similar to that. One of the reasons I ask is there is a difference in volume between modes (ZF is a bit louder), but more disturbingly, there is a slight image shift when switching between modes. I noticed this when using a 1khz test tone. The image shifts a bit to the left when moving to ZF.

Per my previous question, the ZF resistor is the 1.9K resistor in the schematic and PCB? I assume so, but just wanted clarification,

[kevin gilmore]

depends on which version of the pcb.

[Mirko]

1 hour ago, Pars said:

Per my previous question, the ZF resistor is the 1.9K resistor in the schematic and PCB? I assume so, but just wanted clarification,

That's correct. R50/R51 on cfa3productionss.pdf

1 hour ago, starcat said:

Guys, where can I get some more information on the implementation of the SS/ZF switching board? Appreciated all the great work you are putting in. 

There is none but you can do it like I did and use relays to short/open the positions.

[Kerry]

Work in progress...

I should be able to test soon 🤞

[starcat]

Very nice, Kerry! Let's have a group buy to test jointly 🙂