and now for something completely different part 3

[bdinnev]

11 minutes ago, Pars said:

I do recall on the one CFP3 I worked on, half the LEDs were different, so I changed them all out for the correct ones. Later, the builder said he ran out of the normal ones and used what he had. Not the right move.

All of the ones in both boards at present are the same (all purchased in one batch from Mouser), but I will try swapping them all out for the ones MLA mentioned above and see if it makes a difference - I am ordering all new PNP/NPN transistors (I think I ordered the batch I have at the height of COVID when stock was hard to come by and although everything else was sourced from Mouser, those may have come from somewhere less reputable) and some new resistors / capacitors to bump up the GRLV's to 30v so tacking on some LED's to the order won't make much of a difference in the scheme of things. 

[audiostar]

Just adhere to full specs and never have issues. Don't rush. Measure  and check components if possible prior soldering, make sure nothing is wrongly placed and badly soldered... then everything comes up magically, nothing to worry about.

[bdinnev]

OK, a bit more testing. The previous tests I did were all with the SS jumpers in place. I have taken them off and jumped all the ZF jumpers and get some different results. 

In ZF mode, on the board that was reading -2.5v the DC offset comes down considerably - 145mv and -81mv @ ~150mA bias. 

 

On the other board that was measuring -500mv it still measures the same in ZF mode, however I need to adjust the 5k trim-pots a fair amount to get back to ~150mA bias - I think I saw a post a few pages back with a similar situation so will go back and read the thread again!

[Satyrnine]

2 hours ago, bdinnev said:

I have noticed that the LED's on the -ve side of the board don't glow as bright as those on the +ve side of the board - is that normal or has anyone else noticed this in correlation with an issue? I will try changing the LED's and see what happens. 

Not normal, unless they are dif models. Its a sign you’ve got a pretty hefty inbalance somewhere, as your offset is showing.

31 minutes ago, bdinnev said:

OK, a bit more testing. The previous tests I did were all with the SS jumpers in place. I have taken them off and jumped all the ZF jumpers and get some different results. 

In ZF mode, on the board that was reading -2.5v the DC offset comes down considerably - 145mv and -81mv @ ~150mA bias. 

 

On the other board that was measuring -500mv it still measures the same in ZF mode, however I need to adjust the 5k trim-pots a fair amount to get back to ~150mA bias - I think I saw a post a few pages back with a similar situation so will go back and read the thread again!

This might be a good clue for someone more versed with the ss/zf parts of the cfa3 circuit than I. 

[justin]

38 minutes ago, bdinnev said:

OK, a bit more testing. The previous tests I did were all with the SS jumpers in place. I have taken them off and jumped all the ZF jumpers and get some different results. 

In ZF mode, on the board that was reading -2.5v the DC offset comes down considerably - 145mv and -81mv @ ~150mA bias. 

 

On the other board that was measuring -500mv it still measures the same in ZF mode, however I need to adjust the 5k trim-pots a fair amount to get back to ~150mA bias - I think I saw a post a few pages back with a similar situation so will go back and read the thread again!

measure the DC voltage to ground at every node in the circuit, and write it down on the schematic, will be very helpful

also do you have pF caps across the feedback resistor in SS Mode?

Edited August 2, 2023 by justin

[bdinnev]

1 hour ago, justin said:

measure the DC voltage to ground at every node in the circuit, and write it down on the schematic, will be very helpful

also do you have pF caps across the feedback resistor in SS Mode?

I will get probing soon and see what the results are. Is going to take me a little bit to make sense of the schematic and how it refers to the physical board but that is what learning is all about....

On the learning topic - not sure where the feedback resistors are. The boards are fully populated except for the 2 x surface mount resistors on the underside. Here is a picture - 

[JGergo]

Here is a solution for the ZF/SS problem worked out by Mirko.

The SMDs on the back side are alternatives to the 47uF caps.

[justin]

I decided to order some of these, 4oz copper, panelized/scored. Gilmore Purple People Eater, because purple is the most uber color

the PCBs will be available if anyone wants a set

 

[DouglasQuaid]

I am beyond behind nowadays and don't even know what this is.  I suddenly want one though.

[justin]

UberAmp2. it's like a headphone amp, but with more voltage and current. 4 boards = 2 balanced channels

[kevin gilmore]

acually that is 10 boards total for 2 balanced channels.

 

[audiostar]

Full size mono blocks, thats it. With trafo and caps in the middle.

And I surely want a set 👍

Edited August 22, 2023 by audiostar

[justin]

6 hours ago, kevin gilmore said:

acually that is 10 boards total for 2 balanced channels.

 

yes but I ordered them as a scored panel

[MexicanDragon]

On 8/21/2023 at 12:10 PM, justin said:

I decided to order some of these, 4oz copper, panelized/scored. Gilmore Purple People Eater, because purple is the most uber color

the PCBs will be available if anyone wants a set

 

@justin - Would this be a good project as a first build should I want to bring @cetoole out of retirement for "guidance"?

[justin]

Colin should build it

[MexicanDragon]

4 hours ago, justin said:

Colin should build it

By the time @cetoole would build it, I'd have a job and could afford to pay you to do it.

By then, you'll have 2-3 new amps out.

[Satyrnine]

I'm hoping to run a sub with my balanced cfa3. The sub only has SE RCA inputs, or speaker level inputs. Would this Jensen transformer (special low freq edition designed for sub inputs) jt-112p-2hpc.pdfbe a good way to get a SE sub output from the cfa3? Was thinking I could tap the signal after the volume control, before the CFA boards. Thoughts? 

JT-112P-2hpc - 39k:47k - 1:1.10, +20dbu max input.

Edited August 24, 2023 by Satyrnine

[mikeymad]

On 8/23/2023 at 11:34 PM, MexicanDragon said:

By the time @cetoole would build it, I'd have a job and could afford to pay you to do it.

By then, you'll have 2-3 new amps out.

Besides he has to help me rebuild my PSU for my ES1 first.. 

[Thai Tao]

Hi,

What's the current stable gerber file for CFA2? There is too many version in the google folder.

Thanks!

[Pars]

I would think cfp2hmt as the latest one.

[justin]

On 8/25/2023 at 5:19 PM, mikeymad said:

Besides he has to help me rebuild my PSU for my ES1 first.. 

isn't that just a couple of wall warts?

[mikeymad]

14 minutes ago, justin said:

isn't that just a couple of wall warts?

It can be based on history... 

[pontif_]

Just got the first channel of my CFA3 build up and running. Got the bias dialed in at 150mA.

Everything seems to be fine, though the Pk-to-Pk voltage of the positive output is about 1V lower then the Pk-to-Pk voltage of the negative output. Is that something to be concerned about? Seems to be slightly frequency dependent.

[mrjayviper]

can someone please share the link to the schematics/documents? I think it's a good drive link but I cannot find this link. Thank you.

[JoaMat]

7 hours ago, mrjayviper said:

can someone please share the link to the schematics/documents? I think it's a good drive link but I cannot find this link. Thank you.

look here  

https://drive.google.com/drive/folders/1r3g2TAtBUaBdiMorTWX7yYgeJ7maQbYW?usp=sharing
https://drive.google.com/drive/folders/152thxfZafBmisG0CKCv6X82V-Ch9TjMH?usp=sharing

lots of good stuff

Edited September 4, 2023 by JoaMat