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CFA + GRLV + DA build


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Hi All,

I have been going cross-eyed of late poring through the various threads for the projects required to get a complete amp together and hoping to get a few pointers.

I was originally looking at building a Dynalo based amp but after some feedback from Pars and others I had a look at the CFA2/3 boards and think I have decided to go with a CFA3 based build.

I am going to build a balanced in / balanced out setup in dual mono so for the amp boards, it will be 2 x CFA3 (based on 89753654_cfp3rssfixedssw-CADCAM.zip) - I am pretty comfortable that this seems to be the most recent version of the CFA3 board.

Where things seem to get a bit interesting is the GRLV power supply. Reading through the thread, there seems to be quite a few evolutions of this design and a few different ways of completing it. Based on the GDrive archive, goldreference6d.zip seems to be the way to go but looking through the thread for it, there are a number of evolutions of the design since then including a large cap version and options for 6min/6plus, 7min/plus,  79xx/78xx etc etc - the head starts to swim when going through it. Taking a KISS approach, what is the easiest board to build in this regard especially considering effort / perfomance .

Lastly, just to make the build that little more complicated, I am going to go with dual digitial attenuators. My first thoughts were to go with the delta 1 board but then I stumbled upon the digital attenuator designs here by Kevin and Kerry. The through hole version looks easier to make but is a 6 layer board which is not the cheapest to get made in small volume. The SMD version looks better but it is 3 layer which most of the small run PCB houses do not seem to support and from memory there may be a component or 2 that have to be done with a oven / hot air due to solder pads that are not accessible. Should I just stick with the delta1?

Lastly, I am happy to go off and get a bunch of boards made for each however if anyone has any boards they are willing to part with that will definatly steer my decisions. Most board hoauses seem to do qty's of 5 or 10 and with me requiring 2 of everything, 5 is a shitty number as having 1 board left over does not help my minor case of OCD so I will get 10 of each made - I may use 4 of each so will have a few left over if anyone wants any (note, this is not a group buy, once decided upon, I am not going to wait for people before placing an order, I will order them and if anyone is interested down the track I should have some).

Any tips would be appreciated.

Cheers,

Ben

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Hi Ben,

I think I have all the versions of the digital attenuator boards including a new design I’ve just finished.

I’ll PM you. 

Regards,

 Kerry

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It’s great to see more people working on the CFA-3, it should get more attention!

Regarding the GRLV, this is the one I have been using in the Dynalo, Dynahi and forthcoming CFA-3. It’s version .47, dated 2018 with small caps (25mm diameter). I’m not so sure about the name because I downloaded it and renamed to something easier to remember.

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Edited by thuytn
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1 hour ago, thuytn said:

Regarding the GRLV, this is the one I have been using in the Dynalo, Dynahi and forthcoming CFA-3. It’s version .47, dated 2018 with small caps (25mm diameter).

 

Going through the various files and looking at them in a gerber viewer, .47 is goldenreference6drflipto220.zip. .48 seems to be the latest Kevin version which is the goldenreferencelargecap.zip and then v2(?) seems to be the Kevin + Kerry version.

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^ The large cap version allows a shorter height board for use in a 1U chassis. The version which thuytn mentions (.47) also uses the to220 schottky rectifiers, and has dual outputs. This is the version I would use unless I needed the shorter height.

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  • 3 weeks later...

Thanks to a few people on here, I managed to dodge getting boards made and managed to buy existing boards for all the bits I need. I am still waiting on a delivery tom come in over the next week or so with the CFA boards and a few other bits and bobs but have received some GRLV boards and a set of v1 attenuator boards and a v2 board.

I have done some SMD work in the past with the soldering iron but thought I would up my game this time round and give a hot air rework gun a go. Kerry sent me 2 v1 attennuator boards - 1 already populated and one bare, as well as all the parts to build it, so I finally pulled my finger out today and built it up -

 

20200802_174432.jpg

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I had some parts left over and thought what the heck, I might as well do what I can on the v2 board. I was short a few of the resistors I had so need to get a few extras as well as a few other bits and pieces that differ between the v1 and v2 boards, then need to decide which one I will use - I like the form factor of the v2 board.

After my first couple of hours with the heat gun I have to say I dont mind doing SMD work this way. Once you get some heat into the board the process goes pretty smoothly and the components just latch in to place which is nice.

Now I need to start getting some components together for the GRLV and CFA boards and will then get to work on them.

20200802_190251.jpg

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  • 4 weeks later...

A little more progress - have the first or 2 GRLV's 98% done (at least until I figure out casing and heatsinks)

Mouser were out of a couple of the default resistors so I had to change a couple to higher power (1/4w) which has resulted in a cramped fit for a couple of them but nothing too bad.

20200826_231527.jpg

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Tip for the future - in situations like that look to flip the larger component on the bottom of the board.  As long as you are using standoffs that will allow for clearance to the chassis it ends up with less of a cramped situation and the potential for leads to get closer to things than you would like. 

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The main issue was that the resistors were longer than the hole spacing so the leads need to tuck back in to fit - I could have placed the resistors vertical and had the leads hook back over. I still need to order parts for the 2nd GRLV so may order some different resistors as part of that order and swap them out.

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19 minutes ago, Pars said:

Those are 500R? 499R is the standard value (E96?) in that series and should be readily available.

There is an issue with the 10k, 500R, and 2k resistors. They are all too big for the hole spacing. Interestingly, I just rechecked the BOM you posted on the gold reference thread back in April and it lists all 1/4w resistors, so not sure what has happened here.

Looking a bit deeper, for the values where I could not get a direct hit on part number, I moved to 25ppm (default was 100ppm), same series (RN) same resistance and same wattage (1/4w) but guess the lower ppm results in a larger body which I had not paid attention to. Live and learn . . .

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Those look like RN65s. The RN60Ds are 1/4W rated (Mil Spec) but are actually 1/2W. The PPM rating should not have anything to do with physical size.

Edited by Pars
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18 minutes ago, Pars said:

Those look like RN65s. The RN60Ds are 1/4W rated (Mil Spec) but are actually 1/2W. The PPM rating should not have anything to do with physical size.

Well spotted. Went back and checked what I ordered, and yes, RN65's - RN60's were not available for those 3 items . It does say on the spec for each item that they are physically larger, I just missed it at the time, I looked at resistance and wattage and figured same same at the time. I think I was swimming in BOM's with GRLV, CFA and 2 versions of DA to build a list for that I was getting a bit cross-eyed late in the night and missed it.

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