Potato Cakes

eBay 1073 Boards NEW thread
« on: March 15, 2019, 03:26:33 PM »
For some reason I cannot add the schematic in my second post of the eBay 1073 boards post as I keep getting "Page isn't working HTTP 500 error". I'll try it here.

I'll move this over to the first one with all the related information when that gets resolved.


I just started over, so no going back to try to fix it. Everything has been reposted here.

Thanks!

Paul
« Last Edit: March 17, 2019, 09:40:10 PM by Potato Cakes »


Michael Tibes

Re: ebay boards 2
« Reply #1 on: March 15, 2019, 05:24:48 PM »
For some reason your previous post doesn't even open on my computer, it just shows a blank page.

Michael

Potato Cakes

Re: ebay boards 2
« Reply #2 on: March 15, 2019, 05:26:48 PM »
I saw that it is doing that on Safari and my iphone as well. Chrome gives me the error message. I hope it gets sorted as there's a bunch of information necessary to make the eBay 1073 DIY boards work and I don't want to have to retype it all.

Potato Cakes

Re: ebay boards 2
« Reply #3 on: March 16, 2019, 11:25:45 AM »
Apparently the GDIY server ate my other post on this topic. I emailed Ethan to see if anything can be done about it but I have not heard back. I will try to remember all the info included with the original post.....

As I had stated on the first thread, there are 1073 preamp/EQ boards on eBay that I had acquired and that I've seen other people selling here. I been in contact with the designer and have helping him debug these boards as I am needing them to work for a particular project. After an intense and sleep deprived series of days, I now have a fully working 1073 circuit using these boards with an EK20033 switch. The following posts will list the corrections that need to be made as well as some other helpful information for the 2-74, BA283NV and BA283AV boards that I'm using.

The photo attached is the pic of the one of the boards pertaining to this discussion. This particular board is a little beat up from all of the testing that I took place and I eventually removed the parts and transferred to another board to start over. The transistors being used are MPSA18s, which require being oriented backwards from BC184/550Cs.

Thanks!

Paul
« Last Edit: March 16, 2019, 12:50:58 PM by Potato Cakes »

Potato Cakes

Re: ebay boards 2
« Reply #4 on: March 16, 2019, 11:30:06 AM »
First up is the 2-74 board. This is pretty handy as it contains two make up gain amplifiers that are found on the original BA284 card. Here's what needs to be corrected:

First correction to make is the connections for G and H pins on the 9050 inductor. These are backwards as they relate to the MF selector switch. All traces touching both pins have to be cut. Then a jumper needs to be installed from C1E to Pin H. Pin G is then tied to ground. Also, the ground connection from R51X has to be reconnected to ground as its original connection was through Pin H, which is now cut to make this correction.

The next thing relates to the MF 10k potentiometer. This board and the provided schematic are missing a 6k8 resistor from CCW to the CW connection as shown in the original schematic on the B211 board. The quickest way that I could come up with (at 4am) was to lift the side of R1E closest to the 9050 inductor and the one leg of R2E towards the inside of the board. An additional 6k8 resistor is added from the lifted R1E pad and those two resistors are tied together above the board. A jumper wire is then used to connect the lifted sides of R2E and R1E. Probably a cleaner way to do this but this is the fastest way I could come up with at the time.

The last item is the SW1 (1a) on the LF switch. It is supposed to tie to the LF wiper with SW7 (1b) to pass audio in the OFF position. Cut the trace at switch pin 1 and then run a jumper to the LF wiper connection.

The shield connections on the 2-74 board only connect to themselves and nothing else. They need to be jumped to the EQ-GND connection to do anything useful.
« Last Edit: March 16, 2019, 12:53:59 PM by Potato Cakes »

Potato Cakes

Re: ebay boards 2
« Reply #5 on: March 16, 2019, 11:47:17 AM »
The next part is the preamp boards (NV and AV). The NV board is first amplifier in the BA284 and the AV is the same as the BA283/AV from the original 1073 schematic. Using the attached schematic, here's how these boards connections translate with an EK20033 switch:

Stage 1 In - AV Preamp IN
Stage 1 Boost - AV F Gain (be sure to use the pad not connected to 0V)
Stage 2 In - NV In
Stage 2 Out - NV Out

R Gain, R10X, R44X on the AV board as well as the Boost connection on the NV are to be left empty. If doing a preamp only configuration, the Preamp Out connection needs to be tied to the Stage 3 Input on the AV board. This will give you unity gain with the switch set to 0dB.

Potato Cakes

Re: ebay boards 2
« Reply #6 on: March 16, 2019, 12:29:31 PM »
For the connections between boards I used all shielded cabling. The shield is connected on one board per connection as I have all of the 0V connections connected to the star ground as well as the chassis solder pad that connects to the ground plane. This seems to prevent any ground loop between the boards and blocks radio/EMI interference, which is something I have to consider where I am.

External PSU or switched internal is recommended for this design. I have built other units that used a different Neve style preamp card with the toriodal transformer on the opposite end and experienced no issues, but this does not seem to be the case here, even with Mu-Metal shielding that I'm using for my build. JLM audio has some very clever SMPS units and PSU boards that address this issue. I have some on order that I will swap with the PSU I currently have installed when it arrives. I did find that when I attenuate the output about 10dB this makes the noise inaudible, and there is still a ton of gain. I have found that I really can't go any higher than 40dB talking into a dynamic microphone before I've reached the headroom limit on my converters, so there's plenty of room to work with if I decide to rewire the output transformer for lower level. Still, I will swap this with the JLM solution when it arrives. and use this for future similar builds.

Something else that I guess I should have mentioned first is to use the provided schematics for these boards as a guide for component designations and not the BOM as there are a number of discrepancies. Some of the changes were based on alterations to suit different tastes while interacting with digital audio, but I found just using the original values yields a great sounding unit.

These are really handy boards for standalone operation as well for make up gain in summing amps or building a stereo EQ rack. and I found it's one of the easier ways to build an authentic (based on the original unit's serial number being used for comparison) 1073 without the need for all the original cards and intricate wiring network.

Thanks!

Paul

Potato Cakes

Re: ebay boards 2
« Reply #7 on: March 16, 2019, 12:46:28 PM »
I also found out what killed the original post. I had tried uploading the EK20033 schematic which was a 800kb JPEG file and it gave me the HTTP 500 error page, even though the first post had a JPEG attachment. I tried to go back and repost as different format but for some reason it would not let me access that thread nor will it currently. I ran into that same issue on the first one and a different post, but I was at least able to go back and repost with a different file format. I don't know why JPEGs give this site the fits sometimes. It definitely stokes the rage within after one spends all that time typing to have it be all for naught.

Back to the thread at hand, these boards do work with the changes listed above. I know the designer is sorting out other pressing matters, so revised boards with the corrections won't be anytime soon. However there have been several other wonderful projects here that required fixing errors on the PCBs that no one seemed to mind doing as this is DIY. I think these boards are another great option to consider when considering builds using this particular circuit flavor.

I can help answer some questions if you have these particular boards and are struggling, but I don't know if I'll be much help if you don't already have a moderate level of experience with DIY. This is definitely not a project for those who are new to this arena.

Thanks!

Paul
« Last Edit: March 17, 2019, 03:52:57 PM by Potato Cakes »

Potato Cakes

Re: ebay boards 2
« Reply #8 on: March 17, 2019, 04:36:28 AM »
Update regarding the PSU. For the particular build I am doing I am also using two BA283AM boards a mixer. These boards are next to the toroidal transformer that has the Mu metal shielding and they are quiet. So I started poking around with the preamp output gain as this was the sole source of the noise, which was fairly negligible. In a silent room I can hear a faint hum that is associated with linear PSU near a single ended circuit, but with any ambient sound you can't tell it's there. What I wound up doing is wiring the output transformer to be -2 according to the data sheet and this seems to make the noise disappear. The noise doesn't seem to increase with gain, and since there is so much available in this preamp it really doesn't matter. I would still want to put a SMPS in there to be certain, but if only have a linear one to work with you can still make it work with these boards.

Thanks!

Paul

Re: ebay boards 2
« Reply #9 on: March 17, 2019, 01:06:27 PM »
Just FYI but your other thread is loading ok for me. Seems to only work when I'm logged out.
« Last Edit: March 17, 2019, 01:12:14 PM by trashcanman »


Potato Cakes

Re: ebay boards 2
« Reply #10 on: March 17, 2019, 03:44:33 PM »
Weird. I'll put a note on it with the link to here as I've already reposted all the information that would have been in the first one.

Thanks!

Paul


Oh wait, I guess I can't because I would have to be logged in to do so..... Oh well

Potato Cakes

Re: ebay boards 2
« Reply #11 on: March 17, 2019, 04:28:24 PM »
One of the other boards that he sells that I am using are BA283AMs, which is the output stage of the original BA283/AV schematic. These are great for make up gain for stuff like a summing mixer, or pretty much anything that needs compensation for insertion loss. The version that I have need to add a jumper so that all shield, P GND, and A GND points are connected per the associated schematic. For summing duties, I used 15k buss resistors. With R44X removed and R Gain left empty this gives me -0.7dBu through an output transformer wired 200:150 ohm (-2 I believe).

He also has a dual AM PCB which came out after I got the single versions.

He has some cards for gain switches using 3x12 Grayhill switches to simplify. And while it was fun learning how to build the EK20033 switch, I think future endeavors will be along the lines of how Don the Classics does theirs with 0-66dB so I don't have to deal with a pad switch or second transformer.

Thanks!

Paul


groselicain

Re: ebay boards 2
« Reply #12 on: March 17, 2019, 04:43:47 PM »
Thanks for taking the time to debug and post about these. I've had them in my watch list for quite some time and never knew if they were worth the purchase.

Potato Cakes

Re: ebay boards 2
« Reply #13 on: March 17, 2019, 05:15:21 PM »
They're definitely worth the purchase if you are looking for this particular circuit style. I'm using a combination of Ed Anderson and Carnhill for this custom build and it sounds as good as any Neve type circuit I've come across. Plus having the ability to do the concentric style controls on board makes this much easier and faster than the traditional method of doing concentric controls. And the fact that each board can have a standalone purpose makes them even more useful than just building a 1073. As I stated the designer is going to revised boards, but when that is undetermined. Besides, someone engaged in the madness of DIY should be totally fine making some corrections to a PCB if it gives them something that would cost them about $3k to build (approximate cost of 1073CV reissue that still requires a chassis).

No, I don't get a cut of sales but I should probably ask for one after all of this...

Thanks!

Paul

Rocinante

Re: eBay 1073 Boards NEW thread
« Reply #14 on: March 19, 2019, 11:03:19 AM »
Same here, thank you for such a thorough job in addressing the various issues.
If there's a harder way to do this, I haven't found it yet.


 

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