RCA BA-31 Racks.

[13engrsapper]

We are in the process of building a set of racks for the BA-31 series preamplifiers. As I have been a hermit the last few months, I thought I would share some pics of the concepts and progress. All of the work, other than powder coating, is done in-house.

At this point the bottoms, tops, sides and backs have been sent to the powder coater. They should be back to use in a couple days. The inner faces, and faceplates will be machined in the next couple days. The faceplates are cut from 0.187" thick 6061 aluminum stock. The look will be based on the standard we created with our very last rack prototypes; which were the RCA BA-1, BA-2, and BA-11 racks made for Stone Point Studio here locally, pics posted elsewhere here. (I did attach on pic of two of three of those racks).

VERY ROUGH conceptual render.


Project progress - I think we are running 10-12 racks.

Modules awaiting restoration.

machining tops and bottoms

finished bottom, before a trip to the powder coater.

Rack with internal divider placed before the sides, backs tops and bottoms went to the powder coater.

Dual 48V phantom power supply concept.
View attachment 69682184607__33722C31-0AA8-4A08-AC49-51CB483D738B.MOV


tooling needed for phantom boards


revised board concept


cutting phantom boards


phantom boards cut and tinned - ready to solder. Heavy boards (0.13" thick) with 4 ounce copper.


first two boards populated and soldered


Today I am cutting the support brackets for the phantom boards, inner and outer faceplates, and the switch MECB's (Mechanically Etched Circuit Boards) for each channels phase, pad, and phantom power.


More to follow...


Take care, my best to everyone.

Tony

 

[13engrsapper]

Original RCA BA-31 pairs we will be racking up to sell. I am sure Doug (EMRR) has seen this before but we have not. In that serial number list is one marked M-3421 with a note in parenthesis. This is a unit which has an error in the serial number. Clearly an employee/s at RCA was having an off day, or could not read his bosses handwriting and just said "eff it! I am going to put an exclamation mark anywhere I can't read this old farts handwriting or maybe this was one, I dunno I am tired of him. I have to do 1000 of these today for minimum wage, because I run a typewriter in the 60's and therefore am a women. "Captain crap for brains" blames me for most of his mistakes, I think that is what he hired me for, he can just suck it. I am not redoing this."

I may keep this one, unless Doug chimes in and says he has seen a thousand this way.

This was a generation in the US that was putting people on the moon, mistakes and substitutions/changes happen. But it's not late 70's early 80's, 90's, 2000's ugh USA, etc... where corporate profits came before quality checks or concerns... "Oh crap. Did I say that or did I think that? did I say that or did I think that?..." (might as well be "Tony's Mantra")

Why can't I tell my photos to not be upside down?

 

[emrr]

that is a funny typo, don't recall seeing one like it.

 

[dmp]

Have you tested the EME05US48 for phantom yet? You may want a LC filtering stage on those boards you built. They are spec'd to have 200mV ripple.
Also, having a pad and phase on a preamp is pretty standard, if you aren't done with your design yet.

 

[13engrsapper]

that is a funny typo, don't recall seeing one like it.

I guess I better keep that one

 

[13engrsapper]

Have you tested the EME05US48 for phantom yet? You may want a LC filtering stage on those boards you built. They are spec'd to have 200mV ripple.
Also, having a pad and phase on a preamp is pretty standard, if you aren't done with your design yet.

Yes we have thoroughly tested them before buying a large lot, as well as the switches used to control all of it. They sure are spec'd at 200mV ripple, most we have used in the past were even noisier. Filtering these further will be quite easy. Also, if you measure ripple at various loads on a group of different models, you are going to find that specification less useful.

The rough rendering of the complete units has 3 toggles per channel. Phase, pad, and phantom. The holes had not been cut in the faceplate yet - still have not decided on layout - that is today.

All of that additional outside circuitry, including any needed filtering for the supplies rides on another mechanically etched board on the back of the panel mounted toggle switches, I should be getting to making those today or tomorrow. So far the supplies are VERY quiet compared to the others we have used over the last decade or so. I left room on the output side of the phantom board to add components there as well if we find the need later.

Long term reliability is key to us, as well as not drawing much power/producing tons of unnecessary heat. I may have to build my own smaller version, but these work great for now. In fact the noisier ones we have used and tested in the past with no filtering have yet to show up as a problem at all in recording/use. I have gone nuts trying various filters on phantom, making the very quietest supply... There are much bigger fish to fry. We have also made our own linear supplies in the past, no better practical performance in use for the work and costs involved; just more heat and construction time. Sure you can see and measure the lower ripple at the loaded/unloaded supply. But in practice, it not as big of a concern as we often make it.

The issues we typically see in repair/service/use of other manufacturers equipment have never been related to noisy phantom supplies (and there are many!), it is usually premature component failure on the cheap supply, heat does not help, or switch issues. Switches actually made for 48V dc, are not usually used by most manufacturers (many use switches rated at 28V), but your pad gets hit and switched with phantom on it - so that switch also needs to be properly rated, phase as well, or you can expect to see premature failure there due to arcing.

Keep in mind I am only speaking on phantom power, and personal experience/testing. When we design the power supply units for rack modules/channel strips themselves they are filtered to the manufacturers specification or greater, even though most modules have on-board filtering/regulation. I don't service/build microphones, but if I did I certainly would not be depending on the phantom supply manufacturers power being clean. I would design it some rudimentary on-board filtering. I am assuming most mic manufactures do the same to some degree.

I am all ears though, dmp, and do appreciate your feedback!

I will try to get some pics up of the progress today. The phantom supply rides on a small aluminum bracket we made. it is designed to hold two of these boards for up to 4 channel racks. I need to finish cutting them to size today. The onto the final faceplates (inner and outer), and finalizing the layout of the switching boards. We have added another rotary switch or pot to the face since the last rough rendering, so my switches need some repositioning.

Thanks again. Sorry for any redundancy/mistake in the post - I am doing ten things at once this morning.

-Tony

 

[MidnightArrakis]

Yes we have thoroughly tested them before buying a large lot, as well as the switches used to control all of it. They sure are spec'd at 200mV ripple, most we have used in the past were even noisier. Filtering these further will be quite easy. Also, if you measure ripple at various loads on a group of different models, you are going to find that specification less useful.

The rough rendering of the complete units has 3 toggles per channel. Phase, pad, and phantom. The holes had not been cut in the faceplate yet - still have not decided on layout - that is today.View attachment 104487

All of that additional outside circuitry, including any needed filtering for the supplies rides on another mechanically etched board on the back of the panel mounted toggle switches, I should be getting to making those today or tomorrow. So far the supplies are VERY quiet compared to the others we have used over the last decade or so. I left room on the output side of the phantom board to add components there as well if we find the need later.

Long term reliability is key to us, as well as not drawing much power/producing tons of unnecessary heat. I may have to build my own smaller version, but these work great for now. In fact the noisier ones we have used and tested in the past with no filtering have yet to show up as a problem at all in recording/use. I have gone nuts trying various filters on phantom, making the very quietest supply... There are much bigger fish to fry. We have also made our own linear supplies in the past, no better practical performance in use for the work and costs involved; just more heat and construction time. Sure you can see and measure the lower ripple at the loaded/unloaded supply. But in practice, it not as big of a concern as we often make it.

The issues we typically see in repair/service/use of other manufacturers equipment have never been related to noisy phantom supplies (and there are many!), it is usually premature component failure on the cheap supply, heat does not help, or switch issues. Switches actually made for 48V dc, are not usually used by most manufacturers (many use switches rated at 28V), but your pad gets hit and switched with phantom on it - so that switch also needs to be properly rated, phase as well, or you can expect to see premature failure there due to arcing.

Keep in mind I am only speaking on phantom power, and personal experience/testing. When we design the power supply units for rack modules/channel strips themselves they are filtered to the manufacturers specification or greater, even though most modules have on-board filtering/regulation. I don't service/build microphones, but if I did I certainly would not be depending on the phantom supply manufacturers power being clean. I would design it some rudimentary on-board filtering. I am assuming most mic manufactures do the same to some degree.

I am all ears though, dmp, and do appreciate your feedback!

I will try to get some pics up of the progress today. The phantom supply rides on a small aluminum bracket we made. it is designed to hold two of these boards for up to 4 channel racks. I need to finish cutting them to size today. The onto the final faceplates (inner and outer), and finalizing the layout of the switching boards. We have added another rotary switch or pot to the face since the last rough rendering, so my switches need some repositioning.

Thanks again. Sorry for any redundancy/mistake in the post - I am doing ten things at once this morning.

-Tony

Very interesting photos!!! Which.....leads me to a question!!! -- You have the in-house capability to insert PEM-nuts and other PEM hardware into your sheet-metal work??? Are you geared more for prototyping and/or low-volume or in large quantity high-volume production? And.....can you directly import 3D CAD-files and spit out sheet-metal? Or, do you still need 2D sheet-metal fabrication drawings? I have seen that several of the prototype sheet-metal shops located in the New England states can directly import SolidWorks 3D CAD-files and fabricate sheet-metal work from them.

Just wondering.....

/

 

[13engrsapper]

We are in the process of building a set of racks for the BA-31 series preamplifiers. As I have been a hermit the last few months, I thought I would share some pics of the concepts and progress. All of the work, other than powder coating, is done in-house.

At this point the bottoms, tops, sides and backs have been sent to the powder coater. They should be back to use in a couple days. The inner faces, and faceplates will be machined in the next couple days. The faceplates are cut from 0.187" thick 6061 aluminum stock. The look will be based on the standard we created with our very last rack prototypes; which were the RCA BA-1, BA-2, and BA-11 racks made for Stone Point Studio here locally, pics posted elsewhere here. (I did attach on pic of two of three of those racks). View attachment 104431

VERY ROUGH conceptual render.
View attachment 104432

Project progress - I think we are running 10-12 racks.

View attachment 104434Modules awaiting restoration.

View attachment 104436machining tops and bottoms

View attachment 104442finished bottom, before a trip to the powder coater.

View attachment 104440View attachment 104441Rack with internal divider placed before the sides, backs tops and bottoms went to the powder coater.

Dual 48V phantom power supply concept.
View attachment 104451View attachment 104433


tooling needed for phantom boards
View attachment 104443

revised board concept
View attachment 104444

cutting phantom boards
View attachment 104445View attachment 104439

phantom boards cut and tinned - ready to solder. Heavy boards (0.13" thick) with 4 ounce copper.
View attachment 104446View attachment 104447View attachment 104448View attachment 104449

first two boards populated and soldered
View attachment 104450

Today I am cutting the support brackets for the phantom boards, inner and outer faceplates, and the switch MECB's (Mechanically Etched Circuit Boards) for each channels phase, pad, and phantom power.


More to follow...


Take care, my best to everyone.

Tony

So - those old RCA Tube pre's we made for Mark Bryan turned up in this Ernie Ball Video last week. The other half of amp-haus, Mikey, gets a mention in the video: