Motown Direct Amplifier-inspired Preamp?

[ruffrecords]

I've done CF 600 Ohm outputs with different power tubes like EL84, ECL82, 807. Sounds excellent. The old tech knew their stuff.

Any chance of posting schematics???

Cheers

ian

 

[ruffrecords]

Cool an 807 CF!!!!!!! Last time I used an 807 was back in the 60s for pirate radio RF output stage.

Cheers

Ian

 

[DaveP]

Am I right in thinking that after 19 pages of detective work and super enthusiasm, no-one has made the thing?

best
DaveP

 

[ruffrecords]

I think we have a pretty good idea what was in the original and how to replicate it using tubes available today but you are right, I don't think anyone has actually built one yet. Personally I have a hankering to do ab octal base version with a 6V6 output stage.

Cheers

Ian

 

[DaveP]

I can understand making a single channel version, but who would want the original 5 channel?
Only someone who wanted to copy exactly how Motown made their records with multiple artists playing together at the same time?

Best
DaveP

 

[Ricardus]

I can understand making a single channel version, but who would want the original 5 channel?
Only someone who wanted to copy exactly how Motown made their records with multiple artists playing together at the same time?

Best
DaveP

I would love to do something more like a 2 channel version in case I ever wanted to track something in stereo.

But yeah. The old methods were cool, and it's nice to go back to them from time to time, but we have the benefit of doing things differently now.

 

[ruffrecords]

I can understand making a single channel version, but who would want the original 5 channel?
Only someone who wanted to copy exactly how Motown made their records with multiple artists playing together at the same time?

Best
DaveP

The original was designed for the specific needs of that studio. For today's workflow I agree a single unit makes more sense.

Cheers

Ian

 

[MidnightArrakis]

Am I right in thinking that after 19 pages of detective work and super enthusiasm, no-one has made the thing?

best
DaveP

As someone who just loves to design stuff so it can be actually built.....I have been somewhat following this thread and waiting for a completed and finalized schematic of this piece of Motown gear just to see what it would take to get started with doing exactly that. I don't feel like going back through 19-pages of postings to try and find if someone has posted a "finalized" schematic, so if one actually exists in here, please let me know the Post #.

A common theme that I have seen within so many similar types of threads on this forum is that someone will post a schematic and then 2 or 3 months later, someone else will make a comment that "this resistor value should be changed from 'this to that' in order to bias a transistor a particular way". Then, another month later, someone else yet again will post a comment stating that a specific capacitor value should be changed to "this value" in order to change the R/C time-constant to allow - this - to take place, etc.

Meanwhile.....nobody actually updates the "finalized" schematic. So.....in order to derive a -- REAL -- "finalized" schematic, you need to take the so-called "finalized" schematic and then update it by including all of the comments that were posted over the next six months or so while hoping that you not only didn't miss something important, but also in hoping that all of the new updates make sense and are actually real and workable!!! And.....the person who had posted the first "finalized" schematic seems to never get around to including all of the new updates into their design and reposting a new "finalized" schematic and they end up just leaving the schematic "hanging".

Since I am not a circuit designer, I have always worked from the perspective that the engineers who design the circuits know what they are doing and they provide me with their schematics to design a new piece of equipment once they have gone through everything it takes to satisfy their minds about the circuit operating as it is supposed to. I just provide the designs to have it become a "physical reality". So.....show me a completed/debugged/tested/validated schematic of this piece of vintage gear and I will take a look at what it might take to have it built. Fair enough???

>> Mechanical, PCB designs and hand-built by "me" by only working from "completed/finalized" schematics:
----- First prototype chassis -----


/

 

[ruffrecords]

Since I am not a circuit designer, I have always worked from the perspective that the engineers who design the circuits know what they are doing and they provide me with their schematics to design a new piece of equipment once they have gone through everything it takes to satisfy their minds about the circuit operating as it is supposed to. I just provide the designs to have it become a "physical reality". So.....show me a completed/debugged/tested/validated schematic of this piece of vintage gear and I will take a look at what it might take to have it built. Fair enough???

Since I am not an end user I always work from the perspective that the customer knows what he wants and they provide me with their Functional and Performance requirements so I can design a circuit. So show me a completed/debugged/tested/validated Functional and Performance Specification and I will take a look at what it might take to design a circuit. Fair enough??

Cheers

Ian

 

[DaveP]

"As someone who just loves to design stuff so it can be actually built.....I have been somewhat following this thread and waiting for a completed and finalized schematic of this piece of Motown gear just to see what it would take to get started with doing exactly that. I don't feel like going back through 19-pages of postings to try and find if someone has posted a "finalized" schematic, so if one actually exists in here, please let me know the Post #."

Midnight, I can understand your frustration but a couple of points should be made.........................

The 19 pages were actually very interesting reading and showed the co-operation of GroupDIY members at its best, it was just disappointing that no-one chose to make it at the end.

The basic circuit was worked out during the text and it could easily have been constructed by anyone familiar with tubes, it was 100 times less complicated than the computer based box you posted.

As you like designing gear, then the design process in those pages would probably have been of interest to you.

best
DaveP

 

[MidnightArrakis]

Cool an 807 CF!!!!!!! Last time I used an 807 was back in the 60s for pirate radio RF output stage.

Cheers

Ian

[back in the 60s for pirate radio RF output stage] -- From the early-60s and up until 1969, I was part of a group of "radio broadcast enthusiasts" who operated a "bootleg radio station" in the state of Indiana here in the U.S. The FCC field-office in Chicago spent -- YEARS -- trying to track us down and put us off-the-air!!! They finally succeeded in doing so in the Spring of 1972, but I was "fortunately" in the Army at that point-in-time, so I missed out with being arrested on U.S. federal charges.

Our "bootleg radio station" became so well-known & popular among the high-school kids and the "twenty-somethings", that in either 1968 or 1969 when NIELSEN published their radio station "Ratings Chart" that shows who and when an audience is listening to what station, their chart listed -- 10 -- radio stations serving our broadcast area WHEN THERE WERE ONLY -- 9 -- LICENSED STATIONS!!! WHOO-BOY!!! Did THAT ever rankle the radio management where I used to live!!!

/

 

[Dave Obergoenner]

[back in the 60s for pirate radio RF output stage] -- From the early-60s and up until 1969, I was part of a group of "radio broadcast enthusiasts" who operated a "bootleg radio station" in the state of Indiana here in the U.S. The FCC field-office in Chicago spent -- YEARS -- trying to track us down and put us off-the-air!!! They finally succeeded in doing so in the Spring of 1972, but I was "fortunately" in the Army at that point-in-time, so I missed out with being arrested on U.S. federal charges.

Our "bootleg radio station" became so well-known & popular among the high-school kids and the "twenty-somethings", that in either 1968 or 1969 when NIELSEN published their radio station "Ratings Chart" that shows who and when an audience is listening to what station, their chart listed -- 10 -- radio stations serving our broadcast area WHEN THERE WERE ONLY -- 9 -- LICENSED STATIONS!!! WHOO-BOY!!! Did THAT ever rankle the radio management where I used to live!!!

/

Your background sounds much like my own!
Back in the 1960s when I was still in High School, I had built transmitters and mixing consoles for 5 different "pirate" AM stations in my home town. All tubes in those days of course. I'm still doing broadcast engineering as my day job (legally these days).

As to this topic/thread, I've continued to follow it, and have found it very interesting. A lot of it has been similar to other projects I've built in the past. A 2-channel version is still on my back-burner.

I wanted to do an "all octal" version. Perhaps 6SL7 to 6SN7 to 6V6 output...three of my favorite tubes on each channel. Enough gain for some over-drive if desired...or clean if not. It might have a switchable "speaker simulation" EQ curve pot on one channel.

The chassis I was going to use (an old Gates modulation monitor) turned out to be unsuitable for doing the all octal plan, since it was all miniature 9 pins, and the steel chassis was very thick, and I didn't think I could do proper punches through it. I'm not very good at that mechanical part. Still looking for the right chassis, with 6 octal sockets and a suitable power supply. When I stumble into one, I'll likely use it to build the 2-channel version I have in my head.

I'm still an active bass player, and the guitarist in my band is also a tech-head. We'd love to be recording through something like this. That's why the 2-channel version is in my plans.

Many thanks to all that have contributed!

Dave O.

 

[MidnightArrakis]

As to this topic/thread, I've continued to follow it, and have found it very interesting. A lot of it has been similar to other projects I've built in the past. A 2-channel version is still on my back-burner.

The chassis I was going to use (an old Gates modulation monitor) turned out to be unsuitable for doing the all octal plan, since it was all miniature 9 pins, and the steel chassis was very thick, and I didn't think I could do proper punches through it. I'm not very good at that mechanical part. Still looking for the right chassis, with 6 octal sockets and a suitable power supply. When I stumble into one, I'll likely use it to build the 2-channel version I have in my head.

We'd love to be recording through something like this. That's why the 2-channel version is in my plans.

[A 2-channel version is still on my back-burner] -- Should you be able to cobble together some manner of a complete and finalized schematic, even if only hand-drawn, I will assist you in getting started and off the "back-burner".

[The chassis I was going to use (an old Gates modulation monitor) turned out to be unsuitable] -- The chassis shown in my Post #368 is one I had custom mechanically-designed for that project. And, with you being a Broadcast Engineer, you may be interested in knowing that -- THAT -- chassis was the "world's first AM & FM Digital Radio Broadcast Exciter" that allows radio stations to broadcast both analog and digital signals -- at the same time and on the same frequency -- without any co-interference!!! Pretty cool, huh???

[I'm not very good at that mechanical part] -- I get by!!! https://app.box.com/s/ppsp38kb5rijeadt6i73q4u99nwurqqv

[I'll likely use it to build the 2-channel version I have in my head] -- Get a schematic together along with the details of what it is that you are looking at and/or thinking about and I can create for you some mechanical concepts like these:





[We'd love to be recording through something like this] -- Well.....OK.....then, start getting it together!!! You do your part and I'll do mine. Sound like a plan???

/

 

[olhsson]

I'm back to correct a couple things I had wrong.

First, the early descriptions of the amp are correct. It did not use inverted microphone transformers like I had mistakenly believed.

Second, the six microphone preamps in the console were not Langevin. They were Altecs from the time Western Electric broadcasting gear was transitioning into Altec. The are branded "Altec."

 

[daristiguieta1]

Thanks for giving us so many details, Mr. Olhsson. I'm a young engineer, and I particularly loved reading everything you've said about the musicians playing quietly and the approach you guys took to recording back in those days. This information is priceless.

 

[Dave Obergoenner]

Ok...I'm still following this, and still really do wanna build at least a 2 channel version of it. (guitar and bass).

I did want to do an all octal version, but the chassis I wanted to use was all full of 9 pin miniature's, and no octals at all. I'd still really rather use some old junked piece of gear, and be able to reuse the chassis, and at least some of the power supply in it.

I'm so honored to be reading the comments of Bob Olhsson! Those and what info Bob Babbitt confers to us is as close to "the horses mouth" as we are likely go get. Babbitts comments about "the bass always going into #5" sure imply that the bass guitar pretty much always would have come through this box. How much different channel #5 was from the others (if at all)?... we may never know until someone is able to actually examine the original box. Perhaps it had an input transformer, and the other channels did not? Transformer DI's do nice things for bass guitar.

6V6 driving the OPT seems easy to believe. I'd call that a good choice. Although most broadcast gear that used 6V6 to drive the outputs usually used P/P pairs of them...but that's likely WAY more output than the studio would EVER need for a line input! A single tube in cathode follower should give a decently low output Z to drive the OPT. But it shouldn't necessarily have to be that way. A triode connected 6V6 with more conventional plate loading can still give us a couple of watts via a properly capable output transformer.

As to the input...I wonder if they might have looked to the standard of the day...Fender.?. I think anyone would agree Leo had designed some pretty successful guitar preamps. Perhaps they copied something of his? Like the Fender Princeton, Showman, etc, minus the EQ.?. Two stages of a 7025 can give pretty good gain...and we really only need about 34db to get to +4dbm out. (guitars are a lot hotter than mics)

All the above is just some food for thought, until we can get some more concrete info on the real deal.

Dave O.

 

[abbey road d enfer]

6V6 driving the OPT seems easy to believe. I'd call that a good choice. Although most broadcast gear that used 6V6 to drive the outputs usually used P/P pairs of them...but that's likely WAY more output than the studio would EVER need for a line input! A single tube in cathode follower should give a decently low output Z to drive the OPT. But it shouldn't necessarily have to be that way. A triode connected 6V6 with more conventional plate loading can still give us a couple of watts via a properly capable output transformer.

Re-read post #48. It gives the most plausible explanation of each tube's role.
The 6V6 is needed only if you want a monitor output.

 

[olhsson]

The difference in the channels was gain. The idea was for the musician to turn their instrument up all the way and then the engineering staff would set the volume to peak at zero VU on that channel's meter. That way, when they used "their" channel, they could just turn up all the way and go.

 

[CJ]

Here is Joe Messina with some info on the use of the 5 channel amp, starting at about 14 minutes in,

 

[DaveP]

What a nice guy, thanks CJ, good info
best
DaveP