Gately (ProKit) SM-6 mixer and EQ schematic?

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Wildfara

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I was given one of these units and would like to find a schematic for it. Preservation Sound has some old info on them. Its kind of cool (to me) 70's SS gear. Solidly built. I am trying to get it going again and while its not too complex really I'd like to find more info on it.  A schematic would be really cool. Anyone?
 

PRR

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It was in Audio Amateur at the time, with schematics.
http://www.audioxpress.com
http://www.stereomanuals.com/man/rep/g-misc/
https://www.cc-webshop.com/The-Audio-Amateur-on-CD-ROM-1970-79-AA-CDAA070S.htm

The input transformers are very high ratio (1:14?). This was a mistake for the '301 opamps used. The secondary impedance is significantly higher than the OSI of the bipolar '301 chips. A kit-built SM-6 "should" have "sockets" (annoying individual stampings). The instant upgrade would be TL071, pin-equivalent, low-low input hiss current. This makes it around one of the lowest-hiss 150r inputs around. The 3-5pFd comp cap for '301 can stay; won't annoy the '071.

If you are driving all 10K loads (modern studio), you can use TL071 all the way through ('072 if the sidecars adopted dual opamps). For true 600r work the output driver might favor '5534 and the plan needs study.
 

Wildfara

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It has Danish input trannys 1:15 ratio (Beyer maybe) and NE5534's in the preamp (probably not original). I got some channels working...the switches were miswired and also dirty/worn out. For what it is it sounds not bad really...I'm missing the Molex connector for the EQ so haven't messed with that yet but might just make something that will work.
 

Wildfara

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And yes it does have those spider sockets...Some of the legs were touching I realized after rebuilding the power supply and they are tarnished...I'm replacing them with proper sockets even though I got everything mostly working...The worn out switches are the biggest signal flow issue...even with cleaning etc...They are just old
 

mjrippe

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Those Danish transformers might be Jorgen Schou - highly regarded, especially by the moving coil phono stepup audiophools.  But great for mic preamps too!
 

PRR

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The iron in mine was Beyer. I don't know if there were production changes; however I don't recall it being in production very long (maybe only one batch).

I'm quite sure the early ones were '301 opamps, decompensated. I recall knowing they were "741" but without such a slew-rate problem as Jung was starting to teach. At gain high enough to decompensate, the '301 is a perfectly fine opamp, *except* the input hiss current is non-negligible. Hi-Z source will induce hiss.

1:15 is what I recall also. 1:225 impedance ratio. Face a 200r mike. This is a 45K source. But the function of hiss current was not widely understood in 1975 (vacuum tubes had none, and older Ge/Si had multiple hiss sources to confound the designer). For more fun: the '741 data I just found does not even list hiss voltage. '5534's hiss is well characterized.

The 200r mike's self-hiss reflects over 1:15 as like 2.3uV/20KHz. '5534's hiss current is typ 0.4 pA/rtHz. In 45K source this is 2.6uV. The "low noise" '5534 is hissing worse than the mike's self-hiss. We would prefer 2X to 5X lower.

The 1:15 iron on standard mike impedances is just too steep for conventional bipolar inputs. Not a mistake, but in retrospect they sudda gone 1:10 or 1:7. Not sure what OSI is for '741/'301, but for '5534 a 1:5 is the middle of a broad optimum; 1:15 is off the high side of the quiet zone.

Which is why I was gonna go TL071. The hiss voltage is still nominal 2uV, but they are so cheap you can select-out the worst and find six nearer 1.5uV. The hiss current is dead-zero for our purpose. The slew is plenty fine. That was 20+ years ago, but my project stalled. Today there are sexier FET-in chips, though I do like the excellent stability against layout and bypassing of the TL07x family.

BTW: What I did do before stalling was bang six or a dozen 1/4" jacks in the back so I had six separate preamps or/and a 6-in line mixer. That's what the Molex was for, but 1/4" is more all-purpose today. But life moved on, 6-in was too much for holographic stereo and not enough for the big jazz band, so stall.
 

PRR

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Apology: some meditation on '741/'301 input hiss suggests that 1:15 _IS_ a good fit for its input hiss. Nevertheless, the '741/'301 input has so many "issues" re: hiss that it just is not a first-choice for any low-hiss chore (unless it is 1975 again, which it was when the SM-6 appeared).

And the 3dB-4dB noise figure of this affair is really not-bad in context. Many tube preamps did not struggle to beat 3dB. An awful lot of amateur work was done with wild mis-match of mike and input, NF 10dB and up. For louder acts onto slow-speed tape, this may not have limited the S/N of the recording (I rarely complained).
 

Wildfara

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Thank you for all your input PRR! I appreciate it. I'll probably update the switches on front and back and it already has three holes punched for 1/4 inch which were used for something else and i could easily make three more.  I like the idea of independent direct outs as well. All in all its a fun little unit with cool styling. Fairly simple doesn't sound terrible and was free. No complaints :)
 

Bill Wilson

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I have a copy of their Mocro Mixer. this followed the pro kits; it was marketed under Moms Wholesome audio. The preamp & eq amp are 301's; the output summing amps are listed as 709, but I believe they switched to 748's in later production.

I had to rent a prokit mixer to do a master tape for aq church record after I had sold out all my location recording gear. It was barely acceptable. I still have an original sales brochure for the Prokit line.
 

Wildfara

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So I found a local guy  that has the right molex connectors to connect the EQ  to the SM6. They are blanks so I have to wire them. no big deal. But he also has the schematics for both units which is cool. The SM6 has NE5534's in it which I think are not stock and the EQ has LF351's. I'm getting the schematic tommorow and will know for sure.
 

Wildfara

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I also discovered two of the input trannys had shorted secondarys. I removed those and just for fun and because I had some around I stuck a UTC O1 in place of one...Its works OK but has less output than the Beyers. I have some Reichenbacks I might try and also a couple new JT15K's (jensen) I may temporarily pull from a different build of mine just to try in the thing.
 

MidnightArrakis

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So I found a local guy that has the right molex connectors to connect the EQ to the SM6. They are blanks so I have to wire them. no big deal. But he also has the schematics for both units which is cool. The SM6 has NE5534's in it which I think are not stock and the EQ has LF351's. I'm getting the schematic tommorow and will know for sure.
[I'm getting the schematic tommorow] -- Would you still happen to have those schematics of the SM-6 here 3-years later? I bought 3 of the SM-6 kits back in the early 1970s and built them for doing "On-Location" recording onto a CROWN SX-722 stereo tape recorder back then. The 3 units gave me 18-channels of mic inputs that allowed me to do a "LIVE" stereo mix on headphones while driving my CROWN tape deck. I recorded big bands, acoustic guitar groups, jazz ensembles, small orchestras and rock bands in nightclubs. But, I have been looking for the schematics of those GATELY SM-6 mixers for a long, long time.

If you could scan them into PDF files, that would be GREAT!!! You can reach me here: [email protected]

I would GREATLY appreciate any assistance in your getting me this schematic. THANKS!!!

/
 

mjrippe

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Dang, I did not gather these when they were available. The World Radio History site was asked to take down their copies of Audio Amateur. You can still buy them on CD-ROM at
 

MidnightArrakis

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Dang, I did not gather these when they were available. The World Radio History site was asked to take down their copies of Audio Amateur. You can still buy them on CD-ROM at
Well.....the originator of this thread hasn't responded, so maybe he's gone to "The Great Audio Equipment Warehouse In The Sky" after contracting this COVID-19 virus!!! Who knows??? In any case.....some guy on the West Coast is shipping me his aging GATELY SM-6 mixer, that he says has been just sitting in his garage forever, so I can "Reverse-Engineer" the circuit board and create a schematic of the unit myself. I remember the PCB being a "single-sided" board, so it shouldn't be too difficult to do. A few years ago I did a "Reverse-Engineer" project of a PCB that was originally designed in 1979 and was used in the control electronics for U.S. fighter jets, so I believe that I can handle a simple 6-Channel audio mixer project.

I also sincerely appreciate the Audio Amateur CD information that you posted. That may be worth purchasing just to have all of the great information that that publication used to offer. GOOD STUFF!!!

/
 

MidnightArrakis

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Dang, I did not gather these when they were available. The World Radio History site was asked to take down their copies of Audio Amateur. You can still buy them on CD-ROM at
I just bought this CD this evening in the hopes that it contains the one single piece of information that I am looking for!!! I can only hope!!!

Yesterday (7/12), a guy on the West Coast has shipped to me his GATELY SM-6 mixer so I can "Reverse-Engineer" it and derive a schematic from the PCB. That will certainly be lots of fun!!! Then, earlier today, he sent an e-mail asking me that since I am going to be taking his mixer apart anyway so I can "Reverse-Engineer" it, if I could then essentially - re-build it - by purchasing all new parts of everything and replace all of the capacitors, resistors, IC chips, switches, etc. WOW!!! I didn't see - THAT - coming!!! I could only respond by telling him that I will need to work up a Parts List and find out how much all new parts will cost, plus my labor, and see if he is willing to spend whatever number all of that comes to. What do you think about doing all of that???

Right now.....I am going to be interested in seeing how (if) the Audio Amateur CD schematic compares to the one that I "Reverse-Engineer" from the PCB. I can only hope and pray that they (somehow) end up being identical. However, should they end up being different, I'll go with my "Reverse-Engineered" schematic because it was obtained from an actual production unit and not a "piece of paper" that probably had changes to it before being finalized. What do you say???

/
 

hodad

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I have schematics for the EK6 Echo Unit and the EQ6 Equalizer unit if you have any need. I may have the SM6 info somewhere, but it's not at hand at the moment.
 

hodad

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Random jpegs I found in an old email:
 

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MidnightArrakis

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I have schematics for the EK6 Echo Unit and the EQ6 Equalizer unit if you have any need. I may have the SM6 info somewhere, but it's not at hand at the moment.
WOW!!! GREAT!!! If you can send me any really clear PDF files of these schematics it would be - GREATLY - appreciated!!! I built 3 of the SM-6 mixers from kits in 1973 that I used to start doing "On-Location" recording with. These 3 mixers gave me 18-inputs that I could mixdown to stereo using headphones to feed my CROWN SX-722 tape recorder. I even - STILL - have those tapes!!! I would be interested in seeing the other GATELY schematics just in general to see how and what they did back then. Of course, the SM-6 schematic is what I am really interested in. THANKS for responding!!!

/
 

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