Category Archives: Vintage Audio Gear

Polyribbon Photos

My good friend Sandy Andrews happens to be a commercial photographer in Columbia, SC, so when I travelled there for the IPMS Nationals, I brought the Polyribbon with me and we headed over to his studio. These shots are the result. Sandy does catalog work for some very high-profile clients, so he’s got the chops (and the equipment, and the space) to shoot some really nice images. Hopefully you’ll see these in Mix Magazine someday!

While this looks like a vintage mic, everything in it is brand new. Les Watts, the designer, is a little bit neurotic when it comes to accuracy and quality… everything on this mic is executed with tolerances that are extremely close, which makes building these very time consuming and expensive. The banding around the headbasket is hand-filed brass that is then nickel-plated, the edges of the grille are all soldered. The frame that holds the magnets are assembled with dowel pins instead of screws, since screws have microscopic gaps that affect the magnetic reluctance of the frame. The wrinkle paint finish on the body is a custom formulation that Les had made just for this mic.

This mic has plain knobs because Les had trouble finding a laser engraver who could maintain the proper accuracy. Since each knob has to be handmade, a screw-up by the engraver would cost hours of work, so they have to be extremely careful. We’ve since located a supplier, so the new mics will have knobs with laser engraved and infilled legends. A simple silkscreened legend is much easier to make and looks the same at first, but these rub off after a few years. Les builds these with an expected lifespan in excess of fifty years, and all materials are selected for longevity.

These mics really need to be seen- and heard- to be appreciated. If you’re interested in acquiring one for your studio, contact me for a demonstration!


A Ribbon Microphone- Design 001, Rev A

Since I have to give away the Austin Ribbon Mic that I built, I decided that I wanted one of my own. I purchased raw materials for four more ribbon mics and have been working diligently on another mic. It isn’t completed yet, but I’ve done enough (and it looks good enough) that I can show off some preliminary photos.

My progress so far on ribbon mic no. 2, which incorporates a large number of design changes from the previous mic.

This microphone is similar to the Austin ribbon, but it’s a completely new design inside. The body style is similar, and I’m using a similar motor frame of clear acrylic plastic with drilled vent holes as a frame for the motor, but that’s where the similarity ends.

The Austin mic sounds great, but my outboard preamps are… well… let’s just say they aren’t top-of-the-line models. (Except for my lovely pair of VP26 pres from Classic Audio Products of Illinois, but I don’t have a Lunchbox yet to mount them in. I’ll get them racked one of these days, but the studio needs to generate some income first.)

So as a result of my gear, I’m having to crank the preamps up a good bit on the Austin mic. It sounds great on a source like an acoustic guitar, but for voice it requires a super clean preamp. (The Crest preamp that I recently purchased is a significant improvement.) This new design is an attempt to increase the output a little so that I can get a better signal with more common equipment.

My redesigned ribbon motor frame with magnets in place. A central groove is milled in the plastic for positioning the ribbon. The magnet spacer is just a piece of 4mm aluminum.

I’ve redesigned the motor frame using magnets that are slightly larger at 5mm x 10mm, and a ribbon that is slightly narrower, about 3.5mm. It’s counterintuitive, but narrower ribbons have a higher output. I’m using a 2.5 micron aluminum ribbon foil. The plastic frame is machined with a slot down the middle to hold the ribbon, and a pair a milled aluminum clamps to hold the ribbon in place. I didn’t want to use copper here because of galvanic reaction concerns. Everything is held in place by 4-40 capscrews, which are magnetic & will probably be a pain in the ass to install, but we’ll see. I’m waiting until most of the work is completed before I install the magnets and the ribbon, since the magnets will attract bits of ferrous crud in handling & the ribbon is so very fragile. That’s why they aren’t in place in the photo above.

The frame installed on the motor mounting tube. The ribbon clamps have been machined and are in place. I’ll probably secure the wiring with a dab of glue once the ribbon is installed.

Another difference is in the motor mount. I’ve built a secondary can that slides inside the mic body from a small piece of galvanized fence tube with a fender washer silver soldered to the top. This will shield the transformer almost as well as a Mu-metal can, and it makes a sort-of “mic-within-a-mic.” This same type of construction is used with great results on the Electro-Voice RE50 reporter’s mic, one of my favorites. This sub-assembly is isolated from the outer shell of the mic with a wrap of foam. This will be of limited benefit, since a ribbon mic is never handheld except when used as a prop in music videos. But I did want some way to take the mic apart and put it back together as a single unit… the Austin design has the motor pressed against the mic body with strips of neoprene foam. It works well, but isn’t ideally suited to taking the mic apart. I expect to do that a bit more with this mic, as I experiment with things like silks around the ribbon or waffle-plate resonators.

I’m calling this one Revision A, since I redesigned & rebuilt the mount to correct a grounding problem. I’m already working on Revision B, which will be largely similar except for the ribbon clamps and  more space at the bottom of the frame for mounting the motor with screws. (Revision A’s mount is secured with glue.) I’ve got some other ideas to try with magnet sizes and frame designs, but I need to give these an extensive listening test first.

I’m still waiting on a few parts… the transformer and the XLR, mainly… but I hope to have this project finished soon, and I’m anxious to hear the results. In the meantime, I’ve started milling parts for another one.

The semi-completed shell. I still need to machine the brass cap at the bottom and mount the XLR connector. Overall length is just about six inches.

The cost for this project is fairly high, mainly due to the amount of time that is spent in construction. If you add in the cost of the machine tools, the cost goes from fairly high to astronomical. I’m using a benchtop drill press, a 7×10 Chinese lathe and Taig milling machine to make these. All three have been essential for various parts of the work. While it would be theoretically possible to build a mic with hand tools, it is a lot easier to get good-looking results in less time with some heavy machinery. (If you lack the tools, Rick Wilkinson’s Austin ribbon mic kit is highly recommended, see my previous post.) And actually, my setup is pretty minimal… I could use a larger lathe & a CNC mill for faster and better results… but now we’re talking about an investment that would require going into business as a mic manufacturer, which isn’t my intent. These are experiments. I’ll probably make a few available for sale at some point, just to recoup some of the cost of the parts. And I expect the price on them to be rather high, just because they take so very long to make. But these are primarily built for my own satisfaction. It won’t hurt the resume, either.

I owe a great debt to Rick Wilkinson and Les Watts (former mic designer with Shure and EV) for teaching me a large majority of what I know about building ribbon mics. Their help is very much appreciated.

UPDATE: I’ve very nearly completed this mic… I recut an existing XLR connector on my lathe, so now it fits the microphone. The magnets were fitted to the frame, and I mounted a 2.5 micron ribbon yesterday. I’m guessing it’s about 3.6 mm wide. It’s a nice, tight fit. The ferrous capscrews were a pain in the ass, but not impossible to deal with.

The ribbon motor completed, with magnets and ribbon installed. Using 2.5 micron ribbon material is much easier than signwriters leaf, though it’s still not a simple process to install.

Now I’m just waiting on the transformers to arrive. These will be a special custom-wound ribbon transformer that should meet or exceed specifications from the usual suppliers. Unfortunately, it probably won’t arrive in time for the DIY seminar… I was hoping to have this working before then.

This mic comes with a custom walnut mic box that I had built by a local cabinetmaker. Nothing on this mic is sourced from Chinese suppliers… that sort of thing is easy enough to get from just about anywhere these days. If nothing else, this mic will be different from the common stuff that is so prevalent these days.

UPDATED UPDATE: When I went to use this mic recently, I discovered that the glue had failed on one of the magnets and it had separated from the frame, bringing the two together and turning the carefully-placed ribbon into aluminum dust. So while this is an easy-to-build example of how ribbon mics work, it isn’t the best design in terms of longevity.

My new design incorporates a steel frame rather than plastic. This is slightly better from a magnetic perspective, and it’s naturally stronger for threads, etc. I’m thinking of trying a frame made from small pieces of 1/4″ square steel. Machining from solid would be a possibility, or I could even get crazy and go to the blacksmith shop and forge something… I was formerly a full time blacksmith and still have access to some large and heavy tooling. And I’m pretty sure that nobody else is hot forging their ribbon mic parts.

But the key design element will be a small notch to hold the magnets apart. I should have done this before, as it could be incorporated into my earlier frame design. It’s yet another thing to put on my long list of projects.

The finished mic in its custom-built, handmade walnut box.

Austin Ribbon Mic Completed

The completed Austin ribbon mic. This one will be given away at the Producer’s and Engineer’s Summit at Welcome To 1979 in Nashville, coming up in November.

Here’s a look at my Austin ribbon mic, I completed it yesterday. Building this mic certainly was actually really easy, except for one part… installing the ribbon in the frame. I had to do this several times… six, to be exact. I  had various problems. One, for example, didn’t show it’s ugly head until I’d completed an installation… tiny tears all along the edge of the ribbon. I learned they were caused by the ruler I was using, which had a cork backing that was set slightly behind the ruler’s edge. This small unsupported space allowed the foil room to stress and tear. I corrected this by using a length of rectangular aluminum as a straightedge, this pressed down on the foil right at the cutting edge.

Another problem I had was corrugating the ribbon. I was trying to protect the ribbon by corrugating it with the release paper on the top and bottom, but doing so a) causes the ribbon to curl up, and b) makes the corrugations shallower. If the ribbon isn’t sufficiently corrugated, it is extremely difficult to get it tensioned properly. The tension is important… the ribbon can neither sag in the frame, nor should it be too tight. I had the latter problem, and the ribbon developed a longitudinal curl, so scratch that ribbon.

But thanks in no small part to Rick’s patient support via several emails, I finally got one in. It wasn’t perfect… it could be centered just a hair better… but it looked ok, so I closed it up and finished the mic.

And considering everything, it sounds quite lovely. The last time I used a ribbon mic was 25 years ago, when I did my thesis recording using a pair of RCA TK77’s that the university owned, so I don’t have much of a frame of reference, but it seems to have a nicely balanced frequency response. From what I understand, construction errors show up as poor highs or lows. I don’t have a frequency analyzer set up yet so I can’t give any numbers, but my subjective analysis says “nice.” Now, like all ribbons, the output is rather low, and I did my testing using a rather crappy mic preamp. On voice, one has to crank the gain up quite a bit, and this gave me a lot of preamp noise. For someone who is a low talker, this wouldn’t work. But I got a rather useable level on my acoustic guitar.

Again, I can recommend Rick’s kit quite highly, especially if you’ve never built a mic before. He’s done everything that can be done to insure a good outcome, and the one I built certainly worked out well. That’s not to say it’s simple… you need patience, and good, steady hands will help as well. But I’ve already got parts here to build four more for myself!

The Archetypes at OnLine Audio

I don’t have much from my old studio days. We had a few photos, but Robert (Graves, studio owner) and I can’t seem to find them. The equipment, of course, is long gone… I especially miss the Neumann U87 and KM84 that we had. About all I have to prove I was there is a small number of test cassettes and a portfolio of graphic designs. (This includes one OnLine Audio “Don’t Worry, We’ll Fix It In The Mix” T-shirt… my best design.)

Up until the last year or two of the studio’s operation, I held two jobs… I’d work at the studio from about 10AM-2pm, then drive across the bridge to do the news at Channel 2. So for many years, I would do daytime sessions, and Robert would do the nighttime. (though for the last year or two, I had resigned from the station and worked at the studio full time… Robert was getting really tired of being there every night during our busy periods.) Most of the serious musicians wanted to schedule at night. And since he was the owner, Robert got first right of refusal on sessions. That meant I did a LOT of rap music and people who had never been in the studio, so many of the projects I did were… well… not so notable.

But some were. I believe that my very favorite project where I did the majority of the album was the Archetypes. I can’t remember how it came to pass that I got this one and not Robert, but if I remember correctly, I did most of the tracking and mixing on this album. Perhaps not all of it… I think Robert might have done some work on it as well.

The Archetypes, circa 1989

Since nearly all of our artists were self-financed, we did all the basic tracks… guitar, bass, drums, and usually vocals… on the same pass, since setting up and tuning a drum kit could take a couple of hours. We’d cut eight songs in a single day. The bass was recorded direct, drums in the drum room, rest of the group in the main studio. (Though we learned later to put the guitar amp in the drum booth, then record the drums in the main room, which was big and “live…” maybe 18×25 or so, with high  ceilings and hardwood floors…) OnLine Audio was in a business incubator at 701 East Bay St., in the shadow of the old bridge to Mt. Pleasant. The place has gone condo now.

Once the basic tracks were laid, we’d do overdubs and punch-ins. Our Otari MX80 was great at this, and is another machine I wish I could afford.

An Otari MX80, 24 track version… a sweet machine.

While this method keeps the studio time affordable, it also tends to make mixdown a little harder, since you have the same basic sound to work with, and I remember having to struggle a bit in order to get the songs on the album to sound “good but different.”

Two of the songs  from this album have been posted on ReverbNation, and you can listen to them here. If you like the songs, buy the album (and tell them I sent you!)


Hurricane Hugo in 1989 put an end to the studio. While we were mostly able to repair the water damage and held on until 1990, the drop in business volume and rising monthly costs forced us to throw in the towel. I went off to grad school, and Robert went into real estate and renovation, where he was very successful until the market crashed. Unfortunately, tinnitus has severely limited his recording activities, but he made some really good records at OnLine Audio.

The Archetypes in 2010

Read an article about the Archetypes from 2003 in the Charleston Post & Courier here, another from the Charleston City Paper here.

POSTSCRIPT: If you recorded at OnLine Audio, please drop me a line… I’d especially like to get a copy of any photos or music that you might have. Thanks!

Creation Audio Labs

If you’ve been reading this blog for awhile, you know that I’ve been setting up a small studio. The heart of the studio will be my analog mixer, my 1981 Soundcraft 800, which I found in Atlanta for $500. The heart of this mixer is the master module, and the master module didn’t work. There were a number of baffling problems with it… no tone osc, no headphone signal, left side meter read off the scale while the right side read nothing… so I was a little afraid to try to tackle these repairs myself. And a cursory inspection showed no obvious problems that I could see… no burn marks, bulging caps, or exploded bits. I needed professional help.

I had no idea that Creation Audio Labs existed until I read a recent article in Pro Audio Review, where someone had their Soundcraft Ghost extensively rebuilt and upgraded by these folks. That they are only 100 miles away in Nashville, Tennessee, was a bonus. I exchanged some emails with Alex Welti and found out that yes, they could help me. He gave me a rough estimate and I sent the module off to have the work done.

It took them awhile to get to it, but I just got the word yesterday that my module was repaired and on the way back. Reading over the work order reveals that this was the smartest move I’ve made in some time. Apparently, someone else had tried to fix the module and thoroughly f^$&ed it up. They had to repair many broken traces on the PC boards (there are two main boards stacked on top of one another, and another small board for the meter… another reason I didn’t want to tackle it) and found a number of bad transistors, replaced and socketed several ICs… three and a half hours of bench work. While this is a lot of time, it’s also amazing that they were able to get it all done in just three and a half hours. It would have taken me three and a half days, and I’m sure they found problems I’d have missed.

I’m really grateful that these guys are in business, I’d have been in big trouble otherwise. The work was fairly priced… I feel I got a REALLY good deal, since without them I’d have nowhere to turn. I recommend them highly.

Building a Studio- The Soundcraft 800

Work on my new studio space continues steadily. And while things aren’t necessarily moving as fast as I’d like, I’m getting things done one job at a time. Today was blowing insulation day, which was a messy, nasty, dusty affair. But it’s

My studio as of Jan 14th... there's a LOT of drywall mud to sand yet.

also probably the most effective low-cost solution for my roof space, as it pretty much fills all the gaps between the drywall ceiling and the underside of the roof deck (with a layer of QuietBrace screwed on for better isolation).

Old Busted or New Hotness? Depends on who you ask, but probably a little bit of both... my Soundcraft 800

And just as I was getting completely overwhelmed by the magnitude of remaining jobs I have to do, I gave myself a morale boost by taking delivery of the centerpiece of the studio, a Soundcraft 800 26-channel mixer. While it looks impressive (to me, at least… but some say I’m easily amused), it has some issues with the master section that will need to be addressed. The age of this mixer means that it will pretty much need a full rebuild.

I’ve already corresponded with the good folks at Creation Audio Labs in Nashville, they specialize in mixer rebuilds. (There was a great article by Rob Tavaglione about rebuilding a Soundcraft Ghost in a recent issue of Pro Audio Review.) I’ll be doing some of the upgrades myself, and I’m going to let them do some of the work. Part of the reason I wanted an older Soundcraft was the individual channel strips… this makes regular maintenance and repairs much easier than a newer mixer like the Ghost.

While this mixer isn't quite as nice as the Soundcraft TS12 that I formerly used, it didn't take four guys and a truck to move, either. While it's certainly a "midsize" mixer, these are a more practical choice for a smaller studio like mine... and they are a lot easier to resell when the time comes.

Fortunately, this mixer came complete with the original owners manual with schematics, a newly recapped power supply, and a bag of extra parts. The extra parts are a bit concerning… it means somebody has been poking around under the hood with a soldering iron, which can be a bad thing if the maintenance maverick isn’t particularly skilled. Since the electronics bench is a part of the studio, I won’t be able to start work on the mixer until the studio is complete. Fortunately, I’m not facing a particular deadline, so I can take the time to do things properly… but I’m sure anxious to start working on it.

The nameplate on the mixer gives a clue to its age. This one was built, I believe, around 1981. Note how the connectors are individually screwed to the chassis and not held in place by a common PC board... common in older gear. The downside is that connectors often need to be replaced... tedious because there are so many, but a fairly easy upgrade.

The DBX 900 Series

Way back in the stone age, we used some equipment in the studio that was really neat stuff… very high-quality circuitry, mostly discrete, handbuilt equipment that I used to record some pretty good records, even though you’ve never heard them. One of my favorite pieces of outboard gear that we had in our rack was a DBX 900 rack. This was a 19″ wide power supply with spaces for nine 5 1/4″ x 1 1/2″ modules. Two other companies made similar systems- Valley Audio (we had a Valley rack as well, and we liked it better than the DBX) and API. Of the three, only the API Lunchbox has survived, and now there are hundreds of modules manufactured that can fit API racks, and Radial Engineering has just released their own version of a rack cage and power supply for 500 modules. Very nice, but very pricey.

My DBX900 rack, almost identical to the one we had at my studio 30 years ago. It's taken several years to put this together.

In contrast, a DBX 900 rack can be found used as low as $150 on eBay (though I’ve seen some crazy prices lately) and individual modules go for around $100-200 each. One other company besides DBX made modules for the 900 series, and that’s Aphex. These folks make some GREAT compressors, but as far as I know, only the  9721 Dominator and 9651 Expressor is available for the 900 rack, though there may have been others. Because of size constraints, the Dominator doesn’t have all the controls of the 19″ rackmount version, but it’s a very sweet compressor.

The DBX 904 noise gate module for the 900 series rack

Don’t overlook modules that need repairs, either. I was lucky enough to find some 900 units on eBay that were being sold as non-working, parts-or-repair-only. I took a gamble and got these for about $30 each. One was a 905 parametric EQ. This one turned out to be an easy fix… a disc capacitor had blown itself in two.  Thanks to DBX’s unselfish policy of publishing their schematics, I was able to figure out the value and replace it, and it works! Sometimes a blown part is a symptom of other problems, but so far, nothing else has smoked.

Next up was a DBX 903 compressor limiter. This one exhibited some general wierdness in terms of the signal, and the LED meter on the front was out. The 900 series all use the same meter driver board, which helps. I traced the signal at the meter board’s input, and confirmed that it was getting a signal, so I pulled the board and swapped it with another from a working unit… problem fixed. Now we know the problem is somewhere on the meter board. Examining with a microscope showed a resistor with a tiny burn mark around the middle. Replaced the resistor, and presto! The meter board works.

The business end of the 904. The board on top is the meter driver.

The last problem piece is a 904 noise gate, the donor for the working meter board used to correct the compressor. This one was a bit tougher to fix. Reinstalling the now-repaired meter board shows that the unit is detecting properly and gating a signal according to the settings, but there’s no output.  I poked around with a meter, and got about a .4v signal at the input. I started working my way back from the output, and found a non-polarized electrolytic capacitor that wasn’t passing any AC. So to test my theory, I removed C3– a 4.7uF non-polarized electrolytic cap– and replaced it with a pair of 10uF capacitors wired back-to-back, i.e., negative tied together, positive side out… and it works, passing a clean, gated signal!

After a proper 4.7uF NPO cap arrived from Digi-Key, it was soldered in and tested… that fixed it. While I was at it, I ordered enough Nichicon capacitors to re-cap the entire board… fortunately, DBX designed their circuit boards to accommodate either radial or axial-leaded caps, so either type will fit.

The problem cap. Replacing this fixed the unit. Fortunately, the problem wasn't under the big square metal case... that's a DBX discrete voltage-controlled amp (VCA), which is mostly transistors packed very tightly onto another circuit board. Repairing one of these would be really difficult, and replacement would be impossible.

That’s the other big advantage of this old stuff… it’s possible to fix it when it breaks. When parts fail on new gear… likely built overseas, by robots, using surface-mounted components… you’re pretty much done and replacing the entire board is the only option. Sometimes sourcing parts for vintage gear is difficult or sometimes impossible… germanium transistors and diodes come to mind. But vintage gear can almost always be rebuilt, and if the quality is there to begin with, it’s worth the effort.

The 904 fully recapped. The job wasn't that difficult or expensive, but you do need to be careful and take your time.

Using The EMT 140 Plate Reverb… Sort Of…

I love working with classic audio gear, and I’m lucky enough to be “of a certain age” that I’ve been able to get my hands on some really nice knobs. These knobs almost always belonged to someone else… either recording studio, television station or pressing plant. And once you’ve had a taste of really top-quality gear and enjoyed the benefits, it’s really hard to go back.

But in our brave new economic world, creative jobs with access to nice hardware have seriously dwindled, and the handful of folks who have those jobs generally stay put. So, like most of us, I’ve got to bankroll my own hardware addiction, which means that there are some pieces of gear that are just plain off limits… no matter how nice they sound.

The EMT 140 plate reverb frame. The control electronics were in a separate rack unit in the studio. The plate was often located in a quiet location away from the studio.

For example, let’s consider the EMT 140 plate reverb. One can be bought for about $1500, which isn’t too bad, really. But plate ‘verbs are large, heavy pieces of gear that require a quiet, vibration-free location.  Usually found only in large studios, they were generally installed and left alone. So what’s a starving self-funded engineer/producer to do?

Enter Universal Audio. These folks make plugins that model classic gear, and they are very well done. I’ve had a UAD2 Solo/Laptop co-processor for quite a while now, but haven’t had the chance to use it much. But while mixing a recent location recording for Claire Lynch, her lovely vocals were begging for a second reverb. (The Solo comes with RealVerb Pro, and I was using this for the instruments.) I tried some free/shareware plugins, and although they sounded pretty good, I didn’t like the interfaces… I felt like I was writing Fortran code back in college rather than mixing, and never could get a very musical result. (like I said, I’m “of a certain age.”) I still had a credit with UAD from when I bought the Solo, so I sprung for a software version of the EMT 140 plate reverb.

Universal Audio's EMT 140 plate reverb plugin interface looks similar to the original, it's intuitive and easy to use.

I’m happy to report it works like a charm. They are the perfect complement to Claire’s vocals. UAD’s graphic interface mimics the original very closely, and the original control panel is easy to figure out. I can make adjustments simply and get great results without having to “hunt around” for a particular parameter. (if you’d rather enter adjustments numerically, though, that option is available through keyboard shortcuts).

I don’t buy many plugins, since they’re only going to last as long as your current computer. When I can afford it, I prefer to buy the hardware version of the gear that I need. But in this case, I’ve gotta admit that the plugin has some significant advantages over the real thing. It’s far cheaper, infinitely more portable, fun to use, and most importantly, makes Claire’s voice sound like a million bucks.

The RE50- A Broadcaster’s Swiss-Army Mic

I first encountered these mics at my first television station, WCBD, over 20 years ago. Electro-Voice RE50s were in some of the reporter’s kits but not everyone had them. Whenever we’d encounter a problem mic, the first thing we’d do is try a ’50. This often corrected problems.

RE50s are dynamic mics, so they don’t require phantom power. Their output is a little on the low side, but even so, they are usually fairly quiet. They’re omnidirectional, so they don’t suffer from proximity effect. This makes them excellent for interviews, but less great for live sound as they’re more prone to feedback.

The best feature, though,  is the isolation. They are built almost as a “mic within a mic.” The microphone diaphram, electronics, and transformer are housed in a closed cast aluminum chassis. This chassis is suspended by foam inside the mic body itself. The result is the mic is very well insulated from handling noise, and especially wind gusts. I’ve actually used these in live weather reports during a hurricane.

My current collection of ElectroVoice RE50s. More than I need, probably, but I like having them in my kit.

Whenever I see these on eBay for cheap, I snap them up. I currently have four in my inventory, two RE50s and two RE50B. One of these I bought for ten bucks as a parts mic. When I got it, I opened it up to find the foam surround completely gone. I cleaned out all the old adhesive and foam crumbs, made a new surround with a thin strip of foam around the base, added a circular bit inside the mic basket, and now it works. I’m trying to locate a source of OEM foam surrounds for these, but no luck so far.

New Manuals page added

I’ve just finished adding a “manuals” page above to house some of the old gear manuals that I have. Right now, there’s only the Sony MXP61 there. I didn’t see this info anywhere else, so I’ve just finished scanning it and that’s where it’ll live. The MXP61VU is a great little desk, with individual channel strips. The schematics show a provision for direct outputs at one of the circuit board connectors, but this feature was

The back of the MXP61VU. The pair of D15 connectors in the center are the Cascade in and out... a good spot for a custom direct-out mult cable.

never implemented. There is, however, a pair of cascade input and cascade output connectors that are likely to never be both needed, so one of these could be converted into a direct output mult without major surgery.

Any vintage mixer could likely use some new capacitors, and could also benefit from updated operational amplifiers, and this one is no exception. But this model features typical Sony construction… it’s built like a tank.

Classic Audio- the RTS Systems HPM-41 mixer

As much fun as all the latest and greatest software-based audio technology is, I still like old analog circuitry. It has it’s quirks, of course, but there are lots of cases where high-quality analog still sounds outstanding… as good as, if not better than, digital.

The front panel of the HPM-41 mixer by RTS Systems

The front panel of the HPM-41 mixer by RTS Systems

One of the mixers in my collection is the RTS Systems HPM-41, which is a 4-input mono mixer. Background info on this unit has been very difficult to find. RTS Systems abandoned the mixer business years ago to concentrate on intercom systems for television and broadcast stations. It looks like these were built to compete with the ubiquitous Shure M67 4-channel mixers in use in  just about every radio and TV station in the country. The Shures are built like tanks… dependability is critical in broadcast… but the RTS mixer has some big advantages over the Shure. Some are apparent from the front, and others you can see once you open the unit up.

The rear panel of the HPM 41

The rear panel of the HPM 41

Each channel has a two-position pad to drop the input signal 15 or 30 dB. There’s also a 75Hz and 150Hz high-pass filter, and a real bonus, individual limiters on each channel. On the back, each channel can be phase inverted, and channel 1 and 2 has phantom power, which can be switched between 12v A-B powering or 48v phantom. (I like this arrangement better than my brand-new and very expensive Shure FP33 mixer. To change the phantom powering, you have to open the unit up and poke around the battery compartment. It’s tight, your fingers are constantly touching the circuit boards, and it’s easy to forget the settings.)

All the switches on the HPM-41 are recessed toggle switches, which gives the whole thing a higher-quality feel.

This mixer is really heavy. This is due to the large mains transformer inside the unit. While it has a provision for battery power, it’s really designed for stationary operation rather than fieldwork in a bag.

Inside the HPM-41. The large rectangle on the left is the RF shield covering the AC mains transformer.

Inside the HPM-41. The large rectangle on the left is the RF shield covering the AC mains transformer.

Once you open the unit up, the differences between this and a Shure M67 become immediately apparent. The pots are Bourns sealed type, probably conductive plastic. These give better performance than the usual carbon type. Four big electrolytic capacitors are also immediately noticed. The 25-volt, 3300 uF monsters will be hard to replace since they are axial-lead type, and this type of lead is not  normally stocked in better grades. Electrolytic capacitors can degrade over time– especially through lack of use– and it’s usual to replace them in vintage equipment. But capacitors that are larger than their minimum requirements do last longer. I’ve even heard it suggested that with caps, more is always better. (but within reason, of course.)

Beyer input transformers

Beyer input transformers

ICs in this unit are 5532s and TLO84s. While there are some other IC’s that might yield higher performance (such as the Burr-Brown 2134), the general consensus seems to be that 5532’s are pretty good chips. Also noted, but not usually seen, are four Beyer Dynamic German-made audio input transformers. Some good info on these and other circuits can be seen on the kubarth site.

The RTS Systems HPM-41 is a comparatively rare mixer. My guess is that these were very expensive units judging from the components, especially when compared to the Shure utility mixers from the same period. I don’t use mine very much… the weight and power requirements mean that I can’t use it in a bag, running around under battery power, which is 95% of my business. And it’s usefulness is further limited by being a mono mixer. But I expect to find a good use for it as a preamp or base for modification. Several ideas come to mind, including placing the heavy power transformer into a separate case, changing out the power plug to a 4-pin xlr, and adding direct outputs. If you happen to find one cheap, I’d go ahead and buy it, or let me know about it. Also, if anyone has any documentation on these, I’d very much appreciate a copy and I’ll add it to these pages.