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Even the Federal Communications Commission makes a mistake once in a while. And in the case of a potential financial liability, that can be good news for the stations concerned.

The commission cancelled several Notices of Apparent Liability for Forfeiture that had been issued to three radio stations in North Carolina — Radio Hatteras, CTC Media Group and Pirate Media Group.

[Read: Out-of-Date Online Files Being Investigated by FCC]

In the case of Radio Hatteras, the FCC said that station WHDZ(FM) in Buxton, N.C., had failed to file a timely license renewal application for the station, which was due Aug. 1, 2019. The FCC said the license renewal application was not filed on time — the FCC said it was filed Oct. 25, 2019 — but in reality Radio Hatteras filed the application on July 30, 2019. In reality, the filing made on Oct. 25, 2019, was an amendment to the application. Since the application was timely filed, the FCC cancelled the NAL.

The same was the case for CTC Media Group, which is licensee of FM translator station W282CQ in Bridgeton, N.C., for the same alleged offense: failing to timely file a license renewal application for the station. The background is the same as it was for Radio Hatteras — the FCC said the station failed its renewal by Aug. 1, 2019. In this case, however,  the commission had actually issued the initial license for the station on Aug. 12. 2019, therefore there was no need for CTC to file a renewal application.

The commission also cancelled a Notice of Apparent Liability for a Forfeiture issued to Pirate Media Group, licensee of FM translator station W281CH in Washington, N.C., for the same alleged violations. But in this case, too, the commission had already issued a license for the station on Sept.11, 2019, so it was impossible for Pirate to file an application to renew the station’s license.

In all three cases, the FCC has cancelled all of the forfeitures.

 

The post FCC Moves to Cancel Forfeitures After Catching its Own Errors appeared first on Radio World.

Streaming service tools provider StreamGuys has reworked its native media player, SGplayer.

Version 3.0 has a new GUI along with “greater continuity between desktop and mobile experiences; and additional GDPR- and CCPA- compliance tools for media enterprises leveraging targeted advertising,” according to a release.

“SGplayer 3.0’s new interface puts the visual focus more heavily on the branding and artwork of the broadcast station or podcast while more cleanly integrating additional elements such as song metadata and advertising. Supplemental functionality such as stream or episode selection — always visible on-screen in earlier versions — has been moved into collapsible menus to minimize distractions and streamline the user experience,” a release details among a number of user experience improvements.

Content search functionality has also been improved and expanded. 

Additionally, there has been added compliance features, “Of particular interest to media companies serving; European and Californian listeners, new tools for GDPR and CCPA compliance allow SGplayer’s targeted advertising to be disabled based on user preferences.”

Other new goodies include: support for both HLS and ICY protocols for HTTP-based delivery; automatic fallback from AAC to MP3 live audio streams for compatibility with older devices; authentication of tokenized streams to ensure user entitlement; Nielsen SDK integration for enhanced online audience measurement; Google Analytics tracking; and a customer-hosted persistent player option for enterprise clients wishing to combine SGplayer even more closely with their own custom development.

SGplayer is now available.

The post StreamGuys Revamps SGplayer appeared first on Radio World.

Frequent Workbench contributor and consultant Frank Hertel of Newman-Kees is not one to brag, but he has quite a bit of experience in dealing with mice. After 50+ years of servicing some really bad transmitter sites, he has a number of tips to share with readers.

Getty/anuwat_meereewee

1. Inspect the seals of all doors and windows and cable entries to the outside world, to ensure they fit tight.
2. Screen all fan openings and air exits with 1/4-inch galvanized hardware mesh, to keep critters out.
3. Make sure to plus the main electrical service entry conduits with stainless steel wool or copper wool and caulk. (Mice will eat through caulk alone.)
4. Resist the temptation to “dress up” your site by adding dropped ceilings; they provide an ideal location for nesting of mice.
5. Never take food or soft drinks into the building. Even a few crumbs or an empty soda can and will invite mice.
6. The same is true for any food-scented wrappers or containers. Keep them out of the transmitter building. Also use a trash can with a tight seal to dispose of everything. Better yet, always take your trash with you as you leave a transmitter building.
7. Realize that food scents in the building can entice mice. They will gnaw through some types of exterior wall surfaces if they get even the slightest scent of food.
8. Don’t use rodent bait; it actually attracts mice! And although it works, many times the mice often crawl off into some secluded space to die and make the building smell. Furthermore, most rodent bait will decompose over time and turn to dust — which you end up breathing. If you ever go to a transmitter site and find they have used mouse bait, don’t ever sweep or vacuum the floor without a respirator.
9. Instead of rodent bait, use something safe like “Peppermint Oil” to repel mice. It works! Here’s a video example showing its effectiveness.
10. On visits to infested sites, be sure to take a change of clothes and a bag to put your dirty clothes in! Otherwise you are infesting your vehicle with all the nasty stuff from the transmitter building.
11. Carry a jug of water, a bar of soap, a roll of paper towels and a bottle of alcohol, and clean yourself when leaving and before getting into your vehicle. This is especially helpful if you take a break to eat.

[Don’t Let Mice Kill Your Transmitter]

Frank adds that he has a personal reason for helping you to manage your exposure to rodents. 

For a long time, he suffered from an unusual medical condition. Whenever he at something sweet or drank a sugary drink, he would get an extreme pain where his esophagus entered his stomach. He tolerated this for 25 years, and had a number of tests during those 25 years; nothing was diagnosed.

One Thanksgiving, after eating a couple of those miniature Hershey bars, Frank was in deep distress and was taken to the hospital. Initially, the doctors thought it was a heart attack. Among the tests they performed was a “bore scope” down Frank’s throat. When Frank awoke from the anesthesia, the doctor had identified the problem: five small bacterial-based ulcers. Frank asked whether exposure to mouse bacteria, from contact with urine and droppings dust, could have caused the problem. The doctor’s reply was an emphatic “YES!”  

A 20-day treatment with Amoxicillin worked. But Frank no longer views mouse-infested transmitter sites the same way. His business does not provide routine service/maintenance; he is usually called in just for an emergency, and too many facilities have not had routine cleaning. 

He now carries a face mask and respirator in his vehicle. Mice are not to be taken lightly. More than just your equipment is at risk.

* * *

Wiring maven Steve Lampen attended a recent tips webinar sponsored by Telos. From our discussion of AoIP installations and the tons of analog wiring that is usually removed, Steve suggested that engineers Google “copper scrap reclamation” for information on turning your old wire into money. 

A recent Bloomberg headline stated, “Copper Tapped as the Next Big Metals Trade of 2020.” 

* * *  Fig. 1: A compact recorder and mixer from CEntrance.

I was commiserating with an engineer about remote broadcasts of the 1960s and ’70s and how they’ve changed.  Many stations load their jocks up with a tablet or a smartphone, and it’s show time! Even the gear required for news interviews has been simplified thanks to several codec manufacturers.

Using a smartphone for an interview is fine, but there are times where you’d like to mix two signals. That’s where CEntrance comes in.  

The MixerFace R4, pictured in Fig. 1, is a high-quality mixer, recorder and USB interface. The rugged metal enclosure is about the size of a smartphone, and can record to an SD card or the phone.

Fig. 2: This is not some kind of science fiction monster; it’s two people holding a MixerFace. Identify the hands and maybe you’ll win a prize.

In addition to gain and monitor controls, each channel has a switchable high-pass filter (to reduce on-location wind noise) as well as a Hi-Z/Low-Z selector switch for each channel. Longer recording sessions are assured with an 8 hour battery.

The MixerFace R4 is available through broadcast distributor Broadcasters General Store, which is sponsoring a fun contest. Look at Fig. 2. The first person identifying the hands holding the MixerFace R4 will win a $25 coffee card. Send your entry to my email and maybe include a tip or a picture of something to share from your gallery (not required). Only one winner, and the time/date stamp on your email will be the determining factor. 

Earn recertification credit when you share a tip published in Workbench. Thank you for sharing your tips and high-resolution photos by sending them to  johnpbisset@gmail.com.

John Bisset has spent 50 years in the broadcasting industry and is still learning. He handles western U.S. radio sales for the Telos Alliance. He holds CPBE certification with the Society of Broadcast Engineers and is a past recipient of the SBE’s Educator of the Year Award.

The post Frank Hertel’s 11 Tips for Dealing With Mice appeared first on Radio World.

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Media Bureau cancels Notice of Apparent Liability for Forfeiture issued to CTC Media Group

MB cancels a Notice of Apparent Liability for Forfeiture issued to Pirate Radio Group, LLC

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Media Bureau Cancels Notice of Apparent Liability for Forfeiture issued to Radio Hatteras, Inc

The Adam Hall Group has unveiled its Palmer brand’s new active studio monitor, the Studimon 5.

The Studimon 5 comes in compact bass reflex housing with wooden sidewalls. It has a 5-inch ferrite custom subwoofer, 0.75-inch neodymium silk diaphragm tweeter, and a frequency response of 70 Hz to 20 kHz.

[Check Out More Products at Radio World’s Products Section]

The two-way monitor, with an output power of two 30 W (RMS) amplifiers is intended for home studios as well as professional audio environments.

The back of the Studimon 5 features a 1/4-inch jack and XLR inputs, and a volume controller for tuning stereo balance.

The Studiomon 5 is priced at $269 each.

Info: www.palmer-germany.com/en/

The post Palmer Releases Studiomon 5 Studio Monitor appeared first on Radio World.

Steve Newberry

Steve Newberry will step down from his role as executive vice president for industry affairs and strategic planning at the National Association of Broadcasters this spring. 

Newberry is leaving the broadcast advocacy association to serve as CEO for ad sync technology company Quu Inc. He will remain with NAB through March 31.

“While we hate to see him leave, we’re delighted Steve will be with us through the completion of our move to a new headquarters this spring. We’re also pleased that Steve will be fulfilling his entrepreneurial passion with QUU, an auto dashboard initiative that uses technology to improve the listener experience and drive higher radio station revenue,” NAB President/CEO Gordon Smith said in the announcement. 

Smith added, “I will miss Steve’s daily presence at NAB and will always be grateful for his friendship and many contributions to the success of broadcasting.”

Newberry became a station owner at 21 years old and went on to serve as a NAB Radio Board chair and NAB Joint Board chair. He also served as president of the Kentucky Broadcasters Association and chairman of the Authority for Kentucky Educational Television, as well as a national board member for America’s Public Television Station. 

Quu was founded in 2007 by Joe Harb, who also serves as chief innovation officer. According to the announcement, Quu’s “technology enables radio stations to take full control of the RDS/HD in-car stereo display with the ability to monetize through ad augmentation.”

The company is based in Mercer Island, Wash., but Newberry will remain in D.C. He will also continue to serve as chairman for Commonwealth Broadcasting of Glasgow, Ky.

The post NAB EVP Newberry Plans Exit appeared first on Radio World.

The author is CEO, Digital Radio UK.

LONDON — It looks like 2020 is going to be another milestone year for digital radio in the United Kingdom with digital listening expected to increase to over 60% of all radio listening.

Ford Ennals

The growth in digital listening is being driven by the continued expansion of national commercial digital stations, with nine new national digital stations added in the last year, the fitting of DAB in just about all new cars, and the rise in online listening in homes driven by the strong take-up of smart speakers.

EXPANSION

This is also the year when the U.K. government will play a key role working with the radio industry on a Radio and Audio Review supporting the long-term health of the radio sector, announced by the Digital Minister in May 2019, and by determining the future of the U.K.’s national and local commercial radio station analog licenses.

The consultation document on analog license renewal published by the Department for Digital, Culture, Media and Sport on Dec. 23 confirms government support for digital radio and the intent to sustain progress. The U.K. government has been a long-term supporter of digital radio dating back to the 2010 Digital Radio Action Plan and the passage of the Digital Economy Act.

Photo Courtesy of Teracom SE

This support was reiterated in the consultation document that highlights the department’s digital radio strategy and the potential options for analog station license renewals. The consultation has been prompted by the fact that the national and local commercial station analog licenses start to expire in 2022 and as government recognize that there “is little prospect of a radio switchover before the mid-2020s,” they will have to take action to support the continued stability of the commercial radio sector and the continued growth of digital radio.

The document details the progress made post the Digital Radio Action Plan and the set of government initiatives announced at the end of 2013. It highlights the development of a “competitive DAB network used by nearly 66% of adults; the expansion of both national and local DAB coverage; the launch of new services; the fitment of DAB in new cars,” and the growth of digital listening to nearly 57%.

DCMS emphasizes that while a “decisive shift to digital has started, progress is not uniform” and that analog still has an important role to play, accounting for more than 40% of radio listening, and with local stations still having the majority of listening on analog.

NEXT STEPS

Consequently government needs to consider what steps to take with regards to commercial analog station renewals and has proposed three options, which range from letting analog licenses expire to renewing licenses for 5–8 years. It is reluctant to support a “do nothing” approach, as it wants to maintain the stability of commercial radio and the incentives to support the further development of DAB in the U.K.

The consultation also looks forward to the launch of new ultra-local small-scale multiplexes, which media regulator Ofcom is planning to license in the U.K. later in 2020, and the potential prospect of some local commercial stations having the option to satisfy their DAB carriage license obligations through distribution on the new small-scale DAB multiplexes.

The outcome of the DCMS consultation on analog license renewal, which closes on Feb. 21 (responses to analoguelicence@culture.gov.uk) and the DCMS/Industry Radio and Audio Review are unknown at this point and will be shaped by industry and stakeholder response and feedback.

What is clear is that in 2020 the government is working to support the development of the radio sector and the long-term transition to a digital future for U.K. radio.

The post U.K. Government Restates Support for Digital Radio appeared first on Radio World.

Fig. 1: A 1960s phasor with commonpoint controls added.

Our previous article “Find Your Modulation Sweet Spot,” published in the Oct. 9, 2019, issue of Radio World, is still available online, just Google that headline. It sets the stage for a two-part discussion of AM directionals, beginning here.

As you surely know, fewer engineers are qualified to work on AM directional antenna systems today. Younger ones who maintain these marvels of engineering may not be as well versed as their predecessors.

If you are a member of the new breed, my advice is to be careful not to do the wrong thing when tackling a problem. Don’t make adjustments without analyzing a situation first.   

PROBLEMS

If you find antenna monitor phase and ratio readings are off more than a few degrees or a tower radio is off more than 5%, don’t start adjusting the phasor to compensate. Keep your cool. Write down all the phasor dial readings for future reference. Do a complete physical inspection, including eyeballing the inside of the phasor cabinet and antenna coupling networks. Look for broken connections everywhere and on lines running to the towers. Go out and measure the monitor points. You may find they are in spec and that your real problem is in the antenna monitor or other part of the sample system. 

Jumping to the wrong conclusion could result in chasing your tail to fix an antenna problem that you don’t have. 

TOO MANY KNOBS

An engineer maintaining a two-tower AM directional antenna station called me for advice recently. He is one of the engineers I am mentoring. 

A station’s commonpoint impedance (RF input to the phasor) was difficult to adjust because the variable commonpoint resistance coil was at one end of its travel. All had been well a few months before. Today’s solid-state transmitters want to see exactly 50 ohms with near zero reactance, as you know, so setting the commonpoint impedance correctly is very important. 

As it turns out, the phasor has phase and ratio controls for both towers. In this case, it was too many knobs.   

The ratio controls could be tweaked on either tower to keep the station in specs. This led to the commonpoint problem when he used both to get the correct antenna monitor phase and ratio numbers. The phasor’s input matching network was looking at a phasor “buss” impedance that was not according to the original plan. 

PHASOR DESIGNS

It’s important to understand how phasing systems are designed and built. A transmitter feeds RF power into a phasor cabinet, where there is a  three-coil impedance matching network. It feeds RF energy to a point called the “buss.” This is where power is rationed out to phase and ratio controls for each tower. The buss is rarely 50 ohms, and it is normal to have the impedance change a bit as an engineer tweaks phase and ratio controls to maintain FCC licensed specifications. The input matching network normally has enough operating range to compensate for these adjustments.    

Not all phasors have a front panel adjusted ratio control for the reference tower. That is for good reason. The reference tower normally gets more power than the other tower or towers. There is normally no need to adjust power to the reference tower after the station is initially tuned and licensed. It is the standard/reference that the other towers or towers are compared/referenced to. 

I told the engineer to carefully adjust the reference tower ratio control to full, or close to full on, while keeping the other tower ratio and phase correct. Then, don’t touch the reference tower radio control again. Mark it as “don’t adjust.” That solved his commonpoint problem. He then had good resistance and reactance control because the buss impedance was as expected in the design. Also, running both ratio controls down to their lower ends could cause some phasor components to run hot. 

DESIGN EVOLUTION Fig. 2: Commonpoint controls were added to this phasor.

Phasor systems did not typically have front-panel adjustable input matching networks years ago when tube transmitters were the norm. That changed when solid-state transmitters came along. Now input resistance and reactance controls are required to keep reflected power low and transmitters happy. 

Fig. 1 shows a 1967 vintage Gates three-tower phasor. It did not originally have an input matching network that is adjustable from the front panel. I added those knobs to help control the input impedance and transmitter power when switching from 5 kW non-directional day to 5.4 kW directional night. One control is for resistance, which is tweaked to keep the input at the licensed 50 ohms. The other is commonpoint reactance. Fig. 2 is the dial I normally adjusted to get the transmitter to make just the right amount of power at night. 

In this case, the day non-directional antenna coupling unit has clips on fixed coils for adjustments. Once set, it was good to go. The maintenance procedure is to get the transmitter running at the correct power level in the day mode, then switch to night and adjust the night commonpoint reactance control to get the correct directional antenna power. It is that simple.

You’ll also note there are FCC-required operating parameters listed on the front of the phasor and transmitter. They are right where needed most.     

Yes, that is a Gates BC-5H Transmitter next to the phasor. It has been in full service, running 5,000 watts day and 5,400 watts night since 1973. That’s 46 years! This transmitter is on its third high-voltage transformer, third set of AC contactors, fifth set of high-voltage rectifiers and the solid-state audio driver section has been rebuilt four times on site without sending it to a factory for repair. The transmitter lives on, but will likely be replaced by my engineering successor when the next serious failure occurs. Fortunately there is a Collins 5 kW AM to back it up. Both are excellent tube designs. 

ANTENNA EFFICIENCY

Can you assume that all is well when the monitor points are below FCC limits? Not necessarily. You might have serious impedance mismatches and power divider mismatches, as described above. RF power could be turning to heat. 

You can get a readout on antenna efficiency by going to the original proof of performance documentation and making six or more measurements in the major lobe or lobes. The readings should agree, although there are seasonal variations. RF travels better over frozen ground so winter signals are inherently a bit higher. It is not a big deal in the first couple miles from the transmitter. Ground loss changes become more apparent the further out you go, especially at  20 miles and beyond.

OOS, OOM

Just because the phasor doesn’t have active components, that doesn’t mean it should be ignored. Rodents get in sometimes and need to be dealt with. Loose hardware is common on RF contactors because they are usually operated twice a day with plenty of vibration in the process. RF contacts wear and should be replaced before they fail completely. 

HEAT

Get one of those infrared temperature meters and go through the phasor, then antenna coupling networks looking for hot spots. Use it around electrical load centers too. You might be amazed to find hot electrical contracts and wires that are about to fail. Best to take care of the problem before it causes an off-air emergency at a bad time.      

PAPERWORK Fig. 3: Keep good records.

Keep good visit-to-visit documentation on an AM directional (Fig. 3). It is a history of how the system has been behaving. You don’t just log that everything is OK. AM directionals have many parameters to keep track of. That includes phase and ratio readings on each non-reference tower, dial settings on the phasor, transmitter PA readings, commonpoint current and monitor point readings. along with date and time. You’ll likely see seasonal changes on monitor point measurements.

Fig. 4 shows a phasor adjustment crank. Note that normal counter dial reading is labeled nearby for easy reference. This is one more way to prevent an “oops” from becoming a major problem.

You should keep accurate phasor schematic documentation on hand at the transmitter site. Designs and “as built” are often a bit different. I recommend you pencil any changes on the original schematic. Also, mark down the number of active turns on each coil in the system. As you know, silver-plated straps with clips are used to short out unused turns on fixed coils. They are set once and then normally not touched again. It won’t take but an hour to do the documentation and will save a lot of headaches in the future. Lightning can blow up a coil or capacitor beyond recognition. Having parts values and settings on a schematic diagram can be a life saver.

Fig. 4: Mark your normal dial settings for easy reference.

A nearby station was visited by vandals one night. Somehow they got into the antenna coupling networks and pulled clips off the fixed coils. No other damage, just mischief. It took the engineer only an hour to put the coil clips back in the right spots, plus do a little tweaking, to get the antenna system working properly again. Imagine trying to start from scratch to get the system operational without that knowledge. Ouch! 

By the way, spare parts and equipment manuals belong where the equipment is, not back at the studio. That includes books and programming information for remote control systems. 

The best is yet to come. Stay tuned for an upcoming issue, where you’ll find a real-life story about a 197-foot tower that came down in the parking lot at a directional AM station.

Comment on this or any article. Write to radioworld@futurenet.com.

Mark Persons, WØMH, built four new AM directional systems, from the ground up, using only schematic diagrams and parts. He is an SBE Certified Professional Broadcast Engineer and was named SBE Engineer of the Year in 2018. Mark is now retired after more than 40 years in business. His website is www.mwpersons.com.

The post Best Practices for AM Directional Systems appeared first on Radio World.

Breadboarding the circuit.

Ever get a song stuck in your head that you don’t necessarily mind being there? My latest benign earworm happens to be “Frankenstein” by the Edgar Winter Group; probably due to what’s been going on at my workbench lately. 

In our first installment, we walked through the audio circuit of “THAT Thing,” a mic preamp design built around THAT Corp. ICs.

POWER SUPPLY Gathering the parts.

In this “episode,” we start with the power supply. It’s a fairly common, straightforward design. The audio chips require bipolar DC power at a maximum of ±20 Volts. A +48VDC rail is needed for phantom power.

We start with an AC transformer that takes 120VAC from the wall and steps it down to 48VAC with a center tap, 24VAC for each side of the bipolar supply. 

Following rectification through BR1, we get two pulsing DC rails. From there, the pulsing DC goes through a set of electrolytic capacitors, C101-C104, to level out the bumps. Then, the actual regulation occurs with U101 and U102, positive and negative 18VDC regulators. Next, each rail gets another dose of filtering through C105-108 to take out any remaining ripples. 

Etched PCBs

C109 and C110, a pair of polyester capacitors, remove any RFI sneaking in through the power rails. D101 and D102 are there to ensure that the positive and negative rails stay that way. Any negative voltage appearing on the positive rail shunts to ground and vice versa. D103 and D104 protect the regulator ICs by ensuring that the output voltage never exceeds the input.

Finally, LEDs 101 and 102 in combination with their respective current limiting resistors, R104 and R105, indicate the presence of actual voltage on each rail to show that the supply is functioning correctly, a good aid in troubleshooting.

Power supply board

For the phantom power section, the entire 48VAC secondary winding of the transformer is used. After filtering and rectification through C111, C112 and BR2, we’re left with about 70VDC. Additional RF and ripple filtering is accomplished by C113 and C114. Regulation is performed by U103, a TL783 adjustable regulator. R101 and R102 determine the output voltage of the IC, and C116 filters out any output noise. 

Additional stability is provided by C115 and R103. 48VDC phantom power must be ruler flat to prevent any noise being introduced at the mic inputs, where the audio circuit is the most sensitive.

BREADBOARDING Curt etches the PCBs.

At this stage, I began breadboarding the circuit to test a few component choices and layout. Here’s where I found out firsthand the importance of filter caps C7-C10. 

Without those critical components in place, the circuit made a nice white noise generator, especially in the unprotected environment of the workbench! 

I also found that I had pretty wide latitude in my choice of C6, the high-pass filter capacitor. I settled on 1 µF because it offered, to my ears, the best balance between getting rid of rumble and being able to go high enough for extreme roll-off, if necessary. Anything — even as high as 47 µF — will work, as long as the gain is high enough.

Once I was through experimenting with circuit topology, I imported my schematic into ExpressPCB and worked on the circuit boards. In order to maximize flexibility, and to be able to possibly repurpose the design, I opted to keep the power supply and each audio channel on separate boards. 

Once I had all the correct parts together and etched the boards, I was able to bench test the finished power supply and one completed channel. Surprisingly, the only issue was that I had wired the phantom power LED on the audio board backwards! An easy fix for a change! It was only mounted directly to the PCB temporarily, anyway. Its intended location is the front panel with the other controls.

Testing the preamp assembly with a microphone. Testing the power supply assembly.

Speaking of which, while thinking about how I was going to house this creation, I came across an abandoned 1RU chassis that was just right. I stripped out the guts and replaced the front panel with a 1RU blank that could be punched and drilled specifically for this project. I put the input XLR jacks on the front panel, taking a cue from a previously built kit in my studio. The output jacks are 1/4-inch TRS for easy interface with my 1/4-inch TRS patch bay.

CONSIDERING IMPROVEMENTS

Never one to leave anything alone if I think there’s room for “improvement,” I started thinking of potential modifications to this design. Looking at some of the design notes from THAT Corp., and discussing this project with other DIYers, I settled on two relatively simple things to try. 

The faceplate after drilling.

First up, an alternative to the gain pot is a rotary switch with several positions, each position providing a different fixed gain. The advantage here is better component matching between channels, which translates to more accurately repeatable settings between channels. High quality reverse log pots of this resistance value can be hard to find at reasonable prices. Besides, more precise adjustments can be made further down the signal chain, or in the mixing/editing stage.

The other modification I looked into was replacing the initial input stage with a transformer. While I suggested in the first installment that transformers are expensive compared to capacitive coupling stages, this is a case where the custom build aspect and its benefits perhaps outweigh the added cost. 

True, the concept behind chips like the THAT1512 is to obviate the need for a transformer, which is perfectly valid, if one is building numerous preamp stages or a 16-channel mixer. On the other hand, a transformer provides way better common mode rejection, kills RFI, eliminates hum loops and also mitigates against any phantom power faults possibly cooking the ICs. Placing a transformer on the input eliminates several other components: C3, C4, R3, R4, R5, R6, R7 and D1-D4 all go away.

VERSION 2 The version 2 preamp assembly with transformer installed.

In version 2 of THAT Thing, I went ahead with the input transformer and the rotary gain switch with six positions.

The transformer I used is OEP’s A262-A3E, which I borrowed from a tube mic preamp in my rack. It’s much less expensive than a Jensen or a Lundahl and, hey, it’s what I had! Good thing it was cheap because while desoldering it from the other preamp’s PCB, I somehow managed to fry the secondary winding. Oops! It had a good run. R.I.P.

Once the replacement arrived from www.Newark.com, I set about testing it within the circuit. It’s important to consider that the input transformer adds some gain of its own to the circuit, about 16 dB. It took some experimentation to settle on the gain levels for the rotary switch, but I ended up with a range between 19 dB and 50 dB.

Looking inside.

So, how did it sound? Super clean, and the transformer definitely adds some character. Either version works very well with just about every mic I tested, from a Shure SM58 to an MXL ribbo n mic, to an Audio Technica AT4040. Two to four channels of “THAT Thing” would nicely compliment a Mackie 1202 or 1402 mixer’s line inputs, should you find yourself running short of mic inputs. Or connect it straight to a PC’s sound card input.

TRY IT YOURSELF Inside closeup

For anyone willing to take a stab at this, I’m happy to provide the schematics, PCB layouts and other notes. 

“THAT” Thing in the rack.

You’ll need to download ExpressPCBPlus (free at www.expresspcb.com) to read and print them out. All parts except the input transformers are available from Mouser Electronics or most other suppliers. The transformers, as mentioned earlier, can be ordered from Newark.com.

Happy soldering!

Curt Yengst, CSRE, is a contributor to Radio World and an assistant engineer with WAWZ(FM) in Zarephath, N.J.

Email us with your own DIY ideas at radioworld@futurenet.com.

The post Let’s Finish Our Solid-State Mic Preamp Project  appeared first on Radio World.

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