Fixing the SANGEAN PR-D5's low headphone volume

The Sangean PR-D5 is a very good AM-FM Stereo radio.

It looks like a mini-boombox, and is fairly loud through its high quality 2.5 inch speakers.

The Sangean PR-D5, an excellent Long Distance AM and FM stereo portable, with an AUX IN jack so you can listen to online, streamed radio stations and music also.

The PR-D5 radio is easy to use. It has five memories on AM and five memories on FM, which are easy to program: you just hold a memory button for about a second and it stores the station. It has a clock, and has an AUX IN jack (on the left side of the radio) which makes it even more useful.

There is a mono / stereo switch for FM, if needed for clarity (sometimes FM stations from the next metro come in clearer in mono than stereo, where you sometimes hear more flutter). FM, naturally, is stereo through the speakers and through the stereo headphone jack on the left side of the radio. Through its speakers FM stereo sounds great. Just like a small boombox.

The PR-D5 also receives RDS on FM, which works fairly well (RDS is a data service on FM -- the radio's LCD readout will scroll a station's call letters, ID, or a song title while you're listening to the station).

It will tune the AM broadcast band (known as Medium Wave, Mellombølge or Mellanvåg in parts of Europe) in 10 khz (the Americas) or 9 khz steps (Europe and the rest of the world), and it is easy to re-program the khz step if needed. The radio comes with a noise-free AC adapter.

A set of good heavy duty batteries (6 C Cells) can last a couple weeks or more in the PR-D5, and will last a bit longer than that if you use headphones.

I got my PR-D5 late last year because I kept reading about it being a good Long Distance AM radio, and I wanted to see how it worked with Long Distance AM band listening. I was also interested because it seemed to resemble a small boombox -- which in a sense, it actually is.

And I have a thing for boomboxes.

Naturally, the PR-D5 has stereo FM through its two speakers, and I figured I could run my tablet into the AUX IN and use it to play music and online radio that way.

Just like a boombox!

As soon as I got into my car after buying the radio I took it out of the box and put the batteries in, and fired it up. I switched to the AM broadcast band and immediately heard 1500 KSTP, which is a fairly long haul -- Minneapolis and St. Paul, Minnesota are over a thousand miles from Seattle (about 1400 air miles). And here I was, hearing ESPN from Minnesota in my car. I was very impressed.

TWO PR-D5 VERSIONS

The PR-D5 has had two variants so far: the older version of the PR-D5 apparently had a standard analog IF chip and PLL tuning. In fact, on the front of my PR-D5 it says "PLL Synthesized Receiver". The PR-D5 was apparently re-designed with a SiLabs DSP IF chip some time in late 2012 (according to the schematic they kindly sent me). So, technically, my PR-D5 is a "PR-D5B" (as it says on the schematic).

The newer version of the PR-D5, which I have, has a SiLabs digital IF chip (Si4731), and the AF power chip (UTC2025 / UTC20205) is possibly a different one, also. The digital chip may or may not be an improvement. The SiLabs digital radio chips can 'tune' the radio automatically to the antenna and receiving conditions, which makes the radio very sensitive to signals. The SiLabs series of radio chips have low noise amplifiers, digital to analog converters, and then the tuning, filtering, and amplification of the radio signals are done through a software program inside the chip.

The newer PR-D5 version also has the main PCB installed in the radio differently from the first production runs, and also has twin coils on the 200 mm loopstick antenna, where the older version just had one coil (twin coils can sometimes add to the sensitivity of an AM radio, make it pull in more stations).

A COUPLE SMALL DRAWBACKS...

As impressed as I am with the PR-D5, it has two drawbacks, one minor, and one not so minor -- if you are a Long Distance AM band enthusiast.

The first drawback is ironically also one of the PR-D5's AM band strengths: the 4 khz selectivity, which is great for Long Distance listening, but which also cuts down on some of the high frequency audio response.

(To non-radio nuts, 'selectivity' -- or 'bandwidth' -- is the capability of a radio to separate two stations which are very close to each other. If a radio has wide 'selectivity', a strong local station can overpower a much weaker station right next to it -- like a station in a distant city. With a radio with wide bandwidth, the local station will drown out the weaker station right next to it. With a radio that has narrow bandwidth -- like the PR-D5 -- the weaker, more distant station will more easily be heard.)

This radio has probably the best, narrow selectivity of any AM Long Distance portable I own.

The Sangean PR-D5 AM-FM portable radio with the back off, showing the 200 mm twin coil loopstick antenna (the long grey cylinder at the top of the green PCB board). The large size loopstick antenna pulls in lots and lots of AM band radio signals. The two coils of wire wrapped around the loopstick antenna help boost signals also. Most AM radios have just one coil on the loopstick antenna.

USE A GOOD SET OF FLAT-RESPONSE HEADPHONES

However, the excellent 4 kilohertz selectivity on the AM band gives the PR-D5 a midrangy, and slightly boomy sound, especially through some headphones. The narrow 4 Khz bandwidth cuts some of the treble on the AM band.


Some PR-D5 owners have complained about this.

Through the speakers, the sound is OK -- but through headphones (and many DXers, like myself, use headphones) the boominess of the PR-D5's audio can cover some of the highs. This is why you want to choose the correct set of headphones.

I've found that you can compensate somewhat for the the midrange and boominess (from the radio's apparent loudness circuit), by using a set of headphones with very flat audio characteristics. Headphones made for extra bass just won't sound great on AM plugged in to a PR-D5.

I have a set of Sony headphones (that came with my Sony SRF-59 headset radio) that sound great on all my radios except the PR-D5. When plugged in to the PR-D5, they add to the bass, and it makes IDing stations with the PR-D5 a challenge. They make the PR-D5 sound muddy.

So, with my PR-D5, I use a another set of older Radio Shack headphones (I don't remember the model number) that have a flatter response -- they have really good clarity, but they don't emphasise the bass like some headphones do. When I use the Radio Shack headphones, the PR-D5 doesn't sound muddy, and the highs come through better.

When I use those headphones, I find it much easier to DX with the PR-D5 on the AM band.

I have used cheap headphones from dollar stores that sound good with the PR-D5 also. The ones I got have a very flat response. Some cheaper headsets can have very flat audio response, and can sound really good with this radio.

SLOWER AGC THAN MANY OTHER RADIOS

One feature that may or may not be a 'drawback' is the PR-D5's slower AGC. AGC is the ability of the radio to keep the volume at a relatively constant level: when a signal drops in strength, AGC will boost it a bit to keep it from dropping out. Most portable MW and SW radios have fairly "tight" or "hot" AGC, some of them have AGC that is so tight it pumps. Not so with the PR-D5. The AGC on this radio is more natural, but sometimes when a signal fades you will definitely hear a momentary volume drop before it comes back up to full (this applies to newer PR-D5's with the SiLabs DSP chip. The older models with analog chips may not have AGC this slow).

It seems to be part of the design of the DSP section of the SiLabs IF chip -- possibly because the SiLabs chip 'sees' background static as 'noise', which it is attempting to 'silence'. However, the PR-D5 has no soft muting -- where the audio drops substantially when the signal drops a bit, almost sounding like the signal is disappearing -- which can be an annoyance to a MW DXer. Fortunately, there are no such extreme signal dropouts on low signals with the PR-D5.

The slower than usual AGC may be a contributor to the PR-D5's tendency to allow pulse noise through more than other radios. Pulse noise, like AC hash, shows up a bit more on a PR-D5 than some other radios, like the Sony ICF-38 for example, which softens it a bit.

LOW HEADPHONE VOLUME ON NEARLY EMPTY MW/AM CHANNELS

One other drawback is the one I deal with here in this blog post: Low Headphone Volume on nearly empty AM band channels.

The PR-D5's stereo headphone jack has drop-down resistors that reduce the volume so much that Long Distance AM stations can be virtually inaudible on some channels, mainly in the 'Top Band' or 'X-band' between 1600 and 1700 khz, where there are less stations than usual, and much weaker overall signal strengths (Although some radios' performance drops off above 1600, that is not the case with the PR-D5 -- the radio performs the same across the band).

This is frustrating, because the radio's audio chip is capable of putting out almost a watt. Yet on some nearly empty channels you will hear nothing -- even the static is barely audible.

One night, soon after buying this radio, I found myself tuning to 1650 Khz and cranking the volume all the way to the maximum to try to hear a very weak station from far away, a NOAA Weather station from the Oregon Coast. I could barely even hear the static on an otherwise empty channel. Bad deal.

I tried removing the drop-down resistors on the radio's stereo headphone jack. Woops. :-(

I nearly ruined the headphone jack trying to do that -- the surface mount parts were impossible to bridge without special techniques. In my ineptness, I wiped out the left headphone channel. Obviously -- I am not good with messing with surface mount wiring. :-(

The open backed Sangean PR-D5 with the new mono headphone jack wired in parallel with the radio's right speaker. You can see the jack in the middle of the back of the radio, with two wires going to the speaker connections of one of the speakers. I used a mono jack because a) I had one, b) it would be much, much easier to wire it, and c) the AM radio band broadcasts in mono anyway. If you look closely you can see silicone glue, which helps keep the jack in place. It was a tight fit into the hole I drilled, but I used the glue just to keep it from ever moving.

A MONO JACK IN THE BACK OF THE RADIO WORKED BETTER

So I did something better (at least for me): I wired a mono headphone jack in parallel with one of the speakers. That way, through a very simple wiring procedure that only took 15 minutes, I was bypassing all the drop-down resistors, and could take advantage of the radio's full volume if needed (well, half volume -- it's a loud radio!)

The mono jack worked great because a) it was simple, and b) AM radio is mono, anyway.

After doing this mod, all of a sudden my headphones were usable for Long Distance listening ('DXing') the mostly empty channels like 1650 and 1660, just as in all my other radios.

DOING THIS SIMPLE MODIFICATION

The first step, naturally, if you want to add a mono headphone jack is to open the radio.

First, remove the two tiny screws that lie just under the top of the back of the radio. They are embedded in the silverish part of the radio just behind the whip antenna. When you have taken them out, throw them away, or toss them into your junk parts box, because they are so cheap the heads will probably strip if you ever have to take them out again. Trust me.

There are five main screws that hold the PR-D5's case together. Four of these screws are easily seen in the back of the radio case -- the fifth one is in the battery compartment. These screws are decent quality plastic screws and are relatively easy to take out. Once the five main screws are out, the PR-D5's back comes off easily -- this radio is designed quite well, like many old Japanese boomboxes were -- built for easy repair if needed. No prying, wiggling, etc. needed.

Once you have the back off, drill a small hole in the back of the case, just above the right speaker, using a drill bit, and you can use a circular file to make it just big enough for your mono headphone jack if the fit is too tight. Press the headphone jack through the hole, and wire a wire to the jack from each of the right channel speaker's terminals (I used the right speaker because there is more room there).

Use a little silicone glue to secure the headphone jack to the back of the radio, by dribbling a small bit of it around the outside of the jack on the radio back's inside surface. Leave the back off of the radio for a few hours, or overnight, to let the glue set.

Reassemble the radio and you're ready to 'DX' (do some Long Distance listening) with headphones.

The AF chip (a UTC2025) in the new PR-D5's has internal thermal protection, according to its datasheet. So you can wire a mono headphone jack into the audio chain and not have to worry about the AF chip frying if somehow it were able to get shorted. And chances of shorting a headphone jack by just using your headphones is pretty minimal, anyway.
The only caveat using a headphone jack in line with the speakers is you have access to about 800 MW of audio -- so CAUTION! Make sure you don't turn your volume all the way up when using headphones! You won't need that much, anyway!

Always be careful when using headphones on a radio! You've only get one set of ears!

I never have to turn my radio's volume control higher than 1/3rd or so while Long Distance listening.

The back of my PR-D5 after modification. The new mono headphone jack I added can be seen in the middle left part of the radio, just above the battery compartment door. It's unobtrusive, and works well.

UN-NEEDED FOR FM RADIO LISTENING

The modification I just described only really helps with the AM band. FM is loud enough through headphones that no modification is needed. FM stereo sounds rich through this radio -- the fact it is a mini-boombox helps, also. It's loud enough to fill a small room with high quality sound, and loud enough to listen to sports outside while gardening, etc.

THE PR-D5 IS A GREAT AM BAND LONG DISTANCE RADIO

The PR-D5 is probably my best overall AM Long Distance radio. It will hear practically everything there is to hear on the band, even without an external loop.

I still use my other MW Long Distance radios, though, for fidelity, convenience, or just for the heck of it.

USING A LOOP WITH THE PR-D5

Using an external loop with a PR-D5 (at least the newer PR-D5's with the digital IF chips) can be tricky. Some guys have complained about the PR-D5's 'soft muting' making it difficult to use with a loop while Long Distance listening. I haven't had much problem with any muting. But there's a trick to using an external loop with the PR-D5, because of the way the radio's DSP IF chip 'tunes' to the external loop.

One of the chips (either the digital IF chip, or the 4066 'Quad switch' chip -- a gating chip in the audio chain apparently used for noise reduction) seems to mute the radio during noise voltage spikes, or quick volume peaks. When the noise spike is done, it goes back to normal. And, from what I've read, SiLab digital IF chips like the one in the newer PR-D5's also apparently 'tune' to the antenna, peaking signals as you tune up and down the AM band. So maybe when you use an external loop, the digital IF chip is trying to 'tune' to it as well, slowing the process.

Either way, what I've found is with a PR-D5 you have to keep the external loop farther from the radio than you do with other AM Long Distance radios.

With a PR-D5, you keep the external loop away from the radio by about 5-6 inches (120 mm to 150 mm), and you can peak the signals with the loop OK. You have to fine tune the loop a bit slower, though, to hear the signal peak through the speakers or headphones.

I've found an external loop can boost the signals on a Long Distance AM signal maybe a DB or two.

But you've got to keep the loop about 5-6 inches (120 mm to 150 mm or so) away. Any closer, you don't get any benefit, and peaking the signal with the loop is nearly impossible.

EDIT: YOU CAN ALSO USE A LOOP RIGHT IN FRONT OF THE SPEAKER.

A couple years after writing this article I discovered -- by accident -- that if I placed my Select-A-Tenna right in front of either speaker, the PR-D5 will boost very well. It is as strong as it is 5-6 inches off the side of the radio. I don't know why I didn't try this earlier. Behind each speaker is where the twin coils are located (as you can see in the above photographs), so this makes sense.

So if you have a PR-D5, and need a boost in your DX signals, try placing your external loop in front of the left or right speaker on the radio. Sometimes this works better than having the loop to either side -- and other times, having the loop to either side of the radio is better. But at least there is another option.

The Sangean PR-D5 with a Kindle plugged into the AUX IN jack on the left side of the radio. It has plenty of volume for listening to online music.

ONLINE RADIO LISTENING USING A TABLET AND THE AUX-IN JACK

I frequently use my PR-D5 to listen to Foreign and domestic radio stations by plugging a cord between the headphone jack of my Kindle Tablet and the PR-D5's AUX IN jack.

The PR-D5 has plenty of volume, and the AUX IN jack is stereo, so you have stereo sound. The radio is loud enough to use outside on the patio, or in a room. 

Foreign stations I usually listen to are the Norwegian NRK stations (P3, P1, NRK Norsk Folkemusikk, and sometimes non-NRK stations NRJ and Radio Tromsø) and a couple stations from Sweden (Sveriges Radio P1 and P2). There are Saami language programs on both Sveriges Radio and NRK that I also listen to. The Saami programs are very interesting, because they play a lot of tracks made by popular and rising Lappland musicians. I listen to these and other stations using TuneIn, as well as directly off of the stations' websites.

SANGEAN PR-D15

There is a newer model of Sangean radio that looks like the PR-D5 that has a few extra features. This radio is called the PR-D15. It has a SiLabs digital IF chip in it. My guess is that when Sangean started making the PR-D15, they changed the circuits to the PR-D5 at the same time, saving money at the factory (both radios are basically in the same case).

For PR-D15 owners, the external loop trick I mentioned here may also work.

It's also possible the mono headphone modification would work, too, if you have a PR-D15 and find the headphone volume is too low on some AM band channels. But -- never having used a PR-D15 or seen the inside of one, I have no idea whether such an addition would be necessary.

Finally, remember that if you try to do any modifications, or take apart the radio, you are undoubtedly voiding your radio's warranty.

Ball Cat says happy Distance Listening!

Well, Happy Long Distance AM band listening to any 'DXers' out there -- and, for those of you non-radionuts out there who suffered through this post, hope you are had a great Summer, and are having a great Fall also! Halloween is getting closer here in the U.S. (and I know there are some other countries that celebrate Halloween also).

Have a safe and happy Fall!

CC

RE: POWER BUTTON ISSUE

Addendum, 8-12-2017: After a couple years of use, I've noticed an issue with my PR-D5, albeit a minor one: when turning it on, sometimes the radio wants to go to the 'Alarm' setting function. Why this is, I don't know. The radio still turns on as usual, though, and otherwise operates perfectly. I think it may be a software glitch -- the radio thinking the power button is the 'alarm' button. Or it could be a small static electricity caused glitch. Either way, the power button still feels solid, as do all the other buttons on the radio. I still use the radio every night while writing, sometimes listening to DX or regional stations' programs through either the speakers or headphones. I still think the PR-D5 is a good value for the money.

Addendum, 8-24-2017:
After changing the batteries to do some Solar Eclipse MW DXing (my power meter was down to one bar for several months when the power button thing started happening) the power button glitch disappeared. Fingers crossed. It's possible the low batteries had something to do with the 'glitching' of the power button. The glitching was happening even when on AC power, but the batteries may still present themselves when the radio is plugged in... Not having a schematic to this radio, I don't know. All I know is that the glitching is gone. Works good enough for me. :-)

Addendum, 9-9-2017:
My power button still is a little bit funky. Sometimes it still goes to the "ALARM" function, then when I press it again it goes to the radio. Sometimes when pressing it, it does nothing (more rare). Then I press it again, and it works fine a bunch of times. I think it's the shape of the power button -- it has a concave front -- and also because the button has had plenty of use. I haven't had any issues with the PR-D5 not turning on, just this glitch. I've had no issues whatsoever with the other, rounder buttons on the front of the radio -- some of which I've used almost as much, and even more. The glitch doesn't happen all the time, so I don't think the button is failing, or it would probably happen all the time. I may end up installing a rounder button, eventually -- one with a more positive feel -- like the rest of the buttons on the front of the radio. Or I will super-glue a round plastic surface to the front of the power button for more positive action.

Also: I've noticed that a Select-A-Tenna works very well right in the front of the radio. You don't have to place it 5-6 inches away from either side. I just never thought of trying the loop in the front of the radio before. The sweet spot seems to be in front of either speaker -- probably because that's where the loopstick's twin coils are located. (I've added this information inside my article). For some readers, placing an external loop may be easier off the front of the radio than a few inches to either side.

Addendum 10-20-2017:
Spraying some tuner cleaner down the sides of the power button seems to reduce the issue. Like I've said before, the power button never has NOT worked. I use the PR-D5 every night and it always works well. It's just that the power button is shaped poorly, and over time it probably needs tuner cleaner or exercising. Note to Sangean: Concave front power buttons aren't the best.  :-)

Addendum 10-23-2017

RE-SET / RE-BOOT THE RADIO!

I did a little research online. There isn't much info on Sangean PR-D5 power button issues, but one man said when he hits the 'Step/Band' button, sometimes it acts like he hit a memory location button, and switches the radio to one of the 5 stations in the radio's memory. With me, sometimes when I hit the Power button it acts like I hit the 'alarm' button.

This tells me that it is probably not a physical problem, because the buttons are actually working. It may be a firmware/software problem. The 'reader' program in the brain chip, that scans the buttons, may be seeing the wrong button pressed now and then.

I RE-SET my PR-D5, by unplugging the AC supply, and taking out one battery for about 20-30 seconds, and the power button worked instantly after I powered the radio back up, where before there was a bit of a lag. When you re-set the PR-D5, you have to reset the clock, which isn't that big a deal.

I am hoping this may be the solution. If all it takes is re-setting, that's easier than taking the back off and troubleshooting the button board -- but I don't think the issue is the button board. I've found a photo of a clear PR-D5 -- it looks like the buttons are encased in a board attached to the front of the radio. Fairly securely. The buttons on my radio don't feel loose at all. They still have a firm feel to them. This leads me to think that the issue is possibly firmware, and like with a computer, sometimes firmware needs a re-set. 

I guess I'll have to wait and see. :-) If RE-SETTING the radio is the solution, I will put up a short blog post on here about it to make it easier for other PR-D5 owners to find it.

10-24-2017:
So far, the power button works instantly, and has all day, on battery or on AC adaptor. Fingers still crossed.

Addendum, 11-2-2017:
The power button fix (by re-setting the radio) is still working. The power button works instantly like it is supposed to.
I have added a blog post about re-setting the radio for those interested:
https://interrocknation.blogspot.com/2017/10/how-to-quickly-fix-sangean-pr-d5-power.html

Addendum, 11-16-2017:
The re-boot/re-set fix is still working. Almost a month now. Definitely the reset cleared the issue. :-)

Addendum, 11-19-2017:
I added some info into this article, on the changover from PLL to DSP chipped versions; and added a sentence to this blog entry about the slower than standard AGC making the PR-D5 a little more susceptible to pulse noise. My reboot fix is also still working.