Stereo Aficionados

Posted on July 25, 2015 by jwk

D1MFitR

Posted in Audio, Commentary, Stereo | Tagged , , , , , | 1 Comment

Old rocker complains about new technology

Posted on July 15, 2015 by jwk

According to Rolling Stone, Neil Young is pulling his catalog from all streaming music services over complaints about the sound quality. I don’t see this impacting me personally since I don’t listen to him and indeed can’t even name a single one of his albums or tracks, but apparently he’s still considered a noteworthy figure. At least enough that when he makes noise, Rolling Stone will still listen.

I’m not sure they should, though, when he’s mostly just making questionable noise:

“It’s about sound quality. I don’t need my music to be devalued by the worst quality in the history of broadcasting or any other form of distribution. I don’t feel right allowing this to be sold to my fans. It’s bad for my music.”

That’s a shocking generalization. Being born in 1945, he was around, alive and listening to music before the invention of even FM broadcasting, which arguably was the first time “high fidelity” audio was broadcast anywhere. Does Mr.  Young really think even today’s best-capable AM, with frequency response limited to only 10.2 kHz, sounds better than a Pandora stream?

He might, actually. Age-related hearing loss is a real thing, after all.

“AM radio kicked streaming’s ass. Analog cassettes and 8 tracks also kicked streaming’s ass, and absolutely rocked compared to streaming,”

Neil is simply wrong, purely factually incorrect, about AM radio. And the AM radio of his youth was even worse than the AM radio of today. Let’s see about some of those other formats.

Analog cassettes? Nominally better than AM radio, anyway. Cassette tape quality varies greatly based on the recording substrate, degrades with usage of the tape, and depends heavily the quality of the tape player in addition to the tapes themselves. While a top of the line tape deck like a Nakamachi could theoretically reproduce 16 Hz – 22 kHz, most consumer-grade mid-fi decks would reproduce about 25 Hz – 16.5 kHz. We’re getting close to high fidelity, but still a long ways to go! Not to mention, while 16-bit digital formats offer a theoretical SNR of 98 dB, the physical process of recording/playback on a compact cassette limits the effective maximum possible SNR to 50 or 60 dB. 8-Tracks would have fared about the same.

The one possible area where Young isn’t full of it, relates to compression artifact noise. The free streaming tier of Pandora Mobile, for instance, is nearly un-listenable garbage. It’s at an awfully low bitrate and compression artifacts are very apparent at those low bitrates. Moving up to the desktop, though, and you jump up to 128/192 kbps AAC+ streams which are very near to CD quality. For most people listening to music, even on the free tier of these streaming services, the limiting factor in sound quality will be the listener’s speakers and amplifier – not the quality of the source material. Moving up to the paid tiers which offer even higher quality, and you can achieve true CD-quality streaming. And heck, not that I support anyone giving Jay-Z any money, but his streaming service Tidal offers truely lossless audio streams for the ultimate in audio quality.

Most of the complaints against the sound quality of digital music date back to the early days of the technology. First- and second-generation MP3 encoders weren’t very good, and the MP3 format itself relies on some questionable psychoacoustic assumptions when performing the encoding. Modern audio compression codecs, especially those optimized for streaming, do a very good job at capturing and reproducing their source material very faithfully and in excellent quality across the overwhelming majority of use cases.

Bottom line being, from nearly every objective measure, streaming music services offer plenty-good audio quality and in many if not most cases, a true high fidelity listening experience.

Mr. Young may legitimately believe himself, that AM radio offers superior quality to Internet streaming radio. But I suspect that claim is grounded more in nostalgia than in reality.

When the quality is back, I’ll give it another look. Never say never.

I don’t think the quality ever went away. Sure, it’s not the same as listening to your own studio masters on speakers and amplifiers which cost as much as a house, but it’s not bad by any sense of the word.

What do you think?

Posted in Audio, Commentary, Ideas, Music | Tagged , , , , , , , , , , , , | 8 Comments

1950s Motorola Modded Standalone Tube Amplifier Measurements

Posted on July 6, 2015 by jwk

I had an unusual project through the shop recently. It’s a Magnavox tube amp from the late 1950s. The owner brought it in reporting he’d purchased the amplifier, pulled from a damaged console stereo and modified to be a standalone stereo tube amp, from a Craigslist posting. After a scare involving un-inspected vintage equipment giving up the magic smoke unexpectedly, the amp came in for an inspection which turned up a few recommendations.

It’s a simple amplifier with a 12AX7 and pair of 6V6s per channel, using a 5U4GB rectifier tube. The chassis was thoroughly cleaned and polished, unnecessary parts stripped, and various jacks and controls were added to make it into a standalone product.

Underneath, the wiring was nice and orderly. The previous technician was a hobbyist who’d done good research, and the work which was completed was of surprisingly good quality. My only suggestion would have been to use shielded wire runs to the RCA jacks, but it proved not to be a problem in this implementation. The electrolytic filter, coupling and bypass capacitors (the 4-section can and two components below the chassis) were original, though, and that could cause a problem down the line.

The electrolytic capacitors in this amplifier hadn’t been replaced, but the paper ones had. In some later ’50s gear, it’s entirely possible the original filter capacitor can was still working, but it’s on borrowed time and should be replaced for sure. I soldered a terminal strip with a grounded lug to one of the can’s ground lugs to make a solid starting point for the can rebuild.

Attaching the filter capacitors, associated wiring, and dropping resistor to the terminal strip:

There were also two electrolytic coupling capacitors, 20 uF 25V capacitors, replaced with Nichicon Fine Gold 22 uF 63V electrolytics:

As well as a bypass capacitor, attached between the balance pot and ground. The old lugs for the replaced electrolytic can were cut off to ensure no connections could be made to them in the future.

While inside, I also touched up the solder joints for the new neon power lamp, which had broken free. Then, it was on to testing! This amplifier’s specifications are unknown, so it’s time to measure them.

Using the Keithley 2015 THD Multimeter, HP 3585A Spectrum Analyzer, and Sencore PA81 Stereo Power Amplifier Analyzer I made measurements of the amplifier’s characteristics. The channels are slightly different power. Measurable but not really audible. The amplifier measures about 10W per channel at 1.0V sensitivity. Output was highest into an 8 Ohm load, which means that’s the correct output impedance for the transformers.

At maximum output, volume control full clockwise, 1.0V input signal into 8 Ohms the amplifier produced 1.197% THD. While that sounds high, it’s not bad at all for the time and implementation. In addition, tube harmonic distortion is often considered pleasant to listen to, as opposed to the distortion generated by solid-state devices.

At normal listening volume of 5W, it was about 0.621% THD.

At 1W of output power, the amplifier produced 0.208% THD and at 0.5W it produced 0.129% THD. Driving very high efficiency speakers, this would be a low distortion hi-fi amplifier by standards even well into the ’70s or ’80s. The frequency response was “flat” +/- 3 dB from 70 Hz – 20 kHz.

Bass response in this case is almost certainly being limited by the amount of iron in the output transformer; with less iron, the core will saturate more easily and be able to transfer a smaller amount of lower frequencies. The coupling capacitors are sufficient value not to impact the frequency response in this case.

Overall, with a rebuilt power supply and new coupling and bypass electrolytic capacitors, this amplifier has been overhauled and should be reliable for a long time to come. It’s a little different looking, but it works well and sounds good – and that’s what matters!

Posted in Audio, DIY, Electronics, Hi-Fi, Projects, Radios and Tubes, Vintage | Tagged , , | 3 Comments

Eric Engineering Model 357 High-Fidelity FM Tuner

Posted on June 23, 2015 by jwk

I recently got to work on something quite unusaul, the Eric Engineering model 357 hi-fidelity tuner. Built by obscure outfit Eric Engineering in Santa Monica, CA in 1961, there’s relatively little known about these units. It’s a fairly simple ratio-detector mono FM tuner with a dual mono audio output but no MPX output. The no-frills control panel offers only an on-off switch and tuning knob connected to the dial pointer.

No schematics are available for these units, but fortunately they’re pretty straightforward, and this one came to the shop in good shape. It wasn’t receiving anything, though – time to pull it apart.

It uses five tubes, 12AV7, ECC85, ECC85, 6AU6, 6AL5, and a selenium rectifier.

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I replaced the selenium rectifier with a terminal strip and silicon diode, and relocated the three capacitors and their associated dropping resistors to the new strip. The power supply used a 3-stage RC Pi filter with B+ being finally taken off the third filter cap.

I also replaced the Bumblebee line-to-ground capacitor with an X1Y2-rated safety cap, the ratio detector electrolytic (which in this case was most likely responsible for the lack of audio output), the output capacitor, and both dial lamps:

Finally, it was time for an alignment. The Sencore SG80 AM/FM Stereo Analyzer comes in handy for that. This design used both a ratio detector, and I believe lacked a limiter on the FM, so it’s a bit more sensitive to variations in the received signal strength than some other designs, and a ratio detector offers lower fidelity than a full discriminator, so an alignment was a must to get the most out of the tuner.

The best way to align an FM receiver like this is through distortion analysis which shows precisely how well the radio is working at converting the RF into audio. By bringing the front end into alignment by adjusting the oscillator for best tracking (which can also be measured through distortion), then work through the IF chain starting at the input to the discriminator or ratio detector. Adjust each element for lowest distortion, then move and repeat for the next stage back.

The alignment had drifted with age, while on station the dial was mis-aligned and it was receiving with excess distortion.

The oscillator adjust is a variable core near the front of the radio:

Then the antenna pre-selector:

But it only significantly cleaned up with adjustments to the IF chain:

There we go! Finally settled at 0.029% THD, which is quite respectable.

It peaked up very nicely! Ratio detector FM was more of a budget design but it still manages to sound quite good.

This was pretty fun – I doubt many people have run into these before and I doubt I’ll see another.

Posted in Uncategorized | 5 Comments

1974 Sony STR-6200F Receiver Overhaul and Alignment

Posted on June 19, 2015 by jwk

I recently got to work on a pretty big, fairly rare Sony receiver from 1973-74: the STR-6200F. It’s a powerful receiver featuring 60W per channel of power available, with quite a few inputs and outputs, and a strong FM tuner built in.

The owner brought it in complaining of poor sound quality. Not particularly surprising given it’s age!

First up was component replacement. All the on-board capacitors were replaced with new Nichicon Fine Gold electrolytics. This receiver had seen some minor service in the past: there was evidence of soldering, and one transistor on the FM discriminator board was replaced at some point.

This receiver was laid out pretty well. Most of the boards were easy enough to slide out, flip up, and service from beneath.

Time for the lower boards:

The power supply was a little tricky to re-work, but not too bad. Sony soldered many of the leads directly to pads on the bottom, so you had to be careful to make sure it didn’t come apart.

The power amplifier board was similar.

Time for the main caps. Two smaller ones, and two huge ones.

The new capacitors used screw terminals, so I soldered spade connectors to the ends of the old wires for a strong, durable connection.

All set!

Time for a first power-up. Not smoke, and it sounded okay, but not at all like it should. Time to check the adjustments. First, the power supply reference voltage. It was pretty close, but I adjusted it anyway.

Rather than provide test point jacks, the service manual called out junctions of resistors for probing the voltage. Not my favorite method but it works. Then onto DC offset, which was WAY out of spec. One channel reading 73.1 mV, the other 100.2 mV. Both reset to zero, though.

Bias was also way off, starving the transistors of power and introducing some distortion. Both channels call for 25 mV across their emitter resistors, but it was more like 5 mV per channel. I adjusted both up to 20 mV, which provides plenty of power but will run a tiny bit cooler.

Checking the temperature of various components on the driver board with a laser thermometer while playing into a dummy load.

The sound was much improved – and the measurements showed it, too!

With all this, the amplifier itself sounded fantastic, but the FM left something to be desired. This is a pretty well-regarded FM tuner, so something wasn’t right. I hooked up the FM test signal generator, distortion analyzer, and dummy load and measured the REC OUT port and found that it was receiving with fairly high distortion, indicating the alignment needed to be adjusted. Then proceeded to align the FM through distortion analysis, adjusting the various cores in the order described in the service manual. Instead of aligning curves on an oscilloscope, though, I made each adjustment for minimum measured distortion. This is faster, more accurate, and more reliable than an oscilloscope alignment, thanks to modern technologies.

Adjusting the front end:

Centering the discriminator:

And finally the discriminator’s DC balance:

There we go! Much better, exactly where I’d expect it to be. The sound really cleaned up, too, now it’s bringing in clear highs and powerful bass over the air just like it should.

All told, 76 components were replaced in this overhaul, followed by amplifier adjustment and FM alignment.

Another classic preserved! This Sony is going to sound fantastic for a long time to come, and it looks great!

Posted in Audio, Electronics, Hi-Fi, Projects | Tagged , , , , , , , , | 4 Comments

The Speaker Spotter – Speakers of Craigslist: June 3rd, 2015

Posted on June 3, 2015 by jwk

It’s back – the Speakers of Craigslist, a periodic round-up of what’s interesting on my local Craigslist these days. Sorry for the hiatus, putting these together is a bit of work! As always, I am not affiliated with any of these listings, and you should contact the poster of the add with questions or to make a purchase. Craigslist moves quickly, so if the ad is gone, it’s probably already been sold but the info is still good for getting a feel for the market. And so without further introduction…

1. Pioneer CS-88 Lattice Grille Speakers

Down in Tacoma there’s a decent set of Pioneer CS-88 speakers for sale. Pioneer’s vintage speaker line is known to sound quite good when fixed up, and this would be a perfect pairing for an amp or receiver like the Marantz 2245, for example. They could use a quick shot of blush remover, Howard’s Restore-a-Finish, and some wax (about the most basic refinishing you could do)  but look like they’re intact and solid. They’re asking $100.

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2. JBL L220 Vintage Monitors

Old-school JBL sure commands a high price sometimes, and these L220s are no exception. They just received new foam, and the veneer looks to be in good shape. They even have the original grilles, although those look a little discolored. If you like JBL, you’d like these for sure, if you’ve got deep enough pockets. The owner is hoping to trade for a travel trailer, or $2200 cash.

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3. Vintage LTC100 Loudspeakers

Originally selling for $680 a pair between 1976-1980, these speakers look to come with an interesting bipolar design (similar to some Infinity speakers of the same era) with a rear-firing tweeter along with the compliment of front drivers. They look like they’re in great shape, too. $265 in Marysville, WA.

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4. Realistic Mach One Speakers

Realistic, Radio Shack’s house brand before their slow decline and eventual demise, are actually a somewhat underrated speaker. A 3-way design with a large woofer, multicell mid, and horn supertweeter they’re certainly a commanding presence in the room with the multicell tweeter aperture visible above the grille.  These look to be in average condition and could certainly use a good cleaning or light refinishing (and maybe a crossover recap by now) but look to be all there. The seller is looking for $175. There’s a review on Audiokarma, too.

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5. “Decorator” Klipsch Cornwall Speakers with Crites Upgrades

Klipsch is still one of my favorite speaker brands, and if you’re familiar with them at all then you know about the Cornwalls. The big brother to the Heresy, these feature an extremely efficient (>100 dB 1 W/1 m) 15″ woofer and EV mid-range and tweeter horns. The owner indicates they’ve received Crites upgrades, too. They’re in what I might call “polarizing” mid-century modern style cabinets that could use some touching up, but the seller’s asking price is extremely reasonable for what they are at $850.

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6. Early Klipsch Heresy Speakers

Speaking of Klipsch, the Heresy is a fantastic smaller speaker. Originally designed for sound reinforcement in public-address applications back in the day, they’ve been in production for quite a few years, but these early variants are from the ’60s and fully operational on their original components. The seller speculates these use an EV woofer (along with EV tweeters) rather than the Eminence woofer found on some later variants. These early speakers, with the ’60s grille cloth and early emblems, sure do look nice. The seller is asking $650 for the pair.

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7. Bose 901 Series I Speakers with Equalizer

For whatever reason, Bose speakers seem to command a real premium that isn’t always well justified, but this seller is right on the money. He’s got a set of Series I speakers with the matching Active Equalizer (necessary for correct sound reproduction) for a spot-on price. The Series I and II used cloth surrounds, too, so there’s nothing that needs to be re-foamed although at the time of posting, the seller wasn’t aware of that fact and listed the surrounds in unknown condition. (The equalizer might need some service though, even if it currently plays – check out Rain City Audio for help with that!) A fantastic deal at $300.

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8. BSR Model 158 Speakers

I’m mostly familiar with BSR for their work in turntables, but apparently they’ve made some speakers, too. While I’m not up on the specifics these sure do look interesting with a large woofer, midrange, and something that looks suspiciously like a ribbon or planar tweeter. I haven’t done much research on these, but suspect they’re worth a bit more than the $100 the seller is asking currently, so this might be a real bargain.

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9. Knight Floor Speakers

Knight speakers were originally kits back in the day, and like Heathkit speaker kits, there were quite a few versions. Without some more information it’s tough to tell for sure, but some models were more or less University/Altec speakers you put together yourself. Even the more entry level offerings would turn up with Utah and other prized drivers. I bet these are a great bargain no matter their drivers at $30 for the pair, though.

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10. Lewis Erath LWE 1 Vintage Speakers

Reported as tri-amp capable speakers in their original condition, these feature the excellent EV T-35 horn tweeter, a 5″ midrange and a 15″ Eminence woofer. They look a bit rough around the edges, but I’d expect performance similar to a Klipsch Cornwall if I were to guess. Certainly worth $200 the seller is asking.

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Posted in Audio, Collections, Commentary, Speakers, Vintage | Tagged , , , , , , , , , , , , , | Leave a comment

Hands On with the new Acer Chromebook 13

Posted on June 2, 2015 by jwk

I was recently in the market for a new laptop to replace my aging ProBook 4415S. It was a middle of the road HP business laptop from 2009, and over the years I’d upgraded the RAM to 4GB and installed an SSD, and replaced the battery three times. Even with those modifications it was still feeling the effects of six years of wear and tear, and so I demoted it to shop laptop and decided to pick up a modern replacement.

I thought for a long time about what I needed in a replacement machine. Gaming would be great, but I really wanted something with a long battery life and small form-factor. A high-resolution screen and good graphics was a must, too. I pretty much always have Internet access either at an access point or by tethering to my T-Mobile phone’s built-in free hot spot, and about the only thing I ever use a laptop for anyway is web browsing and document creation. I use a desktop at home for the heavy lifting.

Ultimately, I ended up with an Acer Chromebook 13, part of the CB5-311 series – it’s a big change of pace from my previous computers, but I think it’s the right choice.  I’ve been using it for a solid 2 weeks as my daily-driver laptop and while not without a few quirks, I’m overwhelmingly both impressed and satisfied with its functionality and quality. Keep in mind throughout this review, that this is mostly just a platform for a web browser: there is limited to no support for apps and limited offline functionality of any kind.

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Overview

The “CB5-311-T1UU” is a pretty impressive machine when compared with most of the other Chromebooks out there. It’s powered by a quad-core 2.1 GHz nVidia Tegra K1 CPU, nVidia Kepler GPU featuring 192 CUDA cores of the same variant found on desktop GeForce cards (in contrast, a middle-of-the-road current generation GeForce might have 1280-1536 of those same CUDA cores in it’s arsenal – but it’s an impressive graphics compliment for a lightweight device.) All this power pushes a 13.3″ 1080P Full  HD screen backed by 4GB of RAM and a 32GB solid-state drive.

As far as ports go, there’s a pair of USB 3.0 host ports, a full-sized SD card slot, a full sized HDMI port, and the charging port. It also features the fastest and latest 802.11AC WiFi.

When closed, it’s less than an inch thick and weighs only 3.31 lbs., so light I barely notice it in my bag.

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The Good

As mentioned before – it’s quite light, and the powerful CPU and GPU combined with the SSD make it incredibly quick to boot up, and I’ve been unable to get it to slow down and lag on me in normal usage. As I’m writing this, I have 11 tabs open including a large PDF, and it’s chugging along quite nicely. Transitions between tabs are quick and scrolling is smooth, although there is a small delay to render a change to the screen on the PDF that I don’t experience with the desktop when zoomed in on a big file.

The system boots up from cold in about 10 seconds, from powered off to usable, and it only takes about 5 seconds to restore from standby. Not bad at all! It’s also shockingly powerful. I was able to side-by-side stream a 1080P Netflix video, and a 1080P YouTube video simultaneously each on half the screen and neither suffered any lag, stuttering or artifacts.

Acer rates the battery at about 11 hours of usage in normal conditions, and I’d consider that accurate. I certainly manage a full day’s usage on a single charge, plugging in at night and using it in several 3 to 4 hour sessions throughout the day. I bet it would be possible to push 12 hours if you kept the brightness low and worked only one or two tabs at a time to keep the load down. And all this at $377 – a high end Chromebook for the price of a low end Windows machine.

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The “Different”

I wasn’t sure if I’d consider the Chromebook an actual “laptop” at first, but I’ve decided it qualifies. There are a few differences, though.

  • Keyboard

The keyboard has dedicated Chromebook functions arranged in the top key row in place of function keys by default (although, you can override this in settings and turn them back into unlabeled function keys.) There are hard buttons for refresh, tile windows, brightness, sound, and a combination log-off/power-off button in the top right. There’s also a dedicated “Google Search” button in place of caps-lock which calls up a search box instantly from any screen.

The keys feel okay, but not great – they don’t offer a huge amount of tactile feedback, but I adapted quickly to the typing style. Some commonly used functions like Home/End/Page-Up/Page-Down are missing – but if you hold Search and press an arrow key those functions are available but unlabeled.

  • Touchpad

The touchpad is a little odd. It has a single physical button along the bottom but not marked separately on the surface. I found (and find) the mixed gesture input system a bit disjointed, personally. Tap or click to left-click, two-finger tap to right click, and a three-finger tap is a “middle click” to open in a new tab. Unfortunately, though, I find it difficult to actually touch three fingers to the surface closely enough in time to actually register a middle click and it ends up either left-clicking or right-clicking somewhat unpredictably. I’ve adjusted to just right-clicking and selecting “Open in New Tab” as appropriate.

  • Browser Support

Although the Chromebook does manage to support Flash (as well as the latest and greatest HTML5 technologies), it’s uncommon enough that some sites don’t deal well with it. HBO Go, for example, won’t load. Installing the “User Agent Switcher” extension which lets you tell your browser to identify itself differently to a web site, and telling the browser to identify itself as Chrome for Windows instead of Chrome for Chromebook, seems to fix all of those problems. HBO Go itself works just fine when accessed with this trick, but it will give you a thoroughly broken text-only page if you’re identifying yourself with the default user-agent string.

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The Ugly

  • Power Management

Closing the lid puts the laptop to sleep but it continues to draw power, and it will do so until the battery dies unexpectedly, leaving you surprised and muttering expletives under your breath when you pull the laptop out and find yourself without any power. I’ve not found a setting to change the power management behaviors, either. Snapping the lid closed should only be for a short break – you should always remember to hold the power button down until it logs off, then powers off, to make sure you don’t drain your battery.

  • VPN Support

Don’t count on a Chromebook to connect to most VPNs. Google’s Product Forums trash PPTP VPNs as being fundamentally insecure, and state that as a security-focused product (everything locally is strongly encrypted all the time)  they won’t offer support for an insecure technology. In the same breath, they admit PPTP is better than nothing, but don’t support it and don’t have any plans to. Given that most commercial VPN services, workplace VPNs, and home VPN router hosts use PPTP this is incredibly frustrating. You’re stuck with a few variants of L2TP, and OpenVPN, if you want to secure your Internet traffic over your access point. Great if you’re a Linux system administrator in your spare time, less great if you want something that “just works”.

This lack of functionality means I’m looking for a replacement for my ~1.5 year old, $150 Asus router/access point, and frankly, it’s downright arrogant of Google to refuse to support the most commonly deployed VPN technology for questionable ideological reasons that won’t resonate at all with the general public.

Overall

I’ll rate this Chromebook a 4/5, overall, and give it my recommendation. At only $377, it’s capable enough and very portable which is the majority of what I want from a laptop these days. It’s not without some caveats, though, as noted above – and while you can get a Chromebook down to around $200, the less powerful versions might offer a noticeably less powerful experience and lower resolution screen. Either way, though, a $400 Windows laptop would be a very entry level piece of gear with poor battery life, so considering what you’re getting it works out very well.

It’s absolutely not for everyone: if you do any gaming at all, or need access to any apps at all, this isn’t the machine for you. On the other hand, if you’re mostly interested in browsing the web, streaming video and some light document creation this could be a good choice and it’s definitely worth looking into at least.

[Acer Chromebook 13 CB5-311 Series from Amazon $377.99]

Posted in Commentary, Computers, Gadgets, Technology | Tagged , , , , , , , , | 2 Comments

Marantz 2270 Stereophonic Receiver Overhaul and Adjustment

Posted on May 26, 2015 by jwk

I recently got to work on another iconic piece of hi-fi history, the Marantz 2270 stereo receiver. I’ve had this model through my shop before, as well as a couple of other 22xx receivers and they’re well built and generally pretty straightforward to service. This particular model offers 70W/channel at less than 0.3% THD into an 8 ohm load, with frequency response from 7 Hz – 50 kHz.

This unit’s owner pulled it out of storage and started listening, but reported the sound steadily got worse and worse. Good thing he sent it in before something worse happened! The capacitors were in pretty bad shape, including a visibly leaking main filter capacitor:

There are quite a few circuit boards in this receiver which all need serviced for a full recap. With only one or two exceptions, all parts were replaced with Nichicon Fine Gold electrolytic capacitors. There’s the FM MPX board:

The regulated power supply board:

Tone amplifier board:

Phono Pre-Amp board:

FM IF strip:

New main filter capacitors, which happen to be much smaller and offer better airflow:

New capacitors on the final modules:

The AM board:

And not pictured, the demodulator and quieting circuits, which are in a tough spot to photograph but had 3 or 4 capacitors on each board. Then, it was time for power-up testing. First was to adjust the regulated power supply’s reference voltage, which had drifted high up to 38.35V over the years.

With that squared away, it was time to check and adjust the DC offset and idle (bias) current before hooking up the speakers. One channel’s DC offset weighed in at 69.4 mV, the other at 11.5 mV; both were reset to 0.

Functional testing revealed that the FM circuitry was suffering from poor reception and distortion, but the owner declined to have that function repaired, so it was on to the AM board for an alignment:

Several fuse lamps were burnt out and when they arrived, it was time to install. Seen here an old fuse lamp and a new LED fuse lamp. The LEDs offer similar brightness and evenness, but draw much less power and generate less heat, which further relieves some stress from the receiver’s power supply and will help it to last longer.

Looks great! With the cover still open, it was a good time to do some frequency response tests:

Flat +/- 1 dB, not bad at all! It sounds fantastic, too, and registered < 0.1% THD across the power band, significantly beating it’s factory specifications. Doesn’t she look great?

Quite a few parts came out:

All in all, this Marantz should offer many more years of faithful and powerful service back at it’s home in sunny California.

Posted in Audio, Electronics, Hi-Fi, Projects, Stereo, Vintage | Tagged , , , , , | 3 Comments

ANOTHER fine achievement in radio set design

Posted on May 23, 2015 by jwk

Radio Retailing, Apr. 1929

Posted in Collections, Vintage | Tagged , , , | 1 Comment

Need 45V batteries for your old radio?

Posted on May 21, 2015 by jwk

Rayovac has been making batteries for over 100 years, and their batteries were commonly found in use with many types of battery-operated tube radios. Most commonly, radios would operate on 45V batteries with a tap half-way (for 0-22.5-45V). Two in series would give you 67.5V and 90V for bigger radios. This style has been out of production for many years, but Rayovac has a good modern replacement for the older Type 783 batteries, the 45V-HD.

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It has connections for a modern connector as well as the old-style connections:

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If you have a ’20s or ’30s battery radio, and want something more original than using a stack of 9V cells, this looks like a good bet!

Yours for $19.95 with free shipping from Amazon.

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