Vintage Documentary: How Stereo Turntables Work

September 2, 2015 Leave a comment

Documentary Tube on YouTube has digitized an excellent early video documentary discussing the newest hi-fi invention of the time: stereo! In this 4-minute video, the narrator compares mono with stereo recordings on vinyl. Worth checking out!

Adding Capture to a Vintage Scanning Electron Microscope

August 31, 2015 Leave a comment

Applied Science over at YouTube has a great video about adding a capture capabilities to a vintage scanning electron microscope, including some great videos of that instrument in action. Check it out:

Creek 4140 S2 Overhaul and Voltage Conversion

August 23, 2015 Leave a comment

From the Rain City Audio Repair Blog:

This Creek 4140 S2 amplifier is a bit newer than most through the shop, although it’s getting up there. This particular one was constructed in 1989, and came via eBay from the UK configured for 220V power. The owner wanted it checked out and converted over to a U.S. power supply.

It’s an unassuming little amplifier, delivering 30W per channel at 0.1% THD. Inside, it’s pretty simply built but very clean. The shop has a universal power transformer that accepts nearly every plug style in both voltages, so it was easy to check out. The amplifier “worked”, although you had to crank the volume all the way up to maximum – the signal was getting attenuated along the way but it was still passing all the way through.

Because of the small number of capacitors in this unit, I recommended they all be replaced, and found that two of the small signal capacitors had gone very low in value towards being open. With the capacitors replaced, the unit came to life on 220V just fine.

The owner supplied a 120V transformer for this amplifier to swap. Theoretically, according to the schematic, the transformer has a split primary which can be wired in series or parallel for either voltage, but in practice there was no sign of the extra taps, so it was just a direct swap-over.

Transformer leads are enameled wire, which needs to be scraped down to the bare copper in order to take solder. Then the leads were joined back to the same colors.

Finally, it was time to swap the plug with a U.S. fitting.

Time for some testing! The Creek 4140 S2 is rated for 20 Hz – 20 kHz, with 0.1% THD at 1 kHz. How’d it do? The Audio Precision System One analyzer gave some insight. Frequency response from 20 Hz – 20 kHz was flat +/- 1 dB, which is fantastic.

On the extended range frequency response test, the actual -1 dB point was at 20 Hz on the low end and 30 kHz on the high end; +/- 3 dB at 10 Hz and 60 kHz. The channels are slightly imbalanced, even after bias adjustment, but not enough to worry about tracking down.

The amplifier delivered < 0.07% THD at 1 kHz, and overall had acceptable distortion performance.

Quite a few parts came out of this one!

A listening test proved this little amp sounded great, and so it was time to clean up and send it home.

New Test Equipment Day!

August 19, 2015 Leave a comment

I’ve added a new analysis system to my stereo bench…the Audio Precision System One.

Amplifier measurements just got a whole lot more precise.

1963 Fisher FM-100-B Stereo FM Tuner Overhaul

August 9, 2015 2 comments

Cross-posted from the Rain City Audio repair blog:

Something a bit unusual came through the shop recently, an old tube-type Fisher FM-100-B Stereo FM tuner.

Anyone who knows classic tube audio knows Fisher, and the FM-100-B sure lives up to the name. It’s a 12-tube FM/MPX Only tuner with a solid-state rectifier, designed to mate with a similar line of pre- and main amplifiers. These were occasionally found standalone, and also built into wide stereo consoles.

Some of the Fisher’s great FM performance came from the “Golden Cascode” 6DJ8 RF amplifier stage on the front end. You can’t have great-sounding stereo without a strong input signal, and the Fisher’s input stage delivers.

The rest of the tubes are 6AU6s, 12AX7s and 12AT7s primarily. Underneath, there’s a lot going on:

The owner wanted a recap and alignment, reporting that while it had been working the last time he used it, it wasn’t sounding great. There’s a handful of dipped capacitors, along with the power supply electrolytics, which needed a good going-over. Where possible, I replaced 0.5-1 uF electrolytic capacitors with film for longevity.

Next, on to the power supply. It’s a set of 4 x 40 uF capacitors in a can. I’ve selected a set of top of the line Nichicon capacitors with a 10,000 hour minimum lifetime and ripple tolerance about double what this set will experience. First step was to attach some terminal strips to mount the new caps:

By using terminal strips in this fashion, it’s easy to just move the components over to the new tie points and easily preserve the wiring layout with a minimum of disruption. A second strip on the other side finishes out the set of 4 caps:

The replacement is finished off by clipping the now-useless terminals from the can capacitor, so it will never be used again:

After the first power-up, though, there was no sound. Time to check the tubes:

Found a dead 6AU6! That would do it, no signal was making it past the final demodulation step. A replacement fixed it right up. Then, on to the alignment.

First step was to reset the output level to 0 dBm (0.77V).

Then it was time for the alignment, by adjusting the cores for minimum distortion:

I also adjusted the MPX sub-chassis, including 19 and 38 kHz coils and the stereo separation adjustment, achieving equal stereo separation nearly -30 dB per channel. Not too bad. Solid-state tuners can achieve a little better separation, but not much.

Replaced parts:

All fixed up and adjusted, this Fisher tuner sounds fantastic with a great deep and rich tone and great clarity all the way up through it’s frequency range. Paired with a strong antenna and matching stereo system, it’ll be a fantastic performer.

Bose® 901 Series II #101043 Repaired

August 4, 2015 3 comments

Cross-posted from the Rain City Audio repair blog:

Another Bose® 901 Series II Active Equalizer came into the shop recently for a full overhaul. These equalizers are getting pretty old and even if they power up and pass some sound, they’re almost certainly not performing as they should anymore and need some reconditioning to bring them back to peak performance.


You can see evidence of some outgassing from leaking capacitors on the shield foil inside the cabinet:

This one’s mostly original and frankly I’m surprised the owner reported it was making any sound at all.

The output capacitors had bulged out from the inside due to leakage and heating:

And the main filter capacitors weren’t doing so hot, either:

It looks like the main filters were replacements from some point in the past, too:

They’re all coming out to be replaced with new models:

Here’s one of the bad main filter caps. Nominally, this should be about 470 uF and have a very low ESR (<0.1 Ohms). Shown here measuring 6 uF and  140 Ohms ESR.

And an output capacitor measuring 19 Ohms ESR.

The silent channel had a totally dead output cap:

Time to replace parts:

Carbon composition resistors like these absorb moisture from the air over time and drift in value; this 22K 10% tolerance resistor has failed and no longer meets it’s spec of 19.9 – 24.2 kOhm:

The rest of the resistors are a simple swap-and-replace job:

The Series II and later generally have reliable film capacitors, but for the SI and SII they’re always replaced.

And finally to replace the electrolytics:

On a standard service, we’d be done here, but the owner requested upgrades to audiophile-grade film output capacitors, with a much lower dissipation factor to offer improved clarity in the output:

After testing, it was time to proceed with the other upgrade requested by the owner: gold-plated panel jacks. Panel jacks are a great upgrade if you’re planning to use new, thick interconnect cables (like Monster® or similar) but the modification is irreversible since the original jacks mounted on phenolic board are destroyed in the removal process.

And making the final connections:

With this, all resistors, electrolytic and film capacitors, and panel jacks have been replaced:

And a quick confirmation test shows everything is still perfect after the jack swap:

With that, it’s ready to go home! With all new top-quality parts and a thorough cleaning, it’s going to sound fantastic for a long time to come.

[Rain City Audio Bose® Active Equalizer Repairs]

T-Mobile’s WiFi Calling Not Quite Ready for Prime Time

August 3, 2015 Leave a comment

T-Mobile recently re-introduced Wifi Calling to their entire line-up of phones, and have made a pretty big deal about it. And on paper, I can see why – no more worrying about cellular dead zones, and you can take your U.S. number out of the country with you and still receive calls and texts as normal from anywhere in the world as long as there’s a WiFi network available.

Sounds great, right? This feature was available on the T-Mobile G2 Android phone several years ago, before disappearing for a generation of phones, and finally re-appearing on all current models. The only trouble? It’s just plain not very good. Much inferior to their previous version of the same technology, in fact.

Screenshot_2015-08-03-09-14-30

 

I have a small, low-end LG phone which I use for business and seems to do “okay”, but on the Sony Xperia Z3, it’s very unreliable. And the extensive troubleshooting guides don’t cover an important situation that, really, should never exist in the first place: a successful connection that just silently fails to pass any calls or texts.

Arriving at home and auto-connecting to the wireless network? Expect, even though Wifi Calling shows its enabled successfully, to have to toggle it on and off at least once before you’ll get anything other than a beep-disconnect making a call or an error message sending a text. Then, it’s only a matter of time before it silently fails again, continuing to indicate it’s connected successfully but blocking all inbound and outbound calls and texts. In this state, even Google Voice calls won’t go through, as apparently those don’t legitimately use the data connection but still take voice channels.

There’s no error message, no notice, and apparently no heartbeat or auto-reconnect functionality built in. Combined with the fact that my home is basically a dead zone that even the Personal CellSpot can’t bring to life it’s very difficult to use my T-Mobile phone. The only reason I’m still with them is because of the price and plan (although, if I can’t use it effectively, maybe that’s not a good argument.)

Anyone else have a T-Mobile phone, and is frustrated by their inability to deliver on Wifi Calling’s promises?

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