Tuesday, October 27, 2009

In Celebration of Speaker Day

Around our household we celebrate a number of unusual holidays. One of my favorites (and my wife's) is Speaker Day. On this day all adult males haul out the speakers they have been storing in closets and unused bedrooms and make them ready for the next stage in their lives. While not as festive as the International Day of the Sock, it nonetheless is a lot of fun. Speaker Day could be celebrated pretty much every week around our house.

After a two year drought and a summer of screaming heat, Austin is evidently now enjoying a fall monsoon, so Speaker Day was at risk this past Sunday. But the sun was sort of out, and the ground was sort of dry, so it was on with the celebration.

The star of the festivities was this bottle:

Yes, that is a really old bottle of Sta-Wax I found at an estate sale. (Guess how much I paid for it.) This stuff has an odd, strong smell, sort of like cherries, but it is a wonderful product. It should be used much like lemon oil, but it is much more effective. It is great on open grain wood like the JBL 4410 it sits on. The photo doesn't do it justice: the right half has been treated and the left half hasn't.

Next up, a classic marriage killer:

This is a Knight 2300C speaker in very lovely dark walnut, or maybe mahogany. If you are the sort of husband who can't bear to leave a pair of large real wood speakers to the hazards of a thrift store, be forewarned. You will be shocked to learn that the wife will not like them. Too honkin' big. But if you do save them from further insult at the hands of barbarians, you will discover they have nice Jensen drivers. The 10" woofer is one of their better finished models, with a horn mid and a very interesting looking tweeter. The crossover is nicely done and worthy of some cap rolling fun and games. Oiled up they look great.

Onward to a long sought after speaker: the Optimus 10. Long ago (as in at least 30 years ago) I read a very nice review on them and thought I would like to give them a listen. Time passed... This is the one an only pair I have ever seen and I literally pulled them out of a huge salvage box at our crazy Goodwill dumping ground. The grill was shattered and the foam surrounds were long gone. I out them back together and even put a nice cap on the tweeter. It is just amazing what a male of the human species will endure for the love of a loudspeaker. The Optimus 10 has a decent dome tweeter with an 8" woofer and a 10" passive radiator. And the tweeter control even has a nice response curve which no doubt is completely accurate. I have yet to give them a real listening, though, I guess I need to find the time after all that effort.

Last on tonight's program is a very sweet EPI 100W, the real walnut veneer variety. I have had a soft spot for these speakers since '74 when I dropped most of a paycheck on a pair with the lovely brass inlays. Peter Frampton sounded great for a week, but then I was burgled, so I have been compensating for that loss ever since.

I neglected to take picture of several other Speaker Day participants, including entries from JBL, Mirage and Heathkit. The next Speaker Day is not that far off, so I better keep that camera warmed up.

Saturday, October 24, 2009

A New Sign O' the Times

Austin Stereo Service got a new sign today:

First, new carpet, and now a new sign. The club house is looking pretty swank these days.

The Sounds of Failure

As the title suggests this will be an attempt to document the sounds of failure in hifi gear. This will no doubt be just a start, so I will revisit this entry as I learn more. This is not a simple topic. In our discussions Mike emphasized there is even variability between manufacturers, eg. failing preamp transistors sound a bit different in Marantz vs. Pioneer receivers.

Perhaps the most common sound of failure is that scratchy noise you hear when you adjust your volume, balance, bass or treble control. You turn the knob and it sounds like gravel in there. The good news this is caused by the accumulation of oxidation on the contacts and this is easily eliminated by a product such as Caig's Deoxit. The bad news is that your controls are not always easily accessible. Many integrated amps and receivers require peeling the face of the unit, which means pulling all the knobs and removing the retaining nuts.

Oxidation is not limited to potentiometers. Switches (eg. the push button FM mute or rotary function selectors) suffer the same problem, but the characteristic sound tends to be lower volume, distortion or silence. The solution is the same: douse the switch with a product such as Deoxit.

The whole process of cleaning the controls of a typical receiver is worthy of a post of its own.

One switch that is not obvious to the typical listener is the relay. Relays are circuit protection devices and are typically buried in the heart of the amplifer and they are prone to oxidation. This can be manifested in a weak, distorted or missing channel. When working properly they make that click a few seconds after you turn on your receiver. They are essentially little copper fingers, at least one per channel, that make the final connection after the protection circuitry has determined all is well with the unit. Relays are typically plastic enclosed cubes soldered to the circuit board and are not dousable with Deoxit. They typically need to be removed from the board and the plastic cover removed, and then they are burnished with a very fine file or sand paper. Again, this process is worthy of a post of its own.

Next up: silence. Oxidation as described above can be severe enough to kill one of both channels. I have encountered several slightly corroded fuses that have silenced a my gear. Don't forget to check your fuses!

More seriously, two dead channels suggests something amiss in the power supply. This is typically capacitors, but can be any number of devices. The power supply takes AC from the wall and transforms it into the various DC outputs that drive each section of the receiver, so trouble here and take the whole unit down.

One channel of silence can still be the power supply, but can indicate a problem anywhere in the preamp or amp.

In a comment Kenny asked about 'rushing and hissing' in a vintage European integrated amp. Rushing and hissing can be caused either by faulty caps or transistors, especially in the preamp. Mike and Robert have been preemptively replacing the preamp low noise-high gain transistors in many of their restorations in addition to the usual cap replacement. Robert describes the sound as 'spitty', but Mike emphasizes the wide variation in the sound of preamp transistor failure.

A very striking sound of failure is that of the differential transistors in the power amp. Mike calls this tiny pair the keystone of the power amp. Their failure results in a very distinctive and violent spike of noise.

When I get a chance I will update this post with a discussion of hum (fascinating!), DC in the output and much, much more...

Friday, October 23, 2009

Cioppino: Yummy Fish Stew

I am afraid this episode of the blog is going to be a frightful mess. No, not that scary little Marantz again (ahh, just you wait...), rather this will be whatever is hanging around, fit to be thrown into the stew pot. If I was half as good a writer as Mike is a cook, this would be a savory treat like his cioppino of a few Saturdays ago, but I fear I will fall short.

First up is an addendum to this ESR meter post. Those of you who have used a DMM to check the viability of a speaker in the box know (or should) that this is a very crude measure of health. Those caps in the crossover block the dc of the meter so all you get is the resistance of the woofer. Useful, but is there something better? Well, glad you asked, because the handy dandy ESR is that something better.

I recently found a salvageable pair of JBL 4410's at a local thrift. (Yes, the thrift gods were smiling on me that day. Perhaps I should sacrifice a Yorx boom box in their honor?) The DMM told me the woofers were there, 6.2 ohms each. Mike pulled out the ESR meter and, interestingly, one measured 9.1 ohms and the other 7.2 ohms. Hmm. Different from before and different from each other. What was up?

The ESR meter is evidently able view the entire network of crossover, pots and drivers and arrive at a more complete picture of the health of the speaker. The 4410 has a very sweet pair of mid and tweeter pots that we had verified were set the same before and after, but in general pots are a prime source of sonic grunge. The JBL pots are beefy works of art complete with holes in front large enough to squirt with Caig's Deoxit. The pots were doused generously, wiped 30 times and reassembled. On retest they both tested at 9.1. We were both perplexed that the higher number was the healthier one and can only surmise that we were now seeing more of the system.

Next up is the general issue of questions left in comments. (Yeah, I get comments. Sometimes. I swear.) Blogger lets me know they are there via email, but I am sometimes miss them in the blizzard. But the biggest problem is they do not have an address for a response. So, you will need to explicitly leave an email for me to respond. I'll try my best.

Questions left on older posts are an interesting variation of the problem. If I post a comment in response I am never sure the ask'er will even return to read it. Some time ago Kenny left a question on the Dual/Philips amp write up: he has an identical unit that makes a rushing, hissing sound when it warms up. What causes that? Good question, one worth a blog of its own. I talked to Mike about this and hope to write it up this weekend. Mike doesn't like to divulge the secrets of the Krell, but I caught him in a moment of weakness.

Now for something with a picture. Among my several obsessions is vintage CD players. Here is a quite lovely Rotel RCD 955AX. Orion's Blue Book says it was $450 in 1992:

Note the soon to be cioppino ingredients in the background. Sometimes you have to compete with dinner for a bench at Austin Stereo Service.

Here it is with its top off and Imogen Heap locked and loaded. Lots of air off to the right, but the smallish main board has some very nice bits as you can see below.

Lots of film caps, brown and blue, make the walk from left to right past the Philips chips set. The black electrolytics at the right are Black Gates, tasty, like Mike's fish stew.

That's it for now. Next up: the sounds of failure.

Friday, October 2, 2009

The Perils of Li'l Mar: Like Pulling Teeth

In our last episode things were looking up, as usual, in my efforts to restore the Marantz 4220 receiver. The sliders had been clipped and the power switch bypassed, the unfortunate result of years of actual use. Mar evidently lived in a dorm room, not a closet shelf. And unfortunately, despite all my efforts, my work was not done.

On testing she seemed to work, but moving and flexing the preamp card caused all sorts of symptoms: hum, drop outs and distortion. (Just shoot me now.) I resumed chasing bad solder on the card, and eventually made a discovery. At the corner opposite the slider-snipping were 5 posts: front/rear, left/right, and ground heading back to the amp section. Several of these posts were loose, with the ground post in the middle wobbling like a loose tooth. I realized touch ups were futile so I clipped the card free and reached for the pliers.

The ground post was pulled:

The preamp card is double sided, a major source of this receiver's problems. Each side has the ground trace running along the outside, away from the front of the unit. The ground post bridges the two sides of the ground, or would if it were actually soldered. The two ground wires wrapped around the post had obscured the less than ideal solder work made worse by the several removals from the unit. This work would have been much easier if I had just bitten the bullet and removed the card at the first sign of trouble.

Anyway, I fashioned a new post out of some solid core wire and bent one end at a right angle. I scraped the traces above and below to copper and replaced the post. The bottom right angle followed the trace and provided a good anchor for the solder. After the bottom cooled I bent the upper part a bit down the trace so the top would be stable and was generous with the solder. Here is how it looks from the top:

This is before trimming... (to be continued.)

The Acme-825 ESR Meter

Acme Enterprises currently has a version of the Dick Smith ESR meter designed by Bob Parker. The price is $89 with free shipping. Acme is a hard site to link to so you will have to navigate a bit via Test Equipment to see the meter. Here is a photo of the Acme-825 next to an original Dick Smith kit that Mike built years ago:

Dick Smith is an Australian electronics retailer that marketed the meter on the right as a kit for many years, but it was recently discontinued. The Acme meter on the left is made by EVB out of Portugal.

ESR stands for equivalent series resistance. The Wikipedia definition:

"Equivalent series resistance (ESR) is an effective resistance that is used to describe the resistive parts of the impedance of certain electrical components."

Basically, components such as capacitors add resistance to a circuit. Film caps should add very little, electrolytics (when young and fresh!) and tantalums should add more, but still very little. But we all know the passage of time is not a good thing for electrolytic capacitors and this often shows up as an increasing ESR. Check the little ones: they dry out quicker and make that tone control circuit or that phono section sound terrible. Or worse, they blow up those rare output transistors.

Here is the Acme-825 manual (pdf) for a good description of both the meter and ESR. Here is a very nice web site that provides a good explanation as part of a DIY ESR meter project. Here is another explanation using an original Dick Smith meter.

These ESR meters are actually small computers powered by a Z80 chip (please wait while I flash back to a software project in 1983... ah the joys of CP/M). The meter essentially pulses the cap with a very high frequency, very low voltage alternating current to measure the resistance. The low voltage prevents transistors from turning on and allows testing in circuit (but not on!)

Since the lion's share of electronic sleuthing involves the electrolytic capacitor it should come as no surprise that Mike's ESR meter ranks behind only his soldering iron and Fluke DMM in importance. He has been prodding me for years to get one. Well, I did.

My initial impression of the Acme-825 is that it works well, but is very much a lightweight compared to the original Dick Smith kit. Mike's original is cosmetically whipped, but it still works well. The plastic case is very heavy duty plastic which no doubt helped it survive in a commercial setting. Fortunately, my situation should be less demanding, but I think I will put a bit of thinking towards shock proofing the case a bit.