More fun refurbishing audio stuff

Let your stereophile run loose! Talk gear, media, and other electronics that makes music for your ears.

Moderators: Bookworm, starkruzr, MrFireDragon, PrettyPrincess, Wapsi

User avatar
Dave
Posts: 6910
Joined: Tue Jul 31, 2012 5:58 pm
Location: Mountain View, CA, USA

More fun refurbishing audio stuff

Post by Dave » Sun Sep 09, 2018 9:10 pm

I'm not crazy about the modern "electronics are disposable" mind-set. I understand why it exists... modern electronic devices are so complex, and use such small components that the labor cost of repairing them is usually prohibitive... but I hate to see stuff thrown away. There''s still a lot of very usable gear of a certain age that's going off to landfill (or, if we're lucky, to some sort of authentic recycling) simply for lack of some TLC and gentle servicing.

On the other hand, that means there's lots of stuff for hobbyist nerds like me to pick up for-cheap. I've been lucky lately at my local electronics-oriented swap-meet/flea-market.

A couple of years ago I picked up a thoroughly filthy Proton D940 receiver - I think it had been stored in a barn - with a broken power switch. I paid around $30 for it. After a thorough blowing-out, some contact cleaner on the switches, a power switch, and a tuner alignment, it was ready to make music. This is a really sweet little receiver - 40 watts/channel continuous, a huge ability to handle musical peaks without clipping, and a sensitive tuner with the Schotz noise reduction circuit. I stuck it on a shelf until I needed it.

That turned out to be May, when I stumbled across a pair of Minimus 77 mini-speakers... one of the long line of metal-cabinet bookshelf speaker systems Radio Shack marketed... they're surprisingly good for the price, and there's a big cult-enthusiast community updating and modifying them. The ones I found had rotted-out surrounds (inevitable at this age). I got the pair for under $10, replaced the surrounds (another $10), built an upgraded crossover (the "Zilch" design), and put them up in one of our bedrooms with the Proton receiver driving them. Very nice-sounding although they're too small to have much "low end". They really need to be used with a subwoofer, so I've had my eyes open for one (or for drivers that I could use to make one from scratch).

A subwoofer was this Saturday's big find. One seller had a Definitive Technology ProSub 800 (8" cone, 8" passive radiator, and a MOSFET power amp and active crossover built in). Quite good reviews on-line. It looked to be in very decent shape, so I asked about it... he said "it works, sounds good, but the control knob on the back is broken off". Sure enough, the low-pass crossover control knob was gone - the shaft was broken off inside the plate amplifier. For $45 I figured it was worth a try - the cones were pristine - so I bought it.

The control was well and truly busted - I think the owner must have slammed the knob against a wall somehow and jammed the shaft into the amplifier. I took out the amplifier and found that the potentiometer on the amp board was completely shattered - the body was broken and the leads were bent. No way it would work, in that condition - I rather suspect that the seller thought he was scamming me by selling me a dead subwoofer. A look at a schematic, and a few minutes with a soldering iron improvised a solution - I took out the pot, and jumpered around it with a couple of 7k-ohm resistors (fixing the crossover frequency at about 90 Hz) until I can get a suitable "dual 20k" replacement pot. Closed it up, hooked it up, and tried it, and it works... it can rattle the room if I turn it up too far. At a modest setting it works very nicely with the Minimus 77s - it fills in the low octave-and-change that the little bookshelf systems can't manage.

A few minutes after I bought the subwoofer, I saw another guy selling a sadly-dirty-looking pair of Minimus 7 speakers (the original, smaller variety). He wanted $5! I paid. Got 'em home, found that both were filthy behind the grills (easily cleaned) and that one had a badly-busted tweeter. Best as I can tell, somebody dropped that cabinet onto its back from a height, and the weight of the shielded tweeter assembly actually broke the tweeter loose from its mounting plate (the screw attachment points were shattered). Disassembled the tweeter, carefully epoxied the plate back together, sanded it down flat when the epoxy cured, re-mounted and re-sealed the tweeter. Put everything back together today, and after a short break-in period both speakers sound good. The repair seems to have been successful and there's apparently nothing else wrong with them other than dirt and some paint chips. I did the "quick" version of a crossover upgrade for them (replaced the electrolytic cap with a film cap for better fidelity) and put them in the garage to wait for a new home. These will probably end up being hooked to our TV, as A/V speakers.

User avatar
TazManiac
Posts: 3326
Joined: Fri Nov 29, 2013 6:53 pm

Re: More fun refurbishing audio stuff

Post by TazManiac » Mon Sep 10, 2018 1:15 am

You da Man, Dave. I'm still trying to convert more of my Theory & Book Knowledge (from last Century btw) into more

"I took out the pot, and jumpered around it with a couple of 7k-ohm resistors (fixing the crossover frequency at about 90 Hz) until I can get a suitable "dual 20k" replacement pot..." action.

Lately I've been coming across free but orphaned SubWoofers, but they are non-op due to missing the Sound Bar to bluetooth to and/or in the case of a Bose; I have the Cable and Woofer-in-a-box but no DVD/Digital Control Box, let alone any Mid/High Freq Speakers that might have completed the set.

In the mean time, I doubt I'm ever going to fill in an OEM package so I'm looking to either externally amp these or find an external potentiometer action to control the volume...

User avatar
Bookworm
Posts: 559
Joined: Sun Jul 29, 2012 11:59 pm
Location: Houston, TX
Contact:

Re: More fun refurbishing audio stuff

Post by Bookworm » Sun Sep 16, 2018 7:07 pm

The biggest reason that electronics are now 'disposable' is ROHS. Once the solder cracks, they're toast. Lead based solder can last decades, but straight tin cracks in just a few years under thermal stress.
I'll get a life when it's proven and substantiated to be better than what I'm currently experiencing.

User avatar
Atomic
Posts: 2540
Joined: Tue Jul 31, 2012 12:39 am
Location: Central PA
Contact:

Re: More fun refurbishing audio stuff

Post by Atomic » Sun Sep 16, 2018 7:15 pm

Bookworm wrote:The biggest reason that electronics are now 'disposable' is ROHS. Once the solder cracks, they're toast. Lead based solder can last decades, but straight tin cracks in just a few years under thermal stress.
Another "Improvement" (Lead Free!) that is worse for the user. "Preservative Free" == "Guaranteed to Rot"
Don't let other peoples limitations become your constraints!

My Deviant Art scribbles
The Atomic Guide to Basic GIMP Stuff

User avatar
Dave
Posts: 6910
Joined: Tue Jul 31, 2012 5:58 pm
Location: Mountain View, CA, USA

Re: More fun refurbishing audio stuff

Post by Dave » Sun Sep 16, 2018 8:39 pm

And don't get an electronics-reliability engineer started on the subject of tin whiskers, unless you have several hours and a good set of earplugs.

I finished the repair on that subwoofer yesterday. A quick eBay transaction got me a half-dozen two-section 20k-Ohm linear pots, with mounting nuts and knobs, for under $10 (delivered). They look OK, they're within 20% tolerance (plenty good for this application) and they're the right physical size. It took about half an hour to open the amp up again (more thoroughly this time), remove the temporary resistors, clean out the PC board holes, put in the new pot, solder it (with good 63/37 eutectic solder), and close everything up again. All good. When I watched "How To Train Your Dragon" on the bedroom TV, Gwen asked "What's all that thumping?!?"

User avatar
Dave
Posts: 6910
Joined: Tue Jul 31, 2012 5:58 pm
Location: Mountain View, CA, USA

Re: More fun refurbishing audio stuff

Post by Dave » Sun Sep 16, 2018 8:43 pm

TazManiac wrote:Lately I've been coming across free but orphaned SubWoofers, but they are non-op due to missing the Sound Bar to bluetooth to and/or in the case of a Bose; I have the Cable and Woofer-in-a-box but no DVD/Digital Control Box, let alone any Mid/High Freq Speakers that might have completed the set.

In the mean time, I doubt I'm ever going to fill in an OEM package so I'm looking to either externally amp these or find an external potentiometer action to control the volume...
One of the gotchas there is that the manufacturer may have chosen a less-than-wonderful set of drivers, or a dubious cabinet design, or satellite speakers with an uneven frequency response, and then "glued it together" into a tolerable system by using a lot of frequency equalization and filtering... which would be very system-specific. If that's the case, a normal amplifier or control system might leave you with a poor-sounding result, as it wouldn't include the necessarily equalization.

It's worth a try, though! Orphan components like that might just work out very well.

User avatar
TazManiac
Posts: 3326
Joined: Fri Nov 29, 2013 6:53 pm

Re: More fun refurbishing audio stuff

Post by TazManiac » Mon Sep 17, 2018 7:08 pm

Better yet is the Cambridge Soundworks Passive Sub I just got ahold of. It's just like the one I had bought new, way back when, except for the color.

btw- It's got four posts on the bottom end for amp'd Input and Stereo output to a pair of Speakers to handle the Mids and Highs. It must therefore have some sort of Cross-Over in there, natch, and a Dual Coil Driver is likely.

It doesn't solve the situation of supplying a self-amplified Subwoofer (handling the line level output of a Surround Receiver for example), but it does go well with a set of smallish 'bookshelf' speakers that can provide those Highs as well as Stereo Separation.

I think I'll have a chance to test the thing in real life this week; I'll report back if the Magic Smoke has been retained or not...

User avatar
TazManiac
Posts: 3326
Joined: Fri Nov 29, 2013 6:53 pm

Re: More fun refurbishing audio stuff

Post by TazManiac » Mon Sep 17, 2018 7:11 pm

(ps- I miss ol Henry Kloss...)

User avatar
DinkyInky
Posts: 2407
Joined: Tue Jul 31, 2012 9:38 am
Location: Where there's more than Corn.
Contact:

Re: More fun refurbishing audio stuff

Post by DinkyInky » Sat Sep 22, 2018 11:12 am

Atomic wrote:
Sun Sep 16, 2018 7:15 pm
Bookworm wrote:The biggest reason that electronics are now 'disposable' is ROHS. Once the solder cracks, they're toast. Lead based solder can last decades, but straight tin cracks in just a few years under thermal stress.
Another "Improvement" (Lead Free!) that is worse for the user. "Preservative Free" == "Guaranteed to Rot"
Then there's the whole, "Acid free pages attract bugs" v. "Acid treated pages are light sensitive and degrade faster" debate. Personally, I'd rather keep my library in the shadows when not being read over going to reach for my book only to find it literally being a bug colony(I still have nightmares over that one).

Years? I have a battery powered bell clapper style alarm clock I got for kiddo that I have to resolder twice a year. If I could find an antique key wound bell clapper alarm clock, I might go broke for it just because no dang solder.
Yanno how some people have Angels/Devils for a conscience? I have a Dark Elf ShadowKnight and a Half Elf Ranger for mine. The really bad part is when they agree on something.

Aphyon chu kissa whol l'jaed.
--Safyr Drathmir

User avatar
Bookworm
Posts: 559
Joined: Sun Jul 29, 2012 11:59 pm
Location: Houston, TX
Contact:

Re: More fun refurbishing audio stuff

Post by Bookworm » Sat Sep 22, 2018 12:42 pm

DinkyInky wrote:
Sat Sep 22, 2018 11:12 am
Then there's the whole, "Acid free pages attract bugs" v. "Acid treated pages are light sensitive and degrade faster" debate. Personally, I'd rather keep my library in the shadows when not being read over going to reach for my book only to find it literally being a bug colony(I still have nightmares over that one).

Years? I have a battery powered bell clapper style alarm clock I got for kiddo that I have to resolder twice a year. If I could find an antique key wound bell clapper alarm clock, I might go broke for it just because no dang solder.
They still make wind up alarm clocks. You can also get older ones from ebay, or shopgoodwill.com

I just looked at the Goodwill site. In six hours, there's ending a Sheffield wind up clock. It'd probably be $20 after shipping.

Acid paper doesn't just degrade in light. They degrade when in the darkness. I have some books I bought in the 80's that are solid yellow, and they've never been in the sun. I'm going to have to dismantle them and scan them in before they finish disintegrating. (cheap paperbacks, but it always feels wrong to take a book apart)
I'll get a life when it's proven and substantiated to be better than what I'm currently experiencing.

User avatar
DinkyInky
Posts: 2407
Joined: Tue Jul 31, 2012 9:38 am
Location: Where there's more than Corn.
Contact:

Re: More fun refurbishing audio stuff

Post by DinkyInky » Sat Sep 22, 2018 1:58 pm

Bookworm wrote:
Sat Sep 22, 2018 12:42 pm
DinkyInky wrote:
Sat Sep 22, 2018 11:12 am
Then there's the whole, "Acid free pages attract bugs" v. "Acid treated pages are light sensitive and degrade faster" debate. Personally, I'd rather keep my library in the shadows when not being read over going to reach for my book only to find it literally being a bug colony(I still have nightmares over that one).

Years? I have a battery powered bell clapper style alarm clock I got for kiddo that I have to resolder twice a year. If I could find an antique key wound bell clapper alarm clock, I might go broke for it just because no dang solder.
They still make wind up alarm clocks. You can also get older ones from ebay, or shopgoodwill.com

I just looked at the Goodwill site. In six hours, there's ending a Sheffield wind up clock. It'd probably be $20 after shipping.

Acid paper doesn't just degrade in light. They degrade when in the darkness. I have some books I bought in the 80's that are solid yellow, and they've never been in the sun. I'm going to have to dismantle them and scan them in before they finish disintegrating. (cheap paperbacks, but it always feels wrong to take a book apart)
I don't use meBay if I can help is, but I'll definitely look up Goodwill, thanks.

We shall have to agree to disagree on this one, because opening a loved book to find it heavily infested is my least favourite way to find a book, and I have many hardbacks from the 80's and earlier that are yellowed, but pest-free.

E-readers in general are brutal on my eyes, which is another reason I avoid excessive amounts of time on them.
Yanno how some people have Angels/Devils for a conscience? I have a Dark Elf ShadowKnight and a Half Elf Ranger for mine. The really bad part is when they agree on something.

Aphyon chu kissa whol l'jaed.
--Safyr Drathmir

User avatar
Bookworm
Posts: 559
Joined: Sun Jul 29, 2012 11:59 pm
Location: Houston, TX
Contact:

Re: More fun refurbishing audio stuff

Post by Bookworm » Sat Sep 22, 2018 3:39 pm

Don't see how we disagree.. I'll admit that none of my really old books have been eaten, but they predate acid free wood paper. They're probably cloth.
I'll get a life when it's proven and substantiated to be better than what I'm currently experiencing.

User avatar
DinkyInky
Posts: 2407
Joined: Tue Jul 31, 2012 9:38 am
Location: Where there's more than Corn.
Contact:

Re: More fun refurbishing audio stuff

Post by DinkyInky » Sat Sep 22, 2018 7:22 pm

Bookworm wrote:
Sat Sep 22, 2018 3:39 pm
Don't see how we disagree.. I'll admit that none of my really old books have been eaten, but they predate acid free wood paper. They're probably cloth.
Misread your reply, sorry. Think I need more zzz's.
Yanno how some people have Angels/Devils for a conscience? I have a Dark Elf ShadowKnight and a Half Elf Ranger for mine. The really bad part is when they agree on something.

Aphyon chu kissa whol l'jaed.
--Safyr Drathmir

User avatar
TazManiac
Posts: 3326
Joined: Fri Nov 29, 2013 6:53 pm

Re: More fun refurbishing audio stuff

Post by TazManiac » Sun Sep 23, 2018 1:25 am

Be careful Dinky, the dude's very name is bookworm...

User avatar
Bookworm
Posts: 559
Joined: Sun Jul 29, 2012 11:59 pm
Location: Houston, TX
Contact:

Re: More fun refurbishing audio stuff

Post by Bookworm » Sun Sep 23, 2018 1:53 am

TazManiac wrote:
Sun Sep 23, 2018 1:25 am
Be careful Dinky, the dude's very name is bookworm...
I'd ask if you were insinuating something, but that sounds more like a blatant innuendo.
I'll get a life when it's proven and substantiated to be better than what I'm currently experiencing.

User avatar
TazManiac
Posts: 3326
Joined: Fri Nov 29, 2013 6:53 pm

Re: More fun refurbishing audio stuff

Post by TazManiac » Tue Sep 25, 2018 1:27 am

Don't worry BW everybody needs a little roughage in their diet...

:P

User avatar
TazManiac
Posts: 3326
Joined: Fri Nov 29, 2013 6:53 pm

Re: More fun refurbishing audio stuff

Post by TazManiac » Tue Sep 25, 2018 10:56 am

btw- My next month or so will likely include

- reConing a few pairs of Speakers

- Setting up a 7.1 Surround Test Bed 'to see what all the fuss is about'...

- Binding Subs w/ Dedicated Powers Supplies (Amps, and/or 'plain stereos' as Sub Amps)

- Upgrade the Media PC's storage and bring it forward into more everyday use. (Truthfully It's a crappy/scrappy dual-core w/ built in 5.1 and an antient video card that outputs SVHS to a big ass'd CRT TV...) W/ an video card upgrade I might go HDMI... :o

I'm soooo behind the Cutting edge, well, it actually IS funny...

User avatar
Bookworm
Posts: 559
Joined: Sun Jul 29, 2012 11:59 pm
Location: Houston, TX
Contact:

Re: More fun refurbishing audio stuff

Post by Bookworm » Tue Sep 25, 2018 1:25 pm

Hey, I'm an IT guy, and I don't even have a MythTV running.
I'll get a life when it's proven and substantiated to be better than what I'm currently experiencing.

User avatar
lake_wrangler
Posts: 3657
Joined: Sun Aug 05, 2012 8:16 am
Location: Montréal, Québec, Canada

Re: More fun refurbishing audio stuff

Post by lake_wrangler » Tue Sep 25, 2018 6:26 pm

Bookworm wrote:
Tue Sep 25, 2018 1:25 pm
Hey, I'm an IT guy, and I don't even have a MythTV running.
Of course not: you said it yourself, it's only a myth... It would need to be substantiated, first, before you could make it work... :P

User avatar
Bookworm
Posts: 559
Joined: Sun Jul 29, 2012 11:59 pm
Location: Houston, TX
Contact:

Re: More fun refurbishing audio stuff

Post by Bookworm » Tue Sep 25, 2018 8:24 pm

lake_wrangler wrote:
Tue Sep 25, 2018 6:26 pm
Bookworm wrote:
Tue Sep 25, 2018 1:25 pm
Hey, I'm an IT guy, and I don't even have a MythTV running.
Of course not: you said it yourself, it's only a myth... It would need to be substantiated, first, before you could make it work... :P
Ah, but it's a Myth. That means it's Transubstantiated.
I'll get a life when it's proven and substantiated to be better than what I'm currently experiencing.

Post Reply