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"Restored" My Speakers!

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currentkills91

Sat Jul 06 2013, 02:22AM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

I "restored" the speakers from my old tube amp (which sadly has left me) as the paint was peeling really bad, and I just wanted to share!!

I sanded down the cabinets with a sander and stained them a red mahogany (I forgot to take pics before doing this) and touched up the black on the inside edges.

I had previously gutted them and rewired everything with new wire, keeping the original crossovers.

All I need to do now is find some new cloth stuff to cover them, as the stuff that was on there was old and nasty..

They have a claimed frequency response of 25Hz to 25kHz, a power rating of 20 watts, and an impedance of 8 ohms.

1373077226 3831 FT0 1059477 1385978124954428 1361748696 N

1373077226 3831 FT0 998026 1386109204941320 1059489308 N

1373077227 3831 FT0 934950 1386109021608005 427876988 N

1373077227 3831 FT0 1006239 1386108828274691 1833800591 N

1373077227 3831 FT0 1044079 1386108471608060 1321355526 N

Now that I have them looking good, time to build a nice amplifier to go with them. Any suggestions?

Sulaiman

Sat Jul 06 2013, 05:32AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I would look fo a used domestic Hi-Fi amplifier, integrated amplifier, tuner/amplifier etc.
or for battery operation a used car stereo.
Check eBay and local charity/thrift shops.

If you consider the cost of case, knobs, switches, power supply etc.
it just isn't worth building your own.
For a very reasonable cost you can proobably get one with remote control and A.V. switching to work with TV and cable/satelite TV etc.

IF you still want to self-build, then to my ears, the most important feature is 'damping factor'
a low output impedance makes cheap speakers sound much better/more expensive.

currentkills91

Sat Jul 06 2013, 05:39AM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

I probably have every part I need for any amplifier I wanted to build, and when it comes to a case I'm gonna build one tomorrow out of some wood I have laying around.

Cost isn't my concern, as I will eventually upgrading my speakers, so i want to have a nice amp to go with them.

I was thinking maybe a 20 watt class A amp, something like one of Elliot's designs.

Conundrum

Sat Jul 06 2013, 05:47AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

I have a speaker with a damaged cone, originally from some sort of ear busting multi gigawatt bass setup.
Found in a hedge (!)
Seems a shame to waste it, got any ideas?
The coils etc are all fine, its just the cone which is cooked.

-A

Steve Conner

Sat Jul 06 2013, 08:43AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, you could use it as a frame for a deluxe tin foil hat.

I'd recommend replacing the capacitors in the speaker crossovers. They are often non-polar electrolytics, and electrolytics don't age too well. Certainly more likely to give an audible benefit than replacing the wire.

I've built various kinds of tube and transistor amps, see

My favourite is the Douglas Self Blameless. Rod Elliott has solid-state designs that are simpler and will sound pretty much the same. (The whole point of the Blameless, or indeed any high-quality solid-state design, is that it doesn't have a "sound" of its own.)

You can buy small stereo Class-D amp boards based on the Tripath chipset very cheaply on EBay. I know a few people who have bought these and been pleased with them.

currentkills91

Sat Jul 06 2013, 03:48PM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

The crossover components are fine as far as I have tested, I only bothered with the wire because it was old single gauge stuff and the casing was cracking.

I would love to build a small tube amplifier for these. I have a few matched EL84 tubes, and a bunch of matched preamplifier tubes.

I just haven't seen any designs that I really like..

Steve Conner

Sat Jul 06 2013, 04:20PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Tube amps are great fun!

From a scientific point of view they're nothing but a waste of electricity that you'll eventually have to junk when the industry stops making tubes, but there's something about the thrill of high voltage and neat glowing bits that invalidates this argument.

To make a stereo tube amp, you'll need a matched pair of output transformers, possibly the hardest part to source. You may end up having to buy them new. Edcor offer pretty good value for money.

currentkills91

Sun Jul 07 2013, 03:38PM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

I happen to have an old pair from the amp I had that died, so I have just about everything I need. I just need to find a good design.

Conundrum

Mon Jul 08 2013, 06:44AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Has anyone considered using a wideband MEMS microphone to fine tune the filter to match the speaker?

It occurs to me that using a somewhat older technology ie CdS photoresistors in the filter elements would be very effective and allow precise tuning which could not be done with an FPGA.

Would also work with JFETs or OCJFETs as this approach is used to tube amplifiers so the output stage remains stable at any volume.

-A

Steve Conner

Tue Jul 09 2013, 10:56AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

In traditional speaker systems, the crossover is tuned at the design stage. It's assumed that the drive units will stay consistent in production and won't age.

Some of the latest high-end speakers, like the B&O Lab 5, use a DSP crossover that can tune itself with a pop-out microphone, but this is mainly to compensate bass room modes, not changes in the mid and HF drive units. An excellent idea IMO as many rooms have terrible bass resonances.

I have an old Tektronix distortion analyser that uses your other trick, a notch filter tuned by photoresistors, but it's not recommended for new designs. There was talk of banning CdS cells due to the cadmium content, but they still seem to be on sale. JFETs and JFET optocouplers have pretty poor distortion performance when used as linear attenuators, not really good enough for hi-fi.

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