Sunday, 20 November 2016

Thank you.

Well, some time last week, my humble website slipped past 40,000 page hits.

Thank you all so very much.

Here's some stats since it's inception back in May '14

Friday, 18 November 2016

A quick look at the Quad ESL 57 loudspeaker.

Remember the Quad gear I got a while back? Included were a pair of the famous Quad ESL 57 speakers.

I've been dreading looking at these, because the serial numbers indicated they were quite early units, dating around 1960 or so... and these don't age particularly well, as the electrostatic panels start to fail with age...

Now, for those not au fait with electrostatic speakers, they work in a different manner to conventional speakers (which have a cone to radiate the sound, driven by a coil of wire and a magnet). The speaker diaphragm itself is a piece of metalised plastic film, which is charged up to several kilovolts. Audio is modulated onto this high voltage by a transformer, which causes the film to vibrate, and produce sound.

The ESL 57 is so-called because Quad started production in 1957. Each speaker has three panels, two bass and one smaller treble panel. All three panels run from top to bottom. Bass left and right of the central treble panel.

This is one of the pair with the back removed. You can see the three panels. There's a large audio transformer in the bottom left, and a smaller power supply unit to the right.

The power supply consists of a transformer, which steps-up the mains voltage to around ~650VAC and feeds a rectifier and voltage multiplier, which derives the ~4KV to charge the panels.

Here's one of the audio transformers...

... and here's one of the power supply units. You can see the transformer, and the multiplier unit above it, thankfully indicating this speaker was rebuilt sometime after May 1972. The other speaker was rebuilt at the same time by Quad.

The mains wiring (externally) was in poor shape, and lacked a safety earth, so was replaced, and the speakers gingerly powered up.... both fired up and produced audio straight away, although they were both quiet. (The temptation here is to whack the volume up, but these speakers are only rated at a few watts (maybe 20), to match the original Quad II amplifier (or a 405-2 fitted with voltage limiters as mine was here.) Winding the volume up causes the audio modulating voltage to rise, and cause the speaker to arc over, and can cause irreparable damage to the panel, necessitating a re-build. ) After a few minutes, the volume slowly increased as the panels charged up.

Now I had never heard a pair before, but I had heard comments that they don't produce much bass. Well, that's true to an extent. Don't expect trouser-flapping amounts of bass, but what there is is very detailed, and the treble is incredible. A pair image fantastically. You do really need to be sat in the right place in front of them to get the best effect, but they are something else. The music seems to be in your head.

I was hooked. I then wasted away a whole evening just listening to music.

Sadly Mrs Doz is not quite so hooked. They're big (although slim), and not exactly matching Mrs Doz' impeccable interior decorating standards... so they must sadly go.

Tuesday, 8 November 2016

Technics SU-V40 amplifier repair.

It's time for this thing's turn on the bench.

It's a rather tatty looking Technics SU-V40 amplifier, dating from about 1986-87

It should be a great performer, but this one isn't...

It works after a fashion, but all is not well. It has a "rustle" on the left channel. Probably a dirty pot, I thought.

The amp has a slightly unusual look to it internally, as the main output stage has a small heatsink, coupled by a "heat-pipe" to a large heatsink to it's left.

This is the current amplifier....

...It's a large "Class AA" IC...

I'm not quite sure what Class AA is, but it's really Class AB1!

This is the driver, or voltage amplifier..

I cleaned up the volume pot, which, whilst noisy, wasn't the source of the rustling sound ...

Then a clue, as the amp warmed up, the current drive LED flickered along with the rustle, indicating the amp was trying to go into "protection" mode and cut out...

Sure enough there was a small DC offset occurring on the left hand output... I cleaned up the two bias pots. This didn't help.

It turns out Q409 is thermally poor and noisy. It starts off bad when it's cold, and gets worse as it warms up! A quick squirt with freezer spray on the cheap proves it's guilt. It's a 2SC2631 in the voltage amplifier. Amazingly, I have one..

Replacing it provides a complete cure. Another saved from landfill, even if it looks like it was already there!

Soak tested with Debut by Björk, a fine album I'd forgotten about...

Sunday, 6 November 2016

Nakamichi Dragon.

Nate called.

"Can you give my Dragon a service?"

Yeah ... why not?

I though I'd share a few photos.

This must be the Rolls-royce of cassette decks. Adjustable everything.

There's a lot going on inside...

It's auto reverse, but in standard form, with two pinch rollers, rather than the "flip the tape round" of the Nakamichi RX series

... here's what makes it special...

... see those 4 gear wheels? They are used to alter the azmuth alignment of the head on the fly.

A truly remarkable piece of engineering, and the pinnacle of cassette reproduction!

I've heard some rumours on various forums that the playback of pre-recorded and tapes recorded on other machines is not so good on these decks. I must say that's not my experience at all. Playback is superb.

Friday, 4 November 2016

"Solder creep" and an unpleasant smell...

Just been sat in the workshop doing a few little jobs, and there's a funny small of something getting too warm. I've noticed it on and off for a couple of days, thought it was the wood burning stove in the other room yesterday, but tonight, it's definitely coming from round the computer area.... immediate investigation required.

After a couple of mins I found it.

There's an extension block connected to the output from a UPS. It's warm. Damn warm....

Further investigation shows the neutral has been overheating. I've disconnected it here. The wire has been soldered! Never, ever solder a mains cable (or any stranded cable for that matter) before fitting it into a screw type fitting. The solder "creeps" up the cable, and leaves a resistive loose connection behind.

This lead was carrying less than 500W ... so nowhere near maximum load.

I wonder how many more of this brand I have?

Not many I hope. This one's for the bin...