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...

Saturday, 22 October 2016

Arduino 1.6.x compiler options...

I'd noticed recently that since I'd upgraded the Arduino IDE to 1.6.x, some programs compiled and were smaller than they used to be. Great!

... the also don't run so fast... not so great.

After some googling around, the compiler options for optimisation had been changed.

So if you need something to compile and run quickly, you can.

Here's how to change it...

Navigate your way to the default Arduino directory in program files, and locate the platform.txt file

On my windows box, it's at C:\Program Files (x86)\Arduino\hardware\arduino\avr
On my Ubuntu box it's Home\Downloads\arduino-1.6.12\hardware\arduino\avr  (Why did I ./ from the downloads folder!!!)

there's also one in the \hardware directory itself. That's not it!

Mine looks like this :

Now I'd rename this to platform.old, so it's there if we screw it up, or wish to revert to slower, but more space-efficient code.

Now, open this file in your favorite text editor (mine's Notepad++ on windows) and do a find and replace on all instances of -Os (that's the letter O) and replace it with -O2 (again, the letter O) There are 3 instances of it in my file...

Bingo, save that as platform.txt in the directory, and you're done.

Here's my modified file...

You can now enjoy faster, but fatter sketches!

.. or not!

Friday, 14 October 2016

NAD 5425 CD player - no display

Just a quick one. This delightful NAD 5425 CD player.

Arrived skipping / not reading discs and no display.

Skipping and intermittently not reading discs was an easy fix, a quick clean up of the optics with an airduster, and very careful cleaning of the lens (DON'T USE IPA HERE! - it can damage the optical coating on the lens. It's easy just to breathe on it, and give it a gentle wipe with something lint-free). That had it playing even the most mangy looking disc!

No display?

Let investigate...

The main board is removed ....

.. and the display cowl removed (there's a couple of screws underneath, and a plastic clip.)

... and an open-circuit incandescent lamp is the culprit...

To improve reliability, and LED and 1K limiting resistor is fixed in place. Note the capton tape to insulate it electrically from the links on the board below. Anode (+ve) is to the right in this picture.

The LED I chose was a wide-angle, warm white LED, which I hope will match the original incandescent lamp closely.

... which is does nicely!

I've not tried these wide-angle LEDs before. They're quite good. These are both warm white examples, although they differ in colour slightly! You can clearly see the focussed "beam" coming from the right hand LED, and the much more diffuse spread of light from the left hand "wide-angle" LED.

Job done. Another saved from landfill!

Sunday, 9 October 2016

Leak 2100 amplifier repairs.

A while back, David (from the motherland) donated some stuff to the cause.

This Leak amplifier was amongst the things he dropped off...

Dating from around 1974, and mostly valueless... eBay prices these at about £30 at the time of writing.

Still, there's no point in it just sitting in a pile...

It's been through the wars a bit, but that's OK. I need something to practise my veneering skills on, for a forthcoming turntable project, so this may do as a test bed...

Typical 70's construction.

I'd labelled the amp up "Hums" ....

There's something unpleasant oozing out of the top of the positive rail smoothing cap... It's a 6,800uF 40V part....

... I have some 10,000uF 63V parts, which are slightly fatter, but much shorter. The fit in the clips OK, so they'll do....

Powering up instantly blows both 5A fuses on the main board. You can see in the photo, I've lifted R3 and R5 on the small vertical PCB. This is the protection board. It's purpose in life is to blow fuses by shorting out the supply rails with a triac in the event of there being more that 0.5VDC on the speaker outputs. A sort of crowbar circuit.

Powering up again, with new fuses and checking the speaker outputs (with no speakers attached) for DC shows everything in order.

R3 and R5 are soldered back into position and power is applied again. All is well. I wonder if one rail came up before the other due to the new/larger caps?

I check round the caps on the main board for ESR. Remarkably, they all check out OK. Every last one of them! I even checked the calibration on the ESR meter because I doubted it!

The power indicator lamp on the front doesn't work, because, well... it's missing. I'll make up some white LED's to go in...

I had a short length of LED strip left over from when I fitted some lighting in my kitchen, so I cut off a short length. The voltage supply for the lamps is half wave rectified, with no smoothing. It peaks at around 20 volts, so I added a 470 ohm resistor to limit the current a bit, and added 100uF to smooth the supply a bit, so the LED's don't flicker.

I removed the original lamp holder, and fixed the strip in place with a spot of hot-melt.

Looks good....

After a prolonged test in the workshop, the amp remains well-mannered, and sounds decent. It's quiet and produces around 30 watts into 8 ohms. I'm actually quite taken with it, so much so, I'm going to put it in the main hifi set up for a bit.. one issue though... the input sensitivity. It's a tiny 140mV for line inputs. We'll need to fit an attenuator on the input I intend to use for the CD player. Thankfully there's an attenuator switch fitted to the Tuner input, which is switched on the back for two different levels. Looking at the circuit, my calculations show it'll do as it stands. Good news!

Now to make up some 5-pin DIN to RCA leads, and order some veneer!

Talking of 5-pin DIN plugs... this Leak doesn't quite follow convention....

1 is Right input
2 is GND
3 is Left input.

4 is Right output for Tape/cassette
5 is Left output for Tape/cassette....

Sunday, 2 October 2016

Wharfdale Airedale SP2 Speakers.

Well, there appears to scant information on the web about these wonderful speakers, so I thought I'd share some pictures of mine up. Sadly they're not going to be with me long, as they're not exactly wife-friendly, due to there huge size (H 88cm W 46.5cm D 44cm!)

They were Wharfdale's top-of-the-range speakers in the mid 70's.

Tweeter. I saw a thread on a forum that said these were ribbon tweeters, but I don't think so. How do you make a round ribbon?

Upper mid-range, with felt suspension...

4" mid-range, again with felt suspension.

... and the 10" bass driver, with rubber suspension.

They sound fantastic, and are in really good condition. Speakers of this age generally start to have problems with the suspension breaking up, but these are just great. Sadly they're just too it's off to eBay with them :(

Quad 405-2 Amplifier - restoration.

The next part of the Quad series. The mighty 405-2 power amplifier. Famed for it's current dumping design.

This amplifier was made around 1984, as some of the RCA transistors are nicely dated.

This amplifier isn't performing too well. It's distorting, and humming slightly.

The amplifier is nicely laid out, although I'm not too impressed with the safety earthing arrangements. The earth is taken to a point a long way from where the supply is grounded. This can exacerbate ground loop issues. This amp hums, and I also have a friend whose 405 hums quite badly. Could this be the cause?

The ground connections to the speakers are also made separately...

Removal of each amplifier board is made easy by removing the two rubber bungs thoughtfully supplied by Quad, which allow insertion of a long screwdriver to gain access to the lower screws securing each board to the large heatsink at the front. The boards fitted to this amplifier are rev. 7 boards, and are also fitted with voltage limiters, so It's suitable for driving Quad's ESL speakers.

First inspection of the amplifier show some of the Red cased electrolytic capacitors are showing signs of age, looking a bit "sweaty" and having cracked cases.

Two of the caps in my amp (C17 & C2) are bi-polar, which is a pain. C2 can be replaced by a conventional electrolytic, with the positive side to ground, but C17 must remain bi-polar... which is a pain , because they're awful and I don't stock any!

Low-and-behold, C5, a 6.3V Electrolytic is leaking and has turned the pin green!

Both of the large 10,000uF capacitors test like new, so they can stay.

I decided, in an effort to mitigate any ground-loop issues, to ground the speakers and the mains safety earth back to the same point.

So after a blanket change of the capacitors, the amplifier powers up, and tests very well, with no adverse behaviour, and there's certainly no perceivable hum! All the unpleasant distortion has gone :)

There are quite a few websites detailing modifications to this amplifier, in particular Keith Snook's site (here), I did think about implementing some of these modifications, but I'm rather taken with it in stock form, so it will stay like that!

Guilty as changed, your honour ! (There's a joke in there!)

Saturday, 1 October 2016

The Nikon D3100 camera disaster, a thank you, and a recommendation.

Back when the weather was fine, I was out in the garden taking some nice photos at a barbecue party. All was well until I dropped my beloved Nikon D3100 camera onto concrete.... The lens developed a bit of lateral play in the zoom, but it was still working OK....

... until it stopped auto-focusing a couple of weeks later ...

Nothing to it, but to investigate.

I proved the lens was at fault by borrowing another lens from a friend. The camera body was fine...

So I stripped the lens down... sadly I don't have any pictures.

There was a bush missing, which was causing the play, so I fabricated a new one and fitted it. Lateral play issue resolved.

I managed to find the old bush, in two parts, jammed up against the primary lens cover.

 Auto focus was still not working... damn.

At this point I decided to get another lens.

Whilst looking on eBay, I spotted a replacement lens. The description was perfect, but it showed pictures of a Cannon lens. I emailed the seller, who replied, thanking me for spotting the error, and they had corrected the listing. By this stage I had purchased another lens from another dealer.

The box arrived after a few days wait..... Now I'd done a bit of research on the lens before I hit the buy button. Nikon's website informed me the lens was compatible "with all DX cameras"... and mine's a DX camera....

... what they didn't say was the auto-focus wasn't compatible with all DX cameras (well, they do, but you've really got to go looking for the information!)... boo. I needed an AF-S lens, and the new one was AF-P.

I emailed the dealer that had originally listed the correct lens wrongly on eBay (the Canon one) asking if they'd part-ex my new, but incorrect lens for the right one.

They emailed back straight away, and said they'd be happy to swap it for me anyway (despite the fact I never bought it from them!) Now that's service. I suppose I could have sent the wrong lens back, but that would have been hassle....

As a deal wasn't done on eBay, I can't even leave them positive feedback....

So thank you eBay seller alldigital0869. (Shop is called The Photographers Bag link here.) You're the best.

The two recommendations are :

1) Don't drop your camera.
2) Use alldigital0869 on eBay with complete confidence!

There's some posts in the pipe-line with photo's taken with my old Samsung camera, but, rest-assured the Nikon is back!

Monday, 26 September 2016

Quad 44 pre-amp. Minor restoration, and some sensible modifications

Along with the FM tuner I got last week, I also obtained a matching 44 pre-amp and a 405-2 power amplifier. Very nice kit!

The 44 is a very interesting pre-amp. It's got a lovely design of tone control. Quad went their own way with adding tone controls, and made theirs with 3 tone filters and an adjustable slope control.

The look of the thing is even unique.

The pre-amp has a flexible card system. Each input is selected by a CD4066 switch, which connects the selected card. This unit has the standard line-up of "Radio", "Disc" for a Moving magnet cartridge (an MC card is/was available), a CD/AUX card and two tape loops. Excellent.

Not only that, but the Disc card allows differing gains to be selected to accommodate for most carts, and switchable capacitance load too. The tape loops are similarly configurable for level and impedance. Nice....

This later "MKII" model has a re-designed main board and ALPS pots....


CD4066? Known for introducing distortion into the signal path. Thankfully Maxim produce the MAX4066. A much better specified, and pin for pin compatible device....

So, before I start, let's make a baseline measurement of THD (Total harmonic distortion) at 1KHz....  0.059% on the CD/AUX channel.

Not too shabby....

Out with the old, and in with the new....

All 4 ICs are changed.

Whilst I'm in there I evict the Red electrolytics, as they're know to fail, although these all read OK.

Let's have a look at the disc card...

It consists of TL071 op-amps.... which are mediocre. I'll swap them out for some better NE5534, which should lower noise a bit, as well as distortion. These are the better NE5534's with 18V/uS slew rate.

... and here is the main issue for me....

The CD/Aux card....

300mV? ... 300mV!!!!

Since when?

Most CD players put out at least a volt...

All this means practically, is we'll need to turn our volume control down everytime we switch to CD. An inconvenience. We *may* overload the input.

I've seen some CD players output as much as 2V, so 300mV is not going to cut it....

It's also originally fitted with a TL072, which I'll change for an NE5532..

I do some googling, and there's various recommendations about changing the resistors in the feedback loop of the card to reduce the gain to unity... but none of the modifications seem to  relate to the input card I have fitted, an M12815:1. I don't have a schematic, so I sketch one out....

... well, it's already a unity-gain amplifier!

So, what to do? I could trace the signal through and change the gain on the main board, but that will leave me with the same discrepancy when switching between CD and disc or radio.... Nothing for it but to add a bit of attenuation in.

Simply adding a 180 ohm resistor across the existing 820 ohm resistor will divide the voltage down to a more respectable level.

... and it's easy to implement...

Don't forget to do both channels.

So after all out mods... how does it measure?

... The THD has dropped to 0.014%....

How does it sound? Noticeably quieter (noise-wise!), but to my cloth ears, I can't really tell much difference in the distortion.

Right, now to the 405-2 Power amp!

Watch this space....