Dansette Junior Deluxe repairs & modifications.

Will turned up for an emergency curry. There was something ominous lurking in the boot of his car ....

It's a small Dansette Junior Deluxe record player...

"Can you take a look?"

Yeah, why not ....

It's in good cosmetic condition, and dates from around 1961.

Further inspection reveals some issues...

The valve (yes, just one!) is rattling around in the bottom, but is thankfully undamaged. The motor suspension has a few bits missing and the platter won't seat. These are really quite minor issues and are soon sorted.

Once the thing is spinning round reasonably, We try playback .... It's awful. Distorted and really low in volume...

The amplifier is simplicity itself. It has a nice mains transformer so it's reasonably safe, even has a 3 core mains lead :)

The output from the transformer is rectifier by a metal rectifier, and smoothed by the 16 and 32uF capacitor block, along with a 47K resistor. The smoothing cap is in really good condition!

The cartridge is a BSR TC8 medium output crystal cartridge,  producing an output of a few hundred mV or so. This feeds the top of the volume control, and straight onto the grid of the EL84 pentode. There's no cathode bypass capacitor fitted to this unit, nor an indicator bulb, but this is the nearest schematic I had ...

The distortion is partially caused by the 0.05uF tone control capacitor (a dreaded hunts), and is changed ...

The rest of the distortion, and the woefully low output is being caused by a poor cartridge. It's terminals have got chronic verdigris, and this means the crystal inside will have turned to goo. It's a very common failure. (It's not all bad though, as this mono heavyweight cartridge will have chewed Will's records to pieces.)

So we dig around in the box of phono carts to find a suitable donor. The big issue here is, we have nothing to mount to, except the original "flip over" mount...

There's a couple of Acos M7 moving magnet carts that may well do ...

... and after a bit of filing, it fits !

Tracking weight is set for about 2.5g, and it manages to track the test record.... but we can't hear it ....

The output from the Acos M7 is around 1mV .... not enough to drive the EL84's grid much at all... we will need to make an amplifier. Also the output from the crystal cartridge approximately followed the  RIAA equalisation curve, so no correction in the amplifier was needed. We'll have to add this, otherwise the output will sound very thin and tinny.

OK, so the above was quickly dreamed up. It's a (very) basic phono stage, and has some simple EQ in the feedback loop, to approximate the RIAA curve. 

  

I've stolen some power from the 6.3V heater winding on the mains transformer inside the record player. You'll notice there's only a half wave rectifier here, as one side of our heater winding is connected to ground. It's imperative to get this the right was round or you'll short out the heater winding on the transformer, and it will burn out pretty quickly... 

C1, R2 and C3 form a filter for this simple power supply. The cartridge is connected to JP2, and it's loaded by R1. C1 couples the audio though, which is biased to half-rail by R3 and R5. This is then fed to the op-amp, which does it's amplifying and RIAA correcting duties, and then passes the audio out via C8 to our existing volume control. C4 provides DC stability, and a little sub-sonic filtration.

A board is etched...

And duly fitted....

You'll notice the cable coming from the cartridge is screened. It was originally a twisted pair, but the hum pick-up was ghastly, as the arm is all plastic and has no shielding, lives over the mains transformer, by the mains input!

... and, because nothing in life is every easy, the mains switch failed open circuit during testing ! It was stripped and repaired....

How's it sound? ... honestly? Pretty damn awful, but at least Will's records are safe (r) 

here's some more pictures, including the obligatory arty valve shot ;)

... the big pre-amp project is coming ...

Kenwood BM250 repair.... and Doz' wholemeal pizza dough recipe

Friday night. Pizza night.

I like to make my own pizzas. I don't particularly like white bread bases, so a few years ago I took to making my own wholemeal pizza base. I use a Kenwood BM250 bread maker I bought about 10 years ago, on it's dough setting to make the dough, roll it out and bake the pizza. Excellent.

Well I'd set the machine going, and it was whirring away in the kitchen whilst I was working in the workshop. *CLUNK* and the house power tripped. The mains monitor text me! I went to investigate. The RCD had tripped, indicating an earth fault somewhere, and refused to reset. I unplugged the bread maker, and it reset... and I was stuck with some half mixed dough...

After ordering domino's... I decided to take a look...

First thing of note was the damaged mains cable ...

Tsk tsk! I should have noticed this before...

Much unscrewing followed, and the mains cable was replaced. Although requiring replacement, the cable's inner insulation was intact, and not the source of the problem...











Here you can see the motor drive for the stirrer thing, and the control PCB. I performed an insulation test on the motor at 1KV, and all was well....

The heater element inside the oven compartment, however, showed very poor insulation of just 10 Kilohms when cold. No good at all.










The element is removed. There's a small screw and a nut holding one end in....










... and a screw and nut holding this ceramic saddle clamp arrangement on the other.











A replacement element was found inexpensively on eBay (£6.39 delivered) and put the problem right. Another saved from landfill, and £70 cheaper than a new machine.

and if you want to try a healthier wholemeal pizza dough ... here's my recipe!

230ml Water

380g of wholemeal bread flour

~30ml Olive Oil ( a good glug! )

1 packet of bread machine yeast.

Some Italian herbs and spices!

Enjoy!

Arduino programming tool. ISP and IDE.

The big hifi pre-amp is on hold for a bit, as I await some parts to arrive.

In the interim, I've wanted to make a programming tool for ATMEGA328 chips, that will ease programming changes when using them in stand alone units. I've looked about on the net, and there's some solutions which are nearly what I want... but nothing quite hits the mark.

The idea is to have a ZIF (zero insertion force) socket into which the blank chip to be programmed is inserted. I want it to be able to program chips with the bootloader, as well as straight from the IDE.

The fitted micro is loaded with the "Arduino as ISP" sketch. The switch, S1 & S2 (actually 1 four-gang switch, I just didn't have a library for it!) is used to switch between ISP programming for bootloader, and IDE Programmer. LEDs indicate various functions. D1 is ISP heartbeat, to show it's OK, D2 is Error in ISP programming, D3 is ISP programming activity, D4 indicates ISP mode, D5 indicates IDE mode (also lights when in ISP mode, as I forgot about the steering diode D5), and D6 indicates slave activity during bootloading (ICP1).

...a simple board is designed and etched....

The keen-eyed amongst you will notice the steering diode, D5 is missing from the layout. I mounted it underneath the board, as I'd missed it...

... and it works a treat !

Oh yeah, a quick note on R2 and R7... both 1 megohm across the crystal. I've picked up this bad habit from the original Arduino design. It doesn't need to be there. It was originally to provide some bias for gate-based oscillators. The ATMEGA328 has bias provided internally. It's a waste of 1 meg resistors! Don't bother to fit it, and I promise never to include it again!!

The big hifi preamplifier project - input selection.

Amongst the ever changing line up of hifi kit at home, I feel the need for more homemade bits of it...

I mean there are some...

This lash up, for example. Built many, many moons ago, and largely undocumented...

It's a Systemdek with a unipivot arm, and a nasty otofon Red cartridge, home made all valve pre-amp with posh stepped attenuator, RIAA and EM84 indicator tubes, and an amp, made from junque parts at the time, featuring a GZ34 rectifier, an ECC82, and two something-or-other pentodes in SE output. A staggering 3 watts on a good day...

The current line up is a bit "not home made enough" ...  The BSR (here) is turntable of the minute, although there are more than a few turntables here! The amp is good, a Rotel 6 channel thing, with two channels bridged (and two unused), and the pre-amp is a Rotel. There's an Arcam CD which I ought to get round to putting a new optical ass'y in, as it's as weak as dishwater...





The Rotel pre-amp is OK, but it's MC phono input is as noisy as a hen with one chicken.










So, after watching a  Techmoan video on youtube (Here) I was somewhat inspired. Yes, I would like more inputs, especially two turntable inputs. It needs to have a phono stage for MM (Moving magnet) as well as MC (Moving coil). I'd like some subtle tone controls. I'd like remote control. I'd like some VU meters or similar. I'd like a nice colour display with touch screen. I like an option to use the new Korg Nutube . I'd like it all to fit in a 2U case.... not much to ask is it?

So I set about sketching some ideas down. Power supply board, main pre-amp board, input and output switching board, microcontroller board, and finally, but my no means least, a decent phono stage.

I'm going to tackle this in a few posts, as it's a big project.

First off... Input selection.

A couple of options come to mind to deal with input selection.
First though was some nice analogue switches. A slack handful of MAX4066 switches would work well, in a similar fashion to those I fitted to the Quad 44 here.  Reasonably easy to implement, but they do add some distortion and noise.
What about a bunch of small signal relays? Essentially noise-free, switching not quite as easy, and expensive ... but I don't want to be doing this twice...
Inputs?
Two phono. 1 CD (1dBV adjustable) , and then 4 line level (-10dBV)
Outputs? Recording output (although I don't really have any recording devices, the option to connect a laptop or something would be nice), and the main output to the power amplifier.

Right .....

From the top... 5V and the control signals come into JP1. K1 (the phono switching relay) is switched by Q1. All the other relays are driven by a ULN2003 darlington array. K2 is a "mute" relay and grounds the output. K1 switches between the turntable inputs. This is output to JP4, which will feed the phono stage. The phone stage will then feed the signal back to JP7, and via relay K3 to the output JP5 which will feed the main pre-amp board. The main pre-amp board then feeds the signal back to JP2 and JP3, and is routed through to the output sockets (via the mute relay in the case of the main output). K3 is the CD player input. Notice it has two attenuators, R2 & R3 to reduce the level a bit to match the other sources. K4 through K8 are the other normal line level inputs. Notice the different grounds, GND is the +5V ground, and used by the relays and associated switching. AGND is the audio ground. GNDA is the phono ground. I've included a link at JP6 should we wish to ground them here. I think it's going to be best to make a start point of grounds at the power supply, but I've included this here for a bit of flexibility.

Want more inputs? Add more relays another ULN2003 and some more sockets! (Don't worry about the number of selector inputs, we can use a shift register if you get seriously carried away)

Got that? Right ....

It should all fit nicely on a single sided board.

 

The red trace is a wire link.

It's duly created using toner-transfer and etched...

... silk screened ...












... and finally assembled.






Relays are Omron G6A-274P (available everywhere, but shop around, prices vary. I managed to get these for £1.79 each from Farnell) and the double phono sockets are PSG01550.

Coming next, the main pre-amp PCB ...

... and just what does CoaSt stand for?

The Korg Nutube 6P1...

It is with much excitement that I opened a box from RS Components....

It's here!

Possibly the only new thermionic device made this century! Oh the excitement!!

It's a tiny double triode which promises "Real vacuum tube sound. The real triode structure produces a warm, unique vacuum tube sound, delivering excellent linearity."

It's built using vacuum florescent display technology, and is tiny. 

Marketing guff can be found here ... http://korgnutube.com/en/

and real data can be found here:

https://docs-emea.rs-online.com/webdocs/15db/0900766b815db1b5.pdf

It already is appearing in guitar pedals all over the internet, and it's going to feature in a project near here very soon.

Tip for drilling homemade PCBs.

Here's a quick tip .... if you're as myopic as I am, try this out...

Here's my PCB drill in it's stand. It's a foul thing. It was dirt cheap when I bought it 15 years ago ... The rubber coating on it has gone all sticky ... yuck...

Now look at the bottom...

I've mounted one of those small 3w LED's there, left over from another project...










Makes alignment of the drill bit with the pad on your PCB a breeze.....


You'll notice it's slightly off-centre, this is avoid drilling through it ....

.... yeah, you know how I found that out!

Modifying the Fellows A75 A4 laminator for making PCBs. Toner transfer the posh way!

Now, if I'm making something up, it's often easy to make a simple single-sided PCB up quickly, and professionally by using the toner-transfer method of PCB manufacturing. I've been doing it for years, but the results are always a bit hit-and-miss. Use google if you haven't heard of it before, there are many guides on the web (although no two the same!) , and I don't intend to duplicate those here.

I have tried many different types of transfer paper over the years, from the proper stuff, to plain old A4 paper, the best I found for years was a copy of the New Scientist magazine! Sadly they changed to thicker, shiney paper a few years ago, which doesn't work well at all. The best at the time of writing seems to be "The Economist", which is a shame, as it's nowhere near as good a read as "New Scientist" before it get's recycled into PCB making materials!!

... anyway ...

The last board I did, I tried an experiment, by borrowing Mrs Doz' laminator from her office. I idea was to see if it would transfer the toner from the paper to the board, whilst keeping a constant and steady pressure on it. Well, results were mixed... it really pushed the board through too fast for proper transfer to take place. I ended up transferring the toner with the conventional clothes iron, and then passing the board through the laminator, which resulted in an improved board after a couple of goes. It did, however give me an idea ... make the motor run slower....

So, rather than incur the wife's wrath and modify her laminator, I picked up a Fellows A75 A4 laminator from Argos for £16....

I initially tested it would take the thickness of the board by passing a blank piece of PCB stock through it... yep, works a treat.

So, to disassembly... There are 4 pozi screws underneath (great, not even some torx or bizarre security screws to bother me!)

So (from left to right) we have an essential mug of tea, the motor, drive rollers and heaters, and finally a PCB on the right....

A couple of things to notice about the PCB... 

There's some sort of timer in there to shut the unit down after it's been on for 30 mins (just in case you leave it running). It's unlikely to bother us much....

The low voltage electronics (the timer, and LED's etc) are driven from a power supply formed by a wattless capacitor dropper... so a word of warning... all of these voltages on this board will appear to be referenced to the mains. This would present us with a shock hazard and a problem if we want to interface to them...

On to the motor....

It's something I used to refer to as a "Le Cruzet" motor. A synchronous motor with built in gear box. As we can see from it's label, it rotates at 4 RPM (4.8 RPM if you live on that funny bit of the planet that uses 60Hz mains). That's a bit of a pain. I was hoping for a small DC motor I could drive with some PWM to get the speed nice and regulated (although if I was building a cheap laminator, I'd be using exactly this motor too!) 

So, how can we control it's speed?

Well, it's synchronous, so we'll need to lower the AC frequency driving it .... Ugh ... don't fancy this idea much.. generating a few tens of hertz at 240 V RMS is not going to be a cheap fix....

What about phase modulation? Daft idea. It may vary the speed, but will destroy the motor's torque, and won't vary the frequency. May cause overheating and failure in the motor's windings because of the resultant unpleasant waveform.

What about PWM? Nope, DC only ..... or is it????

How about really, really slow PWM? Really really slow.... 

I'm talking about switching the AC to the motor on for ~.5 second, off for a second, and so on ......

It'll inch the board forward, cook it for a bit, and inch it forward again ....

It's just stupid enough to work....

So what do I need? 

A 555 timer, a slack handful of passives, a transistor and a relay...

or an arduino (or similar, running a modifed blink sketch!),a transistor and a relay...?

I'll go with the latter, as it'll be easy to adjust by fudging the software, and most of the hardware is built for us.

Enter the relay module, and the weird and wonderful Digistump Tiny85 module... just the ticket, and small enough I should be able to squeeze them into the case.

I've used the normally closed relay contacts, so if I do want to use the laminator without the speed control, it will work fine with the speed control switched off. The relay contacts are connected in series with the motor, and the relay control pin to P0 of the digistump.

A design is laser printed onto a piece of paper from "The Economist", and a test piece of board stock is cleaned up (I know they're a different size, but it's only a test)

The paper is tightly folded round the board so it doesn't move, and stuffed into the mouth of the hungry laminator! The "printed" side needs to be facing the bottom roller, as that appears to be the roller that's heated.

I left the speed controller off (so the unit was running at normal speed) whilst it reached temperature.

I ran a couple of tests, trying different speeds.




and into the sink!













I finally settled on 4 seconds off time, and 0.5s on time.... which produced nice, repeatable results ....

and left us with the digistump code looking like this....

void setup() {
  pinMode(0, OUTPUT);
}

void loop() {
  digitalWrite(0, HIGH); //Turn the motor off
  delay(4000);
  digitalWrite(0, LOW); //Turn the motor on
  delay(500);
}

So the electronics is all boxed up, and driven from a redundant mobile phone charger...

A few words of warning....

We're putting paper in here, which is being exposed to high temperatures for more time than it would be in normal use.... If it should jam, there's a risk it could smoulder and catch fire, and ruin your day... DON'T USE IT UNATTENDED!

It clearly states "Up to 80 Micron" on the box. We're really taking the P*$$ here, as my boards are 1.6mm thick, plus the paper (folded) so don't expect it to last ... but while it does .... get making!









... oh, and you can use the same idea to print a "slik screen"...

Arduino Shakespearean Insult Generator

Hither is a little excit'ment thing I've hath built, to fig thy friends in the words of the bard ...

There are plenty of Shakespearean insult generators out there as webpages, but here's an implementation you can keep in you pocket.... (but someone came along and invented the smartphone, which sort of renders it all academic ... never mind... carry on!)

It's basically an exercise in cramming lots of text into the PROGMEM of an Arduino Uno.

There are 3 words stored, each having 53 variants, giving a total of 148,877 different insults....

Compiling for Uno, shows us the efficient use of memory ..

Sketch uses 4658 bytes (14%) of program storage space. Maximum is 32256 bytes.
Global variables use 85 bytes (4%) of dynamic memory, leaving 1963 bytes for local variables. Maximum is 2048 bytes

Code can be found on my Github ... https://github.com/andydoswell/Shakespearean-Insult-Generator

Have fun !