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Friday, 18 August 2017

Replacing the Under Saddle Pickup on an Electroacoustic Guitar

Over the last few months the pickup on my guitar has developed an unpleasant distortion. The A string produces a gritty buzzing sound. At first it was a very occasional, and intermittent problem. I thought I had cured it by putting a shim of paper between the saddle and the pickup under the A string, but the sound came back.

The guitar is a Tanglewood Odyssey cut-away. It is a "bowlback" design with a fibreglass back - I bought the guitar back in 1992, so it has done good service, but replacing the whole guitar is an expensive proposition. So I started reading-up about under-saddle pickups on the internet. The name ARTEC kept coming up, and their pickups looked very similar to what was fitted to my guitar.

Artec website.

I was particularly attracted to the SF-607 model because of this phrase " It reduces buzzing sound caused by curved bottom of saddle or rough surface of pickup cavity on the bridge of guitar. " - I suspect this may be the "buzzing sound" that I have been hearing, or else the pickup has developed a fault. Unfortunately the Solidflex pickups are not at widely available on E-bay as the PP and PG versions, but I found one in Singapore for about £12 and made the purchase.

The SF-607 is physically very similar to the pickup I took out. It is about a millimeter shorter, but the spacing of the piezo blocks is exactly the same. The 2.5mm jack-plug is finished more neatly than the old pick-up with a metal cover and gold plating on the contact surface. In the photo at left, the new pickup is at top and old one below

The pickup strip is blue and branded, the old one is covered with plain black heatshrink sleeve, but the width and thickness I measured to be within 0.1mm of the original. This was very useful because it meant it was almost a "drop-in" replacement. I say almost because the original was a snug fit in the slot, which required a little judicious filing with a needle file to accept the new pickup. I expect I could have forced the new one into the slot, but I wanted to be able to get it out again if I had to !

The 2.5mm plug means that there is no soldering of wires - and the preamp and EQ unit in the guitar seems to work just fine with the new pickup. Here are a few more pictures:
 The pickup goes underneath the white saddle, which is a hard plastic, or bone material set in a slot in the wooden bridge of the guitar.

A hole is drilled at the bottom end to allow the screened cable of the pickup to pass through to the inside of the guitar. The hole is just big enough to allow the 2.5mm jack plug to pass through. This picture shows the old pickup lifted out of the slot, and the shim which I had added to try and fix the distortion problem.

The new pickup just plugs into the preamp unit. Remember to tidy and tape down the wires inside the guitar before putting on the new strings - otherwise they may flop about and rattle when you play it. I used "gaffer tape" (otherwise known as "duct" or "duck" tape).

It is a useful opportunity to clear the dust out of the inside of the guitar - it had got decidedly mucky in there!
Here's another picture of the EQ unit. - the battery holder and front panel is separate, and goes on the outside of the body, the screened metal box is on the inside of the body, and when the screws are tightened it all clamps up tight in the side of the guitar.

I couldn't photograph that operation because I needed at least three hands to hold the EQ unit, front panel, guitar, screw and screwdriver - I didn't have any appendages left with which to operate the camera.

So does it work?
Yes it does, but it is different to the old pickup. The output is lower and there is a bigger variation in output between the individual strings. The A and D strings are louder than the others.

Here is an image of the six strings plucked one after the other and recorded in Audacity, first with the old pickup:

You can see the distortion on the "A" string, as the envelope looks "broken".

And then with the new:

The output is lower, overall, but the A string and D string are strongest. I estimate the top E to be about 6dB down, but the A string seems to be as strong as the old pickup. The good thing is that the output is clean and distortion-free. So I shall leave the new pickup in place for the time being and see how we get on with it. I will have to crank the volume up on the amplifier a bit to compensate for the lack of output.

Hugh M0WYE

Thursday, 22 June 2017

Another Whistle

I've just made a second whistle, this one is longer - in the key of G and, this time, using the black PVC pipe. I made the fipple block a bit longer and cut it at a sharper angle. This makes it a bit easier to play in my opinion.

If you didn't read my last blog, these are "penny whistles" made to the design of Guido Gonzato.

The black pipe makes a perfectly serviceable instrument, but it is much harder to see the pencil marks, and, conversely it shows the scuff-marks from sandpaper much more clearly! A strip of masking tape along the tube was useful to mark out the positions for the holes.
Here's a picture of the two whistles together.
73 Hugh M0WYE

Saturday, 17 June 2017

Low-Tech Whistle

I've got one of those cheap "Generation" tin whistles in the key of "D". It's quite fun to play, but it is quite high and squeaky and when I try to play with other instruments, it is horribly sharp. I like the sound of the lower pitch whistles, such as you hear played on tracks by Capercailie and on the Transatlantic Sessions television programs, but, although not very expensive, still looking at upwards of £50.

But I found an interesting website by Guido Gonzato here: Guide to making low-tech whistles

Now I have found designs for whistles before, but I have had difficulty getting the same materials as were used in the original. If you substitute a different type of tubing it has an affect on the length and hole position. But I found 2 meter lengths of this 20mm diameter PVC pipe in B&Q and Wickes for 99p and 18mm diameter hardwood dowel which can be made to be a snug fit inside by sanding off about half a mm.

So today I made one, and I am very pleased with the result (photo left). I won't go into detail about how I made it because Guido's instructions (in the above link) are very detailed and I followed them very closely.

I made the Alto B-flat instrument, and I found that I needed to leave the tube about 1mm longer than was specified in the diagram.

In fact, because my tube started out quite long, I checked his overall lengths at F#, G, G#, and A and found they all needed to be 1mm longer than specified - that probably comes down to the type of tube, he says "not all PVC pipe is created equal".

So I wanted to upload a sound-sample for you, but I don't see a way of doing that on Blogger, so it will have to be in the form of a video ...
Sorry I'm playing it a bit like a recorder, it's just to give an idea of what it sounds like! Guido has some much better sound samples on his website.

I'm intending to make some more of these, in different keys, and perhaps even longer and more mellow :-)

Anyway, if you like making simple musical instruments, I encourage you to have a go at making one of Guido's low-tech whistles.
Hugh M0WYE

Saturday, 10 June 2017

Lidl's Vice

I've got a variety of bull-dog clips, clothes pegs and "extra hands" to hold small items when soldering. I did have a small table-top vice, but my son "borrowed it" and it has obviously proved very useful to him ... haven't seen it since :-)

When I saw that Lidl's were offering a table-top vice for eight quid, I thought I would give it a try.
Lidl's Table Top Vice Offer.

Some of their tools are very good value for money, occasionally I have wished that they were better quality!
This product seems ok ... but there are some important things to be aware of. One is quite obvious when you pick up the box in store - it isn't very heavy! It is not made of steel, it is made of an aluminium alloy (clearly stated in the instructions) and this means the casting is not going to be very strong. Don't expect to use it like an expensive Record vice for hammering and bending thick metal, it will break.

The aluminium will likely not be as hard-wearing as steel would be.

The main tommy-bar, used for tightening the jaws of the vice is quite nice, with a detent at each end, so that the bar clicks into place at each end of its travel. However I found that all the screw threads felt rough and "graunchy" - not smooth at all. Although the instructions make no mention of lubrication, the first thing I did was to apply grease to all the threads and the grooves where the moving jaw of the vice slides. I also greased the ball and socket and now it feels much nicer to use.
hopefully that will extent the life of the threads a bit too. Time will tell.

The vice is supplied with soft, plastic covers for the jaws, which could be useful for holding some items, but will obviously be useless for soldering, because they will melt! Underneath the plastic covers are smooth metal jaws, one of which has two grooves at right-angles. The grooves are for holding round objects.

Supplied with the vice is a clamp for holding tubes of between 38 and 43mm diameter. This seems rather a limited range to me, and it is complicated to fit the tube attachment. To do this you have to remove a the jaws, which requires the use of the supplied hexagon wrench. However, the fact that the jaws can be removed does allow for the user to create their own attachments.

I'm thinking that this will be very useful for holding plugs, sockets and circuit broards instead of chasing them round the bench with the soldering iron.

Hugh M0WYE

Sunday, 4 June 2017

Oh bother ...

Wondered why I had no audio this morning. Went to unscrew the cover on the mic jack and it fell apart in my hands. Yuk! cheap plug. Now replaced by a gold plated on - hopefully last a bit longer!

Wednesday, 31 May 2017

TYT MD380 Hands Free Kit - in use

Thanks to Colin G0PHO and Bradley M0XBW for the on-air test today - and enjoyable mobile QSOs! I can confirm that the hands-free kit is working well.
I thought I would add this photo of the radio in the car, although it is a little confused because I still have the wiring for the FT60 handheld here too. There are two toggle switches taped to the cigarette lighter plug, bottom right. the left hand one is for the DMR radio.
The "well" in which the radio sits is in the centre console and the TX/RX switch is just in-front of the gear lever, so it is easy to find without looking.
I use the internal battery of the radio. In the old days you could get more RF power out by running your handheld on 10 or 12V derived from the vehicle supply, but the modern radios produce just as much output when running from internal batteries. Also, this approach prevents alternator whine and ignition noise from the car electrical system appearing on the transmitted or received audio.

The cigarette lighter plug here is a mobile phone charger and nothing to do with the radio set-up.

There are a couple of general comments I would like to make about the TYT MD380, in case you are thinking of getting one. I find the display quite difficult to see out doors in daylight - quite impossible if the sun is shining on it. The colour display is very pretty indoors, when the backlight is on, but goes completely blank when the back-light switches off. I find I am constantly twiddling the volume, or pushing the power up-down button just so the light will come on and I can read the screen.

Also the radio is supplied with a charging stand - with a nice LED that is red when charging and goes green when it is cooked. I like that, but it is powered by one of those horrid little plug-top power supplies and it generates S9 noise right across the 50MHz band - ughh! I don't think it has any filtering in it at all, such a shame for an amateur radio product, and makes you wonder about the safety of the device if they can't be bothered to meet EMC requirements. So no chance of using six meters when the radio is charging.


Sunday, 28 May 2017

Hands-free kit for TYT MD380

I have finally got round to it!
To my shame I see it was nearly a year ago that I worked out the microphone and speaker connections on my TYT MD380 handheld - see the blog here:
Mic and speaker connections for TYT MD380

I have a home-made hands-free set up for operating mobile with my analogue handheld (an FT60E) and I would like to use something similar for the digital radio.

The microphone is a small electret condenser capsule, mounted on a microphone boom of galvanised iron wire (coat-hanger wire!) which is attached to a baseball hat. The microphone is quite close to the mouth, but not directly in front to avoid breath-blast. When I made my first version, I stitched the wire to the front of the cap, which was quite time consuming. The current one is glued to the back of the brim with hot-melt glue. Not very pretty, but quite quick to do.

The transmit switch is a toggle switch that is taped to the side of a cigarette-lighter plug that is located very conveniently beside the gear-change stick. This makes it very easy to flip between TX and RX without taking my eyes off the road. And also doesn't involve drilling any holes in car.

I use a Diamond dual-band mobile antenna on the motor car, mounted on the tailgate and connected to the radio via RG58, a BNC and one of those BNC - SMA adaptors.

On the radio, under a plastic cover on the right-hand-side are two sockets, a 2.5mm diameter jack and a 3.5mm diameter jack. These are dual purpose, the 2.5mm one is used for the speaker connection, the 3.5mm is used for the microphone, and the radio is put into transmit by connecting the ground connection of the microphone to the ground connection of the speaker. The two sockets are also used for a USB type serial link for programming the radio - so don't connect to the unused terminals on the connector they are for data transfer. I used a cut-down, ready-made,  2.5mm audio cable, to avoid soldering to a rather fiddly plug.

So here is a diagram showing the connections to the radio. Note how the microphone positive is connected to the ring of the 3.5mm jack, not the tip. Leave the tip unconnected. Also leave the ring on the 2.5mm jack unconnected, these are the data connections. See how the transmit/receive (PTT) switch is wired between the speaker and microphone grounds. It is important for the microphone to be wired the correct way round, because the radio provides power for the FET amplifier in the capsule.
Here is a picture of the wiring before I covered it all with electrical tape. We don't want any short circuits. But it is always best to test it all before covering it with heatshrink or insulting tape.

Here is the complete set-up. A more glamorous baseball cap would do wonders for the appearance of the equipment ... so would a more glamorous radio ham.

A note about the loudspeaker: I use a cheap car radio speaker because it is in a nice plastic pod, which I can put on the centre console of the car. The radio specification calls for a 16 ohm impedance loudspeaker. The car radio speaker is clearly a 4 ohm part. The radio does seem to work ok with an 8 ohm speaker, but I thought 4 ohms was pushing it a bit. I used a transformer to convert the impedance. I am using just the secondary of an audio output transformer. The winding has a centre-tap and I am using it as an autotransformer. The radio is connected across the whole winding, the speaker is connected between one end and the centre-tap. This gives a 4:1 impedance conversion. The primary of the transformer is left unconnected. Hopefully you will be able to find a more suitable speaker and not have to bother with this!

Testing: I first checked the speaker connections, plugging the 2.5mm plug in and listening to the World-wide talk-group on the local repeater. When all was working on the receive side, I made sure the TX/RX switch was "off" and plugged in the 3.5mm jack. Now, on our local repeater GB7AS, we have a special Talk-group on Slot 2 which echos back the transmit audio after a short delay, for people to test their radios. This is called TG9990 Echo Test. If you don't have this, then you will have to get a friend to listen to your audio and check it is working well. you can see if the TX/RX switch is working because the LED on the top of the radio goes red in transmit.  Have fun!
Hugh M0WYE