Project "Dictogrand Dictograph R-3 Horn Speaker" (2/2)

I managed to fix this speaker up the way I wanted it, and I have to say it works beautifully!

I replaced the cardboard mini horn with a metal one with nearly the exact dimensions. I basically went into Daiso one fine day and went around with the cardboard horn/funnel and tried to find something as close and possible and I'd say I found something very close!

Not bad for $2 eh?

It is a measuring cup meant for bartenders to measure out shots for drinks and it is made of stainless steel.. perfect for my intended use! Just cut it at the joint and make a hole at the end and it is now a mini metal horn!

Like so!

Using a metal cone/horn gives much more clarity in sound over the cardboard one, which to me sounded very bloated and muffled. I read up on the basics of using horns to amplify sounds and the design of the Dictogrand's horn amplifies the middle to high frequencies while attenuating the lower frequencies. In other words: you won't be hearing much bass coming out of the horn, which is okay because I didn't intend to use the horn for dance music anyway! Initial testing showed me that the horn speaker shines when playing acoustic music with uncomplicated arrangements, i.e: simple chill-out tones that do not have an overwhelming amount of instruments.

Moving on, I kept in mind that everything I planned to put into the box of the speaker should be kept replaceable in the event something better comes along in the future. Thus no epoxy or nails should be used or at least kept to a minimum. I attached this metal horn to the horn entrance plate by using hot glue, which can be easily peeled or dissolved with alcohol in the future if needed but strong enough to hold things together for a long time.

The last piece of the puzzle was extending the microUSB charging port from the X-Mini to the outside of the box. I couldn't find any proper microUSB breakout boards that could be mounted vertically and thus had to ask my brother who very graciously provided me with a solution by making one (or two) from scratch. 

Tiny!

I ended up only using 2 pins out of the 5 shown there for +5V and GND which are used for charging. It is possible to use the data pins on the X-Mini for audio playback but I intended to use the 3.5mm jack for that so I kept those pins unconnected. In the process of hooking this USB board up to the speaker I absolutely forgot to take a picture of it wired up before sticking it in. I basically got a standard microUSB cable (also from Daiso by the way!) and cut off one end. I soldered the +5V and GND wires to this breakout board and connected the other end of the cable to the microUSB port on the X-Mini.

All there was left to do was to drill the holes required and fine tune them with a file. I got my father to help with his experienced drilling skills and I fine tuned the holes ever so slightly for a nice fit.

As the interfaces were already extended out as shown previously in part 1 of this post, all I had to do now was put in the switches and jacks and wire them all up. The X-Mini is secured snugly in place by the isolating foam below and behind it, which is forcing it up against the metal horn. I tried shaking the box repeatedly and saw that the speaker did not budge at all so I decided against using any glue or other measures to hold it down.. all in the name of semi-temporal-permanent-ism! You never know if a year from now they come out with the X-Mini Uno EXTREME and I'd be kicking myself while I'm tearing out all the permanent fixtures I made previously to this current speaker. It isn't pretty now I'd admit that, but it will work just fine.

Power switch in place, ready to be wired up

You can see the microUSB port in the picture below on the right below the 3.5mm jack. I applied a generous amount of hot glue to the parts that would be enduring a lot of pushing and pulling.

The volume potentiometer was glued on to a horizontal balsa wood support (also from Daiso! Daiso has everything!) and aligned with the Dictogrand's volume knob, which I forgot to mention, was cut down to a much more manageable length as shown below so that it could turn the X-Mini's volume potentiometer with ease.

Hot glue; it ain't pretty, but it gets the job done!

Finally, I put another piece of isolating foam on the top of everything so that when I close the lid of the box it would sandwich the speaker in place very tightly.

The LED lights up blue when the speaker is turned on, and it changes to red when the USB charging cable is plugged in. The battery in the X-Mini is only 550mAh and is easily replaceable with another battery of a bigger capacity, but that would be a side-project for another time. Also, it is possible to power the speaker solely by USB power alone, so if the battery ever dies one day then the speaker would still be usable by plugging in a microUSB cable.

To celebrate the completion of this speaker, I made myself a 'commemorative' 3.5mm interconnect cable to always be used by this speaker. Just plug one end into the speaker and the other end to any compatible device like an iPhone or a MP3 player and it is good to go!

And that.. is the story of how I got myself a snazzy horn speaker after all!

It works wonderfully with jazz and easy-listening music, or period-correct music, if you will (tunes from the 1920s onwards to the 1970s). What the horn does is add a touch of reverb to every sound, so you can hear an echo that lingers after every note for a few milliseconds which is completely natural due to the acoustical design of the horn.

(Link to part 1/2)

Project "Dictogrand Dictograph R-3 Horn Speaker" (1/2)

I won this obnoxiously big horn speaker on eBay and it finally arrived here on New Year's Eve all the way from the US of A. This is a Dictogrand R-3 Speaker made by the Dictograph company in 1923 according to the information on this renowned website (http://www.radiomuseum.org/r/dictograph_dictogrand_r_3.html) which makes this speaker about 90 years old. The horn is made of brass and is connected to a (cast iron?) elbow that links it to the speaker driver located in the rectangular box made of wood. It has a volume control knob on the front of the box where the brand is stamped.

The funny reason why I bought this obnoxiously big horn speaker is as follows:

I was out in town some weeks ago and I saw a shop in Singapore selling this "Gramophone for iPhone and iPad" which really caught my eye because I am such a sucker for vintage audio stuff as this blog can attest for. I thought it was a wired dock which you can plug your iPhone into and it'll play it through the speaker but it is solely an acoustic amplifier with no electronics or active speakers whatsoever.. kind of steep considering it was selling for $400sgd++ (!!!) if I saw the pricetag correctly.. it looks beautiful though as a decoration piece but I feel it isn't exactly a 'functional' speaker. Also it isn't exactly 'real' vintage unless the horn was taken from an actual antique speaker but I couldn't verify if that was the case.

Image from Restoration Hardware and for your reference only, click to go to their website

I also saw this in another shop for a whopping $700sgd++ (!!!!!??) by enandis (en & is), which is also a really nice decor piece but also has no electronics and depends solely on the iPhone's built in speaker for sound before being amplified by the ceramic horn. Another nice curio for your home if you can afford it..

Image from enandis and for your reference only, click to go to their website

Then finally there's this brilliantly designed project on Kickstarter: the Gramovox, which uses an active speaker to play sounds through the functional horn and even has bluetooth capability to stream music. It costs slightly more than $400sgd++ with shipping included (pricey but at least it has some functionality over the other two) which means taxes are applicable if I do purchase it and that would send the cost even higher.. so no snazzy retro horn speaker for me..

Image from Gramovox and for your reference only, click to go to their website

At least until I found this gem on eBay and won the bid a few days before Christmas for $68USD! It isn't exactly 'cheap' as well but compared to the examples above it is very affordable.. and I would believe it is increasingly rare as well which justifies a little more cost. It is ideal for a modification project because it has a good sized box below the horn where the driver (speaker) sits and I would be able to replace it with whatever I wanted to. As mentioned earlier, it also comes with a volume knob on the front that I should be able to link to a volume potentiometer as well.

The horn is fixed to the back of the box by two easily removable thumbscrews

Once the thumbscrews are removed, the horn slides right off the two screws and will be freed.

It is a good sized horn, no?

The bottom of the box can be removed as well and is held together by two fastening screws on either sides of the box shown here.

Once the screws are removed then the bottom cover comes right off as well.

The bottom of the box carries the now faded and torn instructions on how to use the speaker. There are readable examples available online but the instructions contain nothing useful in terms of modern day technology.

It says: "Best results will probably be obtained by using about 67.5 volts (!!!!!!) of "B" battery on the amplification unit

The antique speaker driver has an impedance of over 1kOhm which compared to modern speakers which are anywhere from 4-16 ohms is a great deal more and would not be compatible with modern day amplifiers because the sound would probably be too soft to be heard, assuming the driver works at all after 90 years! You could use a impedance matching transformer to hook up your modern day amplifier to this speaker but I believe the sound would come out very distorted.

The gears you see connected from the volume knob to the speaker actually adjusts the distance of the speaker diaphragm to the horn entrance. When the volume is turned lower, the gear turns the mechanism inside the speaker that adjusts the diaphragm further away from the horn entrance at the back and it does the opposite when the volume is turned up. I do not have a powerful enough amplifier to hook this horn speaker up as it is and decided right from the beginning that it is time to remove this speaker driver and let modern electronics take over.

The volume knob is held by a retaining pin that can be simply pulled out and the whole knob can be taken out of the box. The speaker driver can then be removed by lightly (or violently, depending on how warped the wood box is after 90 years) tapping on the two screws at the back.

It is time for you to retire!

The back of the speaker driver holds the two (irremovable) screws that can still be used because they are needed to hold the horn in place to the box. The screws have been rusted shut, but a little machine oil left to seep in for 5 minutes helped make the task a lot easier. 

So that is a complete teardown of the speaker. I intend to make this into a self-powered speaker with a rechargeable battery similar to the Gramovox above, but without the fancy bluetooth feature (perhaps in the future). I did my research and found many possible components I can fit inside from sites such as Adafruit where they have a Class D amplifier breakout board together with a USB/DC battery charger that I can hook up together.

Image from Adafruit and for your reference only, click to go to their website

Image from Adafruit and for your reference only, click to go to their website

But then I realized, there is only 1 horn, thus 2 channels for stereo is overkill.. and I couldn't find an acceptable mono amplifier. The other big problem was sourcing for a good speaker: it had to be small, but able to play audio at a good volume with no distortion. The small speakers available for DIY projects (also available on Adafruit) are the common ones with paper cones and are designed for simple tones and buzzes and not built to handle music playback.

Image from Adafruit and for your reference only, click to go to their website

So what then? Well, thankfully, the best small speakers (according to several reviews on the internet) is made right here in Singapore and it is the X-Mini Capsule speaker and it is readily available in all the shops here.

Okay.. readily available except in the black color that I wanted it but heck.. 

The X-Mini is a very common portable speaker that has been around for quite some time now. It has an expandable accordion baffle in the middle that gives the speaker a lot more air volume to work with so the relatively small 40mm driver sound a lot better and louder than it should and so I felt it was very ideal for this current project. The best part is that it has a complete circuit built in, so there's no need for me to design a battery charging circuit with an amplifier with a speaker.. this single device combines everything I intended to build into one small capsule that would (most probably) outperform any speaker I source to use in this project.

The speaker is pretty easy to take apart as well. Remove the four screws on the bottom part of the accordion and the base will drop out, revealing the PCB.

Remove the one screw on the PCB and everything will be exposed. I had no need to modify the upper half of the speaker where the driver is so I left that on its own. I planned to remove the switch, potentiometer and 3.5mm plug and extend it out of the box so I would be able to power on and off the speaker, adjust the volume, and plug in whatever music player I want to without opening the box to do so.

I set about desoldering the components from the board, but I found it extremely difficult to do so because the components were mostly soldered on both sides via through holes and they were a real pain to remove. I yanked out the potentiometer together with its traces and I had to improvise with thin strands of wire to rebuild the traces. It wasn't pretty but it works.. hopefully if your project requires you to repurpose the X-Mini like this then you would have a good desoldering tool to help you.

With the switch removed. The speaker uses a Double Pole Single Throw (DPST) switch but it only actually uses a single pole, thus a simple single pole switch would work.

The black tape hides my demolition job on the volume potentiometer traces. They also act as a strain relief so I don't accidentally rip out their tracks again by moving the potentiometer around.

I desoldered the male 3.5mm connector and soldered a female connector at the end of the longer wire. This female connector will be accessible together with the on/off switch on the outside of the box. I also extended the LED indicator so I would be able to see if the speaker is on or off. I did not touch the USB connector that is used for charging the device, but I ordered a microUSB extension (that has yet to arrive) that I will plug into the port on the speaker and fix the female end to the rear of the speaker box.

TLDR; I will eventually be able to access all the features of the X-Mini without needing to open the speaker box, making it a fully portable standalone speaker.

While the speaker has a 40mm driver, the entrance of the horn is a lot smaller at about 18mm. This means that simply placing the speaker at the horn's entrance would result in a lot of sound energy (volume) being wasted because the sound waves do not all enter into the hole.

I basically needed a small horn to guide the sound waves emitted from the X-Mini into the horn's entrance. I found these hard cardboard cones from the shop "Spotlight" where they sell all sorts of handicraft materials and cut it down to size:

I put everything together as shown below before closing it all up to give it a try, and it doesn't sound half bad! But I would prefer a metal cone rather than a cardboard one so this would only be a temporary fix just to get a feel of how it would fit and sound like. I will be taking a good look around to explore other options over the next few days/weeks and see what I can find.

I made a simple recording of the capability of this project with my phone's camera, and I will make a higher quality video when I am finally done with this project.

(Link to part 2/2)

Project "Mistral MM-1 Hybrid Tube Amplifier Modification"

I bought this hybrid tube amplifier made by Mistral Audio (http://www.mistralaudio.com/Stereo.html) from the shop Precision Audio in Adelphi (affiliated to Ban Leong Brothers Singapore) slightly over a year ago. It sounded really good when I first got it and only cost $169SGD (!!!!) which is the cheapest power amplifier I have seen in the entire building (The Adelphi has many...many high end audio shops with 4-5 digit product price tags).

It uses a pair of 6N1 triodes as well as a pair of 6P15 pentodes for the preamplifier section. The power output utilizes a pair of LM1875 solid state amplifiers capable of 20 Watts each.

After using it for a year I noticed the sound quality started to deteriorate really fast. It started buzzing, humming and distorting intermittently and really got on my nerves and my ears. I did some research and I found out quite a lot of disappointing things from many different forums, mainly:

-It isn't really 'made' by Mistral Audio. This amplifier is a generic Chinese designed and manufactured amp apparently in the same factory as where they build the other Mistral Audio amplifiers that cost more than a thousand bucks. This amplifier that costs $169SGD is made in that same factory (i think?) but wasn't designed by Mistral Audio; it was designed by a nameless company and they just slapped their brand on it...together with a few other brands such as Jaycar (model AA-0474) in Australia which they are discussing on this forum: 

http://www.audiokarma.org/forums/showthread.php?t=277066

and it is also branded as Marriola on Amazon.com:

http://www.amazon.co.uk/Amplifier-4Tubes2x40-Natural-Marriola-RV-100/dp/B006IQ6Z90/ref=pd_sim_sbs_ce_1/279-2282004-0675031

-All the tube heaters are actually over voltage and are running much hotter than they should be. I found this out from the audiokarma forum link above as well as from this experienced person's (cool386) website: 

http://members.iinet.net.au/~cool386/jaycar/jaycar.html

This means that the tubes will fail and burn out much sooner than their normal lifespan, bringing the sound quality down the longer they are run. They are not supposed to be as bright as they look in this picture:

-Also, only half of each triode is actually hooked up to the preamplifier circuit, meaning that while the tubes definitely do contribute to the sound, they are not actually fully utilized.

---------------

The bottom line is that the amplifier doesn't sound bad...it doesn't sound bad at all! But in order to get it working consistently at its full potential, a few modifications had to be made.

The first modifications I did was to reduce the heater voltages. I assumed the tubes were all burnt out after spending a year running hot and ordered a completely new pair of (Bulgarian/Ukrainian NOS tubes) 6N1s and 6P15s from eBay. The forum members on the audiokarma forum suggested putting voltage drop resistors which would work but after tracing the preamplifier PCB I could not understand the logic behind their suggested resistor placement and came up with a new one.

The amplifier can be dismantled easily; just remove all the screws on the edges of the bottom and the entire bottom plate comes off. Use a marker to mark all the connectors you see so you will be able to identify which connector goes back to which later on during reassembly.

The preamplifier PCB can be accessed by removing all the tubes from their sockets and unscrewing the 12 nuts holding the PCB in place.

Be sure to click on the image above to get a closer view. The socket pins bounded in the red squares are the tube heater pins. From cool386's post on this amplifier he stated that the power from the heaters come straight from the 16VAC transformer winding. This 16VAC is fed through a diode to produce about 8.5V RMS which is above the required 6.3V heater voltage of the tubes.

I got 4 x 3.3ohm ceramic resistors rated for 4 Watts each and connected each tube heater in series with the 8.5V RMS source. This would drop about 2V for each tube, bringing it down to a more tolerable 6.5~V whilst each resistor would burn about 1.5~W each.

I apologize for my poor MS paint skills but I think this is enough to illustrate the modification. Cut the traces with a penknife at the red X's and wire up the resistors accordingly. All the resistors are of the same value and the blue colored one is only for the sake of clarity. I scraped away the track coating in the right yellow circle and soldered the resistors to the copper track directly as there were no pads available there. I placed heat shrinks on the legs of the resistors to prevent any shorts.The completed modification is as shown:

The next thing I looked at was the power amplifier stage which holds the solid state amplifiers as well as the power supply:

Since the warranty for this amplifier was over, I decided to overhaul all the cheap electrolytic capacitors on this board to audio grade ones. There were also more electrolytic (decoupling?) capacitors on the top of the preamplifier board to be replaced as well:

The replacement capacitors of my choice were the Nichicon "Muse" Electrolytic capacitors which are supposedly of 'audio grade'. I felt more comfortable having these high quality components rather than the chinese "Robicon" (ripped off from Rubycon?) and ChengX capacitors.

so it was out with the old and in with the new:

Some of the new capacitors were bigger than the old ones thus some slight bending and twisting was required to make them fit back into the chassis comfortably.

The tubes (6N1p pictured) also arrived and I replaced the stock Chinese ones with these NOS Russian ones which are supposedly military grade and more hardy:

After going through all that trouble, I switched on the amp...and...the buzzing and distortion was still there!!! How frustrating!!! You can hear the buzzing and distortion I am referring to in the before and after video at the end of this post.

I realized the distortion only comes during quiet passages of certain songs that were played. The noise got louder every time I increased the treble potentiometer so I traced the circuit from the pot and found that it led to a pair of JRC4558D op amps (the red squares in the picture below) on the PCB, one connected to the treble pot and the other to the bass pot.

I did some research and my description of the distortion matches what is known as "crossover distortion" (http://en.wikipedia.org/wiki/Crossover_distortion) where the distortion mainly occurs during low signal (soft passages in a song) voltages in a "push pull" amplifier but disappears in normal to loud voltages. I won't go into much detail about this but I spotted two transistors down the signal path that might suggest this is a push pull amplifier. Before attempting to try to change the transistors I decided to change the 4558 op amps first just to see if that fixes anything.

I removed the op amps and soldered on 8 pin sockets in their places. After trawling through many forums and webpages I found a suitable upgrade in the form of the LM833N op amp and plugged them in.

I switched on the amp and played the same song that was giving me so much distortion before and...it was perfect! Changing the op amps solved the 'crossover distortion' completely!

I did not connect the LED lighting for the VU meter because I felt it was far too glaring and spoiled the look of this otherwise good looking amp. The tubes also lost their lightbulb glow and is now glowing at what seems to be the correct brightness. The sound of the amp has also improved by a great amount and I don't mean it in the pretentious "the high end is clearer and the soundstage is wider etc etc" kind of way...I mean it REALLY improved and the video below proves it. Be sure to select and watch it in the highest definition to get the best audio quality.

I'm not going to state that the 4558D op amps are better than the 833N because of the sheer amount of arguments I have read on forums all around. I will only state that the issues I had with the 4558 might be because the pair of op amps I replaced were perhaps from a defective batch because they did not sound this way when I first bought the amp. But from the datasheet the 833N claims to be low noise and that justified a try and I'm happy I did.

Take note that the video was recorded using an external mic set on the speakers and that makes it sound worse than it actually does. But you should be able to hear the buzzy distorted vocals that are no longer buzzy after the modifications are made.

*EDIT*: unfortunately I realize that youtube isn't exactly the best place to compare audio quality. the buzzy distorted vocals before the modification sound way worse in the .wav file i saved but I think youtube downsizes the audio quality to 128kbps or so, thus smoothing over the buzzy vocals and making the distortion not that obvious..but take my word for it that switching the op amps in this situation really helped rectify the problem