Another DIY Ribbon thread

[dhenryp]

I've finally completed one of my full size ribbons. It's 47 inches tall and 3 inches wide. It's basically seven of my original prototypes all in one. Here's a picture of the front.

[dhenryp]

Here is a close up.

[dhenryp]

I finally decided to make a propper ribbon pleater. It's nothing fancy and actually a pretty close copy of one I've seen on the web. The only thing of real interest is that I found a source of cheap gears that will work for ribbons up to about 1/2 inches or maybe a little more. They cost all of 25 cents (!) each from BG Micro:

http://www.bgmicro.com/prodinfo.asp?...time_out=44:57

[Mx]

Excellent Job! Keep working.

[dhenryp]

I did not have time last night to do much except post the pictures. Here are more details:

I have not listened to them yet. I still have to re-arrange my test setup as it does not lend itself to testing a four foot tall tweeter. It may take me a day or two to get everything re-arranged and rewired.

I spent this weekend dealing with two basic forces of nature: neodymium magnets and super glue . I decided to attach all the magnets to each vertical pole piece and then connect the pole pieces with the crossbars. I stuck with super glue for the magnets - it's very nice to get an immediate bond. I worked out a process that allowed me to get the magnets placed correctly before the super glue caught. Towards the end it was working pretty smoothly.

The neodymium magnets I'm using are VERY strong and I can't imagine trying to handle something much bigger. It took some real concentration to manhandle those things to go exactly where I wanted them. It also was a very good workout of my fingers. Once I had all the magnets on one pole (21 magnets) I felt like I was holding a loaded gun.

In order to position the two poles, without getting them stuck to each other, I taped a strip of half inch Styrofoam insulation to the magnets of one pole. Then I clamped that pole to the workbench. I then put a couple more temporary spacers in front of that pole before bringing the second pole piece over. The attraction between the two even at a distance of 1 1/2 inches was tremendous. They were pressing so hard against the spacers that it was very hard to rip away the two temporary pieces. Once I had the two pole pieces separated by just the single thickness of 1/2 inch insulation it was literally impossible for me to pull the poles apart.

One last interesting indication of the power was when I started attaching the cross pieces. The crosspieces were pulled out of my hand at about 2 inches and stuck to the steel poles. It was then impossible for me to separate them or even MOVE them with my hands. I had to use a rubber mallet and hit the cross piece hard to move it into position for the screws.

Once the magnets, poles, and crosspieces were assembled, the completed magnetic path made the assembly quite benign to handle, as long as you kept anything steel away from the gap. I HAVE to get some (non-magnetic) stainless steel screw drivers and 4-40 screws that I use to hold the ribbon ends. Several times I had the screwdriver pulled into the gap, ruining a just installed ribbon . I also had the 4-40 machine screws jump out of my hand and lodge in the gap, where it was again impossible for me to pull them out by hand. I had to use pliers, which also were attracted to the magnets. Like I said, I've got to get some non-magnetic stuff.

Regarding transformers; BG Micro also has a good price ($2.00) on what I expect to be excellent toroids for the matching transformers:

http://www.bgmicro.com/prodinfo.asp?...time_out=44:50

It has a little bigger cross section than the ones I used on the prototype. It is made of type "J" ferrite which appears to be better than the type "77" in my prototype toroids. The BH curve of the "J" is more linear than the "77" (the 77 has an odd wiggle that I have not seen on any other ferrite). Also, the two parts of the curve (backwards and forwards) are much closer and quite linear. I think this will reduce core losses and distortion.

I've wound these cores with several different winding arrangements to minimize leakage inductance. I ended up with a primary consisting of three series (per my previous post) multifilar windings of 17 turns each, using 18 AWG wire. This is the equivalent of a single 51 turn primary. For the secondary I used twelve parallel windings of # 24 AWG with nine turns. This gives it roughly the current carrying capacity of 13 AWG. My previous post about parallel secondaries not helping much is wrong - they help a LOT. The parallel secondary windings cut the leakage inductuctance by a factor of 2 or more over a single secondary. The combination primary and secondary multifilar windings I used ended up with a leakage inductance of .09 mh, measured with the inductance range of my multi-meter. Using a single 57 turn primary and a single 9 turn secondary gave me a leakage inductance of 1 mh. This is an excellent reduction.

Note that my multimeter uses a fixed frequency to measure - probably something like 1k. The leakage inductance is effectively in series with the primary so I am concerned about its value at 20k. I did a simple test of putting a four ohm resistor in series with the primary while I had the secondary tied together (this is how you measure leakage). I then ran 20 khz through the pair and found (by ratio of voltage drop) that the XL of leakage inductance at 20k is ~.8 ohms. This works out to .0064mh at 20k (if my math is right). This is quite good and means the high frequency cut due to leakage inductance (assuming an equivalent 8 ohm primary load) is much ess than 1 db.

This post went on longer than I expected. I'm not sure how many of you will make it to this sentence :rolleyes

[dhenryp]

Lots of lookers. Not many talkers. Interested? Not-interested? Speechless? Bored?

[cocolino]

This post went on longer than I expected. I'm not sure how many of you will make it to this sentence :rolleyes

Lots of lookers. Not many talkers. Interested? Not-interested? Speechless? Bored?

This is one thrilling, stunning thread!
I read every single of Your words at least once or twice!

I`m very eager to hear about Your first listening impressions.

[Paul W]

Yes, your work is appreciated

I've been (slowly) working on ribbons for about six months, so I am painfully aware of the bloody fingers and everything else you are going through!

1" ribbon protos

[dhenryp]

Sorry for the blatant appeal for comments.It was a tough day at work today and sometimes you need some responses. Thanks for the input. Onward and upwards!

Denis

BTW:

I did cut my fingers this weekend and even managed to slice off the tip of one finger! Everything is OK and Blue Cross -Blue Shield was not involved.

[gl]

Hi Denis,

Your continuing efforts look wonderful. There are many of us that are doing similar things that are very interested inyour progress. It's just that I for instance don't login every day. Sometimes not for several days at a time.

I am very interested to know what your ribbons sound like. Very much. Now that you're so close to powering them up I'll check in more often.

Why did you break the ribbon up into discreet sections instead of using one long piece of Al with a simple support where you now have the screa down anchor points? Do you have a transformer on each segment or are the segments connected in series with one transformer for the whole chain?

Nelson Pass is about to publish an article that is promising to include data on driving ribbon speakers with transconductance amplifiers. According to NP it goes up on www.passddiy.com today or within the next few days.

Keep up the great work. It's an inspiration. Truly.

Regards,
Graeme