Using a ribbon tweeter with an active crossover

[sardonx]

Is there any way of going around having to put a capacitor in series with the ribbon tweeter when using an active crossover? I've read that simply connecting the ribbon to the amplifier will damage either the ribbon or the amp, or both.

I really don't want to put any capacitors between the amp and ribbon. Are there any aternatives?

I've also read that that you should use a second order passive crossover for this application and that the crossover point should be significantly lower than that of the active crossover (i.e if active crossover point is 2khz the passive one should be at around 1Khz.

Why can't I just use a first order filter with one capacitor at the same x-over point as the active unit?

[planet10]

You could use a transformer -- ie make a tubed tweeter amp...

The idea is to ensure no DC or LF transients get to the fragile ribbon and make it turn into a fuse. If you are comfortable that your direct coupled amp is not going to spew any LF garabage & has no DC offset & you are willing to swap ribbons fairly often then go for it.

How low do you want to cross the ribbon?

dae

[planet10]

Originally posted by sardonx
Why can't I just use a first order filter with one capacitor at the same x-over point as the active unit?

That works... typically one looks at the cap as a protection device and set its pole to a couple octaves below the XO frequency. But you certainly could use it as one of the poles in the XO.

dave

[sardonx]

I'd like to cross the ribbon at 1.8k with a 4th order active x-over plus the one cap before the tweeter should make it 5th order total.

You could use a transformer -- ie make a tubed tweeter amp...

So if I use something like this, I wont have to add a cap?

http://www.tubeaudio.com/page23.html

[planet10]

Originally posted by sardonx
I'd like to cross the ribbon at 1.8k with a 4th order active x-over plus the one cap before the tweeter should make it 5th order total.

Typically when you get that high an even order XO is called for... you would do 3rd order active and make it 4th order with the cap.

So if I use something like this, I wont have to add a cap?

http://www.tubeaudio.com/page23.html

That would work, but not likely the best suited... whenever i think tweeter amp, i think SE with a small OPT (which in theory should give better top end)

What ribbon, that you can cross so low? Anything i know of is big bucks. Throwing an entry level amp like tat one would seem to be a bit odd.

dave

[sardonx]

It's the LCY 130 ribbon - from Solen or e-speakers. The claim is for high power handling and extremely good dispersion on both axxis, among a few other things. They're $250CAN each at solen.

At e-speakers they recommend a 3rd order crossover at 2K for the 130 and the 110 ribbons. They have the exact same motors the only difference is the bigger flange for the 130 which gives it a bit more energy under 2K. The size and shape seems the same as the 9900 revelator with the big 130mm slight horn faceplate.

Throwing an entry level amp like tat one would seem to be a bit odd.

The amp(pre-assembled) will probably run to about $250CAN after tax, x-change and shipping. The 2 ribbons will be around $600CAN inlcuding all that.

I'm only choosing that amp because it's a good price.. and later might upgrade to a SE like you said. Unless you know of one that is just as cheap is this one??

Typically when you get that high an even order XO is called for

It might be a better idea if I just go 4th order active with nothing at speaker level. Ommiting the cap would make me a lot happier!

How come you dont have to worry about shorting the amplifier and turning the ribbon into a fuse when you have a tubeamp/transformer driving the ribbon?

[hermanv]

Most amplifiers are protected against shorts on the speaker leads because that is a fairly common occurance.

Adding a transformer has no effect on the amplifiers ability to handle or not handle shorts.

Transformers can not pass DC so transformers protect ribbon tweeters from seeing a DC component and becoming thereby very expensive fuses.

Most ribbons require a transformer anyway becasue their impedance is typically in the 1 Ohm range.

If you decide on a tube amplifier to drive the tweeter, an output transformer will already be present in allmost all designs. Because this ribbon is 8 Ohms allready, a second transformer is not necessary.

If you decide on a capacitor in series with the tweeter, please pay very close attention to the capacitor quality. Probably a tin foil and polypropolene or better should be considered. These are not inexpensive.

[planet10]

Originally posted by sardonx
LCY ribbon

Those seem to keep popping up, i'll have to check them out fi=urtehr as they seem quite robust (althou my aps would use them 1st order at 7-12k)

The amp(pre-assembled) will probably run to about $250CAN after tax, x-change and shipping. The 2 ribbons will be around $600CAN inlcuding all that.

I'm only choosing that amp because it's a good price.. and later might upgrade to a SE like you said. Unless you know of one that is just as cheap is this one??

You won't likely find much in a kit in this price range, but i believe there is a 6BM8 semi-kit out there (can't find the URL) -- triode strapped (or RH/aka partial feedback) it might be fine. Since most kits are trying to get bottom out of the amp, they are not ideally suited for your ap. An SE OPT is a compromise between getting HF out and maintaining LF, so a small OPT where less concern was made for bass probably provides the best choice for a tweeter amp...

I could pretty much assemble a suitable tweeter amp out of parts in my bins, and i have some surplus OPTs (removed from their holding frame -- so cheap) that would be ideal -- like these

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=5744478713

Add a Power transformer, a couple EL84s, a suitable driver tube, sockets, and some passives, and you have a simple to build amp. With the 8 ohmimpedance of the LCYs El95s (or ELL80) might be a better choice for output tube*

How come you dont have to worry about shorting the amplifier and turning the ribbon into a fuse when you have a tubeamp/transformer driving the ribbon?

Like a cap, the transformer doesn't let DC pass... an amp with OPTs as above probably doesn't go much lower than 100 Hz, and with appropriate choice of coupling capacitor you could raise that up -- even as far as using it as a pole in your XO (which with my 1st order XO would be the entire active XO).

*(my friend actually has an already built amp, that the aforementioned OPTs could be installed in) i know he would be willing to part with. Keep in mind all these amps i'm talking about are 1.5 to 2 W (5W max if you RHed, but the clipping characheristics of the triode are probably better)

dave

[sardonx]

Those seem to keep popping up, i'll have to check them out fi=urtehr as they seem quite robust (althou my aps would use them 1st order at 7-12k)

They have a supertweeter which is meant to be used from 8K and up. But it's up there in price with a raven r-2, if not more. Plus these are relatively unknown ribbons, so it's risky.


Dave, I'm not sure if i'm comfortable enough to tackle a tube amp from scratch.. maybe it would be easy.. I don't know. I'm working on a LM3875 right now which i'm doing all point to point (crimping). I still need to buy a few key parts for it (i.e transformer). I plan on using this as the midwoofer amp.

I just like the idea of driving a ribbon with a tube amp...

How much do you think your friend would want for his amp? And do you think 1-2 watts would be enough?


Sorry for asking this question again but what i still do'nt understand is that if all these new ribbons have transformers, why do I still read that you can't connect them directly to an amp - even when using an active x-over? Confusion!!!

[planet10]

Originally posted by sardonx
How much do you think your friend would want for his amp? And do you think 1-2 watts would be enough?

Now i see where these things might be so robust... they are grossly ineffiencient for ribbons... 1-2 watts would only be enuff if you don't need real loud. & your room is not that big.. (both Chris & i are using 2 watts on 90 dB efficient FR speakers thou, and for tweeter duty alone you would need less power). I'll ask Chris price & let you know.

What are you using for mids? The low efficiency of these i would find a big detriment... the XO point you choose is also in my no XO zone so that wouldn't sway me either)

Sorry for asking this question again but what i still do'nt understand is that if all these new ribbons have transformers, why do I still read that you can't connect them directly to an amp - even when using an active x-over?

They are very delicate. They go up in smoke easily. But ribbons (should be) cheap & easy to change.

dave