Something stirs in the Undergrowth

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IslandPink
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Re: Something stirs in the Undergrowth

Post by IslandPink » Wed Oct 31, 2018 7:00 pm

Yes it seems to be a rule with Supravox that the alnico and ferrite versions of each driver are totally different !
Beyma looks worthwhile, not cheap though ( but cheaper than Supravox ). Have you got a link to 'in a W configuration' ?

Simon ( Ch ) , here's a stab at an amp-internal notch filter for the FE208Ez.
Target of about 3.5dB attenuation around 3.5 to 4kHz.
Think of this being between the driver valve and the GM70. The 'V1' source is the driver valve , the feed to the GM70 grid comes off the upper right corner of the circuit. The first 0.47u cap is your coupling cap.
Grid leak here is 25k and the coupling cap is a bit undersized to give you some roll-off of the FE208 low down.
If the grid leak went to 50k, then ( in the notch bit ) the resistor and inductor would both double in value, but the cap would halve.

The choke here would have to be a 'nice' one because it'll need a core, for that value ( I think... Nick .. ? ) . Current rating would only have to be the same as the driver valve current, maybe 25 or 30ma tops ( again open to arguments on this ) .
So maybe you ask Dave Slagle to wind them and get something like 0.7 to 1.1H with taps every 0.1H .
Notch_internal_1.JPG
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IslandPink
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Re: Something stirs in the Undergrowth

Post by IslandPink » Wed Oct 31, 2018 8:15 pm

Jeffery Jackson doing things properly ( again )
See final picture .
http://myemia.com/_horn.html
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vinylnvalves
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Re: Something stirs in the Undergrowth

Post by vinylnvalves » Wed Oct 31, 2018 10:20 pm

Here’s a picture of the w configuration OB sub... nothing special really.
B3C9D968-0C53-4329-BEDF-C597BDE28A89.jpeg

simon
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Re: Something stirs in the Undergrowth

Post by simon » Wed Oct 31, 2018 10:26 pm

Thanks Mark, that looks a great start! I need to think about it a bit more, but that's an interesting suggestion regarding the choke.

That horn is a serious bit of construction!

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Nick
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Re: Something stirs in the Undergrowth

Post by Nick » Thu Nov 01, 2018 10:12 am

The choke here would have to be a 'nice' one because it'll need a core, for that value ( I think... Nick .. ? ) . Current rating would only have to be the same as the driver valve current, maybe 25 or 30ma tops ( again open to arguments on this ) .
Yep, will need a core, but there is no DC, so Ni is a option. I would think the current would be so low as to not matter, its going to be signal swing across 25k, so for a gm70, say 100v p/p, thats 3ma. You will get more I guess at resonance, but either way I wouldn;t worry about it.
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vinylnvalves
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Re: Something stirs in the Undergrowth

Post by vinylnvalves » Thu Nov 01, 2018 6:39 pm

Mark, I have some pot cores gathering dust from when I attempted winding inductors for a pre- amp crossover, if any good to you. Will have to wait until I am back from the states week after next.

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Re: Something stirs in the Undergrowth

Post by IslandPink » Thu Nov 01, 2018 10:07 pm

Nick wrote:
Thu Nov 01, 2018 10:12 am
Yep, will need a core, but there is no DC, so Ni is a option. I would think the current would be so low as to not matter, its going to be signal swing across 25k, so for a gm70, say 100v p/p, that's 3ma. You will get more I guess at resonance, but either way I wouldn't worry about it.
Well OK, no DC but don't forget the substantial miller capacitance of the GM70 which drives the need for 25 to 30ma in the driver to overcome slew-limiting . However I suspect that would be handled by the design in terms of what power and AC swing it needs to cope with , without distorting.
Now I've just realised that the inductor won't be doing much at HF, where the miller cap comes into play - the cap will be doing the donkey work there, so I've just undermined my argument. Ho hum . :confused4:
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Re: Something stirs in the Undergrowth

Post by IslandPink » Thu Nov 01, 2018 10:08 pm

vinylnvalves wrote:
Thu Nov 01, 2018 6:39 pm
Mark, I have some pot cores gathering dust from when I attempted winding inductors for a pre- amp crossover, if any good to you. Will have to wait until I am back from the states week after next.
Thanks Steve, but it's more likely Simon who's going to try this first. It'll end up at the bottom of a long list of things to do ( urgent ) for me.
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Nick
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Re: Something stirs in the Undergrowth

Post by Nick » Thu Nov 01, 2018 11:11 pm

Now I've just realised that the inductor won't be doing much at HF, where the miller cap comes into play - the cap will be doing the donkey work there, so I've just undermined my argument.
:-)
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Re: Something stirs in the Undergrowth

Post by IslandPink » Fri Nov 02, 2018 8:11 pm

simon wrote:
Mon Oct 29, 2018 8:43 pm
I couldn't get the 400GMF to work well either, but James knows what he's doing and I don't! 600L is like a small wardrobe though!
Well it depends what you're expecting. I put it in Hornresp with no horn and a sealed back volume.
This looks really nice -
Amplitude is more or less flat when you take into account room gain.
400GMF_i.JPG
Phase is really changing very slowly :
400GMF_ii.JPG
If you cross-check MH Audio for the Qtc value that's about 0.43 which is very low , but room gain might have an effect on this and James probably has some adjustment for this and it might be Q = 0.5 ie. transient perfect for this volume.
Should sound really nice - dynamic, lots of bass tone, low enough for almost anything. Qm is 10, so Rms comes out at 1.5, which is very low for a 15" bass driver, so expect tone at low volume levels.
But yes, 600L is nuts - however James should have room for it, if the house is ever finished.
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Re: Something stirs in the Undergrowth

Post by IslandPink » Sat Nov 03, 2018 12:21 pm

"I don't care, I don't care, I don't care if he comes round here, I've got my beer in the sideboard here"

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Ray P
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Re: Something stirs in the Undergrowth

Post by Ray P » Sat Nov 03, 2018 5:52 pm

He has some pretty awesome projects, thanks for sharing Mark.

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Re: Something stirs in the Undergrowth

Post by IslandPink » Sat Nov 03, 2018 6:32 pm

Just fixed the Aurum G3 ribbon this afternoon.
Glad I didn't attempt it on my own , it was not ... that... easy ...
Lenny came round from Llanddulas.
The ribbon is quite a bit thinner than kitchen foil - very delicate and doesn't behave itself when you're trying to get it clear of the magnets on each side over a 100mm length with only a total of 0.5mm clear width to play with. We had an amusing incident early on when the only screwdriver we could get, that had the right Philips head for un-doing the holding block/screws at each end had its (removable) bit pulled out of the end by the neodymium magnets. I had to get Len to fetch some pliers from the toolbox in the back-kitchen to remove that. A useful early lesson because, we had the old ribbon in place at that stage.
Anyway we got it in, stretched about the right amount and not touching the magnet anywhere ( though it could have been more even - the perfectionist(s) in us were slightly frustrated).
G3_repair.JPG
Anyway, have now played it and feel more comfortable - seems clean and resolved, lovely tone, sounded great on sax and high piano notes, so I think it's doing what it should do, I will try to do a test of the pair later on when I have time.
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Re: Something stirs in the Undergrowth

Post by izzy wizzy » Sat Nov 03, 2018 7:02 pm

IslandPink wrote:
Sat Nov 03, 2018 12:21 pm
Cripes !
https://inlowsound.weebly.com/inlow-sou ... -horn.html
Even the midrange one is a fair bit of work :
https://inlowsound.weebly.com/inlow-sound-15-a.html
Golly! That's one hell of a site. So much to take in and admire. Cheers Mark.

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