Sonab OA-4 (mkII) & Visatron TW 70 tweeters?

[Villee]

BTW it´s nice to help, myself I get much crucial information from here when I renovated my OA-6 type 2a

[Martin Dellstig]

Hi

Two things strike me when looking at the pictures from "radiomuseum".
- There is a resistor on the filter there which is news to me, that resistor is not present on your filter.
- If you look at the bottom-side of the speaker the picture shows how it is NOT supposed to be, one port is blocked by the yellow stuffing. The braces should position the stuffing to prevent this.

I would recommend you to try to put it together without changing to bass-reflex tubes for starters.
I don't think you will be able to get much improvement from that, it is more of a risk since you can't say for sure how the present port is calculated.
I think that since the 9710 is not very powerful the potential gain from modifying the port is not so big.

Regarding the value of the capacitor in the filter the impedance from 3 pcs of 16 Ohms tweeters is not equal to 4 pcs of 8 Ohms in series parallel (5,3 Ohms instead of 8 Ohms , theoretically). So perhaps a smaller makes sense.

Regarding fastening of the filters, get something like this http://www.kjell.com/content/media/imag ... /36280.jpg and screw them back in place.
Use some sort of non-magnetic material for the screws if you use the screw-holes inside the inductors.

Best regards

Martin

[Villee]

Oh I didn´t see the resistor:O but otherwise all other compoments looks the same as my OA-6 IIa.

[iub]

Just want to quickly say that I am still working on the renovation, but that things have been slow, so I there has been no need to update.

When you say that I should use 0,5 mH inductors, I assume that means 0.47 mH, right?:)

[Martin Dellstig]

Hi

The ones Sonab used were marked 0,50 mH, they were probably made specially for Sonab, not that it was a strange value, just because their volume was so big.

Best regards

Martin

[iub]

hmm, it seems rather difficult to find 0.5 mH inductors, so I guess I am going to try with 4.7 mH since it is closer than .56 mH.

[Martin Dellstig]

Hi !

If your local distributor can't find exact values they can probably help you anyway:
Take the nearest larger in size and unwind a few coils and check the inductance until you get the right value.

It's no big deal.

Best regards

Martin

[iub]

Hi all,

I have gotten my hands on 6 MT20HFC 8 Ohm tweeters!:D This of course first of all means that I can restore the crossover according to your instructions without worrying too much about the effect of having only 16 Ohm tweeters!

On the other hand, I now have 6x 8 Ohm + 6x 16 Ohm tweeters, so I have been wondering if there is some other configuration I could try, besides the usual OA-4 way. Like For example placing an extra tweeter on the baffle in the OA-5 style.

I feel like experimenting:) any suggestions?

[Villee]

If you want 4 tweeters as OA-5 and OA-6 have you should have eight 8 ohms tweeters... Personally I say that even three tweeters (2x8 and 1x16ohm) sounds just fine. Of course you can do your speakers as OA-12, two sixteen ohms tweeters but what you´re going to gain, perhaps nothing:D

[iub]

Yeah, you are right, changing the tweeter setup would require changes to the filter, I suppose, so I guess I will just stick to the usual 3 tweeter configuration - it is less interesting but has a higher likelyhood of working out right:)