SpeakerTalk

T.O. Chef · Posted: Thu Nov 01, 2018 11:02 pm Post subject:

I'd love to see that schematic AudioLT. Was it intended to be attached?

I guess then my questions are:
How crucial is the value of that cap. In my case a 30uF.
And, can I assume that inductor to be that value?, I was only assuming it based on all other 105 schematics.
Perhaps it's different in this configuration? I will attempt measuring it again. First time I tried my DATS program was unable to manage a value so low, but I can try once more, using a hand held device.

I find it fascinating that this (Tank ??) circuit + an aB should both be present in my 105's. The T-52's are the original versions, with the squared off face-plates. But the rear head coverings and the horizontal pcb position leads me to believe they are later versions. The build date is Nov. 1979.
I have re scanned the B-110b's and it seems the first time around I got a wonky L reading. Confirmed now: Both drivers are so close to published spec's is uncanny. Amazing indeed after all these years!
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audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

https://photos.app.goo.gl/fFrCCrYasywoT8pu6

T.O. Chef · Posted: Fri Nov 02, 2018 12:16 am Post subject:

Alas ... no Google account here.
Reasons abound, but I won't get into them. Suffice to say, After 2 years I was finally able to escape from their grasp.

Oh how I wish we could all just do this within the forum. Post schematics and pictures easily.
I do understand the bandwidth issue though.

I'll PM an email.
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audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

edited, try again.

T.O. Chef · Posted: Fri Nov 02, 2018 12:51 am Post subject:

I see a huge series cap set on the HF input of that 105/2 layout as published by Colin. Not a parallel one.

I've been up and down all 105 crossover configurations, and actually have a set of 105/2 boards.

Maybe I'm blinded by age, but I don't see a parallel C/L on the HF input.
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audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

The 30uF is in parallel with the 0.028uF, thus both in series with the tweeter input. Can you see the link yet?

T.O. Chef · Posted: Fri Nov 02, 2018 3:54 pm Post subject:

AH!!! Thank you Audiolabtower.
So there it is. my filter exactly (minus the aB) and it was the Mark ! version sporting it.
This is wonderful information, I'm so glad to know my crossover is not some anomaly or worse a 3rd party modification.

Now. I wonder what purpose it serves? Note I do have the early version t-52.
I have removed this 30uF cap. At this point I'm relatively pleased with the HF, though I do hear some ringing on classical piano works. Related perhaps to this circuit?

I'll reinstall the component and listen well to what my ears have to say about it, then report further.

Very Happy

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audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

C9 and C11 are open circuit on my board, but obviously there for the aB network if required.

T.O. Chef · Posted: Fri Nov 02, 2018 9:47 pm Post subject:

Guru, thank you very much for that link explaining and calculating Tank Circuits. That has helped immensely analyzing a big issue.

I first reinstalled the aB circuit. Both sides test audibly very close to each other. Much of the tweeter ringing was reduced. To my ears they sound great!
Next, I put the tank circuit cap back in, one at a time. When both done there is a distinct mismatch in tonality side to side.

It must be the values used, they don't match the originals. And I can see from the calculator that a small change in value moves the resonance frequency quite a bit.

So, back to drawing board as they say. I'll remove that 30uF cap and find a way to get a perfect match, though I'm shooting in the dark a bit. At least I know if I can't get that circuit to behave as intended I can always just leave it out totally without much pain.
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Music is food for the soul.

speakerguru · Posted: Fri Nov 02, 2018 11:20 pm Post subject:

T.O. Chef · Posted: Sat Nov 03, 2018 1:05 am Post subject:

T.O. Chef · Posted: Sat Nov 03, 2018 1:10 am Post subject:

MAYBE .... someone saw that crossover configuration on-line somewhere and decided this filter was incorrectly made? Then added the 30uF to match?
That seems feasible.
It doesn't explain the etched trace or the jumper wire to the HF section though.
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Music is food for the soul.

speakerguru · Posted: Sat Nov 03, 2018 12:11 pm Post subject:

T.O. Chef · Posted: Sat Nov 03, 2018 2:13 pm Post subject:

A few pictures here showing the filters "as found".

Note the etched trace on the left side. I have not attempted to decipher that revision, but everything seems to function as it should, aside from what's been discussed above.

https://nofile.io/f/3VCbrxsq8XA

https://nofile.io/f/fFaWtrTZS7e

Hopefully it can be confirmed the existence of the Parallel L/C on the top as shown.
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audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

I assumed the 30uF was part of the aB circuit, only used with the 0.22uF and 3.3/7uF combination. There are certainly designed spaces for these components on the pcb at C9 and C11 (0.22), unpopulated on mine, but no modifications in evidence.

If you look at the 104aB crossover it has an extra 10uF in the same series position but on the tweeter side, the only difference it is in parallel with a resistor instead of the 105 inductor. So maybe the total system design is not so much of an effect at 5.5kHz as the simple 30uF/28uH would imply in isolation?

Interestingly the voltage curve for the unofficial active 105 crossover shows the -6dB point at just over 3kHz, and a slight shaping at 5kHz of a dB or so - if we assume this was made to exactly mirror the original passive response?