Help with xovers please

[john & Jake the dog]

Hi Philip,
I bought some of wilmslows xovers the same as yours when I made some "Isobariks".
I drew the Isobarik internals back in the 80's after I rebuilt my first pair after a fire I finally built a pair for fun 5 years ago replaced 4 years ago by some real ones.
Sold the xovers on , would have been useful now, hey, ho.

[john & Jake the dog]

Hi,
I think this is the Clyde xover.
I am presuming that C2 decides the lowest frequency that the speaker can give.
Or is it there for another reason? Should I put a cap in the low positive line?
Could anyone please tell me what to do to get the low driver to cut at 400hz and what would the value be?

cheers

[Nick]

As money is tightish I thought I would go the passive route.
I have a spare amp but I thought matching a transistor amp to the Kel84 might prove difficult.

Well, IMHO, as you have a second amp already, I would have thought the active solution would be the cheaper one, caps and resistors are much cheaper than inductors, and low and high pass RC networks before a power amplifier are much more likely to do what we want than adding componets to a existing passive xover.

I wouldn't get too worked up about the amps sounding different, the difference in box and driver will make far more of a difference.

[pre65]

Hi-what is your transistor amp ?

Is it integrated or power ?

I believe that if it is integrated,and has a tape in/out connection you can use it as a power amp.

Cant remember how it wires up though !

[john & Jake the dog]

Mornin' Philip,
My amp is a home brew Exposure power amp.
Well up to the job, but I know less about active xovers and I think it will be expensive to find out.
The passive route should be well known by those who know, not me, but I just need a starting point as to where to roll the Clydes off at 400hz.

[pre65]

Well, IMHO, as you have a second amp already, I would have thought the active solution would be the cheaper one, caps and resistors are much cheaper than inductors, and low and high pass RC networks before a power amplifier are much more likely to do what we want than adding componets to a existing passive xover.

I wouldn't get too worked up about the amps sounding different, the difference in box and driver will make far more of a difference.

Hi John-good advice is good advice !

[john & Jake the dog]

Hi Philip,
Nick's advice is good advice and I'm very grateful for his expertise, but I know nowt about splitting the signal before the amp, I've only read about active xovers and it seems very complicated to me.
If there is a passive way of splitting the signal before the amps then that could be a way forward but as I said I no nowt in that direction.

I am confident that I can now make the B200 produce bass from 400hz down but I dont want the Clydes to follow them under 400 hz.
It's a bad idea ,I've read as the amp sees it as a bit of a load and sonicly the effect might be strange.

[Nick]

Nick's advice is good advice and I'm very grateful for his expertise, but I know nowt about splitting the signal before the amp, I've only read about active xovers and it seems very complicated to me.
If there is a passive way of splitting the signal before the amps then that could be a way forward but as I said I no nowt in that direction.

We are talking about a passive split, I think you are hung up on the names, active xovers or passive it doesn;t matter, all you need to provide a 6db per octave split before the amplifiers, is to know what the output impedance of your preamp is, and the input impedance of the two amplifiers. All you need then is the frequency that you want to cross over at and

f = 1 / ( 2 * Pi * R * C )

Where f is in herts, R in ohms, and C in farads

[pre65]

Hi John-as i understand it "active" means having the crossover components between the pre amp and power amp.

So in your case the crossover for the B200 would be before your Exposure copy and the amp would only have to deal with that part of the frequency range.

And with the Clydes the KEL84 would be released from the LF burden.

If it were me i would leave the KEL84 and Clyde connected as they are now,and play with the Exposure and sub as a separate entity using a passive crossover before the amp.

If you look at Petercoms advice on your WD forum post you will see that its not that easy whichever way you go.

PS.some time ago Hi-fi world ran some articles about active speakers using adjustable crossovers from Maplins.I will try to dig them out for you.

[john & Jake the dog]

Hi Nick,
I'm running the Clydes with a Kel 84, BTW the whole problem has been caused by my change to valves, come back Isobariks all is forgiven, so there isn't a preamp in the chain.
My "Exposure" amp is a power amp, I have a Meridian pre, but all these variables must surely be a nightmare compared to making two simple xovers.
The B200 xover would only need a couple of parts and I'm not too fussy where it crosses because it is a mid/bass unit.
I just don't want the Clydes duplicating the frequency, i want them to roll off early though as the bass should be better with the B200.

[pre65]

Hi John-i hope you find the results worthy of your efforts.

[Nick]

but all these variables must surely be a nightmare compared to making two simple xovers.

Yes, but you say that without knowing what is involved to make two "simple xovers". So you don't know how much or not of a nightmare its going to be.

Simple fact is, I don't know how to do what you want to so, so maybe someone else can help you with your request for a simple xover.

The other "complicated way", involves making a splitter box, one phono in, two out (per chan), one goes to the kel, and has a high pass filter in the way, the other goes to the exposure and has a low pass filter in the way. All in the box, add a simple shunted volumn control. Adjust the volumn on the kel and exposure to make the two loudspeakers match what you want.

[john & Jake the dog]

Hi Nick,
I think I'm almost with you now, I thought that I had to have a pre-amp on both amps for the network to go in between , but If I understand correctly it would go inbetween my CD player and the two amps.
If a volume control could be put in and maybe replaced at some time with an equivelent fixed resistor, that could be done, or a pcb variable resistor.
The only snag with this is I don't fully understand the application, is there any info where it is drawn, then I may be able to get my head around it.
The Exposure driving the B200's is an elegant solution certainly and it would make the box implemtation easier too.
Thanks for all your perserverence. It sometimes takes a very heavy hammer to get it in

[john & Jake the dog]

Hi Nick,
found this,
http://www.st-andrews.ac.uk/~jcgl/Scots ... s/lpf.html


Do I alter values to get the two plots to overlay each other then read off the values?

[Nick]

Do I alter values to get the two plots to overlay each other then read off the values?

No, Jim's page is showing the input signal and the output, to show the phase and amplitude after the filter. If the two are the same, you have a length of wire (ie no filter)

You can use the equation I gave earler to work out a starting place, just rearange to give the resistance for a given cap and frequency

R = 1 / ( 2 * Pi * F * C )

In the case of the high pass filter the impedance of your amplifier should be in parallel with the resistor value, and the low pass shoul dhave the source impedance of your pot and any in series with the resistor.

Like any xover final tweeking will need to be done by ear.