As some of you may be aware, I have an on-going speaker rebuild fantasy
bubbling away in the background. The plan is to bi-amp, and part of this
involves a second line output on the pre-amp, to send a signal to the bass
amp. The bass/midrange driver will have no high-pass components in the
crossover - I intend to let the bass roll off naturally, and try to match
the low-pass filter feeding the subs to this roll-off. I'm edging towards
trying to make a prototype filter and would welcome comments...

The pre-amp is a Cambridge A75. The chips it uses are NE5534N op-amps,
evidently low-noise and suitable for high quality audio. My intention was to
use the same chips for my active filter / output stage, on the assumption
that the pre-amp's PSU will be delivering the right voltage(s). However, it
looks like these chips are no longer made - what would be a suitable
alternative?

I know next to nothing about solid state electronics, but my efforts so far
would suggest that I want to use an integrator and a phase inverter. The
integrator provides the actual filtering effect (I think), but is 180
degrees out at the crossover, decreasing to 90 degrees lower down. It would
seem to be a good thing to try and get the subs to be in phase at the point
where they cross over the natural roll-off of the bass/mid drivers/cabs. So,
I reckon the active filter and a phase inverter will do the trick - that
should give me zero degrees shift at crossover, and 90 degrees lag somewhere
low down. (I'm considering a crossover point at something around 60-80Hz.)

Does this sound like it should work?


--
Wally
www.artbywally.com
www.wally.myby.co.uk

Wally wrote:

The pre-amp is a Cambridge A75. The chips it uses are NE5534N op-amps,
evidently low-noise and suitable for high quality audio. My intention was to
use the same chips for my active filter / output stage, on the assumption
that the pre-amp's PSU will be delivering the right voltage(s). However, it
looks like these chips are no longer made - what would be a suitable
alternative?

5534's are very common audio op-amps. You might not be able to find the
exact part number that you are looking for but a search for 5534 opamp
on Farnell's website came up with a few alternatives. You might also
want to look at the dual equivalent - the 5532.

You should also bear in mind that many 5534's are not stable at unity
gain without additional compensation components.

Cheers.

James.

James Perrett wrote:

5534's are very common audio op-amps. You might not be able to find
the exact part number that you are looking for but a search for 5534
opamp on Farnell's website came up with a few alternatives. You might
also want to look at the dual equivalent - the 5532.

If I'm right in my thinking that I need a filter stage and a phase inverter,
the dual might be the better choice. I'll do some searching.


You should also bear in mind that many 5534's are not stable at unity
gain without additional compensation components.

I'll cross that bridge when I get nearer to it- not sure yet if unity gain
is what I'm after. I was planning to try and find the point where the signal
goes into the existing output, and building a second output from that point.
If unity gain is an issue, can I make it with suficient gain to be sure of
stability, and then attuenuate the output? It'll probably be feeding a SS
amp that wants a line level input.


--
Wally
www.artbywally.com
www.wally.myby.co.uk

In article , Wally
wrote:


The pre-amp is a Cambridge A75. The chips it uses are NE5534N op-amps,
evidently low-noise and suitable for high quality audio. My intention
was to use the same chips for my active filter / output stage, on the
assumption that the pre-amp's PSU will be delivering the right
voltage(s). However, it looks like these chips are no longer made - what
would be a suitable alternative?

Erm... despite the magazines, etc, I'd say almost anything would do. :-)

My personal favourite has always been the Hitachi HA12017, but these are
now hard to find, and require more components than most. Despite the
hostility of some of those in audio, you could consider the TL071/81
families as used by Quad in the 34 pre-amp. These are quite easy to use.

I know next to nothing about solid state electronics, but my efforts so
far would suggest that I want to use an integrator and a phase inverter.
The integrator provides the actual filtering effect (I think), but is
180 degrees out at the crossover, decreasing to 90 degrees lower down.
It would seem to be a good thing to try and get the subs to be in phase
at the point where they cross over the natural roll-off of the bass/mid
drivers/cabs. So, I reckon the active filter and a phase inverter will
do the trick - that should give me zero degrees shift at crossover, and
90 degrees lag somewhere low down. (I'm considering a crossover point at
something around 60-80Hz.)

Does this sound like it should work?

Dunno. However I'm not sure what you are thinking of an an 'integrator'. A
genuine integrator has a gain that approaches infinite as you go down to
d.c. and hence is nominally unstable. Its phase lag is 90 deg at all
frequencies.

Have a look at some of the pages on filters in the 'Scots Guide'. This
inlcudes some basic stuff on designing simple filters with ICs.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:
In article , Wally
wrote:


The pre-amp is a Cambridge A75. The chips it uses are NE5534N
op-amps, evidently low-noise and suitable for high quality audio. My
intention was to use the same chips for my active filter / output
stage, on the assumption that the pre-amp's PSU will be delivering
the right voltage(s). However, it looks like these chips are no
longer made - what would be a suitable alternative?

Erm... despite the magazines, etc, I'd say almost anything would do.
:-)

I dare say. :-)


My personal favourite has always been the Hitachi HA12017, but these
are now hard to find, and require more components than most. Despite
the hostility of some of those in audio, you could consider the
TL071/81 families as used by Quad in the 34 pre-amp. These are quite
easy to use.

Righto.


Dunno. However I'm not sure what you are thinking of an an
'integrator'. A genuine integrator has a gain that approaches
infinite as you go down to d.c. and hence is nominally unstable. Its
phase lag is 90 deg at all frequencies.

Then the thing I read about must have a different name... :-)


Have a look at some of the pages on filters in the 'Scots Guide'. This
inlcudes some basic stuff on designing simple filters with ICs.

Scots Guide? One of your pages?


--
Wally
www.artbywally.com
www.wally.myby.co.uk

In article , Wally
wrote:
Jim Lesurf wrote:

Have a look at some of the pages on filters in the 'Scots Guide'. This
inlcudes some basic stuff on designing simple filters with ICs.

Scots Guide? One of your pages?

Erm... Hundreds, actually. ;-)

Have a look at the 'Scots Guide' address in my sig, below. When there, go
to the section on 'Analog and Audio', and you will then find a link to some
pages on active filters. There are bits on related topics scattered around
the 'Guide'.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:

Scots Guide? One of your pages?

Erm... Hundreds, actually. ;-)

Have a look at the 'Scots Guide' address in my sig, below. When
there, go to the section on 'Analog and Audio', and you will then
find a link to some pages on active filters. There are bits on
related topics scattered around the 'Guide'.

Thanks, Jim. I'll have a look over the next few days - I've got a borrowed
scope coming after ther weekend (my own has packed in - one trace down, and
nil timebase - can't do much with a vertical line!), so I'll be wanting to
make a start with the breadboard by then.


--
Wally
www.artbywally.com
www.wally.myby.co.uk

In article ,
Wally wrote:
The pre-amp is a Cambridge A75. The chips it uses are NE5534N op-amps,
evidently low-noise and suitable for high quality audio. My intention
was to use the same chips for my active filter / output stage, on the
assumption that the pre-amp's PSU will be delivering the right
voltage(s). However, it looks like these chips are no longer made - what
would be a suitable alternative?

Don't think you'd find any problems sourcing NE5534AN - Maplin stock them.

--
*If a thing is worth doing, wouldn't it have been done already?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

Don't think you'd find any problems sourcing NE5534AN - Maplin stock
them.

I haven't looked for them yet - found a Phillips data sheet that said hey
were discontinued, so assumed they might be hard to find.


--
Wally
www.artbywally.com
www.wally.myby.co.uk

In article ,
Wally wrote:
Don't think you'd find any problems sourcing NE5534AN - Maplin stock
them.

I haven't looked for them yet - found a Phillips data sheet that said hey
were discontinued, so assumed they might be hard to find.

Could be that refers to an 'N' suffix.

--
*Growing old is inevitable, growing up is optional *

Dave Plowman London SW
To e-mail, change noise into sound.