Simple hi-fi question

[Little Monster]

Anyone know what typical output impedance is with hi-fi separates? (A
tuner in this case) I trust it is fairly generic...

Also building speakers - anyone know correct size of bass reflex tube for
a 6 inch woofer? I think the one I got (2.5 inch) is way too big - and
I've lost my speaker design book :-(

Tia,
Monster
--
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All the girls love me
And I will never grow Ooollldd
I am the sexiest man in the UuuKaaaay!

http://www.the-monstruum.co.uk

 

[Kalman Rubinson]

Anyone know what typical output impedance is with hi-fi separates? (A
tuner in this case) I trust it is fairly generic...

Nope. Anywhere from 10s of ohms to several Kohms, depending on design
and vintage.

Also building speakers - anyone know correct size of bass reflex tube for
a 6 inch woofer? I think the one I got (2.5 inch) is way too big - and
I've lost my speaker design book :-(

No such thing. Depends on the acoustic characteristics of the woofer
and the enclosure.

Kal

 

[Myron Samila]

Nope. Anywhere from 10s of ohms to several Kohms, depending on design
and vintage.


No such thing. Depends on the acoustic characteristics of the woofer
and the enclosure.

Kal

For the tuning port, you need to know all the Thiele Small paramaters and you can plot the
expected response curve. The port only works at the tuning frequency. You can actually
buy adjustable ports, you can lengthen/shorten the tube and "tune" for ideal sound at low
frequencies. (Fs, Qts, Qms, Qes, Vas, and you'll need the Vb (box volume)). It is easiest
to plot this with software.

It is easier to make a sealed enclosure, but the problem is you loose the output you could
have with a tuned port (at the lowest frequency).

I didn't understand what you meant in regards to output impedance for hi-fi speparates.
You mean the output from the tuner (amplified? or just pre-amp signal?). Typically, line
level is 600 ohms (-10dB) on a device such as a CD player/tuner, etc.. (recent
electronics). The output of the amplifier is usually designed to run anything down to 4
ohms/channel (typically). I have a Bryston 3B, capable of 2ohms/channel.

Hope that sorta helps.

 

[Kalman Rubinson]

I didn't understand what you meant in regards to output impedance for hi-fi speparates.
You mean the output from the tuner (amplified? or just pre-amp signal?). Typically, line
level is 600 ohms (-10dB) on a device such as a CD player/tuner, etc.. (recent
electronics).

Nope. Only in professional equipment. Consumer equipment has no such
standard.

The output of the amplifier is usually designed to run anything down to 4
ohms/channel (typically). I have a Bryston 3B, capable of 2ohms/channel.

Again, your Bryston is quite competent (as is mine) but many (most?)
consumer A/V receivers and amps cannot handle a 4 ohm load, let alone
a 2ohm load.

Kal

 

[Little Monster]

Nope. Only in professional equipment. Consumer equipment has no such
standard.


Again, your Bryston is quite competent (as is mine) but many (most?)
consumer A/V receivers and amps cannot handle a 4 ohm load, let alone
a 2ohm load.

Kal

Mmm, thanks for the feedback. The tuner is a 70's vintage Realistic
tuner, of fairly compact size. I just supposed that since separates
generally seem to work well together, there must be some kind of standard.

Thanks for the "speaker notes" - really wish I had my book on the subject
now...

Monster
--
I am the sexiest man in the UuuuKaaaayy
All the girls love me
And I will never grow Ooollldd
I am the sexiest man in the UuuKaaaay!

http://www.the-monstruum.co.uk

 

[Kalman Rubinson]

Mmm, thanks for the feedback. The tuner is a 70's vintage Realistic
tuner, of fairly compact size. I just supposed that since separates
generally seem to work well together, there must be some kind of standard.

As long as the input impedance of the device it feeds is higher by an
order of magnitude or more, there should be efficient voltage
transfer.

Kal

 

[Little Monster]

As long as the input impedance of the device it feeds is higher by an
order of magnitude or more, there should be efficient voltage
transfer.

That is certainly the case, the device it feeds being a valve amp, the
input is 1M ohm approx. However, the amp does not have volume or tone
controls, so at the moment the tuner feeds across a 20k dual pot
(completely guessed value), with the wiper connected to the amp. Trouble
is, the volume goes up very steeply near the beginning of the track - I
was hoping if the pot matched the tuner's output impedance a bit better,
it might make a smoother change. Also, intend extending the simple volume
pot with a baxandall circuit, and wondering about picking optimum values
to start with - ie so the circuit has roughly the same impedance as the
tuner output. Now I am thinking, perhaps what I need is a /higher/ value
for the volume control, to match the amp's input...

Monster
--
I am the sexiest man in the UuuuKaaaayy
All the girls love me
And I will never grow Ooollldd
I am the sexiest man in the UuuKaaaay!

http://www.the-monstruum.co.uk

 

[Kalman Rubinson]

That is certainly the case, the device it feeds being a valve amp, the
input is 1M ohm approx. However, the amp does not have volume or tone
controls, so at the moment the tuner feeds across a 20k dual pot
(completely guessed value), with the wiper connected to the amp. Trouble
is, the volume goes up very steeply near the beginning of the track - I
was hoping if the pot matched the tuner's output impedance a bit better,
it might make a smoother change.

The value is probably OK but you need an audio taper pot, not a linear
one.

Kal

 

[Little Monster]

The value is probably OK but you need an audio taper pot, not a linear
one.

It's log - isn't that pretty much the same?

Monster
--
I am the sexiest man in the UuuuKaaaayy
All the girls love me
And I will never grow Ooollldd
I am the sexiest man in the UuuKaaaay!

http://www.the-monstruum.co.uk

 

[Kalman Rubinson]

It's log - isn't that pretty much the same?

Try wiring the other way around (anti-log). OTOH, if your amp's input
impedance is 1M, you might also try a 100K pot in case your tuner has
a very high output impedance.

Kal

 

[Little Monster]

Try wiring the other way around (anti-log). OTOH, if your amp's input
impedance is 1M, you might also try a 100K pot in case your tuner has
a very high output impedance.

Thanks for all the input - must experiment now Anti log sounds
interesting!

Monster
--
I am the sexiest man in the UuuuKaaaayy
All the girls love me
And I will never grow Ooollldd
I am the sexiest man in the UuuKaaaay!

http://www.the-monstruum.co.uk

 

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Ideally, output impedance must be zero.