Idea for a better volume control...

[jcx]

Lisandro,

I used a BC550 npn, with collector to hot, and emitter to ground. Base was pinned with 1K to ground, and I seem to recall driving the base via a 1K resistor from a 1.5V. I noticed when off the collector had adverse effect on the sound quality.

Hugh

what off V for base?

if the signal was ground ref, the base needs to be a few volts more neg than the signal to prevent major dist from fwd biasing cb diode junction - a well impemented mute/bipolar sw need not add percepatable (much less "nasty") distortion

 

[ChocoHolic]

Hi All !

I am wonderig why the classic bilateral MOS Switches such as
the old CD4066 are unpopular fro this application....?
Especially if we consider there will be much more improved MosSwitches available.....would guess AD, BurrBrown, .....


...afraid of the distorsions due to voltage dependency of Ron ??

Bye
Markus

 

[trigon]

Hi All !

I am wonderig why the classic bilateral MOS Switches such as
the old CD4066 are unpopular fro this application....?
Especially if we consider there will be much more improved MosSwitches available.....would guess AD, BurrBrown, .....


...afraid of the distorsions due to voltage dependency of Ron ??

Bye
Markus

And why not go with something like this pasive pre-amp by Peter Daniel

An externally hosted image should be here but it was not working when we last tested it.

Trigon

 

[ChocoHolic]

@Trigon:

Because of costs???

Costs of CD4066 cannot be the reason...

Bye
Markus

 

[Lisandro_P]

I will give the design on the website i linked early (similar to Hugh's test) a try to see how it works; on the simulator it allows a voltage swing of several volts with no perceptable distortion. Otherwise, 6 DPDT relays will do just fine.

 

[Dave]

I have only tried BJT shunt devices in a simulator and got very good distortion results.

As has been pointed out by jcx when the transistor is off the base must be well below ground level (may as well be negative supply rail) otherwise the signal will be clipped on the negative portion.

When ON the base current needs to be greater than the maximum peak current that will be sourced through the collector of the transistor during the negative signal swing. 10mA is probably a good figure.

 

[EUVL]

Bipolar Shunt

Dave,

> I have only tried BJT shunt devices in a simulator and got very good distortion results.

It would really be a great help if you could kindly post the schematics of what you simulated.


Cheers,
Patrick

 

[Dave]

EUVL,

I no longer have copies of the schematics, however this is a project I'd like to design in the not to distant future.

 

[Steven]

I used a BC550 npn, with collector to hot, and emitter to ground. Base was pinned with 1K to ground, and I seem to recall driving the base via a 1K resistor from a 1.5V. I noticed when off the collector had adverse effect on the sound quality.

I found that the BC550 does not have the best 'short to ground' properties when using them for signal muting, or switching to ground. Far better is the BC337 (or its SMD equivalent BC817). You can use them with the collector to ground and signal to the emitter (upside down) for lowest DC offset, or in the normal way with emitter to ground and collector to signal.
If the transistor should be open and still be able to deal with large voltage swings it is good to keep the base floating. That means that this transistor should be driven from a switchable PNP-current source or PNP inverted cascode transistor. If the current flows, the NPN transistor is switched on; if the current is switched off, the NPN base is floating and the transistor is able to deal with fairly large voltage swings, more than 10Vpp around ground, without the need for a negative supply voltage for the drive circuit.

This is without discussion of the sonic qualities of such a circuit. Such muting circuits are standard in e.g. CD player outputs, but have a bad reputation for sound quality.

Steven

 

[Upupa Epops]

Theoreticaly must be used in this position low Ucesat types, which is not BC 550 / 560 family.