A line preamp schematic working with 12V PS.

[beppe61]

Dear Friends,

after many many ramblings I have set for a line preamp to be powered with a 12V power supply using SLABatteries.
A friend of mine is modding (primarly updgrading input and output connectors) a T-Amp.
The fact that 12V suffice for an amp had convinced me that should suffice even more for a line preamp.
So I am looking for suggestion about a very simple circuit with gain about 3 and with good performance at 2 V output with a load of 10 kohm.
Something of the like of the schematic attached.
Any suggestion about a suitable schematic would be very much welcomed and appreciated.
thank you very much.
Kind regards,

bg

[lineup]

That circuit uses 48 Volt DC.
May be some resistors need other values.

Good to know this:
- 12 Volt single supply
- Voltage gain ~3
- 2 Volt RMS output voltage
~10 kOhm load

this will make easier to give good advice

Regards and thank you very much
lineup

[beppe61]

Originally posted by lineup

1) That circuit uses 48 Volt DC.
May be some resistors need other values.
2) Good to know this:
- 12 Volt single supply
- Voltage gain ~3
- 2 Volt RMS output voltage
~10 kOhm load
this will make easier to give good advice
Regards and thank you very much
lineup

Dear Mr. Lineup,

thank you for your always kind and valuable reply.
1) I know.
I attached the schematic just to explain the kind of circuit I am looking for.
A very simple circuit.
I expect most of the benefits from the battery PS.
2) Actually these should be the normal requirements for a line preamp to be used with digital sources and able to drive most of the power amps to full power.
Anyway I would like to stay "discrete" (i.e. no-opamp).

If you have any suggestion I am here.
Kind regards,

bg

[davidsrsb]

Something like this?
Current drain is about 2.5 mA per channel.

This configuration has good supply rejection.

[beppe61]

Originally posted by davidsrsb

1) Something like this?
2) Current drain is about 2.5 mA per channel.
3) This configuration has good supply rejection.

1) Exactly Sir, thank you very much indeed.
I meant something like that.
Extremely simple but also nice.
2) Very good figure.
Is the current drain constant (i.e. is the circuit class A)?
If so, as I intend to use at least a 6Ah SLAB, the battery should last 6000/5= 1200 hours.
Is my calculation wrong?
3) Well, with batteries this should not be mandatory.
Nevertheless a nice plus.

Have you actually build this circuit?
How does it sound?

Thank you very much again.
Kind regards,

bg

[davidsrsb]

The amplifier is class A and will work from 14V down to 10V during the battery discharge.

I used to use this sort of circuit, at higher current, as a video amplifier.
With normal audio transistors it does not need a compensation capacitor.

[beppe61]

Originally posted by davidsrsb

1) The amplifier is class A and will work from 14V down to 10V during the battery discharge.
2) I used to use this sort of circuit, at higher current, as a video amplifier.
With normal audio transistors it does not need a compensation capacitor.

Dear Sir,
thank you so much again for your very kind and valuable reply.
1) Class A means a constant current draw.
So no big buffer caps are needed at the output.
Very good.
2) I hope the bandwidth and distortion figures are good also at with a low 12V supply.

As I said I thought about a 12V SLAB:
1) on the basis of the great opinions read about a smal wattage (6W/8ohm) high quality power amp powered with a single 7Ah 12V SLAB
2) after reading that the noise of a SLAB is unmeasurable !
3) considering that the current consumption of such simple circuits is very minimal, so that the SLAB's charge should be sufficiently long lasting from a practical point of view (at least about 1 charge/week).

I strongly think that a circuit like this has good chances to sound very good indeed.
Very "black" background for music and very nice transparency.

I will report soon.
Thank you very much again.
Kind regards,

beppe