I'm back - the silly questions guy.

[beppe61]

Dear Sirs,


please excuse my maybe silly following question.
I have a preamp circuit that needs a +/- 30 V dual power supply.
Can I use instead a +/- 24 V dual PS without changing any components value ?
I can understand that the circuit should be optimized for the use of a 30V Ps, but it would be the possible result with a 24V PS?
I ask this because sometime I see amps that can work with different voltage supplies without modifications.

Thank you very much indeed.

Kind regards,

beppe61

[Netlist]

I'm afraid that will be impossible to tell without schematic.

/Hugo

[beppe61]

Originally posted by Netlist
I'm afraid that will be impossible to tell without schematic.

/Hugo

Dear Mr. Hugo,

thank you very much indeed for your kind reply.
I am attaching the schematic.
BC107 and BC303 are the bjts to be used in the original circuit.
Besides, do you think that I can use a BD140 instead of the BC303 ? I like its TO126 package.
It can work also with a single 0-60V supply, but I decided for a dual PS.
I intend to use 24V fixed voltage regulators for the first prototype.
In general I am extremely interested in minimalist circuit for line preamps and I am collecting them in orderd to build the best one day.

Any kind suggestion would be very welcome and appreciated here.

Kind regards,

beppe61

[Netlist]

A BD140 will work but this design was made for a single supply. Also 60 V will be a little high for the BC107.

/Hugo

[peranders]

Originally posted by beppe61
It can work also with a single 0-60V supply, but I decided for a dual PS.
I intend to use 24V fixed voltage regulators for the first prototype.

If you use max 30 volts single supply you can use almost any BCxxx transistor. The circuit doesn't get better with a dual supply, adds nothing really.

BC547-550
BC557-560

BC337, BC327

plus many many more will work.

[beppe61]

Originally posted by Netlist
A BD140 will work but this design was made for a single supply. Also 60 V will be a little high for the BC107.
/Hugo

Dear Mr. Hugo,

thanks for the kind reply.
It is a schematic of a commercial product that was very well reviewed in its time.
I strongly think that it could compare very well also with more modern preamps.
And it is amazingly simple (just 2 bjts) for not being also interesting.
Yes, the power supply is single 0-60V.
Actually I have already built a one-channel prototype and the BC107 does not get warm in any way.
Needless to say the sound was very very promising.
Instead the BC303 needs to be cooled down.
So I would prefer to use a BD140 that has a TO126 package, very much more user friendly.
I thought to use a dual power supply beacuse the vast majority of the solid state preamps use dual PS.
And choosing +/- 24V I could use ready off-the-shelf voltage regulators (very simple, convenient and cheap also).

Thank you very much indeed.

Kind regards,

beppe61

[beppe61]

[QUOTE]Originally posted by peranders

Dear Mr. Peranders,

thank you very much indeed for your extremely kind and helpful reply.
Let me ask you something more about your statements.

" If you use max 30 volts single supply you can use almost any BCxxx transistor ".

I would like to use a high voltage power supply because I read somewhere that this should have a greatly beneficial impact on dynamic response of the preamp (excuse me but my tecnichal background and englis knowledge are both at neanderthal level).

" The circuit doesn't get better with a dual supply, adds nothing really".

I thought about a dual PS because almost all commercial preamps use a dual PS.
Also a dual +/- 24V PS is easily done with off-the-shelf regulators.

Thank you very much indeed.

Kind regards,

beppe61

[tlf9999]

Originally posted by beppe61
I am attaching the schematic.

I have built something very similiar (i call the topology "ultra-linear" pair) and it does sound very good. It doesn't really benefit from dual rails, as indicated by others.

My favorite is a small signal PNP (5401) coupled with a hot small signal n-channel MOSFET (irf510). It sounds great to my ears.

[peranders]

[QUOTE]Originally posted by beppe61

Originally posted by peranders
" If you use max 30 volts single supply you can use almost any BCxxx transistor ".

I would like to use a high voltage power supply because I read somewhere that this should have a greatly beneficial impact on dynamic response of the preamp (excuse me but my tecnichal background and englis knowledge are both at neanderthal level).

This is not true. Often it's in fact a disadvantage to have too high supply voltage. A basic rule is the have enough voltage, not unnecessarily high, and not too low oft course.

[QUOTE]Originally posted by beppe61

Originally posted by peranders " The circuit doesn't get better with a dual supply, adds nothing really".

I thought about a dual PS because almost all commercial preamps use a dual PS.
Also a dual +/- 24V PS is easily done with off-the-shelf regulators.

I'm afraid you have missed the concept WHY you have a dual voltage. The main reason is to get rid of all coupling caps but in your case you can't.

[beppe61]

Originally posted by peranders

This is not true. Often it's in fact a disadvantage to have too high supply voltage. A basic rule is the have enough voltage, not unnecessarily high, and not too low oft course.
I'm afraid you have missed the concept WHY you have a dual voltage. The main reason is to get rid of all coupling caps but in your case you can't.

Dear Mr. Peranders,

I thank you sincerely for your kind and great help.
Let's see if I have understood every thing correctly at the end.
You suggest:
1) to stick with a 0-30V single PS
2) with a 30V single supply I can use all the NPN-PNP couples you mention in the circuit attached without having to change the values of the passive components.
Have I understood well?
Last question: do you think that the coupling caps must be avoided definitely or it is more a problem of choosing the right caps for the task? I mean a great quality film cap.
On the other hand all tube preamps are cap coupled, also those very expensive ones.

Thank you very much indeed for you kind and very precious advice.

Kind regards,

beppe61