Dear DIYers,
I have found the attached schema in an old audio magazine.
I was wondering if this schema is suitable for a simple line preamp.
The voltage gain should be about 3 (if I am not wrong).
The supply voltage is 60 V (single supply).
Unfortunately the two BJTs are not named.
Does anyone have any suggestion for a couple of suitable BJTs?
Thank you very much to anyone.
I have found the attached schema in an old audio magazine.
I was wondering if this schema is suitable for a simple line preamp.
The voltage gain should be about 3 (if I am not wrong).
The supply voltage is 60 V (single supply).
Unfortunately the two BJTs are not named.
Does anyone have any suggestion for a couple of suitable BJTs?
Thank you very much to anyone.
Attachments
Dear Sir,
Thank you very much indeed for your kind and extremely valuable reply.
What do you think about the schema ?
I intend to replace the linear attenuator at the input with a log potentiometer and take the signal off the output coupling cap (this will be a film cap of course, like tho other one at the input).
I think that this kind of circuit is called " Sziklai pair " but I am not sure.
In general I am looking for a minimalist line preamp.
I would like to stay with BJTs even if I understand that the Nelson Pass Bride of Zen is very very good, if well built.
I don't know if this preamp is able to drive my power amp that has an input impedance of about 8 kohm.
Any your further suggestion would be very much appreciated and valuable for me.
Thank you very much again.
Kind regards,
Beppe61
Torino__ITALY
Thank you very much indeed for your kind and extremely valuable reply.
What do you think about the schema ?
I intend to replace the linear attenuator at the input with a log potentiometer and take the signal off the output coupling cap (this will be a film cap of course, like tho other one at the input).
I think that this kind of circuit is called " Sziklai pair " but I am not sure.
In general I am looking for a minimalist line preamp.
I would like to stay with BJTs even if I understand that the Nelson Pass Bride of Zen is very very good, if well built.
I don't know if this preamp is able to drive my power amp that has an input impedance of about 8 kohm.
Any your further suggestion would be very much appreciated and valuable for me.
Thank you very much again.
Kind regards,
Beppe61
Torino__ITALY
Hi.
BC550C and BC557C work well in this circuit. Use polyester btpassed with polysteyrene for good cheap coupling caps.
Super hint😎 make the 120k with 20k from the supply decouple with a good cap and then a 100k to the base of TS7, this removes supply interaction and tightens the sound.
If you are an experimenter then replace TS8 with a p chanenel fet like a BS250 and reduce the values of R33 and R34 for a lower output impedance.
Chris
BC550C and BC557C work well in this circuit. Use polyester btpassed with polysteyrene for good cheap coupling caps.
Super hint😎 make the 120k with 20k from the supply decouple with a good cap and then a 100k to the base of TS7, this removes supply interaction and tightens the sound.
If you are an experimenter then replace TS8 with a p chanenel fet like a BS250 and reduce the values of R33 and R34 for a lower output impedance.
Chris
Replacing the lin pot with a log pot is not a good idea, as the parallel combination of the 27k and 120k resistor bend the curve of the lin pot to an approximate log curve. I think you will be just about OK to drive an 8k load with this circuit.
analog_sa said:
And I'm willing to bet that even this simple circuit will sound
better than any opamp....😀
Netlist said:
The be honest, almost any small signal transistor will work.Chris Jennings said:
fT > 100MHz
Hfe > 100, >300 even better
Min 30 V
BC55x
BC56x
BC54x
Even old BC108 will work 🙂
Ok dear friends,
I have to reveal the little dirty secret.
The schema is "stolen" from that one of the line input stage of and old but very estimable Radford ZD22 preamp.
The full line stage is much more complex including also tone control section (I personally hate it).
Unfortunately, but as usual, the schema doesn't report the BJTs' codes.
So the search is open for suggestion.
I think that TS8 should be cooled with a dissipator.
So a TO92 case BJT wouldn't be the best option, I think.
I was thinking about the 2SA968. An handy TO220 device.
Is it too much ?
Thank you in primis to the Radford designer (who is he/she I really don't know) and then to everyone who takes part in this discussion.
I am very curious in how this extremely simple stage can sound.
Really an op-amp based preamp would be better ?
Don't know.
Kind regards,
Beppe61
I have to reveal the little dirty secret.
The schema is "stolen" from that one of the line input stage of and old but very estimable Radford ZD22 preamp.
The full line stage is much more complex including also tone control section (I personally hate it).
Unfortunately, but as usual, the schema doesn't report the BJTs' codes.
So the search is open for suggestion.
I think that TS8 should be cooled with a dissipator.
So a TO92 case BJT wouldn't be the best option, I think.
I was thinking about the 2SA968. An handy TO220 device.
Is it too much ?
Thank you in primis to the Radford designer (who is he/she I really don't know) and then to everyone who takes part in this discussion.
I am very curious in how this extremely simple stage can sound.
Really an op-amp based preamp would be better ?
Don't know.
Kind regards,
Beppe61
Dear Moderator,
If what I am writing is not allowed please forgive me and delete the following message.
Dear friends,
The original BJTs are:
TS7 = BC107
TS8 = BC303
The BC303 must be cooled.
So I would like to replace the BC303 with a TO220 case Toshiba 2SA968.
Is it possible without other modifications to the circuit ?
Kind regards,
Beppe61
If what I am writing is not allowed please forgive me and delete the following message.
Dear friends,
The original BJTs are:
TS7 = BC107
TS8 = BC303
The BC303 must be cooled.
So I would like to replace the BC303 with a TO220 case Toshiba 2SA968.
Is it possible without other modifications to the circuit ?
Kind regards,
Beppe61
Hi.
Sorry. I miss read the supply voltage earlier, you will need higher voltage transistors.
For higher disipation without the need for heat sinks consider the Zetex ZTX range 1W easy without heat sink, they do get hot but are designed to handle it.
Chris
Sorry. I miss read the supply voltage earlier, you will need higher voltage transistors.
For higher disipation without the need for heat sinks consider the Zetex ZTX range 1W easy without heat sink, they do get hot but are designed to handle it.
Chris
Dear Friends,
I will try to build a prototype of the preamp in the next days and report on the outcome.
If anyone has a similar schema (i.e. a two BJT line preamp, or 1 Fet- 1 BJT) please let me know.
I am looking for high voltage supply, low output impedance and, of course, low distortion.
In general I am looking for schematics of minimalist line preamp.
Anyway thank you very much indeed.
Have a nice day.
Beppe61
I will try to build a prototype of the preamp in the next days and report on the outcome.
If anyone has a similar schema (i.e. a two BJT line preamp, or 1 Fet- 1 BJT) please let me know.
I am looking for high voltage supply, low output impedance and, of course, low distortion.
In general I am looking for schematics of minimalist line preamp.
Anyway thank you very much indeed.
Have a nice day.
Beppe61
Hello,
in this thread there is a minimalist pre, with very low output impedance: cascode pre
Regards
Claudio
in this thread there is a minimalist pre, with very low output impedance: cascode pre
Regards
Claudio
Dear Claudio,
thank you very much for your kind and valuable reply.
My proposal is even more minimalist, just two BJT.
I did not build any prototype yet but I am very curious about the resulting sound of the schematic.
Your is a little more complex than mine.
Strangely in my experience I have found extremely complex line preamps with even 30 active components per channel.
Are all necessary ? I really don't think so.
Take for instance the tubed preamps. Very few active devices used in their best condition for linearity and low distortion.
Why solid state preamps have to be such complicated I really don't know.
Anyway thank you very much indeed.
Kind regards,
beppe61
P.S. Come vedi il mio inglese è piuttosto schifoso. Se vuoi parlare in italiano scrivimi pure privatamente. Ciao e grazie !
thank you very much for your kind and valuable reply.
My proposal is even more minimalist, just two BJT.
I did not build any prototype yet but I am very curious about the resulting sound of the schematic.
Your is a little more complex than mine.
Strangely in my experience I have found extremely complex line preamps with even 30 active components per channel.
Are all necessary ? I really don't think so.
Take for instance the tubed preamps. Very few active devices used in their best condition for linearity and low distortion.
Why solid state preamps have to be such complicated I really don't know.
Anyway thank you very much indeed.
Kind regards,
beppe61
P.S. Come vedi il mio inglese è piuttosto schifoso. Se vuoi parlare in italiano scrivimi pure privatamente. Ciao e grazie !
But is it fair to compare tubes to bipolar transistors? If it were so simple there would be SOA line stages following topologies from the sixties. I have bult a few simple bjt preamps and without exception they suck. You may argue that due to the lack of loop nfb the sound is 'natural' and 'free' but the bass is horrific, the various distortions - just too much, the lack of fine detail - lo fi.
BJTs ain't no tubes.
Dear Analog_sa,
As you mention a sentence from John Curl, rumors are that this is a John Curl old project (but I am not 100% sure).
I would like to mention another big name in audio electronics, that is Nelson Pass.
He says in his article on single ended class a (I have only a paper copy; link www.passlabs.com/seclassa.htm don't know if it works)
" Simplicity and a minimum number of components is a key element, and is well reflected in the quality of tube designs.
The fewer pieces in series with the signal path, the better.
This is generally true even if adding just one more gain stage will improve the measured specs."
and then:
" Maximum intrinsic linearity is desidered"
I remember to have seen some distortion measurements of the Radford ZD22. Not bad at all, really.
In Italy an audio magazine well known used this preamp as a reference to assess sound quality of other pre in the 70s'.
Of course I don't want to say that tubes=BJT.
Still I think that the basic approach followed in design a preamp using tubes can be maintained with BJT.
I am waiting for someone who wants to try and build a prototype.
The 60 V single supply can be the same of the Bride of Zen or a simpler one using the TL783 from Texas.
I have problem of time and space at my home.
Anyway this is my intention in the next future.
I was hoping to stimulate the curiosity of other people here.
Thank you to anyone partecipating to this thread.
Kind regards,
beppe61
As you mention a sentence from John Curl, rumors are that this is a John Curl old project (but I am not 100% sure).
I would like to mention another big name in audio electronics, that is Nelson Pass.
He says in his article on single ended class a (I have only a paper copy; link www.passlabs.com/seclassa.htm don't know if it works)
" Simplicity and a minimum number of components is a key element, and is well reflected in the quality of tube designs.
The fewer pieces in series with the signal path, the better.
This is generally true even if adding just one more gain stage will improve the measured specs."
and then:
" Maximum intrinsic linearity is desidered"
I remember to have seen some distortion measurements of the Radford ZD22. Not bad at all, really.
In Italy an audio magazine well known used this preamp as a reference to assess sound quality of other pre in the 70s'.
Of course I don't want to say that tubes=BJT.
Still I think that the basic approach followed in design a preamp using tubes can be maintained with BJT.
I am waiting for someone who wants to try and build a prototype.
The 60 V single supply can be the same of the Bride of Zen or a simpler one using the TL783 from Texas.
I have problem of time and space at my home.
Anyway this is my intention in the next future.
I was hoping to stimulate the curiosity of other people here.
Thank you to anyone partecipating to this thread.
Kind regards,
beppe61
However in the proposed schematic Loop Negative Feedback is used, as you can see, with the effect to low output impedance and fix the voltage gain to about 3.
The topology I think is called Sziklai Pair.
Regards,
beppe61
The topology I think is called Sziklai Pair.
Regards,
beppe61
Why not do it yourself if you're optimistic about the outcome. It would hardly take more than an hour.
If you want another implementation of a Sziklai pair just see the line preamp section (or output stage) of the famous Leach wide bandwidth preamp.
But I don't know how it sounds, for the moment.
If anyone has a direct experience of this very similar preamp please report.
Thank you very much again.
beppe61
But I don't know how it sounds, for the moment.
If anyone has a direct experience of this very similar preamp please report.
Thank you very much again.
beppe61
Dear Analog_sa,
I did.
It sounds great.
I am just looking for confirmation from people with a much more experience and knowledge of myself.
May be the topology is too simple to excite the curiosity of anyone.
Anyway I have to revise the power supply a bit.
May be using a +/- 30V dual power supply.
I just wanted to share some opinions.
Kind regards,
beppe61
I did.
It sounds great.
I am just looking for confirmation from people with a much more experience and knowledge of myself.
May be the topology is too simple to excite the curiosity of anyone.
Anyway I have to revise the power supply a bit.
May be using a +/- 30V dual power supply.
I just wanted to share some opinions.
Kind regards,
beppe61
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