Hi shaan, thanks for your kind words in post #73 and the attached BOM - already looking for what I have in stock before a Mouser order.
1. Can I ask if you have thought about more "modern" or better audio signal transistors for your BC546 / BC 556 selection - no criticism at all, I am just curious. Obviously these are still freely available and cheap.
2. For the external wiring off the pcb as you have mentioned, can I ask if it is possible to switch in / out the signature pot with an on/off switch. This would I assume give the flexibility to have a totally straight amp or by switching this pot in then adds the extra feature you have designed. Or is the amp straight through with the signature pot in minimum anti clockwise position?
Also I assume it will be a month or so till you have the pcbs on hand to post out where you can?
One other small point - on the schematic in post #1, Q19 is labelled as either KSE340 or MJE340 (should be 350) - BOM is correct.
1. Can I ask if you have thought about more "modern" or better audio signal transistors for your BC546 / BC 556 selection - no criticism at all, I am just curious. Obviously these are still freely available and cheap.
2. For the external wiring off the pcb as you have mentioned, can I ask if it is possible to switch in / out the signature pot with an on/off switch. This would I assume give the flexibility to have a totally straight amp or by switching this pot in then adds the extra feature you have designed. Or is the amp straight through with the signature pot in minimum anti clockwise position?
Also I assume it will be a month or so till you have the pcbs on hand to post out where you can?
One other small point - on the schematic in post #1, Q19 is labelled as either KSE340 or MJE340 (should be 350) - BOM is correct.
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emergence
Hi Gary.
Yes I have. Spec-wise the "modern" ones are impressive indeed. Unfortunately, an "Audio" transistor doesn't exist, but if you put "audio" in the datasheet, there will be followers. I don't wish to offend anyone with this, consider it just the opinion of someone who doesn't believe in the "abilities" of individual components, but is aware of their weaknesses. Also, as I myself possess subjective views on sound quality, I respect other's subjective views, be it in sync with mine or not.
But I guess the bigger question is that, what am I talking about when I say "better". Already with the classic BC pair there is audibly zero noise, high slewrate, stable and reliable performance, easy control over harmonic level, and below 0.001% default THD! The thing is, none of these aspects is due to the individual BJTs - low noise is due to low resistor values; high slew rate due to low-impedance feedback node, stable performance due to layout, easy control over harmonics due to a separate dedicated segment for it, and <0.001% default THD due to very high global negative feedback that works to create a correct replica of the input signal, like a blank slate on which we can doodle (via the SIG control). None of these aspects of this circuit are affected by using a "modern/better" transistor.
(This doesn't mean that I believe one can replace the jFET at the input of a moving coil phono preamp with 2N3055 and doesn't have to climb Mount Everest to make it perform the same.
)
It is totally possible. Pin 2 and 3 of the SIG control are shorted to ground on PCB. You just place the switch to Pin 1 and 2. The SIG pot has no direct connection to the preamp's output, in any position.
Yes.
Corrected schematic uploaded in post #1.
Hi Gary.
Yes I have. Spec-wise the "modern" ones are impressive indeed. Unfortunately, an "Audio" transistor doesn't exist, but if you put "audio" in the datasheet, there will be followers. I don't wish to offend anyone with this, consider it just the opinion of someone who doesn't believe in the "abilities" of individual components, but is aware of their weaknesses. Also, as I myself possess subjective views on sound quality, I respect other's subjective views, be it in sync with mine or not.
But I guess the bigger question is that, what am I talking about when I say "better". Already with the classic BC pair there is audibly zero noise, high slewrate, stable and reliable performance, easy control over harmonic level, and below 0.001% default THD! The thing is, none of these aspects is due to the individual BJTs - low noise is due to low resistor values; high slew rate due to low-impedance feedback node, stable performance due to layout, easy control over harmonics due to a separate dedicated segment for it, and <0.001% default THD due to very high global negative feedback that works to create a correct replica of the input signal, like a blank slate on which we can doodle (via the SIG control). None of these aspects of this circuit are affected by using a "modern/better" transistor.
(This doesn't mean that I believe one can replace the jFET at the input of a moving coil phono preamp with 2N3055 and doesn't have to climb Mount Everest to make it perform the same.
)It is totally possible. Pin 2 and 3 of the SIG control are shorted to ground on PCB. You just place the switch to Pin 1 and 2. The SIG pot has no direct connection to the preamp's output, in any position.
Yes.
Corrected schematic uploaded in post #1.
Thanks for your considered and honest reply shaan, on doing some research today, I have looked at some other more "modern" (if that is the correct phrase) transistors that have been described by the manufacturer as an "audio low noise" type.
The only problem - as always, is they have totally different pin outs to the BC types in your design. So based on what I can find and your answer - no need to take it any further.
The only problem - as always, is they have totally different pin outs to the BC types in your design. So based on what I can find and your answer - no need to take it any further.
There will be a lot of exotic caps out there for those input and output coupling cap positions. Most of them will be physically too big (and too expensive) to fit on the pcb. I would look at an FKP or MKP type Wima cap here for good transparency at a good price as long as they fit the allocated space. I am sure shaan will let you know the type he has used in his build.
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Hi Theodosis.
Yes. All capacitors used as signal coupling components add their signature to the signal. The most linear types add the least of it.
I use polyester film types in both places and sometimes non-polarised electrolytics at C27/28. Using the film types the sound is just fine. Various types of nonpolar eletros are available here, some have excellent and some have awful linearity - a matter of trial and error with electrolytics. So I will leave the choice upto you. Polypropylene is said to be most linear, so you may consider that as well (larger in size and expensive).
Better not to avoid the capacitors, they keep the input and output free of any DC component.
Yes. All capacitors used as signal coupling components add their signature to the signal. The most linear types add the least of it.
I use polyester film types in both places and sometimes non-polarised electrolytics at C27/28. Using the film types the sound is just fine. Various types of nonpolar eletros are available here, some have excellent and some have awful linearity - a matter of trial and error with electrolytics. So I will leave the choice upto you. Polypropylene is said to be most linear, so you may consider that as well (larger in size and expensive).
Better not to avoid the capacitors, they keep the input and output free of any DC component.
Hi again shaan, looking at getting all parts together and tested while I wait for the pcb's from India via Neal in the UK.
Can I ask if you matched any of the BC546/556 transistors for gain in your building and testing of the preamp. If not, do you see any merit in doing this, I have over 100 of each type, so can quite easily match some pairs for HFE if you think it would be of any advantage.
Can I ask if you matched any of the BC546/556 transistors for gain in your building and testing of the preamp. If not, do you see any merit in doing this, I have over 100 of each type, so can quite easily match some pairs for HFE if you think it would be of any advantage.
Links to three videos showing power supply rail behavior, transient output behavior and clipping behavior shared in Post #1 in the Video Snapshots segment.
Updated GB list:
Sadik - 1 pcb - India
Vunce - 2 pcb - USA
Nisbeth - 2 pcb - Denmark
Blek Stena - 1 pcb - Croatia
ItsAllInMyHead - 2 pcb - USA
Deps - 1 pcb - Poland
manniraj - 1 pcb - India
MaryA - 1 pcb - USA
meanie - 1 pcb - SG
iamwhoiam - 1 pcb - UK
PinkPink - 2 pcb - Hongkong
Pistollero - 1 pcb - Portugal
helfred - 1 pcb - Denmark
woodlands - 1 pcb - Ireland
Kokanee - 1 pcb - Canada
lancer - 1 pcb - SG
redjr - 1 pcb - USA
Rajesh - 1 module - India
zebulo - 2 pcb - France
hydrovac - 1 module - India
Rick G - 1 pcb - USA
jls001 - 1 module - India
cats squirrel - 1 pcb - UK
routhun - 1 pcb - USA
Hemant07 - 1 module - India
Kana711104 - 1 pcb - India
NealJ - 2 pcb - UK
CitizenKane - 2 pcb - Germany
RobSoet - 2 pcb - Belgium
Medisinmannen - 1 pcb - Norway
bhrt - 1 pcb - India
pappu - 1 pcb - India
kbhuvi - 1 pcb - India
kartk - 1 module - India
dbwinger - 1 pcb - USA
fencki - 1 pcb - Austria
ecclesand - 1 pcb - USA
danielhk - 2 pcb - Hongkong
Faizal Mansar Alam - 1 module - India
mvictor69 - 1 pcb - Romania
Sadik - 1 pcb - India
Vunce - 2 pcb - USA
Nisbeth - 2 pcb - Denmark
Blek Stena - 1 pcb - Croatia
ItsAllInMyHead - 2 pcb - USA
Deps - 1 pcb - Poland
manniraj - 1 pcb - India
MaryA - 1 pcb - USA
meanie - 1 pcb - SG
iamwhoiam - 1 pcb - UK
PinkPink - 2 pcb - Hongkong
Pistollero - 1 pcb - Portugal
helfred - 1 pcb - Denmark
woodlands - 1 pcb - Ireland
Kokanee - 1 pcb - Canada
lancer - 1 pcb - SG
redjr - 1 pcb - USA
Rajesh - 1 module - India
zebulo - 2 pcb - France
hydrovac - 1 module - India
Rick G - 1 pcb - USA
jls001 - 1 module - India
cats squirrel - 1 pcb - UK
routhun - 1 pcb - USA
Hemant07 - 1 module - India
Kana711104 - 1 pcb - India
NealJ - 2 pcb - UK
CitizenKane - 2 pcb - Germany
RobSoet - 2 pcb - Belgium
Medisinmannen - 1 pcb - Norway
bhrt - 1 pcb - India
pappu - 1 pcb - India
kbhuvi - 1 pcb - India
kartk - 1 module - India
dbwinger - 1 pcb - USA
fencki - 1 pcb - Austria
ecclesand - 1 pcb - USA
danielhk - 2 pcb - Hongkong
Faizal Mansar Alam - 1 module - India
mvictor69 - 1 pcb - Romania