Hi there -
I have a nice little Plinius IIc that I am about to recap. There is a bank of 20-odd caps to replace in the power smoothing section alone.
This little pre is fitted with the 2N5210 & 2N5087 - its a little old now - from the mid-80's. There is a bit of hiss/noise in the phono sections but admittedly I havent tested it with a signal yet to really check out the S/N ratio there.
Are there any modern small signal trannies around that could be subbed in to replace these trannies that anyone is aware of? Some preliminary searching reveals that KSA992 & KSC1815 could be good subs?
Also, in the output section - the originals were replaced with B547B & B556B. I would also prefer to replace these with a more "hifi" sub if I can (or need to), but it may be difficult to find replacements with the same voltage specs (from what I have seen). I dont have the SM or schematic, so its impossible to tell what the originals were that were replaced here.
I have a nice little Plinius IIc that I am about to recap. There is a bank of 20-odd caps to replace in the power smoothing section alone.
This little pre is fitted with the 2N5210 & 2N5087 - its a little old now - from the mid-80's. There is a bit of hiss/noise in the phono sections but admittedly I havent tested it with a signal yet to really check out the S/N ratio there.
Are there any modern small signal trannies around that could be subbed in to replace these trannies that anyone is aware of? Some preliminary searching reveals that KSA992 & KSC1815 could be good subs?
Also, in the output section - the originals were replaced with B547B & B556B. I would also prefer to replace these with a more "hifi" sub if I can (or need to), but it may be difficult to find replacements with the same voltage specs (from what I have seen). I dont have the SM or schematic, so its impossible to tell what the originals were that were replaced here.
2N5210 for example, is likely selected for its low noise figure of 2-3 dB max in the datasheet's standard test method. That's not easily beaten regardless of new or old transistor types and though there are likely others in that class, I wouldn't change them nor the 2N5087 complements unless I was able to find something significantly better on noise figure.
Not all circuits affect noise level but if the semis are working correctly, as designed, why change them? They may also be obsolete but that doesn't mean they need to be updated either if there is nothing to gain.
In the output section, I would have expected complementary type BC546B rather than BC547B. Typo? Actually, there's no such thing as a general purpose, small signal transistor for high end audio applications. Unless the original parts were of different types according to
specific applications, I wouldn't bother looking for something that was likely going to be less suitable than what is already fitted.
Really, there's nothing inferior about garden variety, small signal parts.l If they meet the minimum design spec requirements and have adequate voltage and dissipation ratings, they'll be fine. The power and driver transistors are where the differences typically show up in sound quality.
Not all circuits affect noise level but if the semis are working correctly, as designed, why change them? They may also be obsolete but that doesn't mean they need to be updated either if there is nothing to gain.
In the output section, I would have expected complementary type BC546B rather than BC547B. Typo? Actually, there's no such thing as a general purpose, small signal transistor for high end audio applications. Unless the original parts were of different types according to
specific applications, I wouldn't bother looking for something that was likely going to be less suitable than what is already fitted.
Really, there's nothing inferior about garden variety, small signal parts.l If they meet the minimum design spec requirements and have adequate voltage and dissipation ratings, they'll be fine. The power and driver transistors are where the differences typically show up in sound quality.
I wouldn't if I were you 😉 . Sounds like you might be inviting trouble there. It looks like the designers made the right choice with semiconductors in this case, and a more modern transistor will not improve things as the devices used are already low noise types and probably will not be the main source of noise in the preamplifier stage which will probably be thermal noise from the cartridge loading and cartridge impedance.
If it's not broken, don't fix it. Replace your caps and get out of there my man 😀 ...
The 2N5210 and 2N5089 are among the LOWEST noise transistors you can find anywhere for phono or tape head usage. This is per the evaluations done by Horowitz-Hill. The really big plus for these, in addition to being very low-noise, is that THEY'RE STILL AVAILABLE! And also in convenient TO-92 packaging. This is in dire contrast to MANY of our favorite low-noise transistors from the past, which are usually unobtanium or only in surface-mount. If you're having noise problems, I highly doubt that it is due to these components.
2N5210 & 2N5087 are LOW noise audio BJT,s ---2db and that is good and before anybody suggests changing them they better have a look at the specs.
They have a Hfe bias of ONE ma and a max Ic of 50ma your schematic is set up for them therefore the bias resistors would need to be changed for a start if you just say-- oh I will just "modernize " the BJT,s just for the sake of it then you wont be "making an improvement " .
Can you get ultra low noise ?--- yes but can you get the SAME other specs without modifying your circuit ??
I take it you are talking about BC 547B & BC556B ?
They are/were well used in UK audio circuits in bias circuits and driver positions but not in the critical low noise input end of an amplifier but again they have low Hfe bias current, slapping low noise higher gain more modern ones in wouldn't be needed at the output side and remember STABILITY counts.
They have a Hfe bias of ONE ma and a max Ic of 50ma your schematic is set up for them therefore the bias resistors would need to be changed for a start if you just say-- oh I will just "modernize " the BJT,s just for the sake of it then you wont be "making an improvement " .
Can you get ultra low noise ?--- yes but can you get the SAME other specs without modifying your circuit ??
I take it you are talking about BC 547B & BC556B ?
They are/were well used in UK audio circuits in bias circuits and driver positions but not in the critical low noise input end of an amplifier but again they have low Hfe bias current, slapping low noise higher gain more modern ones in wouldn't be needed at the output side and remember STABILITY counts.
Thanks for the responses all - great to get so many answers.
To clarify a couple of things - the BC transistors were installed as replacements sometime after production, please see the pics. Schematics for these are hard to come by now, so I cant tell what type the originals were. To also clarify - these are definitely BC547B & BC556B that are installed.
Should I install BC546B to replace the 547Bs'?
Thanks also for clarifying that the original 2N5210 & 2N5087's still hold up today - so I will leave them alone, and just do an (easy) recap.
This pre normally sources its power from the partner power amp - it needs plus 33-0-minus 33 VDC. I was able to make the pictured power supply to provide the required power and it seems to be working just fine.
To clarify a couple of things - the BC transistors were installed as replacements sometime after production, please see the pics. Schematics for these are hard to come by now, so I cant tell what type the originals were. To also clarify - these are definitely BC547B & BC556B that are installed.
Should I install BC546B to replace the 547Bs'?
Thanks also for clarifying that the original 2N5210 & 2N5087's still hold up today - so I will leave them alone, and just do an (easy) recap.
This pre normally sources its power from the partner power amp - it needs plus 33-0-minus 33 VDC. I was able to make the pictured power supply to provide the required power and it seems to be working just fine.
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Why on earth does it need all of those capacitors? 😕
Unless the full supply votage is across those transistors (547/556) I would not replace them. Even then I would only replace the 547 for a 546 if it runs the risk of exceeding it's rated Vce.
That PCB looks awfully spread out. Can't be doing the crosstalk performance/hum pickup any favours there...
Unless the full supply votage is across those transistors (547/556) I would not replace them. Even then I would only replace the 547 for a 546 if it runs the risk of exceeding it's rated Vce.
That PCB looks awfully spread out. Can't be doing the crosstalk performance/hum pickup any favours there...
I too noticed the multiple number of capacitors can somebody explain this design philosophy please ?
I can understand separating the power supply from the input circuits but that number of capacitors , I take it at the input of the remote power supply when you are only talking of a split-rail power input needs an explanation considering the increase over time of the ESR of each and future faults occurring ?
I also agree with Classic Audio Ltd. its too spread out inviting external RFI/noise etc to influence the long runs of copper.
I can understand separating the power supply from the input circuits but that number of capacitors , I take it at the input of the remote power supply when you are only talking of a split-rail power input needs an explanation considering the increase over time of the ESR of each and future faults occurring ?
I also agree with Classic Audio Ltd. its too spread out inviting external RFI/noise etc to influence the long runs of copper.
Taking a closer look it seems that there's a lot of lost opportunity for plenty of copper in the ground plane. I really can't see how a preamplifier containing a handful of TO-92 devices can warrant that much capacitance power wise.
There are better ways to reject supply rail noise, such as proper regulation and RC smoothing especially for simple class A stages. Unless of course there are marketing reasons...
'Instantly the soundstage became more dynamic, punch and drive were improved and a sense of air was immediately apparent between the instruments etc...'
The capacitors,
I would guess some designer picked the size and form of the case, then had to make the electronics fit. (One big cap, or lots of little ones?)
I would guess some designer picked the size and form of the case, then had to make the electronics fit. (One big cap, or lots of little ones?)
Maybe so? But why so much capacitance? It already runs off regulated supplies and it looks like there's a tenth of a Farad in there...
Getting a very strong whiff of audiophoolery off this 😀 ...
Getting a very strong whiff of audiophoolery off this 😀 ...
Glad to be of service... Perhaps it would be better to 'de-cap' it rather than 're-cap' it, especially since you've built a more than competent looking linear regulated supply there 🙂 .
Perhaps this was built for areas that suffer from brief power cuts eh?
Save the caps for another project like a nice fat power amplifier 😉 .