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Old 12th October 2012, 11:37 AM   #7551
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Default BC327/337 HFE values and match questions

Hi. I started measuring the BC327/BC337, -40 grade HFE value to match them and got these preliminary results. Just checking if I'm on the right track:

BC327 (PNP), 125/500 tested so far:
Larger variation in the HFE values than for the BC337 (NPN) type,
values vary so far from 298 to 630. Many of them are around 370.
I should be able to get enough around 560-570 to match with the NPN
There is a even a possibility that I found enough 610 to 620 ones...

BC337 (NPN), 25 tested so far:
Less variation than PNP type, from 463 to 624, a lot are around 550-575.

Did you found the same type of variation from PNP to NPN type?

Gain and Matched transistor questions:
-I think the higher HFE, the better for the Gain Cell, right? Is 575 enough?
-I guest I have to match both channels for the Gain cell HFE values, right?
-How close is an acceptable match for the Gain Cell? For example 560 to 570 is acceptable for the Gain Cell?
-What kind of match and HFE values are acceptable for the current mirror and buffer sections?
-Finally, do I need special HFE values for the few 327/337 in the shunt regulator sections?

Thanks...
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Old 12th October 2012, 11:51 AM   #7552
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Stefano, again this thread is long. I have discussed the issue of how big the elcaps have to be with Ricardo here because he also asked what they do. I told him that they affect the response in the very deep bass. Actually they form a high pass with the emitter impedance of the input stage. Ricardo did not come back so far about what he found while experimenting with the elcaps. Maybe he got some answers. In general i have no problem when people experiment with the elcap values. I think it is audible how big they are and even with 4700uF the audible range is not effected much so in a certain system adjusting the elecaps will be the ticket.
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Old 12th October 2012, 11:56 AM   #7553
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Algar, i would use the higher Hfe ones in the input stage. 10% matching from PNP to NPN is fine and with 5% you are on the safe side. The higher Hfe produces less base current at the input ( so less DC into the cartridge ) and the matching makes sure that you end up with the same gain in both channels. If you run into a gain match problem try to adjust the emitter resistors. For absolute lowest DC offset at the input you can also adjust Ube. I found that the Ube difference in the transistors we use is very small anyway. They are very symmetric to begin with. That is one of the reasons i prefer them over other BJTs.
I gave that advice to Stefano and he came up with some numbers.
Hfe value and matching in the current mirrors is less critical. Go for better then 10% and Hfe from 400 up will be just fine. For the PSU i think Hfe is not critical at all, so better then 10% and hfe higher then 400 is more then ok in the PSU.

Last edited by Joachim Gerhard; 12th October 2012 at 11:59 AM.
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Old 12th October 2012, 02:35 PM   #7554
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Quote:
Originally Posted by Joachim Gerhard View Post
Stefano, again this thread is long. I have discussed the issue of how big the elcaps have to be with Ricardo here because he also asked what they do. I told him that they affect the response in the very deep bass. Actually they form a high pass with the emitter impedance of the input stage. Ricardo did not come back so far about what he found while experimenting with the elcaps. Maybe he got some answers. In general i have no problem when people experiment with the elcap values. I think it is audible how big they are and even with 4700uF the audible range is not effected much so in a certain system adjusting the elecaps will be the ticket.
The ElCAP's value has a lower limit which below that the gain at the bottom will collapse.
The 4.7mF in conjunction with the RIAA's value I gave here, offer a precision of 0.1dB (absolute value or +/-0.05 relative) from 20Hz-20KHz so I don't understand what could be wrong with this value.
If you bump that up, you will have a bump between 20-40Hz, given same values for the RIAA, unless you re-correct them to get it back to that kind of precision, but this will result in the SAME frequency response, with MORE ELCAP on the signal Path.
IMHO the frequency response should be as flat as possible (I am not a big fan of purposly bumbing up the low bass freq response) and it is better to have the lowest ELCAP value your frequency response can afford.
I have experiemented with different values and I feel pretty confortable to relate this aspect of the sound.
Obviously my system is full range and doesn't need any push at the bass; on the flip side, if bass response was weak, you can notice it immediately.

I don't want to go against your recommendation, so I will keep it quite now and all I have left to say is just to try that out and let me know!
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Last edited by Stefanoo; 12th October 2012 at 02:53 PM.
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Old 12th October 2012, 04:30 PM   #7555
MiiB is offline MiiB  Denmark
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To keep phasehift out of the base area you should extend it as deep as possible not just to 20 Hz but preferably one or 2 octaves deeper than that. It does the same as extending the bandwidth upward. I think we all can agree on the need of circuits extending beyond our hearing limit of say 15-16 KHz...

I have no respect for your argument on keeping the cap value as low as possible...what should be the benefit of that..??
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Old 12th October 2012, 05:06 PM   #7556
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So will it have a positive efect, to increase further than the 2*6800uf?
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Old 12th October 2012, 06:18 PM   #7557
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Quote:
Originally Posted by MiiB View Post
To keep phasehift out of the base area you should extend it as deep as possible not just to 20 Hz but preferably one or 2 octaves deeper than that. It does the same as extending the bandwidth upward. I think we all can agree on the need of circuits extending beyond our hearing limit of say 15-16 KHz...

I have no respect for your argument on keeping the cap value as low as possible...what should be the benefit of that..??
well try for yourself!
If you don't respect my statement, that's ok, but at least try it first and listen to the difference and then you can disagree with it
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Old 12th October 2012, 08:17 PM   #7558
MiiB is offline MiiB  Denmark
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with the 2x6800 it starts to roll off below app 2 HZ, think that's sufficient...

Stfanoo in your system band-with limitation and subsonic filtering may sound better, but you state is like it's true for all systems. For that you have no valid knowledge. What is good for you may not suit the rest.

I state here why the larger capacitor was chosen with solid arguments.
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Old 12th October 2012, 08:50 PM   #7559
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The optimal is a strait line from dc and up to infinite, or at least as close as reality allows.
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Old 12th October 2012, 09:02 PM   #7560
Salas is offline Salas  Greece
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With due respect passing that low with a TT source is looking for trouble AFAIK. Bloat is waiting around the corner for numerous reasons. That and the nature of masking in the human cochlea can conspire against an open sound. I believe that Stefanoo is on the right track in this IMHO.
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