No. They were 'Low Noise' in the days of MM RIAA preamps running Ic less than 100uA and with effective Rs well over 10k in important frequency bands from cartridges with high L. For that, high hfe was probably the biggest LN factor.
Tomchr is right that their rbb' > 100R cannont be shorted by a LoZ source. Shame on you Guru Tomchr for not having a copy of TAOE. It's a book that even yus gurus will consult well into their old age 🙂
rbb' is a bit difficult to estimate at these noise levels but proaudiodesign confirmed H&H's measurements for some of the Zetex devices at < 2R. These are now the preferred devices for MC preamps .. including mine which was the quietest such device in the known universe for decades .. but is now only the 2nd quietest 😢
But best thing about the Zetex bits ... you don't have to buy them from Ye Olde Unobtainium Shoppe. But their lowish hfe isn't optimal for higher Rs eg LN MM preamps.
Sorry folk, in series indeed. I was thinking a theorethical model. Not a real substantial contribution...🙄
The higher the hFE, the lower the base current and the lower the shot noise of the base current, but you only notice that at relatively high source impedances, such as those of MM cartridges.
The thinner the base, the higher hFE, but also the higher the base resistance for a given number of base contacts. The thermal noise of the base resistance is most noticable at low source impedances, such as those of MC cartridges.
The thinner the base, the higher hFE, but also the higher the base resistance for a given number of base contacts. The thermal noise of the base resistance is most noticable at low source impedances, such as those of MC cartridges.
But if you see philips datasheet, the Cob of BC327/37 is two or three times higher than BC550/60.
A late colleague once told me that the BC337 and BC327 are made in a similar process as the BC547 and BC557, but with three times the die area, so that they are essentially three BC547/BC557's in parallel. He used to work for Philips and he usually knew exactly what he was talking about, so maybe it is true.
You do realize that many reading your post will now ask you telepathically "OK, BC327 is less noisy and ZTX550 has even less noise but does not sound as good as BC560 so..... how is the sound with BC327?"?
BTW Are you sure you have used protection? Unprotected sensitive inputs have a high chance to attract unwanted stuff that may contribute to the noise. Think LED lighting, SMPS, wireless/bluetooth etc. Also sensitive stuff should be in a metal box.
BTW Are you sure you have used protection? Unprotected sensitive inputs have a high chance to attract unwanted stuff that may contribute to the noise. Think LED lighting, SMPS, wireless/bluetooth etc. Also sensitive stuff should be in a metal box.
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That's cos ZTX550 aren't hand carved from solid BS & Unobtainium by Southampton virgins like your vintage Mullard/Philips BC560 🙂
i remember 550/560 have much linear characteristics than 327/337 at sub 10mA range.
is it really preferred to use 327/337 in input stages ?
is it really preferred to use 327/337 in input stages ?
Unfortunately I have only one pair of BC327, so i didn't make a listening test, I only listen the noise..
Overall I am not impressed with the sound of the hiraga, i still prefer the lundahl step up, which is dead quiet, but i will give a try and find other low noise transistors, also i will replace the coupling capacitors, i am using now solen 3.3uf 630v. The power supply is 8x 1.5V alkaline batteries