Designing a phono stage - Page 2

Brownlow · 2nd May 2001, 11:13 AM

A very interesting article. Nice one Alex, I will build this one and see what I can learn from a design point of view.

Alex M · 2nd May 2001, 12:37 PM

Brownlow,

Mail me privately with your address and I'll send you
a photocopy of the JLH article.

Alex

GRollins · 2nd May 2001, 07:14 PM

*28* transistors!?!
Whew!
Clearly, the JLH phono stage isn't designed in the simpler-is-better mode...
I just had a second and took a quick look at the Hart electronics site. You'd think for throwing that much silicon into the thing that they could do better than a 26 dB S/N ratio.

Grey

Alex M · 3rd May 2001, 08:16 AM

Looking at the Williams Hart website, I noticed that the
specification is "26dB below surface noise", rather than
"26dB S/N". I haven't seen this spec before. Does anyone
know what this means? Is there an ANSI standard surface noise?.

I assyme that the real S/N is much better than 26dB.

Alex

Alex M · 3rd May 2001, 09:21 AM

I don't know about the version supplied in the kit, but
the original JLH circuit has 14 transistors per channel,
which seems fairly normal. The stereo board has 28 in
total.

Alex

GRollins · 3rd May 2001, 02:21 PM

Alex,
I understood that it was 14 per channel. (Hoping, anyway. Egad, the idea of 28 per channel is horrifying.) I, for one, don't regard the idea of 14 transistors per channel as encouraging. I do make an exception for circuits that run multiple gain devices in parallel to lower noise and/or output impedance, but somehow I don't think that's the case, here.
It's been a long time since I've seen anyone use the "below surface noise" phrasing. Note the vagueness--surface noise of a new record? of a ragged out party record? of a special test album? It says nothing. It's safest to assume that this thing is noisy, and that they're being vague in order to avoid being pinned down. In the past (and I mean a long time ago) people used to use semantic tricks like this to sidestep measurements that could be meaningfully compared to their competitors' numbers. (Yet another reason not to join the "Specifications Are Everything" crowd--you can't trust many of the published numbers...) Assume that -26 dB is a *best* case scenario and go from there.
Caveat emptor.

Grey

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2nd May 2001, 11:13 AM	#11
Brownlow diyAudio Member Join Date: Apr 2001 Location: UK	A very interesting article. Nice one Alex, I will build this one and see what I can learn from a design point of view.

2nd May 2001, 12:37 PM	#12
Alex M diyAudio Member Join Date: Apr 2001 Location: Hampshire, UK	Brownlow, Mail me privately with your address and I'll send you a photocopy of the JLH article. Alex

2nd May 2001, 07:14 PM	#13
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	28 transistors!?! Whew! Clearly, the JLH phono stage isn't designed in the simpler-is-better mode... I just had a second and took a quick look at the Hart electronics site. You'd think for throwing that much silicon into the thing that they could do better than a 26 dB S/N ratio. Grey

3rd May 2001, 08:16 AM	#14
Alex M diyAudio Member Join Date: Apr 2001 Location: Hampshire, UK	Looking at the Williams Hart website, I noticed that the specification is "26dB below surface noise", rather than "26dB S/N". I haven't seen this spec before. Does anyone know what this means? Is there an ANSI standard surface noise?. I assyme that the real S/N is much better than 26dB. Alex

3rd May 2001, 09:21 AM	#15
Alex M diyAudio Member Join Date: Apr 2001 Location: Hampshire, UK	I don't know about the version supplied in the kit, but the original JLH circuit has 14 transistors per channel, which seems fairly normal. The stereo board has 28 in total. Alex

3rd May 2001, 02:21 PM	#16
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Alex, I understood that it was 14 per channel. (Hoping, anyway. Egad, the idea of 28 per channel is horrifying.) I, for one, don't regard the idea of 14 transistors per channel as encouraging. I do make an exception for circuits that run multiple gain devices in parallel to lower noise and/or output impedance, but somehow I don't think that's the case, here. It's been a long time since I've seen anyone use the "below surface noise" phrasing. Note the vagueness--surface noise of a new record? of a ragged out party record? of a special test album? It says nothing. It's safest to assume that this thing is noisy, and that they're being vague in order to avoid being pinned down. In the past (and I mean a long time ago) people used to use semantic tricks like this to sidestep measurements that could be meaningfully compared to their competitors' numbers. (Yet another reason not to join the "Specifications Are Everything" crowd--you can't trust many of the published numbers...) Assume that -26 dB is a best case scenario and go from there. Caveat emptor. Grey