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Old 28th November 2012, 04:05 PM   #241
iko is offline iko  Canada
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Andy, can you comment on the sound of this 4P1L amp compared to your 300B variants?
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Old 28th November 2012, 04:48 PM   #242
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The sound - yes, certainly. I should start by saying what I listen for. My most important consideration, which is way ahead of everything, is the tone and timbre of acoustic instruments. I'm a classically trained musician and I spent years and years in orchestras and small jazz combos. As a consequence, the sound of acoustic instruments is indelibly imprinted on my brain. I hear a drumkit, a double bass, a grand piano, a vocalist, all the orchestral wind instruments and miscellaneous percussion so clearly in my head that all my amps are an attempt to re-create this sound. I pay attention to the woodyness of clarinets, the overtones and key action of the concert grand, the emotion and nuance in the words of the vocalists, the clang of the harp, the snap of the snare drum and so on.

Well, my whole journey in amp building has been an attempt to capture all this. When I discovered DHTs I used nothing else in all the amplification stages from that moment on - I knew I'd found the tone I was seeking. My crusade led me to several different interstages for coupling - that was the cleanest way I found of joining up stages. My preamp is 4P1L in filament bias just like the first stage here, but with a Lundahl LL1660/18mA. I like the combination of the Lundahl and the Hammond in these positions. Output stage could be any good OPT gapped for 70mA or more.

The big difference with the 300b SETs was in realism. I've known for a year that filament bias is exceptionally clean and clear, and it works great with the 4P1L in triode like it does with the 26. When I used 300b in cathode bias the cathode bypass cap - even a good polypropylene - smeared the sound unacceptably to my ears. I hate all cathode bypass caps, and all caps in general in the signal path. Yes, the 300b is a better tube and the strings in particular were more silky and smooth. If I could run the 300b in filament bias, believe me I would and the same goes for 2a3 or 6B4G. One day! It's a bit of an ask, though.

So for now I'm happy with the 4P1L PSE setup. There is a little treble graininess which is probably due to having three stages of 4P1L and nothing else - the odd harmonics probably multiply. And I haven't matched the 4P1Ls on the output for gain, just for filament draw, so that could be further optimised. But I can't live without the realism of the sound. The grand piano is just incredible - I listen to a lot of piano. Orchestral instruments are very good in brass and wind, a bit less smooth in upper strings but acceptable. Vocals are very real. If I could eliminate the hint of grain in the upper treble I would be very satisfied indeed.

I've had a few people listen to this setup with Alpair 10 fullrange speakers and we all agree that the sound is more real and immediate than with the 300b output stage. In the last shootout we had, the real contender was a single stage SE solid state amp with the Sony 2SK82. But that's another story.
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Old 28th November 2012, 06:58 PM   #243
iko is offline iko  Canada
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Thanks Andy! There's quite a bit of talk about smearing caused by paralleling unmatched tubes. That might be your fly in the soup.
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Old 28th November 2012, 09:36 PM   #244
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I'm not quite sure what "smearing" means to be frank. I used the term for cathode bypasses because the sound goes slightly "foggy" to my ears - loss of detail and timbre and directness. Like if you smeared oil over a piece of glass. Maybe with PSE it refers to something different - one tube interfering with another. That might simply cause more distortion which might be a different subjective sound, like more edgy?
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Old 28th November 2012, 10:25 PM   #245
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I thinks iko means that there are a lot report that one tube sound better then two ...if I remember well increase the 3hd.....
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Old 29th November 2012, 01:39 PM   #246
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by nicoch58 View Post
I thinks iko means that there are a lot report that one tube sound better then two ...if I remember well increase the 3hd.....
There is a slight increase, but minimal when matched mu pairs are used: http://www.bartola.co.uk/valves/2012...p1l-pse-tests/
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Old 29th November 2012, 01:51 PM   #247
Charm is offline Charm  Russian Federation
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If used on each lamp its filament voltage , you can not pick up in pairs.
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Old 29th November 2012, 02:33 PM   #248
iko is offline iko  Canada
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Quote:
Originally Posted by nicoch58 View Post
I thinks iko means that there are a lot report that one tube sound better then two ...if I remember well increase the 3hd.....
Right. The actual word and mechanism why this is so it's where the debate is. I think the consensus is that paralleling two tubes only sometimes sound better than one. I have to say I haven't played with this at all. Got a whole bunch of 4P1L for this but... so little time. I'm also curious of a 4P1L PP.
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Old 29th November 2012, 05:21 PM   #249
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Originally Posted by ikoflexer View Post
Right. The actual word and mechanism why this is so it's where the debate is. I think the consensus is that paralleling two tubes only sometimes sound better than one. I have to say I haven't played with this at all. Got a whole bunch of 4P1L for this but... so little time. I'm also curious of a 4P1L PP.
Right now I am developing PP with 4P1L. C3G (ltp) in front. B+ around 240V. OT 5K:8. I also plan to build PPP version.
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Old 29th November 2012, 09:20 PM   #250
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PP 4P1L is an obvious build, and PPP even more so. Are you thinking of using a CCS under the output stage, or a pentode sink? Allen Wright was using his kind of thing. It eliminates a cathode bypass cap which is always a good thing.

How do you propose to match up the 4P1Ls? I think Ale had a circuit to do this.

You could use one filament supply for each tube. I've thought of doing this with my output stage in filament bias. Easier to match up the operating conditions.
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