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It just occured to me that before jumping into a full blown design of a 26/26/45 amp I ought to get some opinions on how it is likely to sound driven by the 26 preamp I am planning on building soon. I know Sakuma likes to use the same tubes as drivers and output tubes, but is there such a thing as too much of a good thing? I am really impressed with the sound of the 26 preamp you all helped me get the bugs out of; I plan on building it for sure. I especially like the sound of it driving my 300B 91A clone.
I would breadboard the entire amp after I build the 26 preamp, so I guess I could listen to it before I built it. Also, I suppose the exercise of going through the numbers for designing the 26/26/45 would be good practice, so maybe I have just answered my own question.
I would however, appreciate hearing any opinions you all might have on how this combo might sound.
Edits: 08/31/15 08/31/15 08/31/15Follow Ups:
I got to thinking about what I asked Willie about a single tube 26 preamp being equivalent to adding another 26 to the 26/26/45 amp, and it dawned on me if that is true then all i have to do is daisy chain another 26 to test what the 26/26/45 will sound like with a 26 preamp. That would save a whole bunch of time to satisfy my curiosity. I already know the 26/26/45 (let's save some typing and call it a "26 deuce" amp) sounds good with my 76/6sn7 preamp, but I am thinking of replacing that pre with the single tube 26 preamp.
Edits: 09/01/15
If they are operated at similar voltages and currents, it would be a valuable test.
I will speculate that the added 26, operating at the lowest signal level, will be the cleanest and purest sound. Or, if both first stages are in fact inaudibly different after the later stage distortion, there might be no discernible difference.
Let the games begin!
I went ahead and added a third 26 with the same set up as the other two. The currents and voltages should be similar. I also adjusted the cathode resistor of the 45 and the B+ to get as close to the first set of operating points that Palustris suggested for the 45 (220vdc and 36 mA). I measured 220 volts plate to cathode, and 35 mA with a 1130 ohm resistor that I measured 39.5 vdc across, so my operatring points are pretty close.
I am quite pleased with the sound, it certainly is every bit as good as the 26/26/45 playing with the 76 preamp. I actually think the detail is a little better as I am using the same mono source through one channel as I used before and hearing a few small things I didn't notice last time.
So I guess it is onward and upward. The next step will be to build the 26 preamp first, and then to breadboard the deuce 26 amp in stereo and work on getting it fine tuned. If I still like it then I will probably build it or them. Might be best to go with monoblock amps considering all the iron involved, or a psu unit and a front end unit at least, like I did with the 91A clone. Looks like a couple of good projects for this winter.
One thing I am curious about is Tre's comment about the polarity being reversed because of the third tube. How is it any different this way than if the 26 preamp was stand alone and playing into the deuce 26 amp? Or is it the fact it is another 26 that causes the problem? Should the problem be there with the 76 preamp too? I have not noticed any disceranble diference with either. Both sound good, but the deuce 26 with the 26 pre sounds better. I think I may be hooked on all dht triodes for the forseable future.
It's easy.
Each stage inverts phase.
If you have an even number of total stages then the output signal will be "in absolute polarity", if you have an odd number of total stages then the output will be inverted. So flip your speaker wires.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Is that just the number of stages in the amp, or does it include the stages in the preamp as well? If it does we are back to four. The 26amp I was testing had 3 26's and a 45, but the 3rd 26 is actually the tube from the single 26 preamp I was working on earlier. Each of the 26 stages is identical for the amp and preamp.
Edits: 09/02/15
"Is that just the number of stages in the amp, or does it include the stages in the preamp as well?"
Total stages. A one stage preamp inverts and three stage amp inverts. The two in combination do not invert.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Ok, the one stage preamp inverts odd, then the first stage of the amp makes that even, 2nd stage odd and 3rd stage even again, yes?
.
Have Fun and Enjoy the Music
"Still Working the Problem"
nt
"there might be no discernible difference. "
Except the absolute polarity will be flipped with three stages vs. two.
some say that's not discernible so there ya go!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Easy to correct for - if you know about it :^) Thanks for the post!
I will give it a try in the next couple of days.
Thanks!
Theory: If the tubes are the same, and are operated at the same voltages and currents, then the distortion will reliably be dominated by the last one. I think that's what is behind Sakuma-san's work.
Practice: Please post results if you do this!
"Please post results if you do this!"No one knows what he's hearing. If he prefers 5% odd-order products, that's what he'll report as improvement. None of these results have any meaning to the rest of us.
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Buy Chinese. Bury freedom.
Edits: 09/01/15
First, I was attempting to use humor to say that the real world often confounds our simple theories, so it remains reasonable to experiment.
Second, the whole reason for having forums like this one is to crowd-source knowledge that is not available, or unproven, theoretically. By definition conventional wisdom does not lead to improvements in conventional wisdom.
Admittedly, a majority of posts just reveal gaps in knowledge of the conventional wisdom, and another valuable function of forums like this one is to share that knowledge. But for me at least, I also read these forums for the occasional bit of emerging consensus beyond the conventional or theoretically known.
With all due respect for your considerable experience and insight, I really do believe the word "wisdom" has no place in a discussion of the process I was describing. Sorry, I don't think we will agree on this one.
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Buy Chinese. Bury freedom.
Well, I think that was my point. Perhaps the lack of tone of voice and body language has prevented us from communicating successfully - it happens regrettably often. In any case, peace. I do not disagree with you, though I may say it too differently.
nt
Please ... PLEASE
Just give it a rest.
Next you will only want people who
had an independent source measuring
the frequency and distortion before
anyone can post their results.
Let it go man.
DanL
No, I won't let it go. It's meaningless BS that has no place in a forum devoted to furthering this art. It's just like those line cords that improve video definition. If you're in that camp, fine, but don't expect others not to object.
--------------------------
Buy Chinese. Bury freedom.
Edits: 09/01/15
As you said this is art.
Designing is more of an art
than an equation (or series of).
They are useful but not the end.
The inauquious phrase - Please post results
got you going doesn't that tell you something.
Also why discourage new posts, unless
the demise of this asylum is your intent.
If so please go play in another sandbox.
DanL
"Designing is more of an art than an equation "
Only people who can't design competently say things like this.
"please go play in another sandbox."
Nice, a euphemism for STFU. Same to you.
--------------------------
Buy Chinese. Bury freedom.
First you call it an art.
Now you are saying it isn't.
> > the demise of this asylum is your intent.
> > If so please go play in another sandbox.
I don't know if you are reading what I wrote.
Or maybe you need to go back on your meds
like the other poster proposed.
DanL
A different meaning of the word "art".
"The term "state of the art" refers to the highest level of general development, as of a device, technique, or scientific field achieved at a particular time."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
At least that gives me hope Paul, Thanks! I will post my results here, but it may be a while before I get everything together I need and get it all working on a breadboard.
Edits: 09/01/15 09/01/15 09/01/15
I started off with 26s. Lovely tube, that was the inspiration for me to switch to only ever using DHTs many years ago. I used 3 stages because the finals - 2a3 or 300b - didn't have enough gain for 2 stages. Then I started to fool around with 4P1Ls. At some point I realised that if you used a couple of them in PSE you could get away with 2 stages - 4P1L into 4P1L. This tube has a mu of 10, and a low Ra which makes many things possible. Plus it sounds great.
I went back to using 26 for inputs as an experiment, but stayed with the 4P1L because it had better treble and was just a bit cleaner all round. So that's what I'd recommend to you as a driver stage. It will give you a cleaner sound and nicer treble. Plus they're still fairly cheap - I bought a couple of hundred years ago when they were peanuts.
I am still hoarding my 26 . Last used a pair in an SE OTL amp as the front end .
ps . I have recently modified my old 4P1L breadboard to use Morgan Jones' 'Statistical' regulator on both the main HT and DC coupled driver stage . For the cost of £2 worth of zener diodes and £5 of sand and resistors for the CCS it is an interesting experiment . The other 'cost' is 20V dropped by the CCS and 20mA burned off by the zeners , using BZX55 5V6 zeners , there is enough current available for a pair of 4P1L . I bypassed the main HT zener stack with a 50uF film cap . Very tight bass for SE , also very quiet .
Al
Sounds interesting, but I already have a large stock of good 26's that I got at a hamfest a while back. Maybe someday.
Edits: 09/01/15
Sounds interesting, but I already have a large stock of good 26's that I got at a hamfest a while back. Maybe someday. > >I was just reflecting on how different this is from my early days with DHTs. In my wild enthusiasm I bought representative amounts of any DHT that sounded interesting - 10Y, 26, 112, 01A, 46, 71A, 4P1L (came later) and on and on and on. Still have drawers full of them. I then had shootouts between them, built preamps with most of them, and whittled them down to my favourites just in terms of sound. I'm a musician so a bit perfectionist about timbral detail. My short list turned out to be 26, 46, 10Y and 4P1L. The 4P1L was as good as any of them and had the added advantages of cheapness, high mu and low anode impedance. Crucially it works best in filament bias, which is my preferred topology right through. That was the clincher.
I'm still tempted by 46 and 10Y and I have a few of them, but I need a mu of 10 for 2 stages. And just in practical terms, I leave my sound system on just about 24/7 and the 46s and 10Ys are too valuable these days to now care about their value. I still have a place in my heart for the 26, but it hasn't made it into my amps for a good 2 years now. Still, it was the tube that started me off on all this. When I first heard it through my system my jaw dropped and I said out loud "THIS is the sound I've been searching for all my life!". After that and to this day it was just DHTs.
Edits: 09/01/15
I got a feeling I will be right there with you with all dht from now on. I still have not been able to pick my jaw up off the floor from hearing the 26 preamp when I first had it working right. Can't wait to hear the duece 26 amp when it is working as it should.
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