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PostPosted: 30 Jan 2017, 11:47 
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Joined: 29 Jan 2017, 17:55
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Hi all! It's rather self-explanatory why I joined this forum, but yes, I want to TRY to build stereo (not guitar) tube amp :)
I'm noob in that matter, so sorry in advance for noob questions. Also sorry if there are some answers already, but I couldn't find them - You have to know at least SOMETHING to correctly phrase a question :)
I think some basic facts and requirements on my side will be helpful so here it goes.
I can appreciate decent sounding equipment but I'm not a hardcore audiophile so I was aiming at budget configuration. When I was buying my current amp+speakers combo ~15yrs ago I spent nearly a month going to various hi-fi studios, listening to various sets and finally I chose what I have today. I learned in the process that there can be expensive equipment that sounds average at most, and cheap that sounds awesome. Obviously the opposite is common too.
Now, I don't expect my DIY result to be immediately excellent, but as I'm interested in electronics I want to use this project to learn in as productive way as possible.
I'll enjoy the process itself. If end product will sound and LOOK nice it will be double pleasure :)

My current setup:
NAD C340 Amplifier (from data sheet):
Continuous average power output into 8 Ohm 50W (17dBW)
(Min power per channel, 20Hz - 20kHz both channels driven with no more than rated distortion)
Rated distortion (THD 20Hz - 20kHz) 0.03%
Clipping power (max continuous power per channel) 55W
IHF dynamic headroom at 8 Ohm 3.5dB
IHF dynamic power (max short term power per channel):
8 Ohm 100W (20dBW)
4 Ohm 130W (21.1dBW)
2 Ohm 170W (22.3dBW)

Audiowave 171SE Speakers:
Power: 90 W
Impedance 8 Ohm, (6.2 Ohm min.)
Efficiency 87 dB/1W/1m.
SEAS membranes

My room is roughly 5x7m (16x23foot)
I'm not listening very loud and I'm VERY happy with this combo but It's mostly suitable for a bit harsher music like classic rock/acid jazz.
Now I want something for smoother, softer, retro music and I'm sure tubes will be great.

I decided to stay with current speakers. Today I spoke in person with guy who made them 15 yrs ago (he still makes speakers) and he agreed that they should work with tubes nicely.
He recommended tube power output around 30W-50W range with 50W as probably unnecessary power reserve but still OK.

Now, given all data I said above, what are Your thoughts? What are Your Recommendations for me? Would You agree with power range? Is 30W plenty enough for my needs, or is it good to have this reserve that 50W delivers?

I warn You that Your answers may (and will) induce further questions :)

Thank You in advance for all replies :)


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PostPosted: 30 Jan 2017, 18:05 
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Hi, You speakers are a bit lower in sensitivity than many, but not excessively so. So 30 watts is likely quite fine. More would provide some reserve and all things being equal (never really are though) is desirable. My main speakers are 91 dbw and they drive well with just 5 watts in a room 12 X19. But at that power level there is essentially no reserve. I find 25 watts just fine, but I do use a pair my KT120 Oddblocks normally that are 45 watts each. Certainly more than needed but I like the sound of the KT120s better.

Good listening
Bruce

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PostPosted: 30 Jan 2017, 22:02 
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Yes, reserve power is good as clipping your amp is *really* hard on tweeters.

Depends on what you listen to - Classical needs the most reserve power as the dynamic range is HUGE. Jazz lovers like myself, are good with a 50% reserve. Rock tends to be so normalized and compressed, it's almost a 1:1 requirement unless you play it LOUD!

Cheers!

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PostPosted: 31 Jan 2017, 10:50 
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50 watts (RMS) is easy to achieve using standard parts and techniques. Are you interested in designing 'from scratch' or would you be willing to use a proven design and work from a kit or partial kit? What are your metal-working skills and tooling availability? Lastly, none of this is cheap, but a full from-scratch unit will be less costly than a kit where a good deal of the work is done for you. Nor is 50 watts substantially more costly than 30, as the increase is incremental in size of some parts (transformers and tubes), not complexity.

If you have never scratch-built a tube device in the past, I do strongly suggest that you start with a kit - of which there are several very good options out there. There is a LOT of learning involved, even with a kit, but the opportunities for error are much less. Also - 30-50 watts is a sweet spot in kit options.

If your heart is set on scratch-building, I suggest two things:

a) find a mentor (AKA "Elmer") that has some experience and can help you around some of the rough spots - which there will be.

b) Spend some time auditioning already-built tube systems and try to learn as much about the beasts as you can. They are substantially different from solid-state systems - and I would also venture to state that NAD equipment will exaggerate that difference more than many other similarly powered solid-state brands - at least in my direct experience. This is not a negative or positive statement - just a reference to the nature of NAD stuff.

Then, you will discover dozens of circuit options, configurations and layouts, with parts from many sorts of suppliers. Then, of course, tube options. Try to be linear in your thinking - at least to start - and try not to fly down blind alleys or invest in options that are singular in application - one 'for instance' would be a single-ended output transformer (not that you would) - which would be useless in any other application. The more 'generic' you are going, the more flexibility and adaptability you will have during the process, and finally at the other end.

Just for giggles, I suggest you start with the EL34/KT77/6CA7 family in the 30w+/- rms range, then look at the difference between that and the KT88/6550 family at 60w+/-rms.

Good luck with it!


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PostPosted: 31 Jan 2017, 17:31 
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Joined: 29 Jan 2017, 17:55
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Thank You all for kind replies!
Peter especially since You managed to pre-empt some of my thoughts ;)

So, some quick decisions:
I decided to go for 50W, and my heart and nature is hands down towards scratch building, even if it will mean more time and more mistakes.
More mistakes may mean more cost but it doesn't really matter, I expect this project to be relatively stretched in time anyways.

From what I see in most plans, these projects are "retro"/"old-school" made.
So we are talking about basic elements connected by wires and attached to any suitable nonconducting surface.
No micro-electronics, micro-parts and micro-soldering involved, as well as no printed circuit plates necessary?

My workshop tool collection is pretty decent, I'm self-sufficient with typical household electrical stuff but seldom went to electronics level. I'm aware I will have to acquire good solder station and multimeter.
Will I need some lab/workshop power supply? If yes, how basic can it be, and what parameters should it have?
Also, is oscilloscope a must or not?

(As to manual skills, may I humbly present my previous project - large format camera. Almost entirely hand made by me, including bellows. Only lens (obviously), knobs and some custom laser-cut aluminium plates were ordered. Don't want to boast, just wanted to let You know that You can trust me in workshop ;)

More questions will emerge soon :)


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PostPosted: 04 Feb 2017, 02:57 
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I'm doomed, nobody wants to help me...
:(


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PostPosted: 04 Feb 2017, 11:17 
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Location: US Pacific Northwest
Mikuda wrote:
I'm doomed, nobody wants to help me...
Not doomed, but you just really haven't given people much to go on. You indicated above...
Mikuda wrote:
So we are talking about basic elements connected by wires and attached to any suitable nonconducting surface.
No micro-electronics, micro-parts and micro-soldering involved, as well as no printed circuit plates necessary?
So this kind of takes Bruce's OddWatts off the table. You want an old school all vacuum tube design. You also seem to be determined to get 50W. As a warning, this is going to increase the cost of you amplifier substantially, perhaps even doubling it. 50W 20Hz to 20kHz stereo quality tube output transformers are expensive beasts. And the power supply necessary two drive two channels at 50W will also be very expensive.

Here is something else to consider, the difference between 30W (a much more common size and much less expensive) and 50W is only 2.2dB. With 87dB speakers, the SPL at 30watts is about 105dB, at 50W it is about 107dB (these are 3dB higher due to having two channels). This is kind of like running a chain saw in your living room without hearing protection. At these sound pressure levels you will be unable to tell the 2.2dB difference. Also note that these sound pressure level are highly ototoxic. Exposure to sound at this level without hearing protection will cause permanent damage to your hearing in less that four minutes. It will also cause something called "Temporary Threshold Shift" which is where your ear automatically desensitizes itself to try and prevent excessive damage. TTS kills the high frequencies first, then the mid band leaving you with your cochlea taking a low frequency beating. You are of course free to listen at whatever levels you want, but just please be aware of what this is doing to your hearing. I suggest you read this post: "How Amp Technology Affects Volume and Power". This will give you some more information on amplifier power and sound pressure levels.

Moving back to your amplifier. 50W is possible without too much problem. A pair of 6L6GCs in Class-AB Push-pull will give 55W into the output transformers. With conversion efficiency of 90%, you'd get 50 watts at the speakers. You need a power supply capable of providing about 1/2A (500mA) at 450v; expensive but doable. You'll have to search around for the output transformer. Also note this is in pentode mode with fixed bias. It's not like you're going to be getting a SET like sound out of this amp. I'm not sure it will sound that much different from your current amp unless you do some serious "coloring" in the preamplifier.

So I'm going to make a suggestion. Read the post I referenced above and seriously consider what you want and why. Then sit down with a piece of paper and write down your requirements. Things like output power, sensitivity, and distortion. Also think about how you want it to sound. You said above...
Mikuda wrote:
I'm VERY happy with this combo but It's mostly suitable for a bit harsher music like classic rock/acid jazz
See if you can qualify exactly what it is about this amp that makes you say that. Then try and articulate how you would want the tube amp to sound different, and why.

This is a marathon, not a sprint. Best to stretch before hitting the track. :)

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 04 Feb 2017, 16:44 
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OK - some severe miscalculations here.

a) 1 watt = 87dB
b) 10 watts = 97dB
c) 100 watts = 107dB.

50 watts barely gets you to 100dB as the increase is non-linear.

Now, some issues that you will very much _need_ to understand when dealing with amplifier power, tubes vs. solid-state and the concept of DIY in general.

a) Headroom: As you can see, it takes 10 x the power per each 10dB of loudness increase. That is one measure. Which leads to:
b) Peak-to-average: Depending on what you are listening to, the P/A between the average level and peak (momentary) level may be as little as 10dB (heavy metal, highly compressed signal, and similar) and as much as 30dB (A well recorded version of the Saint-Saens Organ Symphony), perhaps a bit more. If you are listening to inefficient speakers in a large room, 87dB as an average will not be uncommon. Meaning that a 60-watt amp will clip if driven with signal with a wide dynamic range. Typically, a tube amp is good for about 2.1 x the rating for one second without clipping. Some much less, some very few only a little bit better. You will have some control of this during the build process. So, a well designed 60 watt amp might give you 122 watts for one second for a loud peak. This will damage neither your ears nor your speakers.
c) Tube vs. Solid State: Some (not all) solid state amps clip very harshly, delivering, essentially, almost-DC into the speakers. Some have protection circuits to prevent this (the NAD does not). Hence the fact that most speaker damage (from clipping) happens with under-powered amps than monster amps - irrespective of speaker rating. Tube amps, on the other hand, clip very softly as output transformers cannot pass DC (amongst other reasons). So, you will notice clipping far more from a solid-state amp than from tubes - and why people state (wrongly) that tube amps are better than solid state for clipping. Better for your speakers, certainly. But neither type of amp likes clipping, and the consequences of a tube amp output transformer smoking itself are a bit more costly than a couple of output transistors - or nothing at all if protection circuits are in place and effective. This is an obscure, but real point for those who prefer head-banging, ear-bleed volumes from tube equipment.

The incremental cost of a 50-watt output transformer is marginal against the absolute cost of any good output transformer at/over 30 watts. Less than US$20 (18%) in the Hammond line, for example, and proportionately in other lines. Similarly, the power transformer. Couple this with the fact that neither type minds being under-driven, both types do mind being over-driven.

Now, there are other considerations - DO THE RESEARCH - DO NOT take my word for it. Ultralinear, Triode, Single-ended, Simple Push-Pull, Williamson, these are all terms you will read/hear in your research. Understand enough to make the most flexible choice to meet your needs. Writing for myself, I prefer Ultralinear PP. That would be me, not necessarily you. And, as it happens, there is a great deal of hardware and well-respected designs around that choice.

It need not be costly to be good (relative to what you *could* pay). There are competent transformers from US companies of long standing and excellent reputation such that you ought to be able to populate your *box* for under US$400 - at your 50-60 watt target. You could easily triple that on a single transformer if that is your choice. Or you could go exotic and use toroidal transformers (Plitron and similar) at a significantly higher cost. It is all in accordance with.... So do the research.

As your camera demonstrates your machining and your cabinet-making skills - measure twice (do the research), cut once.

For your bench, for right now - you need nothing more exotic than a very good VOM (Multi-meter), good hand-tools (which clearly you already have), and excellent lighting. A basic 35-40 watt soldering pencil, 37/63 eutectic solder, will do nicely. And, I STRONGLY suggest you invest in a metered Iso-Variac for testing and applying power with some safeguards. Voltages as high as 500 volts DC are floating around inside tube equipment, which can be anything from embarrassing to fatal if mis-applied.

http://vacuumtubeaudio.info/artwork/pro ... 5220-3.jpg I keep this device. There are others with similar functions from other makers, but this has been a workhorse for the last 20 years.

As things progress and this becomes more of a serious hobby, or your DIY becomes repetitive, or you start in restoring audio items, additional meters such as an LCR and ESR meters will become necessities. Perhaps a scope - but that is way down the line.

Best of luck with it, and enjoy!


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PostPosted: 04 Feb 2017, 20:17 
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Ah... no. The math is correct. Please note:
Suncalc wrote:
(these are 3dB higher due to having two channels)
Two channels doubles the acoustic energy into the space and hence adds 3 dB.

1W = 87dB + 3 dB = 90dB SPL
10W = 97dB + 3dB = 100dB SPL
30W = 101.8dB + 3dB = 104.8dB ≈ 105dB SPL
50W = 104dB + 3dB = 107dB SPL
100W = 107dB + 3dB = 110dB SPL

But regardless of the reader's mathematical abilities (or lack thereof), the argument still holds. And I stand by my original advice. Decide what you want and why you want it, BEFORE you begin researching amplifiers, topologies, and components. Analyze your current situation, decide what is lacking, and what you need to fulfill what is missing. Otherwise you risk getting sucked into information overload.

Think of it this way, before you start a journey it's good to decide where you want to go.

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 04 Feb 2017, 21:55 
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Hi, I'm in agreement with Suncalc. Since you appear to find fault with your present system I believe it is necessary to determine what will make the listening experience better. I caution that the amplifier is only one part of the system and you have to verify for sure that it is the component that is causing your dissatisfaction. The actual type of amplification (SS, tube or class D) can be important, but all have the ability to sound quite excellent. Power output is not usually by itself all that important, nor are most of the other parameters that you will hear mentioned as long as they are within reasonable limits. I have high quality examples of all three types of amplifiers, and each is quite good. They do not all sound the same. That is to not say one is deficient or another better, just different. My personal preference is well known to be with the tube amps. What I recommend is what others already have...carefully investigate the types of amplifiers you are interested in and how each might fit into your vision of what is best for your listening enjoyment. Then with a clear idea of what you want to accomplish come back with specifics. We can better make recommendations or at least eliminate some that are unlikely to suit you. Be aware though, based on my experience owning and designing for a company that makes and sells amplifiers that if you stick with tubes every time (when above about 5 watts per channel) that you double the output power of a high quality amplifier you will probably double the cost. A second and more pragmatic recommendation is to keep the high voltage in diy tube amps below about 475 volts dc. The cost of components rated to handle 500 volts and lower is much more reasonable than those for higher voltages.

Good listening
Bruce

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