Chip vs SS vs tube

[peregrin288]

Hello all...

I am relatively new to the diy thing. I have been looking over various amp kits and instructions and don't know which is the best way to start. I currently am building up a home theater system. I am refurbishing a pair of Martin Logan Sequel IIs and driving them with a B&K Reference 2220 amp. (220 x 2 @ 8 ohms, 350 x 2 @ 4 ohms) This is probably not the ideal combination though. Sunfire amps have been recommended, but they are not cheap.

Funds are short, so I thought I'd try to build an amp. (To replace the B&K) However, tubes don't seem to have the wattage output of SS amps; chips seem to fall somewhere in between, but nowhere near the B&K. Do tubes and chips need that kind of wattage to drive ESL speakers? (The speakers need high current as well.)

I am quite mechanically inclined, so even though I have never built an amp, I am familiar with soldering and reading schematics, designing/building cases, etc.

Any guidance is appreciated. Thanks.

[Gordy]

Hi, I don't know your amp, but surely it would be an idea to try what you have before launching into a project? If it can do 350W into 4R then it's not short of current!

If you are going to build an amp then I suggest you start by defining the technical requirements by looking closely at the impedance curves of the Sequels and working out just how much they really do need. If they need a lot of current then a low output impedance and substantial power supply are called for. You might get this from a bridged chip-amp or a transistor amp, but are unlikely to get it from a 'normal' sized tube amp.

I've not used aussieamp designed parts, but the guy / company is on this forum and they certainly make some high Watt modules you might want to investigate: High End Audio MOSFET Amplifiers

[ChrisA]

The first thing to do is look at your requirement for power. What I'm sure you really want is loudness. Loudness is roughtly the product of power times the senitivity of your speakers. It is MUCH easier to make the system play louder by working on the speakers.

As an example I have a 5W tube based guitar amp. 5W is not much but the speaker I use has about 100 db of sensitivity. In other words it is very efficient. I can be heard inside the house across the street with my 5W amp.

Tubes are expensive to build with and require by far the most skill (more then just the ability to follow a schematic. You WILL, yes WILL need to know how to debug and fix the tube amp. So you need to know some theory and own test equipment) Tube amps are expensive mostly because of the cost of the transformers. Tubes also use lethal voltages (500V DC) and can kill you.


On the other side are chip amps. Not much skill is required if you buy a PCB and solder in the parts. Chip amps can have a lot of power 50W is easy. If 50W is not enough then use two of them. Build a chip amp first. You will not need to invest much. The cost is low. Almost all consumer audio today is chip amps inside.

Tubes are for two groups of people guitar players and audiophile "purists" who are willing to use very efficient speakers and set up their rooms for them.

Why tubes at all? They produce more distortion but the kind of distortion they produce just happens to sound good to human ears, Like the "distortion" of a piano's sound board. Music is built with overtones and the tubes mimic those. Guitar player take this idea and run with it sometimes making the distortion products the primary sound

[peregrin288]

Sorry, I should have been more clear...

I already had the B&K before I found the Sequels. The Sequels were working before I took them apart, but I wasn't too happy with the sound. Don't get me wrong, it was good, just not as robust as I was expecting. So far I have replaced all the original capacitors with new polypropylene caps, and am re-coating the panels with new conductive fluid. Loudness is NOT what I am going for. (If I need loudness, I have a pair of ten-year old DCM 3-way towers sitting around I can plug the B&K into) Presence and balance were lacking.

Who knows, they may sound like a completely different speakers when I put them back together.

I definitely like the idea of bi-amping or at least a monoblock for each speaker. The B&K is a dual-mono design; one massive toroidal transformer but dual everything else. (I would love to have an amp dedicated to driving the mid to high range of the ESLs and their high current requirements.) This is where money is a big problem; amping a 7.1 surround system can get expensive, especially bi-amping the fronts.

As for building a tube amp...I used to work as a lab tech doing fabrication, installation, and design in a chemical engineering/research building at a university, so I have spent considerable time around potentially dangerous (both chemically and electrically) equipment.

Thanks for the info so far. Everything helps.

[Gordy]

I agree with most of what ChrisA says, except that...

Originally Posted by ChrisA

They produce more distortion but the kind of distortion they produce just happens to sound good to human ears

...is based on opinion rather than fact.

If a tube stage is designed close-loop then it is able to be low distortion, and if a transistor stage is run open-loop then it is able to be high distortion.

Line level tube buffers can run an easy 0.02 % and closed loop power amps (such as the Langford-Smith / Aston variant of the Williamson, designed some 50+ years ago) can do 0.025 % at 10W.

It is true that many current tube amp designers deliberately operate their designs so as to create a spray of harmonics because many 'audiophiles' claim to like it that way, however all we can say is 'that is their way of designing', not that it is the default output of tubes, because it is not.

I believe that it is 'horses-for-courses' and there are good and bad amps made with both tube and transistor.


Edit: my thoughts relate only to 'hi-fi' amps, and not guitar amps (... because I don't know much about them)

[thetube0a3]

I agree 100% with Gordy. A properly designed tube amplifier will produce very low distortion.

Most vintage high quality tube amplifiers can pass an extremely clean signal.

However, Even tho I have a mint restored Fisher KX-200 in the bedroom, 99% of my listening is done with chipamps.

[peregrin288]

The info I have found so far supports Gordy and thetube0a3. I have seen tube amps with 10% THD all the way down to Gordy's numbers.

I am also not sure about the wisdom in building an amp to create harmonics or overtones. These are created naturally by instruments and should already be present in recordings. Also, not every instrument builds the overtone series the same way. Clarinets, for example, do not have the first octave overtone; their first overtone is a twelfth above the sounding pitch. A piano will produce the entire overtone series. With timpani the pitch is nothing like what it looks like on an oscilloscope; timpani produce a ninth above the tuned pitch. (I have two degrees in music and percussion.) Some people though enjoy the amps that create harmonics and overtones. Listeners opinions vary greatly.

BTW, Gordy, that link you posted was great. I had not heard of them yet.

[ChrisA]

Originally Posted by Gordy

I agree with most of what ChrisA says, except that...



...is based on opinion rather than fact.

If a tube stage is designed close-loop then it is able to be low distortion, and if a transistor stage is run open-loop then it is able to be high distortion.

Line level tube buffers can run an easy 0.02 % and closed loop.

I think you just made my point. Tube amps, chips amps and any amp ALWAYS have distortion even if only at the 0.02% level. Most real tube amps will run a bit over 0.02% however. 1% is pretty good

But what matters as much or even more is not the THD number but what components or overtones are in the total. A 1% THD amp with all the THD in 2nd and 4th harmonics will sound pretty good. But 0.5% THD amp with all the "D" in 3rd harmonics will sound harsh.

[Gordy]

Originally Posted by ChrisA

I think you just made my point.

Glad I could help. Have a nice weekend

[Conrad Hoffman]

Tiptoeing carefully around the tubes-vs-transistors argument, I do think bi-amping or even tri-amping is something to consider. I've found that the power requirements for each amp in a tri-amped system tend to be much lower. That makes easy 60W SS or tube or chip designs perfectly adequate for almost any sensible SPL level. Once you get used to a properly set up bi or tri system, passive crossovers might never satisfy you again. Active crossovers aren't too tough to design, or you can use the very cost effective boards from Marchand.

Conrad