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Old 10th January 2011, 04:31 AM   #1
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Default Building an amp from scratch - what features would i want

going to start a multi amp build soon. been studying a few schematics as well as tinkering with a few amps in house. my features list.

a. noise cancelling power supply - two power transformers in parallel with one transformer out of phase - the minus ripple from one transformer will cancel out with the + ripple of the other transformer.

b. soft start or warmup switch - this works really well by brining up the amp to partial power before going to full power - really neat when hunting down a circut problem and run away tubes since you can put the amp in partial power mode and do some serious troubleshooting.

c. input transformers - its amazing how much noise an input transformer can kill

d. film caps through out - film caps have a faster rise time than electrolytic caps.

e. chokes, chokes, chokes - been studing grid choes, anode chokes, and plate chokes. defintiely putting in shunt chokes at each stage of the signal path.

f. individual bias - a must to be able to balance out each tube.

g. by pass caps on power supply filters - metal film caps as by pass caps where practiable

h. oversized diodes in rectifiers - countless problems with inrush issues and diode overloads can be avoided using oversized diodes.

j. large value power supply caps - all the amps I've owned that sounded really well have oversized caps. cary runs 1500uf and manley run 3500uf.

k. parallel triode driver tubes - going with 6414's with triodes in parallel for each channel.

l. front panel tube bias probe connection points, adjust points, and selector - just connect your multi meter right to the front pannel, turn the selector to the next tube, make the adjust on an easy access pot for each tube.

ok, your turn
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Old 10th January 2011, 04:47 AM   #2
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hmmmn - looks to me that you have bought into EVERY possible paranoid audiophool delusion in this admittedly highly paranoid and delusional hobby...

b. brought on some special giggles - you must be expecting to deal with a lot of problems regularly. I would have thought a lightbulb, or, God forbid, a variac would have been easier. Got wingnuts on all the chassis fittings? for the ease of servicing of course...

All the physical features are, well, there.

The bit missing (and slightly more important, but only in my estimation I suppose) is some idea of what this mastodon (or more rightly, electronic onanism) of a creation is intended to achieve.

Got any target numbers?

All comments in a somewhat bemused but friendly tone, mind :-)
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Old 10th January 2011, 11:24 AM   #3
Loren42 is offline Loren42  United States
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Originally Posted by speakerfritz View Post
going to start a multi amp build soon. been studying a few schematics as well as tinkering with a few amps in house. my features list.

a. noise cancelling power supply - two power transformers in parallel with one transformer out of phase - the minus ripple from one transformer will cancel out with the + ripple of the other transformer.

b. soft start or warmup switch - this works really well by brining up the amp to partial power before going to full power - really neat when hunting down a circut problem and run away tubes since you can put the amp in partial power mode and do some serious troubleshooting.

c. input transformers - its amazing how much noise an input transformer can kill

d. film caps through out - film caps have a faster rise time than electrolytic caps.

e. chokes, chokes, chokes - been studing grid choes, anode chokes, and plate chokes. defintiely putting in shunt chokes at each stage of the signal path.

f. individual bias - a must to be able to balance out each tube.

g. by pass caps on power supply filters - metal film caps as by pass caps where practiable

h. oversized diodes in rectifiers - countless problems with inrush issues and diode overloads can be avoided using oversized diodes.

j. large value power supply caps - all the amps I've owned that sounded really well have oversized caps. cary runs 1500uf and manley run 3500uf.

k. parallel triode driver tubes - going with 6414's with triodes in parallel for each channel.

l. front panel tube bias probe connection points, adjust points, and selector - just connect your multi meter right to the front pannel, turn the selector to the next tube, make the adjust on an easy access pot for each tube.

ok, your turn
Here are my thoughts:

a. If you full-wave rectify and compare two transformers side by side out of phase with an oscilloscope, the waveforms will still look identical. You would need to shift the second transformer phase 90, not 180 to do what you propose. Good luck with that and why bother?

b. I agree with the previous post. Just buy a variac for your bench. All you need for normal operation is a delay start relay.

c. Yes, going to a balanced line input is superior if your preamp supports it. There may other reasons to support this if you intend to get rid of the phase splitter in the power amp.

d. A wise move is to use better quality caps in the signal path. Not so useful in other places.

e. To choke or not to choke... A choke is one way to build a power supply. Very popular long ago, but that was because large capacitors were not available. They are heavy, take up a lot of real estate, and hit you in the wallet. A regulated supply may be a better path if you really want the best supply.

f. I am not sure I understand this. My amp has a single negative supply from the power supply that goes to two pots, one for each output tube. Each tube's bias can be set with its own pot. That is a standard method to do it.

g. Use what you need to kill the RF and hash, but you quickly reach a point of diminished returns. More on that later.

h. I like the HexFETs for their speed. You must size these so that they handle the inrush current plus some safety margin. Unlike silicon, they do not handle current above their rating.

j. Put the sledge hammer away and simply do your homework on power supply design. If you are so intent on spending all your money to make the best amp, spend the time to learn what you are doing first. Morgan Jones' Valve Amplifiers is a great resource. Simply throwing money at a problem is a poor method to design a good product. You need to understand the details and the supporting physics.

Look at existing designs done by competent engineers. There are reasons why things are done the way they are. Unless you understand those reasons you are simply shooting a shotgun in the dark and missing a good opportunity to learn something. I think this advice applies to many of your points. Something to consider.

k. Why? Explain your supporting logic for your selection, please.

l. I put mine on the top in front of the transformers. I check them periodically, but find I rarely need to tweak them. I would not go out of my way to make them so accessible and I would not bother making a selector switch. I just put small jacks (6 total) that fit the end of my probes. Switches just add another device that can fail and give you an erroneous reading.

My recommendation is to put more effort into understand the design process and the theory of the design rather than simply react to every single golden ear claim by throwing money at it. Much of your strategies are overkill and a waste. It is far better to do the design right and come out of it with an education as well as a great amp then blindly buying into everything you read.

If the theory and learning are not what you want to do, build a preexisting design from someone that knows what they are doing and enjoy your amp. It will cost a lot less and you will have an amp that works better than one that runs on snake oil.
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Old 10th January 2011, 11:59 AM   #4
singa is offline singa  Singapore
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Speakerfritz,

These 2 gentlemen are giving good advice.Be rational
real life does not work like that ,if all the ideas were applicable it would have
produced a super amp and you might argue since it has not been done like this you want to try.Why make things so complicated? In reality it is simple
but man thinks it is not.It is all a mental thing.Stereo does not create concert hall ambience so why should you want to punish yourself?

It would benefit yourself if you learn to know yourself
through introspection and meditation.But if you must travel the road you choose then I wish you good luck.You will discover that eventually you
come full circle and laugh about it.
Best wishes.

Ps examine the works of japanese masters like Shishido or Susumu Sakuma it will surprise you.

Last edited by singa; 10th January 2011 at 12:02 PM.
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Old 10th January 2011, 12:08 PM   #5
DF96 is online now DF96  England
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Have you ever built a valve amp from scratch? If not, start with a simple tried-and-tested circuit. Build it and debug it, ensuring that you understand what every component does and why it has the value it has. Enjoy listening to it, even though it won't be as fancy as the other amps you have owned. Then most of the items on your list will disappear - they sound rather like a Hollywood fantasy of audio, rather than serious engineering. All electronic design is a compromise - for example, chokes can be good but are big and expensive and pick up hum and have HF resonances. Hum is one of the main problems 'discovered' by new builders, as the causes and solutions of it rarely appear explicitly on circuit diagrams. Stability is another issue which foxes people.

When I was a teenager I used to fantasise about the 'perfect' circuit. Now I am older and wiser.
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Old 10th January 2011, 12:15 PM   #6
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Quote:
ok, your turn
As the others pointed out: start with defining what functionality or performance you'll expect to get out of the new machine, and then start solving any engineering issues. Working the other way around may seem rigorous at first sight, but will most likely prove costly and highly inefficient.
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Old 10th January 2011, 01:19 PM   #7
jono1 is offline jono1  United States
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So-called "technical" improvements do not always translate into sonic improvements -- often the opposite is the case. As a general rule, I think simpler is better . . . both economically and sonically. Not always, though.

Remember that all of the "music" also passes through the power supply.

At some point filter capacitance seems to have diminishing returns -- too much can take the "life" from an amp. However, this observation is largely subjective, and certainly debatable.

Study the "classic circuits." Understand the strengths and weaknesses of each. Then copy one of the highly-regarded ones. You'll save yourself a lot of time and trouble in the end ... designing an amp from scratch is full of pitfalls and you will likely spend a lot of time in troubleshooting and tweaking.
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Old 10th January 2011, 01:32 PM   #8
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Originally Posted by jono1 View Post
designing an amp from scratch is full of pitfalls and you will likely spend a lot of time in troubleshooting and tweaking.
Been there, done that. Ended up falling back on tried and tested building blocks to get something that worked without breaking my heart.

I'm with the rest of the guys on this one. It's difficult to make a judgement without knowing what the final amplifier will be used for and at what sort of power levels. But to get excellent sound, you don't have to mortgage your soul for parts. Some of the best amplifiers I've heard have been some of the simplest in terms of hardware.

Personally, I've found the "best" results come from careful planning of the physical layout as well as care and attention during the build. The best components in the world can be used to make something that sounds terrible if the layout is wrong... (and please DON'T ask me how I know!)
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Old 10th January 2011, 03:10 PM   #9
THD+N is offline THD+N  United States
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Coriolis Effect... might have to compensate for this too with some audiophool technology.
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Old 10th January 2011, 06:50 PM   #10
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Lots of good sensible advice from everyone there.
Only place woth putting a choke is in the psu. Go for a straight LC type.
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