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Purity and simplicity of amp design
Purity and simplicity of amp design
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Old 25th July 2008, 05:28 AM   #1
lowtherdream is offline lowtherdream  Canada
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Default Purity and simplicity of amp design

I have been dreaming about tube amps for more then 10 years but never owned one until this year. My original idea was to build my first amp using a simple recipe. I liked the Decware SE84C and was planning to build it. I started sourcing parts last December and was looking at speaker options, speaker cables and interconnects options and diy audio stuff.
Soon, I now had projects to build the amp, the speakers, voltage regulator and all the cables. Too many projects, too little time.
I knew I would not be able to build it all and have the time to enjoy music before 2012.
In an attempt to accelerate the process, I decided to purchase the 1st amp, a simple source and the speakers for my speaker project. So I ordered the Decware Taboo amp, an Oppo DV-980H SACD player and 2 Fostex FE207E drivers.
I am now listening to music with my FE207E drivers installed in Rubbermaid bins. There is very little bass, but the mids and high are much, much better then what I was able to produce with my original Sima PW3000 and Paradigm 5Se speakers.
I have been working since December on the final cabinets for the Fostex drivers. The only time I have available to work on this is usually on Saturdays. The Cabinets are huge I am building a non-folded BLH that should go to about 30Hz. 54" high, 50" deep, 12" wide I hope to be finished in the next 2-3 weeks.
I will post pictures Hope I like the sound ... after the tuning of the compression chamber that is.

And that's not all ...
I am also working on the CAT5 braided speaker cables ... and the braided silver interconnects.

More ...
I have purchased 2 Tubelab SE boards and sourced the components to build one. All I have missing are the 300B tubes.

I have one month vacation planned soon, and I think I know what I will be working on.

I am already planning the projects for 2009 My goal is to build a high quality 300B amp. I know I will have to spend a substancial amount in tubes and iron.

What do you think about the Axiom 300B ?

The Leonardo ?

The WECO 91 and similar ?
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Old 25th July 2008, 09:14 AM   #2
oldeurope is offline oldeurope  Germany
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Default Re: Purity and simplicity of amp design

Thanks for the links.

Try to understand Loftin White.


Kind regards,
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Old 25th July 2008, 11:08 AM   #3
SY is offline SY  United States
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First question: what are the design goals? Power, distortion, source impedance?
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 25th July 2008, 11:59 AM   #4
lowtherdream is offline lowtherdream  Canada
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Let me start by saying my knowledge in audio is very limited. I understand most of the circuits but did not enough experiment to have my own opinion. I feed from internet information and make my own conclusion. A great part of that is my belief that simpler/natural things are better. It is as simple as the sound of knocking on wood compared to plastic. For that specific reason, I refuse to paint or varnish speaker cabinets, or use plastic anchors or Tyeraps in my amps. I prefer point-to-point over circuit boards.
Again, it is not a rule, but more a guideline. That's why I am ready to try the Tubelab SE and make my own opinion. I like Georges way to try new things and share with the DIY community. Maybe one day, I will be able to contribute my share

Power, distortion, source impedance ?

Not power. I believe in the 1st Watt and willing to sacrifice power.
I prefer to limit the number of components, the purity of the material used in the components. 300B with 5K OPT is ok.

Distorsion ? I like the 2nd harmonic in moderation. So I prefer SET over push-pull. Also willing to sacrifice power to reduce distortion.

Source impedance ... I did not collect enough knowledge and information to completely understand impedance and it's effect on a design. Any good reference reading on this subject ?
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Old 25th July 2008, 01:45 PM   #5
oldeurope is offline oldeurope  Germany
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Originally posted by lowtherdream
... 300B with 5K OPT is ok...
Why ?
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Old 25th July 2008, 02:48 PM   #6
Larry Lomax is offline Larry Lomax  United Kingdom
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I do, indeed, prefer original sound from the London Philharmonic Orchestra at the theater.
No added distortion, no added harmonics, just the original, the original way from simple wood and metal instruments.

Nothing happens by itself, you have to work hard to arrange things to make it happen.
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Old 25th July 2008, 05:12 PM   #7
Michael Koster is offline Michael Koster  United States
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Default After the first watt

Hi Lowtherdream,

I think it should be changed from "first watt" to "first power increment giving 93db" or something like that, because the sound of that first watt depends a lot on the efficiency/sensitivity of the loudspeaker.

Paul Joppa suggests enough power to achieve 102db peak at your listening position. My own experience bears this out as a minimum for a wide range of music. If you like listening to Santana etc, at impactful levels you will want at least 3db more headroom.


If you listen to one watt at 93db, 102db gives you 9db of headroom for dynamic peaks in the music. That would require an 8 watt amplifier.

Recorded music used to have a dynamic range headroom from "average" to peak of about 14db. That was based on the capability of magnetic tape and the vinyl system. Nowadays it is much less (like 3db) due to extreme compression employed in the production process. Since I don't like to listen to compressed music, I like 9db to 12db headroom to provide a sense of openness and space. Otherwise, the amp and speakers do the compression for you.

This can be carried to extremes :-0


PS A corollary: If you only listen to highly compressed music, a lot of headroom is not needed and the 8 watt amp will not sound much different from the 1 watt amp at a 1 watt average level.
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Old 25th July 2008, 07:33 PM   #8
richwalters is offline richwalters
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Default Re: After the first watt

Originally posted by Michael Koster

If you like listening to Santana etc, at impactful levels you will want at least 3db more headroom.

Thzat's nothing.The notion that all CD's are level compressed is a complete illusion. In reality the levels are all-over-the-place. Listening to Mike Oldfields "Amarok" with an 8W amp SET amp with high sensitivity LS's will create a simply depressing distorted performance. And I don't want to design an amp with a level overload indicator.
I don't know where one is not going to find uncompressed music material about....I bet the London promenade concert broadcast played live for those audiophiles is also somewhat compressed for FM radio, even digital somewhat equating to CD classical medium.
For those who like somewhat expanded music loud, the standard 50W p-p has all the salts to offer at a thd far lower than a SET design can offer.
Long live push pull.

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Old 25th July 2008, 07:57 PM   #9
bear is offline bear
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Yo lowtherdream,

A few things come to mind.

First of all you've decided to follow a specific "philosophy".
You'll get results comensurate with that "philosophy."
That being, in short hand, the Fostex full range, with SE tube amp and DIY cables.

I've heard a Fostex system sound surprisingly "nice" to listen to on two separate occasions - at the homes of two very well known "personalities" in this hobby/biz.

Neither time I thought that the presentation was of the sort that was any better than pleasing and non-irritating - not that this is an achievement to be skoffed at!

It's not a "high resolution" sound, nor is it going to play Led Zep rockin' out, nor a big choral & symphonic piece! It's not going loud, although the smaller the room, the louder it will seem.

Having said all that... the Axiom is an advanced, sophisticated circuit. The other two are simple circuits. That means absolutely nothing about how they will sound.

How they will sound will depend on both parts and execution. And especially the transformers.

I personally greatly prefer anything run in A2 over A1 - that means DC coupling of some sort to the grid of the output tube so that the grid can draw current - a cap coupling will not permit A2, only A1.

The simple advice is to build something now and as fast as you can with whatever you can get your hands on quickly! Forget about getting it "right" at all. Build something that works. You can improve upon it, or build something else once you get going with it.

Within reason, and assuming you don't care that much about aesthetics (at least to start) you can wack out an amplifier in a weekend or two at most - some folks have built on upside down cake pans, works fine, looks like hell.

Btw, I do not like CAT5 cables at all, but maybe they sound good with fullrange speakers like the Fostex... doesn't matter. Just do something, and get results. Don't wait for making a CAT5 cable if you have everything else, or just SOMETHING to listen to, use phone wire if that is all you have on hand today.

One last bit of free advice - don't be seduced by the flowery words in print. Sure try something because people wax poetic over it, but keep your mind open and find out what works for you - heresy is fine.

Btw, do not skimp on power, given the choice. Within reason almost any Class A SE is lower in distortion at lower powers than at higher power... so paralleled 300Bs SE will likely be better than a single 300B... and have more power... you might end up prefering PP, but maybe not if you are using the higher output Z (lower DF) to "tune" the bass end of your FR speakers...

It's all yin/yang, and one tradeoff against others.
You have to start by doing something and then after time you'll start to see what is what, and make some choices about the tradeoffs you can live with vs. those that you can not.

http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 25th July 2008, 08:03 PM   #10
ambience exists is offline ambience exists  United States
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So... If I pair my 8w push pull with massively efficient speakers, say, 102db, I should get quite the range eh?
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