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Old 23rd January 2004, 08:13 AM   #1
DVDHack is offline DVDHack  Australia
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Default Opinions on Walton Audio 300B Design

I have cut and pasted a section from one of my earlier posts because the subject was changing substantially and I thought we'd get a better overall discussion by seperating it.

Below is the thread I posted and the replies to date, I've cut it inot two as it was too long:


Has anyone got an opinion on the Walton Audio Amplifier?

http://indigo.ie/~walton/300bmk2.html

There is a more detailed section for his first version

http://indigo.ie/~walton/300b.html

It still appears to me that the 300B is the simplest to build at this stage.


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I actually met Derek Walton at the Dublin hi-fi show where he had rented space to showcase his amplifiers more though in the spirit of offering his services for hand-made amps to interested parties but not really as a business venture.I had a chance to talk to him because I am also intersted in building a 300b and we spoke on the phone in order to arrange a further meeting.Very nice and enthusiastic person.However he has completely dropped out of sight in the last few months and all my efforts to contact him have had no result.
His website is great for anyone wishing to build a 300b and quite detailed and simple.
The only caveat seems to me that some experts recommend a good two stage driver for the 300b while he has adopted only a 6sn7 driver approach.
Another good site is the Plitron site where there are a couple of good articles reprinted on a stereo 300b set and a push-pull version with the seemingly excellent plitron trafos.
I would also appreciate the opinion of the "experts" here on what in their humble opinion is the best 300b circuit including the question on tube or silicon rectification , choke vs transistor regulation , grid bias regulation etc.



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Post #98


quote:
Originally posted by protos

I would also appreciate the opinion of the "experts" here on what in their humble opinion is the best 300b circuit including the question on tube or silicon rectification , choke vs transistor regulation , grid bias regulation etc.


I'm no expert, but as has often been stated on this forum, there is no *best* circuit or design; its more a matter of taste. Also, you have to address what your goals are, your budget, your abilities, and where are you willing to compromise.

Having said that though and with the necessary disclaimers, I will offer the following:

I would never recommend a 6SN7 as driver for a 300B.

I would recommend a 6V6 (triode strapped) or other pentode, or other triode as driver.

I would not recommend a two stage approach. "Everything should be made as simple as possible, but not simpler." Alot of people view the two stage amp as the simple and purer approach to designing. Afterall, less parts, less wire, shorter circuit path, what could be more perfect. For me, that viewpoint is flawed in the sense that you are now asking a smaller number of parts to do multiple duties. Which then creates complex interactions which then limits the number of available driver choices down to a few high gain tubes (like 6c45pi). And these tubes, if they aren't rare and expensive NOS, are current production russian which have their own idioyncrasies in terms of their application. So why invite unecessary headaches? And on top of that, a two stage amp in most cases requires you to have an active preamp. Which is basically the third stage which you dropped from the front of the amp because you wanted to *KISS*.

Therefore, for me a three stage approach is best; it allows you the freedom of choice in terms of tubes and topographies. And the use of a passive volume control like a TVC or autoformer which hands down beats all active preamps, period.

An unbypassed 1/2 6SN7 loaded with a 68K-100K resistor makes a darn good voltage amplifier as input tube. A triode-strapped pentode loaded with a choke in series with a resistor would make a decent driver. Cap coupling between stages. If you're game and are cathode self-biasing then direct coupling might be a choice to consider.

Keep the power supply for the output stage separate from the power supply for the input/driver stages. Basically, build two full supplies, complete with CLCLC filtering for each B+. The needs of the output tubes are different than the needs of the input/drivers. Separating the supplies allows each tube to be properly loaded. And while you're at it, and since at this point who cares about costs use fixed bias on both the drivers and output tubes. Thereby eliminating the big cathode resistors and electrolytic bypass caps; and since you have left the 6SN7 unbypased, you have just eliminated a number of parts which if left in would add nasty colorations the sonic signature of the amp. AND thereby also eliminating the need for matched pairs anywhere in the amp. Afterall, *matched pairs* of tubes is the biggest myth in tube audio. AND thereby, giving you complete control of the op of each tube.

Use hybrid rectification, combining tube and silicon rectifiers. Hexfreds or the recently introduced high voltage Schottkys. Better controlled bass response.

Use separate filament supplies for each DHT or shared supply for IDHTs. Use separate filament transformers. DC heated. RCLC filtering.

And finally, keep the power supply on a separate chassis than the circuit components. Connect with a properly shielded umbilical. Keep the last LC or RC section of each PS on the amp chassis. Place the last cap of the DC filament supply right at the filament tabs of the tube sockets. Star ground.

And one more thing, use high quality parts throughout. Especially iron.

Basically, I've just described to you my amp. And since its my first DIY amp, and also a scratch build, and when I started the amp, I knew nothing about electronics, much less amp building or design, I make no claim to being an expert. But, now after 2.5 years of working on this amp, I do have a little experience. So take my humble suggestions FW their W.

Here is a pic:





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Well.... Post #99


Actually it is a matter of whether one wants to outboard the first stage or not; with an additional selector switch.

True, one would need an IC, but then you don't have to contend with signal interaction through the power supply. It is frequency related, bass and then highs the most vunurable. Really messes with the sonics. I prefer the separation and although it costs much more, the sound is better.


Steve
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Last edited by Positron on 01-23-2004 at 06:37 AM

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Old 23rd January 2004, 08:15 AM   #2
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Konnichiwa,

quote:
Originally posted by protos
I would also appreciate the opinion of the "experts" here on what in their humble opinion is the best 300b circuit including the question on tube or silicon rectification , choke vs transistor regulation , grid bias regulation etc.


Well, the subject is complex. First a few notes on gain. If you use the russian 6S45 or any of the following - EC8010, EC8020, WE 417A, WE 437A or triode wired Pentodes like E810F/7788 / E280F / E180F/6688 / E55L et al you can have a driverstahe that can drive the 300B at normal Operating Points (350V60...80mA) to full power with around 0.9 - 1.3V, so with a normal CD Player your systemn is in essence gainmatched with a unity gain Preamp (passive or active), meaning the Amplifier will never receive an input signal that is over around 6db above it's clipping point with the volume full up.

A TVC makes an excellent choice in this case. Daisychaning a pair of 6SN7 Halves or the like not only produces a lot of distortion prior to the outputstage with a lot of upper harmonics, in addition it will also drive the 300B to clipping with around 0.25 - 0.4V RMS, meaning between 8 - 12db attenuation will be always needed.

So you gain nothing by using a dual stage driver, but you loose transparencey and tonality, plus you are ging to be further away from the best sounding range of the TVC (contrary to common misconception the TVC is best turned all the way up!!!) should you use one.

So, unless you need to accomodate very low output sources having more than one driverstage gives no benefit.

The best solution to maximising the performance of such an amplifier IMHO is to use directcoupling with one of the possible variations of the DRD/Monkey/FreeLunch/Stacked Supplies approach, in all cases using a Anode load choke (Tangoe TC160-15 or suitable items from Stevens & Billington, Electraprint or Magnequest).

My gut feeling favours a "stacked supplies free lunch" with a seperate valve rectified supply for the driver and a suitable RL series combo to provide the bias for the Output Valve. In this case you need a suitable interlock that can be conveniently be applied from a Relais that will power up the HT for the output stage once the driver valve draws enough current to bias the output stage.

As for rectification, it is possible to make solid state rectifiers sound very close to Valve ones, but it takes a lot of effort and is poorely documented. The valve rectifier serves two sides for good sound. On one hand it's soft turnon and lack of rectifier noise are hard to match with solid state and secondly, the fairly high power AC heater of the rectifier provides a steady load for the Mains transformer, thus damping the tendency of the transformer to oscillate when current pulses from the rectification of the HT or Heater Voltage try excite the parasitic resonances.

Ideally you use a LCLC or CLCLC Filter with a small first C to bring the supply as close to a choke input supply as possible, with LCLC supplies you can eliminate for all practical purposes any +B supply related noise, so you get an inherently "quiet" rectification and a very clean supply even when using Film or Oil Capacitors (highly recommended).

So an option would be a 350V supply using a WE 274A/B or 5R4GY (or 5AR4/GZ34) in LCLC for the 300B. Add to this a supply with around 250V +B for the driverstage, rectified for example with a 6X5, WE420A or EZ80 and CLCLC filtering. Driver valve of choice would be E55L or E810F or WE 437A, for my taste....

If this is combined with a suitable LC filtered DC supply for the 300B Heaters you would be very close to "edge of art", assuming of course high performance Transformers, chokes etc.

If you have multiple taps on the +B for the Output Valve (maybe including more Current and Voltage for the "super 300B's" and maybe something like a Tango XE20S as Output Transformer plus a pot to adjust the Bias (in series with the anode load choke) and selectable Heater Voltages (2.5V AC, 4V/5V/6.3V/7.5V DC) you can use a wide range of output valves (if you make easily exchanged socket plates even european oddballs), de facto making the amplifier "universal" and making sure you can run whatever valves you get hold of....

Of course, such an Amp would be quite a monster in size and weight, fitted with 2 pcs Mains Transformer, 5 pcs substantial size input/filter chokes, 4 - 5 pcs large Film or Oil PSU Capacitors plus output transformer and anode load choke. And it will be a layout nightmare if you want to avoid magnetic coupling. Of course monoblock chassis with Bronze, Brass or Copper top plate and wooden frame.

Well, it would make for a stonking Amp and yes, it would cost an arm and a leg if you build this kind of design consequently enough, BUT I'm pretty confident it will require a Badge with the incription "Beware - Kicks Butt", despite giving only 1.5 Watt when fitted with a #45!

So, anyway, that's my take for "the best 300B Amp I can come up with if money, space and time are infinite".

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Old 23rd January 2004, 09:35 AM   #3
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Konnichiwa,

Some notes, the "Walton" 300B Amp is basically the JE Labs Amp which in turn borrows heavily from the Fi-Primer and Sun Audio. The only plus of this general design is that it is cheap to realise and extensively documented. It makes a fine first SE Amp build on a shoestring, using Hammond Iron and generic parts to be later relegated 9into a second system or to be passed to non-diying friends....

The basic circuit and parts quality is very similar to a middle of the road 300B Poweramp as manufacturerd by a range of companies, at least in the first Unit from Walton and with JE Labs. There are also strong similarities to the "standard" Audio Note UK Circuit, so if you want an idea what such an Amp will sound like audition an Audio Note Quest or the usual suspects from Cary & Cannary.

It is such amplifiers that are often heard at shows and commented upon, as only a few small companies (best known among them are Wavelength Audio and Border Patrol, also Wavac & Audio Note Japan) make SE Amplifiers not severely compromised by having to be commercial, sellable products.

The best DIY'ers can make when they simply wave any commercial considereations is miles if not lightyears ahead of any semi-sensibly priced commercial SET Amp. Hence my take is: Why spend a lot of money to copy a Ford Ka when you can build something that is better than a Ferrari?

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Old 23rd January 2004, 09:40 AM   #4
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OK, what is better AND proven? What is a no compromise design?
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Old 23rd January 2004, 10:00 AM   #5
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Konnichiwa,

Quote:
Originally posted by DVDHack
OK, what is better AND proven? What is a no compromise design?
I have published the odd "small compromise" design and there are some semi-published ones, including this:

http://www.jogis-roehrenbude.de/Lese...Loesch-Amp.htm

(Sorry for the german text - I'll eventually publish in english when I find the time)

and there are others to be found in older issues of Sound Practices and Glass Audio as well as Valve. I would reccomend to buy the (quite inexpensive for the content) Valve & Sound Practices CD Archives and to read the Glass Audio Back issues index.

There is much practical experience, theory and background in these, plus some absolutely stonking designs such as Ciro Marzio & Christiano Jelasi's Direct Coupled SE Amp (very prosaic Amplifier circuit with ECC83, ECC88 or others driving 2A3 or 300B at low voltage operation, but a seriously overvbuild PSU witout electrolytic capacitors and Chimera Labs 211 Amp.

So basically, my recommendation, read some more before building if you want to build "one" final Amp and learn from others or simply start building the "Standard" (Fi-Primer, JE Labs, Walton, Sun et al) 300B Amp on a shoestring as learning excercise and then build a few more amps and learn from your own mistakes....

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Old 23rd January 2004, 11:15 AM   #6
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No need to translate Thorsten...

the www will do that reasonably well

http://world.altavista.com/tr

Take the rest to http://www.freetranslation.com


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Old 24th January 2004, 07:42 AM   #7
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With the limited knowledge that I have of valve amps the translation is pretty meaningless.

What is it about that particular amp that makes it no compromise. It appears to me from the many circuits available that there is little difference by way of designs - without building them all how on earth do I know which is better?

The Walton design has a revised version which changes the supply by including additional inductors CLCLC type config - the parts have been significantly improved using Piltron TFR and better passive components plus some changes in input stages. The cost appears quite high - think he spent near $4000.

Anymore thoughts on a top design or should I just focus on the best components?

Kuei Yang Wang,

Where are the designs that you have published?

Thanks

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Old 24th January 2004, 09:52 AM   #8
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Old 24th January 2004, 10:12 AM   #9
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Hmm glad I'm making a KT88
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Old 24th January 2004, 11:13 AM   #10
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Konnichiwa,

Quote:
Originally posted by DVDHack
With the limited knowledge that I have of valve amps the translation is pretty meaningless.
Which brings me back to suggesting you read a little more, so you can make informed desicions based on your understanding, instead of following others. The other way to gain knowledge is of course empirical (eg build something) but I find it helps to understand the theory of something reasonably well before attempting to practice.

Quote:
Originally posted by DVDHack
What is it about that particular amp that makes it no compromise.
2-Stages, use of the best available Valves foir each respective Job, attention paid in Powersupply design, LCL Coupling between stages, or in sort, attention to detail....

Quote:
Originally posted by DVDHack
It appears to me from the many circuits available that there is little difference by way of designs
I would not say that. The basic 6SN7-6SN7-300B and my design could not be more different in circuit and execution unless you change the output valve.

Quote:
Originally posted by DVDHack
The Walton design has a revised version which changes the supply by including additional inductors CLCLC type config - the parts have been significantly improved using Piltron TFR and better passive components plus some changes in input stages.
And yet he kept that dreadful 6SN7 Cascade. I could probably think of a worse sounding solution, but that's hard work.

Quote:
Originally posted by DVDHack
Where are the designs that you have published?
All over. There is a list in my Thunderstoneaudio Yahoo group where also a few "un-published" rather extreme designs are available.

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