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Old 14th February 2004, 08:25 PM   #1
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Default Appropiate cabling quality & Regulators

[Two questions, choose your favourite! ]

The most obvious place to use high quality cables is directly in the signal path, from the input to the grids and, in turn, from the outputs to the successive sections.

But where do you draw the lines?

Using Litz silver cables for the heaters would take some seriously good reasoning.

However, how many of you also use relatively high quality wiring in the plate supplies of your amps?

A true Class A has it's supply pretty much directly connected to the output for the entire cylce. And even a Class AB amp has to draw the power for it's output thru the cables it's supply is wired with. Surely cable quality has an effect on transients, fluidity of power delivery and surge current ability?

I have heard good reviews about a number of Van Den Hul's cables and so was considering them. FDE has mention Deskadel but I'm having a lot of trouble finding anything about them in English.

----------------------------------------------------------------------

Finally, how many of you use true tube based voltage regulators? Morgan Jones suggests using the LM317 for plate regulation due to all the problems with stability that tube regulators have.

This seems a bit odd at first. The tube is effectively in series with the regulator. A lot of tube builders would seem to want to avoid putting solid state electronics so close to the signal.

Futher more, he mentions critically damping the regulator for transient rejection. Perhaps I'm missing something, but isn't this a step futher towards a sterile digital sound?

Morgan describes their role as forcing the supply to more accurately track the music. I take it from this that his critical damping statements relate to not allowing the supply's own transient behavior to become part of the signal; as distortion.

But would this not also lead to surges, that would normally induce transients, stopping dead as they're bypassed?

I'm curious because I've been following his advice and I am going to end up with a signficant number of LM regulators in use. This is my first tube amp and I've never experimented with regulators in this way before, so I'm not sure how this is going to sound. Added to that... they need an equally significant number of heatsinks.

The amp will feature two 12AX7 preamp tubes and an EL34 power tube. Later, another 12AX7 will be added.

Controlling each individually will require 8 LM regulators, 4 of which will need to be designed for high voltage use, which requires the use of 4 high voltage transistors... which also need heat sink mounting!

Is there anywhere online that specialising in heatsinks for multiple T022* packages? I'm getting tired of only finding sites for processor heatsinks. I have to be specific, I do not want to start tapping blank heatsinks myself, so they must come with some form of mounting option already implemented.
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Old 14th February 2004, 10:52 PM   #2
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Hi

Regarding regulators I use 2 tube based regulators built with a disimilar triode in my preamp, (I use direct coupling in my amp and therefore use one positive and one negative supply voltage). The last stage is connected directly to the regulator trough a series resistor with bypass caps, (electrolytic + polypropylene) to ground, the amplifier stages are connected in the same manner but fed from the B+ point of the succeeding stage. As I have totally 4 stages in the amp the first input stage of the phono amp is fed trough 4 stages of RC filtering , this is also called graded filtering and used extensively in older equipment.

The reason to use a tube based regulator is because it is not actually trivial to build a solid state regulator with the same performance with regard to high frequency performance and low noise level, I also use a 0B2 gas voltage reference tube as voltage reference as this gives me low noise without a lot of extra components.

The result is that I have an amplifier that is completely hum free and with extremely low background noise level, actually so low that many friends have been doubting that it is really a tube based amplifier.

I dont believe it is necessary to use individual regulators for each stage, (even though some other people dont agree with me!)

Basically I dont think the LM317 based solution is the right way to go, solid state solutions must probably be discrete in order to compete even with simple tube regulators but that is just what I believe.

For Heaters I use a standard 7824 regulator it gives very good results and low noise level

Regards Hans
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Old 15th February 2004, 01:19 AM   #3
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Hi,

Eeka Chu,

Quote:
FDE has mention Deskadel but I'm having a lot of trouble finding anything about them in English.
You only need to ask me once...

DESKADEL

In the U.K Audiosynthesis should stock the silver hook-up wire from Deskadel, amongst others.

As far as regulators go, for the HT supply I use valve regulators exclusively. Using sand there makes the entire stage sound like sand to my ears.

Contrary to TubeTVR I use a separate PSU per stage where it matters most, namely in the phono stages. (Guess I'm one of those guys, Hans.)

Other than that I find myself in complete agreement with Hans, in fact I often find we adhere to the same design philosphy, to the point it sometimes gets a little scary...

Another good reason to use valve based VRs is that when wired correctly, nothing can happen to damage the circuit should one decide to go south.
They're absolutely foolproof, you can even pull a valve without any damage at all...

From experience with so called high-end valved gear I can only say that 9/10 it's that SS regulator that's going to need replacing...
Count yourself lucky to find out what they used and to find a replacement.

So far I never, ever had a single component fail in a valved reg for 15 years of daily abuse.

Cheers,
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Old 15th February 2004, 05:41 AM   #4
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Default Re: Appropiate cabling quality & Regulators

Quote:
Originally posted by eeka chu
[B]But where do you draw the lines?

Using Litz silver cables for the heaters would take some seriously good reasoning.
Hold the phone. None less resistive than rusty old steel lockwire for *any* connections. Takes a big transformer due to all the resistance inside it though...

<Serious>I have to try steel wire some time. Just to give you guys a run for your money (and what money it is).</Serious>

Tim
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Old 15th February 2004, 12:46 PM   #5
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Thanks for the help with this everyone!

I've spent some time this morning reading a bit more about valves against solid state and, as with everything in audio it seems , the first two statements I read where entirely contradictory. I'll show you what I mean.

I found this first response on a simple text based forum and have added italics to the parts I found interesting. I quote -

"... The reason I used gas regulators vs solid state, is
the ability of gas regulators to have a longer time
constant over the attack and release cycle of regulation.
What that gives you is a more smooth voltage transition
of regulation, not like the"chopping" effect of solid state.
You can hear this effect in the audio signal.

Solid state has no place here and in my opinion is
nothing more than someone trying to re-invent the
wheel by limiting component space and cost. Also,
gas regulators provide DC filtering. Many people don't
realize that fact."

Looks like valves are clearly in the lead. I finish reading and have a look in Tube Cad.

[From an article by Glassware, February 99, on high voltage regulation]

"From the above description of a regulator, it is obvious that an all tube high voltage regulator could be designed and built, but it would prove very complex and probably fail to meet, at very least, our third design goal: extremely low AC noise. Two problem areas for tubes are relatively weak transconductance and susceptibility to microphonics, both of which limit the amount of noise free operation we can expect from a tube. So with all due apologies to the hard core tube fans, here is an all solid-state design."

click here for the article

I am not trying to say one is better than the other, I'm just trying to show the root of my confusion with this.

I'm not sure, since I'm not well educated enough with regards to regulators, but this choice, between valves and solid state, seems to be similar to the choice of rectifier state.

I am more familiar with this in terms of guitar amplifiers. A significant part of 'The American Sound" is usually the use of valve rectifiers that smooth the response of the amplifier out and create a warmer, rounder, thicker sound. Where as 'The British Sound', typified by Marshall, seems to be much more achievable using an amplifier with a solid state, diode based rectifier. Which creates a much more upfront, defined and active sound.

Would I be right in assuming the regulator choice to be similar?

I would be really interested to hear how many of you often choose tube rectification to go along side tube regulation. Or even more interestingly, how many use a combination of solid state with valve based rectification and regulation.

At the moment, I am aiming for the slightly sharper attack offered by solid state rectification. I am using Morgan Jone's method, again, and implementing Hyperfast diodes in the rectifier. These use a series of resistors across them to balance the voltage division and 10n capacitors to prevent ringing and reverse voltage indifferences.

I will be very interested to see how these sound! I suspect they will most likely be even more upfront due to their faster recovery times.

Sorry, I've kind of side tracked! But again, thanks. And special thanks to FDE for the link to the Deskadel cable!
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Old 15th February 2004, 01:12 PM   #6
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Hi,

If you so choose go for solid state regulation, maybe you will find that the choice is not so easy as it is on paper, it is a very complex question. But whatever you do stay away from LM317 and other 3 pin regulators, especially if you want something that is faster then a tube based solution, these 3 pins types are very slow and depends entirely on the output capacitor to achieve decent output impedance at high frequencies.

Maybe you should compare reverse recovery time for solid state hex fred diodes to tube rectifiers and the need or lack of need of parallell snubber capacitors.

Regards Hans
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Old 15th February 2004, 01:39 PM   #7
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Default A contrary view

I love tubes, but I keep them out of my power supply. The role of a regulator in a tube amp is to provide stable DC at a low source impedance so that dynamic demands can be met and that stages are decoupled from one another- to the extent that the regulator does that task, it's a good regulator.

Haven't read the article you linked to, but I fully agree with the exerpt. A good solid-state supply will have a lower source impedance and lower noise than a valve supply, otherwise other industries would be using tubes for high-precision low noise laboratory gear, right? Notwithstanding the bleats of the purists, DC is DC. You can objectively know what supply works best with some simple measurements. IMO, most of the objection to the "sound" of a good SS regulator is made by people who are doing an open-loop listening test with the embarrassing knowledge aforehand that there's a chip or a transistor in there sullying the vacuum glory of their amp.

The real test of a supply is in use- the SS supplies I've been using just plain and simple show LESS coupling and noise, lower source impedance, and better efficiency than any tube-based supply I've tried.

Quote:
Maybe you should compare reverse recovery time for solid state hex fred diodes to tube rectifiers and the need or lack of need of parallell snubber capacitors.
I don't understand the analogy to regulation here. Can you clarify this? A HEXFRED raw supply will show the regulator a lower source Z than a tube rectifier-based raw supply. You might want snubber caps with one rather than the other, sure, but why not complain about the tube rectifier needing a heater supply? The caps are cheaper, don't put out heat, and when you're done, you don't have a rather weedy source resistance in series with the raw supply that the regulator has to work hard to overcome.
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Old 15th February 2004, 02:09 PM   #8
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Hi Hans,

Quote:
If you so choose go for solid state regulation, maybe you will find that the choice is not so easy as it is on paper, it is a very complex question. But whatever you do stay away from LM317 and other 3 pin regulators, especially if you want something that is faster then a tube based solution, these 3 pins types are very slow and depends entirely on the output capacitor to achieve decent output impedance at high frequencies.
When you say faster than a tube based solution, do you mean eletrically faster in operation or faster to design?

In the regulator Morgan details, he uses the recommended output capacitor detailed in the manufacturer's pdf, but then critically damps the output using a resistor in series with it, assuming that it's unlikely the tantalum bead output cap will be enough to remove transients in the real world.

I guess this probably doesn't fully take into account output impedance. I don't remember him mentioning it if it does.

Quote:
Maybe you should compare reverse recovery time for solid state hex fred diodes to tube rectifiers and the need or lack of need of parallell snubber capacitors.
Thanks for the advice. I'm reading about it right now!
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Old 15th February 2004, 03:51 PM   #9
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Quote:
In the regulator Morgan details, he uses the recommended output capacitor detailed in the manufacturer's pdf, but then critically damps the output using a resistor in series with it, assuming that it's unlikely the tantalum bead output cap will be enough to remove transients in the real world.
Much of the reason one uses that resistor is not for damping, but rather for reliability on power-up/power-down. You sacrifice a little in high frequency output Z, but at the impedance levels of a tube circuit, and in frequency regions that are already knocked down by the general 1/f character of music signals, a few ohms is pretty negligable.
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Old 15th February 2004, 09:41 PM   #10
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Quote:
When you say faster than a tube based solution, do you mean eletrically faster in operation or faster to design?
Faster in operation, i.e more comnstant output impedance over wide frequency range and good transient performance. What I mean is that it is quite simple to design a tube based regulator with constant impedance up to 100kHz or so, a LM317 or othjer 3 pin type have increasing output impedance from a few 100Hz. To have a constant output impedance I believe is extremely important in order for the regulator to be transparent and not affect the sonic result. It seems that what Morgan Jones suggest, (to use a series resistor) is trying to achieve just that, it sort of counteracts the idea of using a SS regulator in the first place, (modifying a SS regulator to behave like a simple tube based one!)

Quote:
Maybe you should compare reverse recovery time for solid state hex fred diodes to tube rectifiers and the need or lack of need of parallell snubber capacitors.
Maybe I was a bit cryptic but the fact is that a tube diode doesn't have a spec for reverse recovery as there is non, as in Schottky diodes there are no minority carriers present and therefore the diode switch off instantly when reversed, the speed is only dependant on the parasitic capacitance and inductance of the diode package itself.



Quote:
I don't understand the analogy to regulation here. Can you clarify this?
It doesn't concern regulation it is only that I think a choice of components or solution should be based on all facts and the fact is that the problems that can exist with SS rectifiers, (related to reverse recovery) doesn't exist with tube rectifiers and vice versa, (heat and high voltage drop in tube ones). I use tube rectifiers and tube based regulation in preamps but have never thought about using it in my power amps, (today I only build OTL's).


Regards Hans
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