TNT-Audio Readers' Corner
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July 2009

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Grounding and bonding [+filtering]
Hi Mark
Further too my previous Email, perhaps some additional filtering in your own electrical power subsystem would eliminate noise, an outline for this "tweak": ( ;-) > [=balding bearded Smiley]

A Little Project (From: Ralph & Diane Barone (barone (at)

Someone wrote:

"I need to convert 300,000 Volts DC to 240 VAC, 60 Hz. 80 mA is available from a 300 kV DC source which equals 24 kW. This means 100 Amps capability from the 240 volt 60 Hz output of some type of converter.

Does anyone have recommendations or schematic diagrams that would provide a conversion for high voltage/low current TO low voltage/ high current as stated above?
No problem. We have one almost like that where I work (ratings are only slightly different). However, here is the description:

We use SCRs because we are connected to an existing AC power supply and we can let the external supply commutate the SCRs. If you don't have an external AC supply, you will need to use power MOSFETS, IGBTs or GTOs. In our application, each SCR is in an arrangement of 360 devices connected in series parallel (180 series/2 parallel) with the requisite firing pulse isolation transformers (720), RC snubbers (2,160), voltage breakover firing circuits (4,320) and dI/dt limiting series reactors (1,980). Firing pulses come from a custom GE control system which occupies three 3' wide cabinets.

From the transformers, we go into our 230 kV AC bus. We have filters on the AC bus to remove the harmonics created by the conversion process. These filters consist of air core (but oil cooled) reactors and a whole wack of capacitors. These filters occupy approx 300 square meters of space in the switchyard.

After the 230 kV bus, we step the power down to 25 kV, then we have another transformer that goes 25 kV to 240 V with a grounded center tap.If you would like photocopies of our design drawings, please send me five (5) empty 4 drawer filing cabinets and $10,000 to cover copying and shipping. :)

I gather the "final" transformer is a "star" wired 3 phase transformer.

This then still requires pole mounted "Star" to " Delta" transformers before the final "2 phase" 3 wire connection to homes which have a (+) 120VAC wire, a (1) 120VAC wire, and a neutral wire, so each "live" wire provides only 120V of "danger", UNLESS you are silly enough to touch BOTH of the live wires at the same time. BUT large appliances can still benefit from the 240VAC: {drawn using Tahoma 15 font!}

.---------------- "A" phase 240VAC

/ \ | (+)120VAC |
/ "Star"
/ \ |
"C" phase --.----.
/ \.------- neutral "tap" |240VAC
240VAC \ transformer
/ \ | |

/ \ | (+)120VAC |
.---------------- "B" phase 240VAC

The neutrals are actually grounded thru stakes at poles and connections to the incoming home copper [and very old lead]water supply pipes.
Happy Trails!
Kurt in k-k-Kanada - E-mail: :bl733 (at)

Hi Kurt
This is a wonderful description and I do hope anyone who survives the construction describes how it all sounds!
I'm not entirely sure if the δI/δt would be the same in Europe with our 50Hz AC, the 20% slower rise time might demand a change in those snubbers to keep it real. BTW European harmonisation means we've changed our official voltage from 240V to 230V, and the 220V countries are adjusted up. The countries just revised their tolerance so that the power supply companies continue supplying the same old voltage but call it 230V to eccentric tolerances.
Great to see the power engineer's term reactor to described an inductor, much better than the archaic choke so beloved of the audio world.
Happy Trails indeed,
Mark Wheeler

FleXy Rack
I made a Flexy-rack some years back, shortly after you put the DIY design on the TNT site. I made mine with four legs but I can't understand the debate over three or four legs and if you use three legs should there be one leg on one side or at the back. In my opinion four legs gives more stability and there is absolutely no problem in leveling the shelves as you just turn the nuts below each shelf a little one way or the other on the threaded legs, using a spirit level on each shelf in turn to get them all dead level.
With one leg at each corner you also avoid any danger of tipping. If you have three legs; A and B on one side and C in the middle of the opposite side and an amp with a very heavy transformer which comes outside the line A to C or B to C the weight could be enough to tip the rack.
As Lucio says; it's a DIY project so you are welcome to modify it in any way. Maybe three legs instead of four saves a little cost and work, but apart from the potential stability problem I mention above I think the appearance is better with four legs and you sure don't get into any problems with inserting components from the front or back and connecting cables.
I used plywood for the shelves: its easy to work with and more environmentally friendly than MDF. Does any one have experience of using composite shelving, ie, wood/metal sandwich or any other materials? Stone would be great for density but it puts the project out of the DIY category unless you can cut and drill stone at home!
Mike - E-mail: michael.shanahan (at)

Dear Mike, there are many marble/stone FleXy racks out there! You don't need to cut and drill marble or stone (granite?) at home, just ask your local supplier to do the job for you (it is not expensive). Some DIYers have used tempered glass or even Plexiglas® for their racks. Of course costs will go up, quite far from our initial intent of offering a very easy and inexpensive DIY rack design.
Happy listening!
Lucio Cadeddu

NOS vs. OS DAC's
Hi Nick,
I was just reading your piece on the ICON amp at TNT-audio and I noticed that you use the Monica3 as a source for testing of new amps. Like you I have a long and never-ending relationship with Monica and various other NOS DAC's.
However, to put my NOS DAC's in perspective I recently decided to try what I understand to be the best of what the DIY market has to offer in terms of over-sampling dac's: the Buffalo32S from Twistedpear Audio. After just a few weeks of listening I am quite confident that this DAC does everything much better than Monica, especially when used with attenuation in the digital domain.
Why don't you audition this DAC? There are so many NOS DAC reviews on TNT-audio but I don't recall any on DIY OS DAC's.
Just my two pennies. Sorry for filling up your mailbox.
Best regards,
Nicolai - E-mail: nicolai.sidenius (at)

Hi Nicolai,
Thanks for your interest in TNT.I am well aware of the Buffalo DAC, and how good it is, as a couple of my friends own one but there is a problem in getting one for review. Every time that the Buffalo is available it sells out very quickly so the supplier does not have spare samples for review. And of course they don't really need a review either. Not good for us but that's life! ;-)
Nick Whetstone

Miniwatt amplifier
Hi Nick,
very nice review on the MiniWatt. I own it and like it a lot. I would like to try using it with my KingRex preamp and I have a question that no one could answer me so far. Do I turn the MiniWatt volume all the way up and use the KingRex as the volume - or the other way around?
Thank you very much for your advice.
Best regards,
Markus - E-mail: mrufer (at)

Hi Markus,
I am always pleased to hear from readers who have had similar experiences with a piece of equipment that I have reviewed!
To answer your question, yes, I suggest that you use the MiniWatt with the volume control at maximum, and use the pre amp volume control to alter the volume. I had the MiniWatt set to maximum level, and was using the SB3 volume control to control the volume levels.
I hope that you also find the MiniWatt even better with the pre amp. And remember my advice about coupling it to a granite platform and 'treating' the valves.
Nick Whetstone

Vibrations war
Dear Mark:
Thanks for the suggestions. Though originally English I live in the rural US now and the racquet balls are $2.50 per can of three; squash balls and pumice stone are not so easy to find -- but I will have a try. Tweaking does become its own challenge!
I don't know if 'copperhead' BB pellets (copper coated steel shot\?product_id=9222903 are available in the UK but I have found these very effective in damping tray weights, much more so than either steel, lead shot or sand weights.
I do find it more than mildly irritating that something that the CD manufacturers could do at little cost, lining the steel cabinets with anti resonance tape, is left for a chance discovery.
Michael - E-mail: robinsonmf9at)

Hi Michael
My son tells me that copperhead BB pellets are available in the UK, at least by mail order. Lead I believe have long been unavailable, but I have a load of split shot in stock. I do find kiln dried sand good for hollow metal voids (like stand legs) and didn't like lead there, which sounded as if it slowed rhythm although this makes no sense in physics.

I couldn't find the right kind of pumice and a canadian reader sent them to me (thanks Yves), but I have since found them here too. Try druggists or chiropody suppliers.

I could not agree more about $1000 cd players being improved an order of magnitude by $5 of damping and installation time, it makes no sense for manufacturers to omit this obvious cost-benefit winner.

What I've never found in the UK is the popular US speaker-tweaker's favourite Mortite Caulk. Every UK product that looks like an equivalent I've tried has dried out or fallen off (or both), but US comics like Speaker Builder, Audio Amateur and AudioXpress constantly mention this wonder product.
Happy tweaking,
Mark Wheeler

Still on Miniwatt
Hello Nick,
I read with great pleasure your review of the little giant. I'm building my stereo system and frequently follow your reviews on TNT and was just wondering if you could give me an advise: concerning speakers for this amp, would you think the 8" Audio Nirvana would be the right pairing for this amp or should I go for something more "traditional" (and not DIY) like a 91db Indiana Line (hopefully you might know this italian manufacturer) or another good (?) 3-way bass-reflex speaker?
Thanks a lot,
Claudio - E-mail: claudio-a (at)

Hi Claudio,
I can't really comment on specific speakers unless I have experience of them. In my case, both the old MS Pageants, and the Hawthorne Audio Duets worked very well. I would guess that the Audio Nirvanas that you mention would make a suitable partner for the MiniWatt but can't give any guarantees of course!
Speaker matching for amplifiers like the MiniWatt is something that would have been much easier in the days when we all bought our hi-fi from the a local dealer who also sold speakers. Unfortunately, it is obviously not possible to do that when buying on-line although the cost-saving is substantial.
I'm sorry that I can't be of more help on this occasion, and can only wish you luck in finding a partner for the MiniWatt. Of course, hi-fi forums would be great places to ask!
Nick Whetstone

VTA apathy
Hi Mark,
I came across an article on the Michell Tecnoarm you wrote a few years back, and despite reading TNT constantly over the last few years certain things had passed me by.
I am specifically talking about the subject of VTA I have read much on this but as I used to own a Project Debut SE this was irrelevant. However I recently purchased an Acoustic Research Legend with a Linn Basik Plus tonearm (both older than me!), after lots of fettling I was happy with the sound and accepted the 'splashy' treble was 'in' my records until I bought a proper record cleaner.
Then I read one remark on 'tail down' arm setup and suddenly 2 seconds alleviated my annoyance I thought would cost me a couple of hundred pounds to sort.
As you can see this is just a long winded way of saying thanks for the advice and I wish I'd taken it earlier!
Stuart - E-mail: helmns (at)

Hi Stuart
I'm glad to read that you are a regular reader of TNT-audio; it makes it all worthwhile for us knowing that we have benefited at least 1 reader!
You have no doubt read Geoff Husband's pieces on VTA and have now discovered that it can make a difference. However, you have no doubt noticed that 'a little tail down' is good enough, and endless twiddling about from LP to LP is inaudible compared to small tracking force changes, which change the SRA (Stylus Rake Angle) much more dramatically that VTA changes. I'm really pleased that your reading of has increased your listening pleasure. That is all the reward we need at TNT.
Happy Listening
Mark Wheeler

Scythe SDA-1000
Hi Lucio!
I am trying to find the Scythe SDA1000 amp in USA or Europe visiting the enterprises they reccomend in their site and find only the info that this product isn't available or out of production.
After reading your very positive report I think that the amp would be avaiable in some countries like USA, Germany, UK, Canada and others, but the info I get is that the little amp is not more produced.
Did you know about this? Conversely if you have an adress where I can contact and buy one I will be very pleased.
I know it is not your guilt if the factory have discontinued this product, even after your test, if they have done that they must have a very good reason (Yamaha suspended the production of the chip or something like that).
Any news about that will be very apreciated.
Kindest regards,
Dario - E-mail: dariomelo38 (at)

Dear Dario,
it is true that all the stocks of the SDA1000 disappeared in few weeks after our review went online. We didn't expect such a devastating effect. And, of course, Scythe weren't prepared to that assault either. The good news is that in the meanwhile they've decided to completely redesign the amplifier (will be called SDA-1100) and offer it at the very same price (hear hear!). I have a pre-production sample here, together with a pair of two-way small loudspeakers, still from Scythe. A review will appear as soon as possible. The new amp has a completely redesigned main board, better volume pot and a now full-black aluminium cabinet.
Hence, stay tuned!
Lucio Cadeddu

Vibration control
Hello Mark
I have read the piece about the Absorb-Gel for tube damping, and am confused. I'll tell you what I want damping for, and ask you please to tell me what I need. I have a Marantz 8b amplifier, that uses 4 EL-34 tubes. Please make a recommendation. Also give price quote in dollars.
Carter - E-mail:

Hi Carter
The EL-34 is a pentode power valve using an octal base, unless my memory is mistaken (I have none in front of me). The Absorba Gel will not work as they only made them in B9a when i wrote the review. They have not contacted me since then to offer an Octal versions, which is a shame as Octal small signal valves are often more microphonic than their B9a counterparts. Power pentodes like the EL34 would benefit too, especially in guitar amplifiers, where they are deservedly popular.
You are lucky to have a superb classic in the Marantz 8b. I have not heard one.
Happy listening
Mark Wheeler

On MJ's article
I justed wanted to say thanks for writing a few fine lines, which very much say, what I feel about Michael Jackson deceasing - especially at this point of time in his career.
I have the feeling now that many or even most of all music lovers may feel the same - except they were real Jacko Fans. For those this is just a complete catastrophy I think.
Best regards,
Michael - E-mail: michael.rinus (at)

Dear Michael,
thanks for the feedback!
Lucio Cadeddu

TNT FleXy table
Hi David,
I've made one of your FleXy tables from your site which I have been very happy with the past few years. Now I'm upgrading to some Cyrus gear I am going to modify the rack to accommodate. I was wondering if you would recommend putting two legs at the front and one at the back, or the same configuration as the standard rack with one leg on one side and two on the other?
Chris - E-mail: chr_san (at)

Hi Chris,
I didn't design this personally, but use one myself in the standard 'sideways' configuration and have always thought it looks a little strange.
I don't know if physics or convenience of access to the rear of components was a key consideration for the original design. Having two legs on one side gives a bit more lateral stability, but hey this is DIY. You should configure the rack the way you want. I don't think it will make much difference.
But, I'll copy this note to our editor, in case he knows otherwise.
[The original FleXy design had two lateral legs to make rear access and connections way easier. Try it with a leg at the rear: plugging/unplugging cables will easily become a real nightmare :-) Definitely NOT recommended! LC]
David Holgate

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