i'm on a roll... the kgsshv

[mypasswordis]

still a douche i see

if the spacing is a real issue then some solutions can be quite DIY - nail polish or RTV Silicone and and bending the source/collector lead out of line for greater pcb pad spacing isn't going to kill the project

Creepage and clearance is all to do with product safety. Where the regulations apply is when a hazardous condition can arise through breakdown or shorts - for example around a power transformer, either conventional or switching, or in common-mode inductors in power line filters for example. This is particularly important because power lines are subject to high voltage transients through industrial users, power line fault handling, and environmental disturbance (lightning, solar weather etc). Creepage and clearance has to take these conditions into account.

Internal parts in which electrical breakdown does not give rise to an external hazard condition (such as via the chassis, exposed connectors or cabling) are not covered. This thinking is well considered in the European Low Voltage Directive Electrical Safety: Low Voltage Directive (LVD) - Electrical engineering - Enterprise and Industry

In any event, the lead spacing between the wide part of the pins on a TO220 varies considerably depending on the device. Specification and caliper measurement on three devices rated at 800-900V have minimum interlead spacing between 1.02mm (0.040") and 1.35mm (0.053"). The highest voltage device, a 2SA4686A with 1200V Vceo, has 1.65mm (0.065"). In fact there is a lot of evidence that semiconductor manufacturers know about all this, and chose a lead frame that takes device voltage handling into account.

Air breakdown is 3kV/mm, and so these devices are all comfortably derated, with the absolute maximum device voltage being between a third and a quarter of the air breakdown voltage.

If you are still concerned, you can go over the leads, package entry and PCB pads with a conformal coating pen - a bit like solder resist, apart from the fact that you can solder through this stuff if you need to do a repair.

[Craig Sawyers]

if the spacing is a real issue then some solutions can be quite DIY - nail polish or RTV Silicone and and bending the source/collector lead out of line for greater pcb pad spacing isn't going to kill the project

You will note that I actually said "If you are still concerned, you can go over the leads, package entry and PCB pads with a conformal coating pen - a bit like solder resist, apart from the fact that you can solder through this stuff if you need to do a repair"

So what precisely is your point? Specifc RTV (Room Temperature Vulcanising) formulations - and there are very many - have an application on very high voltage stuff, or on multi kV voltage multipliers in TV's and oscillosopes, but looks like a pig's breakfast on something like an electrostatic headphone amp. Nail polish is based on a chemical concoction of agressive solvents (like toluene, butyl acetate, ethyl acetate etc), different from one manufacturer to another, that I would let nowhere near circuit board solder resist, let alone passive components, or even semiconductor packages. I also have no idea what it's high voltage insulation properties are - I seriously doubt that anyone has measured it, and the manufacturers for sure won't know. Back when I was 16 I used it for masking simple self-etched circuit boards, but that is about the only electronic use for it IMNSHO.

If you are going to insulate package lead outs and PCB pads - which is fine and dandy - , use the correct material for the job - it is called conformal coating - and is available from any decent supplier (Mouser, Farnell, RS components, etc etc etc). Available in a spray can, a can of liquid for use with a spray gun, or as a pen for local application.

[kevin gilmore]

Excessive amounts of tobacco seem to do way more harm to high voltage electrostatic

amps than dust or condensation. Especially when combined with dust, the combo is

definitely conductive.

Many of the original T2's toasted the power transformers which were way underrated

for power.

Micromass (now owned by Waters) of the UK continues to sell multi-hundred killobuck

instruments and do things with transistors at 5kv that i would not do at 1kv. No conformal

coatings, no rtv, no nothing. The stuff manages to live thru its expected lifetime of about 8 years.

And in an industrial environment thats full of all sorts of nasties.

If it bothers you, buy a can of DAG and paint it on the transistor leads after you solder them

in. The stuff is good for about 25kv.

[luvdunhill]

jcx: how many pieces of audio gear have you built from start to finish? I remember seeing that overclocked IC thing from many moons ago, any more recent build pics that we can look at and aspire to create?

[jcx]

I love designing electronics - building not so much - you can see my many sims over at diyAudio that I do to illustrate audio applicable circuit theory - I see it like doing crossword puzzles

working in a corporate environment with other engineers, meeting safety, technical performance goals measured by a independent test group gives me a great respect for the depth of institutional knowledge that most audio hackers seem to not even realize exists

I have designed Scientific/Industrial measurement products that have sold in the thousands with ps, sw, packaging engineers handling their parts of the projects, technicians doing the BOM. parts ordering, usually I sat with outside consultants for the PCB layout

I did often stuff the prototypes myself before finer pitch smt became so unavoidable - for some reason I could never communicate my desire for incremental build/test to the techs - and certainly debugging goes faster tack soldering on my mods in front of the scope

I have done everything myself from blank page design to packaged headphone amp as you've seen which involved ~1/2 dozen "new slate" prototypes (mostly just one channel in point-to-point), I'm in awe of people like Kevin's energy/drive for building "finished" amps

personally I don't have much patience for "phone tag", reps insisting on "being in the loop", tracking down vendors and getting them to sell me hobbyist quantities of obscure parts

and I know my machine shop skills are quite basic

I do have a +/-700 V supply on a nice 1/4" phenolic base, a tube of IXYS IXTP01N100, tray of AAvid heatsinks that I haven't done anything with in months - I keep over thinking about another design tweak for the amp circuitry rather than just building up a few options - although at 4 channels for 2 H-bridges I would want to layout a pcb even for prototyping - if can remember how to run Eagle

for an instance of time wasting over-analysis: a "non-switching" Class AB ES headphone amp really wouldn't be "that bad" when you think about the differences working into pure (and tiny) Capacitive load brings - biased for ~ -10dB fullscale push-pull Class A it would always be Class A for the ~3 KHz "music" power bandwidth, the switching artifacts would occur near the slope reversals of the peaks rather than at low levels near zero crossing and get full advantage of temporal masking

the savings in heatsinking and power supply weighed against dealing with order of 10 mA nonlinear current in ps and gnd planes seems worthwhile to me

but I realize that my preferred high feedback approach, op amps of any sort are very unfashionable in audio - despite my confidence that I can advance SOTA in meaningful complex multitone IMD performance on such a platform I doubt I could get a fair listen from those convinced that Class A "simple circuits" are the only way to go in High End audio - nor do I really believe 100x lower distortion numbers would be audibly "better"

but I do hope to build up a SS ES headphone amp of my own design - eventually - hence my interest in these threads

[Craig Sawyers]

Excessive amounts of tobacco seem to do way more harm to high voltage electrostatic

amps than dust or condensation. Especially when combined with dust, the combo is

definitely conductive.

The other real killer in pro-audio gear, which is usually fan cooled and sucks in large amounts of air, is the smoke that is used for stage effects. That puts a layer of mildly corrosive goop all over the inside that buggers circuit boards and puts a conductive layer over everything.

[Craig Sawyers]

Many of the original T2's toasted the power transformers which were way underrated

for power.

Surprising how often transformers are underrated in professionally designed equipment. The calculation is simple for something like a heater transformer, since the secondary rms current rating is just the heater current. But with capacitor-filtered DC, there is a factor to be taken into account as a result of the short pulse-like nature of the charging current. This was originally analyzed by Schade in 1943 ("Analysis of Rectifier Operation", Proc IRE July 1943, 341-361) and resulted in a series of normalised graphical relations, which are still useful to this day. But whatever method of calculation you use (for example freeware PSU Designer II from PSUD2 ), the rms current rating of the transformer needs to be typically 2 to 4 times higher than the dc current drain. The exact factor depends on the capacitor size, the transformer effective DC resistance, the DC current, and the mains frequency.

Incidentally, isn't DAG (Deflocculated Acheson Graphite) conductive? Or is there another meaning to DAG that I've missed?

[justin]

Surprising how often transformers are underrated in professionally designed equipment. The calculation is simple for something like a heater transformer, since the secondary rms current rating is just the heater current. But with capacitor-filtered DC, there is a factor to be taken into account as a result of the short pulse-like nature of the charging current. This was originally analyzed by Schade in 1943 ("Analysis of Rectifier Operation", Proc IRE July 1943, 341-361) and resulted in a series of normalised graphical relations, which are still useful to this day. But whatever method of calculation you use (for example freeware PSU Designer II from PSUD2 ), the rms current rating of the transformer needs to be typically 2 to 4 times higher than the dc current drain. The exact factor depends on the capacitor size, the transformer effective DC resistance, the DC current, and the mains frequency.

Incidentally, isn't DAG (Deflocculated Acheson Graphite) conductive? Or is there another meaning to DAG that I've missed?

i've ordered the "same" transformer from 3 different companies and received 3 extremely different products. usually 2 of them will not work properly.

[Craig Sawyers]

i've ordered the "same" transformer from 3 different companies and received 3 extremely different products. usually 2 of them will not work properly.

That sounds absolutely typical, Justin. Either they overheat, have the wrong voltage under load, or hum. Or all three.

I get mine from Paul Houlden, who used to be TD of Avel Lindberg, then of Holden and Fisher, the founder of Chameleon, and has designed toroidal transformers for most high end audio and pro-audio manufacturers (Krell etc). I work with him to develop a spec, and then he hand delivers them. There are three of his in my T2.

[justin]

That sounds absolutely typical, Justin. Either they overheat, have the wrong voltage under load, or hum. Or all three. .

you forgot one. not adding high-voltage insulation between the secondary windings because the enamel is "rated for 800V" every transformer was dying after 1 week of use. drove me nuts trying to figure it out.

[kevin gilmore]

Actually the DAG is from my picture tube days at zenith. Yep, thats the conductive stuff

we painted the insides of the bells with. DAG is black. I was thinking about the RED

stuff which is definitely a great insulator. Don't remember what we used to call that stuff,

although i do remember the slang term.

[Craig Sawyers]

you forgot one. not adding high-voltage insulation between the secondary windings because the enamel is "rated for 800V" every transformer was dying after 1 week of use. drove me nuts trying to figure it out.

Yup. Forgot that one. My T2 ones have insulation barriers between all windings - including the heater ones because two of them float at -500V. Although the wire insulation is OK in principle, a combination of winding tension, pressure high points, and then friction as the transformer heats and cools makes it last the square root of bugger all time in practice. Same principle is at play with interwinding screens - they absolutely need double insulation barriers on either side otherwise the thermal/friction/tension will always end up with shorts to windings.

[Craig Sawyers]

Actually the DAG is from my picture tube days at zenith. Yep, thats the conductive stuff

we painted the insides of the bells with. DAG is black. I was thinking about the RED

stuff which is definitely a great insulator. Don't remember what we used to call that stuff,

although i do remember the slang term.

Ah - it is Red-X corona dope. A super high voltage conformal coating. The Mr Fixit for balky 7000 series Tek DC restoration and HT supplies (some of which run at 21kV). In the olden days, Tek used a black version of this on the ceramic strips holding the voltage multiplier components.

[Craig Sawyers]

Yes - here it is http://www.alliedelec.com/Images/Products/Datasheets/BM/GC_ELECTRONICS/796-2068.PDF . The red stuff is 1700V/mil, and the black is 3800V/mil.

[Knuckledragger]

The other real killer in pro-audio gear, which is usually fan cooled and sucks in large amounts of air, is the smoke that is used for stage effects. That puts a layer of mildly corrosive goop all over the inside that buggers circuit boards and puts a conductive layer over everything.

I have dealt with this problem on several occasions. Not with pro audio equipment, but with pro lighting gear. Virtually all halogen and arc-bulb club lights have very high CFM fans blowing directly on to the bulb and PCB. I use haze (atomized glycol, a physical reaction, much smaller particles) and not fog (thermal reaction, comparatively huge particles). In my utterly non-scientific experience, extended exposure to haze does less damage to equipment than a similar exposure to fog. That said, I have a small graveyard of blinkenlights that no longer function because of PCB issues. I'm really liking my new LED fixtures which generate almost no heat and don't use fans. </utterly off topic>

[Kerry]

Surprising how often transformers are underrated in professionally designed equipment. The calculation is simple for something like a heater transformer, since the secondary rms current rating is just the heater current. But with capacitor-filtered DC, there is a factor to be taken into account as a result of the short pulse-like nature of the charging current. This was originally analyzed by Schade in 1943 ("Analysis of Rectifier Operation", Proc IRE July 1943, 341-361) and resulted in a series of normalised graphical relations, which are still useful to this day. But whatever method of calculation you use (for example freeware PSU Designer II from PSUD2 ), the rms current rating of the transformer needs to be typically 2 to 4 times higher than the dc current drain. The exact factor depends on the capacitor size, the transformer effective DC resistance, the DC current, and the mains frequency.

...

Craig - Thanks for this post.

I'm still a bit unclear in the calculation. I downloaded the duncan amps PSU Designer. I basically got similar results in LTSpice. On an active battery regulator in LTSpice with a 425V output, DC current draw of about 50mA and front end 340uF capacitance I'm seeing spikes of about 2.5A. I thought maybe to divide by 1.414 to get an RMS value, but that is still 1.77A. You mentioned needing to use 2 - 4 times the DC requirements (which seems right to me). If this is a pure average then I can approximate it around 3x - 4x.

I did a quick scan on the web (looking up schade curves), but didn't see what I was looking for yet. I thought I'd lazy and ask.

[Craig Sawyers]

Craig - Thanks for this post.

I'm still a bit unclear in the calculation. I downloaded the duncan amps PSU Designer. I basically got similar results in LTSpice. On an active battery regulator in LTSpice with a 425V output, DC current draw of about 50mA and front end 340uF capacitance I'm seeing spikes of about 2.5A. I thought maybe to divide by 1.414 to get an RMS value, but that is still 1.77A. You mentioned needing to use 2 - 4 times the DC requirements (which seems right to me). If this is a pure average then I can approximate it around 3x - 4x.

I did a quick scan on the web (looking up schade curves), but didn't see what I was looking for yet. I thought I'd lazy and ask.

Have a look at the PSU Designer line that is the transformer secondary rms current (listed usually I(T1), scroll along to the rms column). You will see that it is a factor of several times (around three) greater than DC current. That factor is precisely the same as that given using Schade's graphical method. The relevant graphs are here Electronic Transformers - Rectifiers with Capacitor-Input Filters . The one you want is called Figure 52 on that web page, top graph line. For a full wave rectifier, "n" = 1 (Schade's method also takes care of voltage multipliers, which have different integer values of n)

[Kerry]

Thanks Craig - I see the value now. This solves one of the mysteries for me. LTSpice is also supposed to have an RMS calculator (Ctrl + right mouse), but it is not working for me.

[Craig Sawyers]

I love designing electronics - building not so much - you can see my many sims over at diyAudio that I do to illustrate audio applicable circuit theory - I see it like doing crossword puzzles

The building is the fun of the chase. I can't understand desiging stuff for the hell of it without reducing it to practice and testing the design in real hardware. It is a bit like designing a bridge using CAD and FE analysis but not knowing whether the design is fit for purpose. Or am I just being wierd?

[kevin gilmore]

Simulation is a great way to find out if you are in the ballpark or not.

If the simulation says it won't work, then it is highly likely that in practice

it reallly will NOT work, and sometimes in spectacular ways.

But taking a successful simulation, producing a board, and getting the

thing to perform as designed is much tougher. Especially with

killovolts of AC flying around at frequencies that can sustain a continuous

arc.

[Lil' Knight]

Stopped by my friend's house today to pick up the PCBs and transformer built by him. Looked great so far, despite the messed-up PCB's color. I'll try to populate the resistors tomorrow, when my gf is busy at the mall.

[DouglasQuaid]

Stopped by my friend's house today to pick up the PCBs and transformer built by him. Looked great so far, despite the messed-up PCB's color. I'll try to populate the resistors tomorrow, when my gf is busy at the mall.

Blue boards add an extra bit of class. If anyone at a meet asks, you could always tell them your boards were coated with a special Gilmore-approved blue dielectric that reduces ultraviolet reflections that might leak through the enclosure and abnormally bias the output transistors.

[livewire]

Stopped by my friend's house today to pick up the PCBs and transformer built by him. Looked great so far, despite the messed-up PCB's color. I'll try to populate the resistors tomorrow, when my gf is busy at the mall.

@Lil' Knight - So you were able to fab some boards, good luck with your build!

What's the second power supply board for? In case you fry the first one like I did?

[Kerry]

That's a nice friend. Very nice work on the boards and transforms.

[livewire]

My Mouser order of repair parts is arriving tomorrow.

Now I can put humpty psu back together and fire it up.

So far, it looks like I've cooked the 2SC3381 and the

2SC4686A on the negative supply rail. Not too bad.

Not sure yet about the IXYS sand upstream on that side.

They dont compare well to the devices on the positive side.

Wont know until I've soldered in the new bipolar parts.

I bought the new IXYS sand just in case I need them.

Wasnt much, about an extra seven bucks.

I'd rather not have to place another order with Mouser.

Everything else checks out fine, diodes, resistors, caps, etc.

I also had an arc flash on the +15 VR. It still works but

doesnt regulate too well. So that is getting replaced also.

It was due to the cheesy, thin theramsil pad chafing through

from a sharp edge on the TO220 mounting lug. Maybe I over torqued it?

Aint gonna happen again. Bought some heavy duty insulator pad material.

Fiberglass reinforced.