Craig Sawyers

Check the T2 thread - chapter and verse in there. Counterfeit ones came via Dalbani in the UK. They replaced them without any quibble.

Check.

If you have a poke around on the T2 thread, I got under the skin of the battery while diagnosing multiple faults (caused by Chinese counterfeit 2SC3675's), including modelling it to work out the strategy for adjusting the original circuit's two pots. KG has updated and upgraded the circuit to get rid of the LED chain and JFET, but the operating principle is the same. In brief: Q4/Q5 are a long tailed pair that compare 10V from the reference with the voltage set on RV2. Q6/Q7 are DC level shifters to keep Q4, Q5 and Q8 inside the VceBR voltage at which they blow up. Q8 is a Widlar current mirror. This has a very high impedance, and is there to increase the gain of the long tailed pair - standard practice in IC's and high quality discrete designs. As you adjust RV1, the current through Q4 and Q5 is forced to be equal by the current mirror - so both increase in step. The output voltage is taken from Q8B - which is electrically equivalent to taking it from the collector of Q5 if we disregard the level shifter.

Hokay - I got some numbers from Charcroft. Note that 6R34 and 169K are not available, since Vishay do not supply untrimmed stock to cover those values. The costs below refer to the VSMP series http://www.charcroft.com/site/pdf/data/Charcroft.VSMP.04.09.Is4.pdf and the SCAR series http://www.charcroft.com/site/pdf/data/Charcroft.SCAR.04.09.Is2.pdf both in 2512 size. Tolerance is 1%, and MOQ is 10 off each value. Tax at 20% would have to be added too. Delivery is around 10-12 weeks. 255R to 16K9, £9.88 each 38K3, £10.52 each 82K5, £11.16 each The 1206 size VSMP are cheaper, but restricted to <25K 255R to 3K65, £6.57 6k04 to 16K9, £8.30 That puts the total cost (including tax) for a stereo attenuator using 2512 size at £360, or balanced at twice that. The 6R34 and 196K would have to come from elsewhere. The 1206 option is cheaper at £235 for stereo, but the 6R34, 38K3, 82K5 and 169K would have be alternative resistors. Multiply by whatever factor is appropriate for local currencies. What is the interest in this level of crazyness? Either on list or via PM.

Yeah - we can be a feisty bunch for sure, but I concur with deep's second paragraph.

Dickens' Martin Chuzzlewit on the Kindle

Well it is actually three days - Thursday, first empty garage and coat of expoxy floor paint. Friday second coat. Today first coat of masonary paint on the cinderblock (breezeblock in the UK) walls. All preparatory to moving all my woodworking gear from the cupboard-sized garden shed to the garage - and then getting on with some serious cabinet making. Knackered. Compensating by drinking - hic.

Local Oxfordshire brew called Dr Hexter's Healer. And very good too, being chased by an unholy amount of sherry, looking forward to some Australian red with the lamb - and I'll see where I get to from there later on. Could be liqueuer of some description or a single malt. Or both

OK - Charcroft said that they had good stock on the untrimmed Vishay 1206 Z-foil. I've just mailed them to ask for the quote to include 1206 too. Larger physical size resistors would have a lead time. After talking to them, it turns out that a major driver of cost is tolerance - so I've asked for 1% - the 1% ones that I have measured are all better than 0.1% (0.009dB nominal, not counting statistics. Even if you do, it will be a rootN thing. So maximum number of resistors = 17, so the maximum error due to 0.1% tolerance is <0.04dB. At -128dB, so who cares.

Good man! It sure is a helluva first (part one of two) episode for this series.

I've been working with some z-foils as part of another project - free issued by the company I'm working with on this one. Very interesting. I've been using both SM and leaded versions. These are nominally 1% tolerance, but actually measure better than 0.1% (ie better than my Fluke 87V can resolve) - which is good. These came from Charcroft, from whom I am still awaiting a quote for the attenuator resistors. The SM ones have the resistance value printed on the top of the expoxy case. The leaded ones have absolutely no markings at all - the only way to check value is with a DVM. I must admit it is a bit daunting to look at a very small pile of resistors and think of the monetary value of them....

I think that Kevin has made the board as flexible as possible for widest resistor choice. Regarding what resistors, I absolutely agree that the super-expensive ones will probably only be justified with equally high quality amps. Such as the T2 and KG Blowtorch clone to name two. So regular few cent metal film resistors are probably just hunky dory for the majority of applications. FWIW I've put myself in for two built ones and four bare boards - and I expect the built ones will be made with the resistors in the BOM - ie regular metal film. I will probably do something moderately crazy with the other four for the T2 or similar.

The problem with multi-layer boards is not with shorts, but with imperfect through-hole plating to internal layers. So the problem is opens, not shorts. The reason that the best possible resistors are important is that there are so many of the buggers in an R/2R ladder, and the number change as you adjust the volume. So yeah - it looks like financial madness, and probably only strictly necessary in the very best high resolution amps - but let's see what Charcroft come up with. At the end of the day this will be similar in cost to an RK50.

I've been talking to Charcroft, and asked them to quote for a set of Z-foil 10k attenuator resistors in either 2512 or 2010 size. There is a good chance that they can trim down to 6R34 and up to 169K. I've asked them to quote for one set, and ten sets. Basically they hand trim to order in darkest Wales - they buy the basic chips from Vishay. Same game with the leaded Z-foils too. I'll let you all know when I know the awful financial truth.

Happy 50th Ethan! Have a beer on me.

Yeah. I've seen this in Arts and Crafts movement furniture. In that case (a large dining table in Cheltenham's museum) the bowties were of different woods and sizes and used partly as a decorative feature apart from the functional.

Well, yes - the Z-foil resistors with leads from (eg) Parts Connexion are $16 to $17 each. So the SM versions are likely to be about that too. But if this attenuator is to match up to the KG Blowtorch, it's gonna need some pretty fancy resistors. I'll get a quote and see how nuts this option is likely to be.

This http://www.charcroft.com/site/pdf/data/Charcroft.SCAR.04.09.Is2.pdf could be an interesting resistor option - the SM form of the Vishay/Charcroft Z-foil resistors. Not sure about availability though. Unless anyone knows of an easy source already, I'll make enquiries.

Yours too, Dusty? Thought it was just mine. Something something something Dark Side.

The stuff I use on copper is a Kester product called Copper-nu. Actually used in PCB production, but is NASA approved for cleaning copper cooling braids for satellites. Takes oxidised or sulphided copper and very quickly produces pink, chemically clean copper. Also works on brass. Kester also do Nickel-nu, but I've never tried that. Also I tend to use Caig De-Oxit and/or Pro-gold. Deoxit is used/recommended by Tektronix and Fluke for minimising switch contact resistance, which kind of says all you need.

^^^ Now that is some serious lurking - 2 1/2 years on the list and two posts.

It's Cardas, so it needs to be a Golden Ratio length

I've just bought one (with 3G, and natty case with light). I am totally smitten with it - what a bewilderingly marvellous product. Just stuffed on the complete works of Dickens. Next it's Trollope and Hardy.

Just catching up with the threads. Biwiring is a semi-religeous thing - there are strong views for and against. When I had speakers with separate binding posts for bass and treble speakers, I used to biwire, and swore I could hear a difference, although I did not have a physical model to give a remote inkling why. Always troubling. For me anyway. Now I listen to a pair of 1964 vintage QUAD ESL, which have a single pair of connections that go straight into the transformer. So there is absolutely no way that I can frig around with biwiring - which solves the do or don't biwire problem perfectly. I have a semi-stalled dipole sub project to add some oomph to the ESL's, following Siegfried Linkwitz's approach. That definitely needs an electronic crossover. The sub amp is a C-audio GB602 600Wpc professional sound reinforcement amp, courtesy of eBay at £150.

Check back through the thread - I posted some UK suppliers that I used which would have no problems shipping to Denmark