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Old 27th February 2004, 12:49 PM   #121
tcpip is offline tcpip  India
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Default C0G caps

Quote:
Originally posted by roadkill
.... They also have C0G grade ceramic capacitors, useful for miller-compensation caps of power amps. C0G dielectric does not suffer from capacitance change with applied voltage or temperature....
Is this grade of cap easily available elsewhere? I saw it on the RS India Website after reading your post (check stock numbers 211 4971 and 264 4652), but don't know how much they'll charge. They have good metal oxide film power resistors for Rs.9 (2W) and Rs.16 (3W) each... these prices compare well with prices abroad, so not everything is untouchable. Does C0G cap imply 5% tolerance? Wherever I've seen them, they seem to have this tolerance. Does X7R mean 10% tolerance? Do we need to bother about these differences in audio circuits (not the tolerance, but the tempco).

While building the Rod Elliott amp, I once encountered one ceramic cap of 500V rating. I don't know why he asked for such a high rating... I've written to him, asking him. Is this in any way related to the stability requirements of the Miller cap? Since I don't understand any of these things of amp design, I'm totally lost.
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Old 27th February 2004, 03:24 PM   #122
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Great going guys...
true to the nick 'tcpip', tarun this has really expanded into a network...and great support from others...
i wish i could contribute...no excuses though...

here are bits and pieces of information i could gather..

Corrson:

Ok for all those interested here's the list of drivers that corrson stocks...

P17WJ00-08
TC14WG49-08
TC18WG49-08
D27AG05-06
D25AG35-06
D25ASG35

Please refrain yourselves from ordering anything now
there has been minor hickups, Vivek and myself are getting it sorted out...will keep u posted of the developments.

Regarding enclosures:
Would it be possible to get enclosures done from these readymade aluminium channels available. If possible i'll try drafting some designs. I think it can be done. I have trouble approaching these aluminium fabricators. Language problem for i dont understand the local language and it goes real crazy...
And am sure we can locate some anodizers and powder coaters...some of them are there along NH7 and should be in plenty in other industrial estates like peenya and all. IF some one who knows the local language can accompany me, probably we can go knocking at those doors.

There are two agencies one is called arrow electronics..i dont remember the exact names, will have to dig up some old business-cards. We used to get all exotic components like some dacs, recievers, opamps etc thru these ppl and another lot from universal. It seems there are couple of shops in SP road which sells stuff like crystal SPDIF recievers, ADI DACs, ADC's, FPGA'a, OMRON relays etc. will find out the details.
For boards, in small quanities there is this place called Hi-Q, they can make u any kind of board...If we plan to have a group buy probably we can consider this option. They are heavily mechanised and 'pricey' but can get those boards done to whatever specs...6 or 8 mil tracks, SOIC's TQFP anything, single to multilayer burried vias...all kinds of them...They used to do PCB prototyping for us. But is not an economic option for small quanities..say one or two boards. TQFP and other fine pitch component soldering is very difficult to be executed manually.and that too by a soldering iron.especially resoldering...first of all the pins are too fragile and close...there is this place called peninsula Electronics who used to do the assmbly...U give them the bom and they do the rest...!Again not a viable option if its not 20 -50 boards...But i'll try to get the details from them. Our requirements(at work) always used to be some high end boards, but still in small quantities..thats y i am sure that these guys can take small orders...but will it balance the overheads involved is something to be looked at.

Ok
i really want to try out the ensloures using Aluminium channels and acrylic. If any one from bangalore has any leads on this please let me know. I've a feeling that the kind of enclosures etc we are looking at, can be easily done by basic machines. Probably the requirement for the numeric controlled species can easily be done away with and roadkill can save his job
what say ppl..?

On Sjp Road, there is a place that sells copper and brass bars. In case some one wants to try something really exotic with these...

And i'm really sorry for the wholly disorganised post..had to hurry

Thanks
ajju.
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Old 27th February 2004, 05:45 PM   #123
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C0G caps: the advantage these provide over "normal" X7R/Y5V/Z5U caps is that the capacitance does not vary with the following:

1) humidity
2) temperature
3) applied DC bias
4) soldering temperature

This usually matters in RF circuits and where the absolute capacitance is important. It's useful in an audio context mostly for Miller compensation caps and for active filters (which is what I'm using them for). The effect of the capacitance varying with applied voltage is thought to be one cause of "capacitor sound". They all come in 5% tolerance (see SMDin's website). Unfortunately, they aren't available in values greater than about 10 nF. Beyond that, film caps are probably the best bet. I remember I had this delusion that someone on Lamington road will stock 5% and 1% film caps, and getting laughed out of every shop! Tempco matters most when the caps are used in active filters. Some filter topologies (I believe the Linkwitz is one of them) are very sensitive to component tolerance, so the response can go crazy as the temp changes. With miller caps, usually the values are chosen a bit bigger than that required to stabilize an amp (for a better phase margin), so temperature-induced variation shouldn't matter too much. Still, you can counter that argument with "why take a chance?"

I'm not quite sure why Mr. Elliot wants you to use a 500V cap. Maybe he meant mica caps, which I've not been able to locate anywhere. Best I could find are polystyrene caps (available at Universal), which I used for Miller compensating a MOSFET power amp. MOSFETs used are IRFP240/IRFP9240, available at Chandan Electronics (opposite Vishal Electronics, I believe there is another shop called Chandan). Cost me a pretty penny (400 bucks a pair).

Tarun, the IEC sockets I bought incorporate an EMI filter as well as a fuse holder. They're quite big, encased in metal for shielding. This should filter out junk on the power lines if it has a good earth connection. They're from Elcom, and cost quite a bit (~Rs. 120). I bought them from Mumbai, "Precious Electronics" (a Tolkein fan, maybe? )

PCBs: the laser print to bromide method is what my PCB guy uses. He returns the bromides too. I wonder if it really makes a diff if it's on normal A4 copier paper or on butter paper.

My circuits: No, these aren't from Elektor, they're the result of browsing through Analog Devices website. They have this amazing device called the AD1954 SigmaDSP: a DSP core with a pre-programmed ROM to implement a 7-band EQ, compressor (good when watching DVDs at night), volume, subwoofer crossover and de-emphasis. It takes in left-justified, right-justified or I2S data, and includes three DACs for left, right and sub. I'm using two of these to implement a 4.1 system. Wish I could attach an image of the board, but it's huge (needs at least 200 dpi when exporting from Eagle to differentiate b/w the tracks and the ground plane). And in case you're wondering, I got the chips from ADI as samples. I mailed the ADI sales rep asking if I'd be able to buy two for prototyping, he said ask for samples. In hindsight, I wish I could have got a more general purpose DSP like the SHARC. I use them at work, so I have all the programming tools. Anyway, the sample rate converter is an AD1892 with an SPDIF input. I plan to run the input to my sound card (SB Live, which can put out all six channels as independent SPDIF signals).

ajju, I'm interested in finding out about DACs, if you have any leads, pass them on. Arrow probably has an MOQ, so we could order together to beat that? I'm also considering an "Elektor-style" cabinet (refer the covers of issues where they present the Crescendo), the case side walls are made of extrusions with front, back, top and bottom bolted on. I've already bought the extrusions from Shri Maruthi Metals (lead provided by Ashwin, thanks!). At my old workplace, we used to give Hi-Q 8 layer boards with BGAs. They can do it, but the costs wll be high. We used to give them prototype boards (ie, just two boards), so quantity is not a problem. If I remember right, the quote for a production run of two 8-layer cPCI sized boards (230x166 mm) was Rs. 12000. This included impedance control, silkscreening, 6 mil tracks... we won't need that kinda stuff, so I'm guessing a two layer non-impedance-controlled, masked board would be ~ Rs. 2k. The tech assistant at work solders TQFPs like he's been doing it since childhood... I guess if the board is soldermasked, it's not so hard. See Numbnut's guide to soldering (funny!) One thing he uses which I've not been able to find is very fine desolder braid. I can add a step to his guide, to coat the pads with liquid soldering flux. Helps if the board is dirty.

Don't know how many of you will be interested by this... Ankit Corporation stocks graphic LCDs which don't have any onboard controllers. They're big, and fairly cheap. I bought a 240x64 display with an EL backlight for Rs. 700. However, you have to make the controller yourself. Initially, I was hoping to use a CPLD, but gave up when I couldn't find one (help, anyone?). I later programmed an Atmel MCU to do this, and it works fine. The MCU also does some processing, so it can receive commands to draw lines, boxes, text, etc, not a string of "put pixel here" commands. If anyone's interested, I can send them the circuit used, including PCB layout. I will be using this in an amp (no, I'm not crazy!)

I have a doubt: what are "Neutrik Speakon" connectors used for? I'm guessing for speakers... I use binding posts from MX, which come in a round plastic cup. Gold flashed, seem to be of reasonable quality, 50 bucks each.

Apologies for the size of this post.
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Old 28th February 2004, 12:39 AM   #124
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Default Neutrik Speakons

Roadkill,

Quote:
I have a doubt: what are "Neutrik Speakon" connectors used for? I'm guessing for speakers... I use binding posts from MX, which come in a round plastic cup. Gold flashed, seem to be of reasonable quality, 50 bucks each. by Roadkill

Yes, u're right, for speakers and amps. This is a live sound connector, that facilitates a more convenient way to jack up the hi current speaker terminals so that it saves time with live sound installation. Very revolutionary new plug. I used binding posts earlier, and work OK and I still use them for my DIY pro-audio gear in my living room but like I said again live sound is a bit different.

Patrick
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Old 28th February 2004, 02:36 AM   #125
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Default COG caps

The stability of the capacitance with applied voltage is the biggest advantage of COG caps when used as VAS compensation. The modulation of the miller capacitance is minimized thus reducing distortion.

Some times a cascode stage is added to the VAS stage to do the same thing.

Angshu
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Old 28th February 2004, 02:24 PM   #126
tcpip is offline tcpip  India
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Default Rod Elliott's high-voltage ceramic cap

I got Rod's answer. He says that it's well known that a ceramic cap goes non-linear when it approaches its voltage rating, let alone exceed it. So, using a ceramic cap of very high voltage rating keeps the cap well within its linear range. And he finished by saying that if I can find it, I should use polystyrene: "still by far the best (IMO)."

How easy or difficult is it to find polystyrene caps of, say 100V rating and small values?

Tarun
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Old 28th February 2004, 02:33 PM   #127
tcpip is offline tcpip  India
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Default Speakons

Quote:
Originally posted by roadkill
I have a doubt: what are "Neutrik Speakon" connectors used for? I'm guessing for speakers... I use binding posts from MX, which come in a round plastic cup. Gold flashed, seem to be of reasonable quality, 50 bucks each.
Me too. But normal binding posts either have no locking mechanism (banana plugs) or have locking but can't be easily plugged in or removed (spade connectors fixed by screws). As far as I can make out, Speakons and other similar connectors have the following features:
  • High current rating (16A or more): good enough for speakers
  • Very low impedance: less than 100mOhms. Good for low voltage high-current apps
  • Locking of some form: no accidental disconnection
  • Easy plugging and unplugging without any unscrewing, shorting, etc
  • Usually, for 3-pole connectors, the earth connection is made before the other connections, so that you can plug and unplug safely when it's live
  • Insulating body (which most banana plugs don't have)

I found quite a few other connectors which have these properties on the RS site. I'm thinking of using some of the cheaper varieties of these to connect an outboard power transformer to multiple amp chassis. Lowish voltage (+/-50V), high current, low contact impedance, high reliability, no accidental disconnection, and three cores in one plug. Very handy, I thought.
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Old 28th February 2004, 02:58 PM   #128
gjo is offline gjo  India
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Interesting posts guys, kdeep it up. I am also interested in some things..MRF Vapocure guy ,Kaveri Coats (P) Ltd near Lingarajapuram did a nice wrinkly coating for my AKSA enclosure, looks better than powder coating. This guy is an expert and does some cars for Vijay Mallya, BTW!.

Tarun I will also be interested in some knobs. Plan to upgrade my new tube preamp volume control to a Noble stepped one, may need a decent knob. Once you get your set, let us know the quantities and pricing with the photo.

I am interested in a source for tubes, I plan to get a spare matched quad of Svetlana EL 34s next month from the US, for my power amp but if these are locally available, then I may want to look at it.

George
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Old 28th February 2004, 04:24 PM   #129
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Default About Neutrik Speakons

Quote:
Me too. But normal binding posts either have no locking mechanism (banana plugs) or have locking but can't be easily plugged in or removed (spade connectors fixed by screws).
Yes exactly...... sorry if I forgot to mention the locking feature which is the main reason wy I use Speakons in the first place. For DIY audio at home I still use MX binding posts because I don't remove them every 24 hours. But I need to carry that convenience in all my homebrewed poweramps for 'live' use.That way my people don't just pull of the wires after an event and a hard days work as they normally do now.

patrick
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Old 28th February 2004, 06:21 PM   #130
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Tarun,
Rod's answer holds good for electrolytics, mostly. Ceramic caps with Y5V dielectric (most common for values > 47nF) change capacitance dramatically with applied voltage, causing distortion. With electrolytics, there must be a DC bias, and if the applied bias is not within around 40% of the capacitor rating, the value will be out of tolerance. This is particularly bad considering elcos usually have tolerances like +80%,-20%. Film capacitors do not suffer from nonlinearity effects, but they do suffer from parasitic inductance. This is not a very observable effect for audio, but makes itself known at RF or in high-speed digital ckts.
The point you mentioned about Speakon connectors making ground contact before signal is irrelevant when it comes to speakers. You shouldn't attach/remove connectors which carry very heavy currents when powered up, because arcing can corrode the contacts. Besides, what if your amp output stage is BTL? This really makes a diff for signal contacts. RCA jacks were probably designed by someone more inclined to cost cutting, since they deliberately make signal contact before ground

gjo, what's an AKSA enclosure? I have two EL34s I removed from my grandpa's old valve radio. Not sure if they work, and their leads are badly corroded. Made by BEL. Actually, my uncle identified them as EL34s, since their markings were all rubbed off.

OK, I got my DSP board back today, and it was a bit of a disappointment... many tracks had shorts to the ground plane . I had a "cure" for this: I got me a 12AH lead acid battery, hooked it to the ground plane and burnt out the shorted sections! Some of the soldermask got damaged, so I touched it up with nailpolish (who here can get me green nail polish? ). Maybe I was being over-ambitious, I had set the ground plane polygon's spacing to 10 mil... I later found that even 15 mil would have worked fine. Silly me. Anyway, next time you guys make a PCB with a plane, you know what not to set the spacing to... Other than that, the TQFP pads have formed quite well, no shorts there.
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