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| Apheared Joined: N/A |  Message [#40] posted on: 02-18-2001 02:21 PM CST (US).   |  |  because it's a fully built single-supply amp stage. This is the test board I used to layout the gainstage and tack it into the szekeres. So it's got + & - input caps and reseviour caps. It's a fully functional amp in it's own right, add output caps and hook up headphones instead of meters! The biasing for the input isn't that specific, you only need a couple volts either way... I think it's 100k/220k or I might have changed it back to V/2, either way doesn't matter with V being 15V. I need to redo the main board, I have to scoot the output caps farther from the source resistors.. the cap cases stay around 60c and I don't like that considering 85c is max... and I'll probably add another opamp and diode to the meter board and go fully rectified. But again, it's just for looks, as long as the needles dance with the music it exudes coolness. :) Well, eventually... that's the plan anyway... the case is a pain to open, the back panel has to come off to remove the lid so you need table space... and my bench is littered with BJTs working on the 200mA discrete portable Class A. |
cmoy  Administrator Joined: Apr. 13, 1999 | Message [#41] posted on: 02-26-2001 02:55 AM CST (US). | |  Apheared, in the meter drive circuit, since the opamp runs from a single supply, is there an output capacitor? What value? [Edited by cmoy (02-26-2001 at 07:06 AM).] |
| Apheared Administrator Joined: N/A | Message [#42] posted on: 02-26-2001 04:14 AM CST (US). | | I don't remember, 100uF maybe? I can't see from the pic and I doubt they could be bigger than that... even 68uF maybe.. it's just to keep DC from leaving the meter pegged, again it was never intended to be a real deal... the rectifier would be better with a lower-drop diodes than a 400x and actually fully rect'd. Not too concerned if I choked off some of the bass as well. :) The builder can decide what he wants to pull off for this himself. Go check out Rod's project #55 on ESP if you want to do it right. Anybody wanting them, Sifam has lots extras nowadays... it seems that Peavey isn't using the AL20SQ anymore in it's amps, they dropped Sifam with no warning... so they are probably sitting on a few thousand of these. IMS seems to be carrying them: Their img for the AL20SQ is missing, but look at the AL20ASQ, it looks just like that but the adjuster is on the back and the needle tip is a spade shape (like the meter pic below the 20ASQ) |
| cmoy Administrator Joined: Apr. 13, 1999 | Message [#43] posted on: 02-26-2001 05:20 AM CST (US). | | Apheared, is the heatsink really near 200 degrees Fahrenheit - near the boiling point of water? Is it so hot that you cannot touch it? The AL20SQ has such an interesting retro look. It would be a great addition to any project. Do you think that IMS will discount it? |
| Apheared Administrator Joined: N/A | Message [#44] posted on: 02-26-2001 12:31 PM CST (US). | | yes, according to my meter's temp probe... right around 200f. You can touch it, well I can... but we could play "chicken" with it, I bet no one with nerve endings can take 20 seconds.. note that the heatsinks are ~30c hotter than the chips and resistors themselves... and it's in a sealed box with no holes. The top gets warm but not hot.. I'd lay a CD on it but not a chocolate bar. the chip is good until 175c, I'm 100c below that on the chip itself. Hmm. Maybe a 1 ohm source resistor. :) edit: DISCOUNT it?! Analog meters cost money dude, you know that. A cheap generic no-name VU spec meter (not just a mV meter with "VU" written on the label) start at $20... I've seen $350/ea ones, and yes I considered buying em. :) [Edited by Apheared (02-26-2001 at 04:35 PM).] |
| Tomo Headphone Council Joined: May 4, 1999 | Message [#45] posted on: 02-26-2001 01:51 PM CST (US). | | Hey, I have the same experience. While I was experimenting on my constant current sources with my Szkeres, I had wired LM317 wrong. At the time, I think nearly 5A were passing though the technically shorted current supplies and Mosfets. Heatsinks were so hot, a drip of water will boil on contact! Well past 100 C. 88 C is fine temperature. This will not damage any parts since air will insulate that very easily as long as they are not in physical contact. I really envy you Apheared. I don't have any power tools and I cannot process chasis. Only chasis tool I have is a reamer. So I can only use "hole"-ly chasis. So my amp will never look so fancy. In fact, my amp still look like junk heap I picked up from junkyard. :< Doh! Tomo |
| Surfsmurf Member Joined: Jan. 1, 2001 | Message [#46] posted on: 03-01-2001 02:30 AM CST (US). | | Hey Apheared, from where in the UK did you buy the meters and what did you pay for them? I just got a price from the Swedish distributor: $90 + 25% VAT for ONE...., and it took them a long time just to reply on my emails. |
| Apheared Member Joined: N/A | Message [#47] posted on: 03-01-2001 06:59 AM CST (US). | | They are expensive man. If you can get them for under $60 USD each, buy a 2nd set for later. :) I got both for about $130 USD... call or email Sifam directly... Farnell stocks Sifam AL series, but I don't know what 35 GBP converts to you. If you want a States distributor I know two; Selco is the US rep, and they will sell low-volume... and IMS (link a couple msgs up) sells em. The only Sweden distributor they list is ACTE, http://www.acte.se hehe, I have the reverse problem. Swedish electronics distributors stock the kinds of parts I'm after, in pots, caps, etc.. but for me to get a 25 SEK item sent here costs me $40 USD and a month of time... international trade just sucks unless you're a importing company. :( |
| Nisbeth HeadWizer Joined: Oct. 15, 2000 | Message [#48] posted on: 03-02-2001 12:56 PM CST (US). | | - Apheared, I just have to ask: Who are those distributors in Sweden you are talking about? - I'd like to know, since audio-grade component supplies are pretty irregular here in Denmark ;-) But, luckily, shippingcosts from Sweden are managable... Regards, [Edited by Nisbeth (03-02-2001 at 04:58 PM).] |
| Surfsmurf Member Joined: Jan. 1, 2001 | Message [#49] posted on: 03-03-2001 12:37 AM CST (US). | | Nisbeth: The price I got on the meters was from Acte, http://www.acte.se. Ordering directly from the UK seems to be the best alternative... |
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