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Post by Deleted on Dec 4, 2011 3:50:45 GMT
Alex, as I intend to use the SBYV28-150 would you care to expand on why you would mount them vertically. RS have them on back order due in about three weeks time......... think they were around 24p each Interested, Alan Hi Alan Will's proposed PCB layout which hasn't been posted yet, is for TO220 type rectifiers which have closer lead spacing.This means that you would need to mount the SBYV28-150 vertically. In any event, the leads of the SBYV28-150 will dissipate more heat when they are longer, not that it is needed here though. Regards Alex |
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Post by Deleted on Dec 4, 2011 9:25:20 GMT
UPDATED SCHEMATIC.P.S. With the JLHs in the Class A 15W,I recommend a 2,200uF 10V low ESR in parallel with a normal 2,200uF 16V electrolytic for each supply rail.The current limiter section is fitted, and uses a 1 ohm emitter resistor and a 1.8K base resistor. A small heatsink should be fitted to each CL transistor. Attachments:
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Post by jeffc on Dec 4, 2011 21:01:52 GMT
X2
cheers.. jeffc
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jonclancy
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Post by jonclancy on Dec 5, 2011 0:31:57 GMT
Hi Guys,
I have some car-related buffoonery inbound. Can I mod a set of Class A headphone amp boards easily to Class A PA??
It would save a load of time and £££.
Cheers
Jon
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Post by Deleted on Dec 5, 2011 2:24:47 GMT
Hi Guys, I have some car-related buffoonery inbound. Can I mod a set of Class A headphone amp boards easily to Class A PA?? It would save a load of time and £££. Cheers Jon Hi Jon You could run short leads from larger O/P devices mounted on LARGE heatsinks to the existing device holes, but how are you going to get + and -20V ? Don't forget that almost all car speakers are 4 ohms. Regards Alex P.S. That means that anybody with a couple of unused HA PCBs would be able to convert them to power amp use if they wanted .  |
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Post by jeffc on Dec 5, 2011 3:54:07 GMT
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Post by Deleted on Dec 5, 2011 4:12:21 GMT
Class A - 4 ohm output.Hi Jeff Due to using 2 x 150VA transformers , you may have a bit more than 2 x 20V AC, so you may be able to increase the voltage rails to perhaps +-22V , which would give you a little more power. Add to that the fact that the original used a single 160VA transformer, and you will have increased PSU current capabilities provided that you use higher current rated voltage regulators. Alex Attachments:
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Post by jeffc on Dec 5, 2011 4:29:50 GMT
OK Alex, I seem to remember seeing this before,  sorry for you having to repeat it.  Hard to guess the sensitivity of my DML panels, but it must be pretty high so hopefully the high curent draw/Class AB issue won't arise. cheers.. jeffc |
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Post by Deleted on Dec 5, 2011 5:00:28 GMT
Hi Jeff A problem appears to be that although there are plenty of pin compatible +VE adjustable 3A regulators, there doesn't appear to be too many -VE adjustable regulator with >1,5A. (LT1033 -Availability? ) The original S.C. PSU was of course capable of the higher currents needed, as it was designed to drive both PCBs. If you wanted to go that route, RCS Radio would have the PCBs, but you would then need to have the rectifiers off the PCB as per the original. Alex P.S. LT1085 and LT1033 would be a good combination. I have since located enough LT1033 for our requirements, despite being superseded. au.element14.com/jsp/displayProduct.jsp?sku=1273556&CMP=KNC-GOO-EDE-SKU-LIN&s_kwcid=TC|15109|lt1033ct||S|p|8171329128 |
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jonclancy
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Post by jonclancy on Dec 5, 2011 8:16:44 GMT
Hi Alex,
Sorry, that was a very ambiguous post is made last night!! What I meant was, can I employ the existing boards to use as a PA in my home? The car thing is going to severely tap time and money over the next couple of years - it involves rebuilding the mechanicals of a '68 MG.
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Post by Deleted on Dec 5, 2011 8:29:01 GMT
Hi Jon
I would expect that they should be usable in a PA as I described earlier today.
You will not be able to power the front end separately, but should be able to power each PCB via a JLH without a current limiter provided that you use the 3A Voltage regulators.
I would try it initially without the JLHs though, but use the Speaker Protector PCB. I can't guarantee how good it will sound that way, as I haven't tried that.
Regards
Alex
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Post by Deleted on Dec 5, 2011 9:24:50 GMT
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Post by Deleted on Dec 5, 2011 9:32:25 GMT
Hi Alan I must admit to wondering why virtually everyone uses both positive and negative regulators with dual polarity supplies. Perhaps there is some reason why manufacturers etc. elect not to do that when +VE regulators are often cheaper, higher performance, and there would be less inventory. Alex |
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Post by Will on Dec 5, 2011 12:27:13 GMT
That's the +/-ve regs I'm basing the 3A build of my pcb on, with normal 317/337 being for 1A duty. It all depends on what you want to do. As you've noticed, much cheaper if a group of us get together for buying them, as it's the same story with the lt1085. |
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Will
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Post by Will on Dec 5, 2011 12:29:14 GMT
Hi Jon I would expect that they should be usable in a PA as I described earlier today. You will not be able to power the front end separately, but should be able to power each PCB via a JLH without a current limiter provided that you use the 3A Voltage regulators. I would try it initially without the JLHs though, but use the Speaker Protector PCB. I can't guarantee how good it will sound that way, as I haven't tried that. Regards Alex Don't forget to put the zobel on the output, which Alex suggested isn't the best idea, to have as a separate circuit. |
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Post by jonclancy on Dec 5, 2011 13:51:39 GMT
Hmmm - OK, in which case I think it'll be easier to go back to Plan A. That's a HA and Pre out of my boards.
So... please may I put myself down for a kit set, Shaun?
Cheers
Jon
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Post by Deleted on Dec 5, 2011 13:59:56 GMT
Hi Alex,
I had a nice single PSU layout ready very easy to carve with the reg. hanging off the edge for off board heat-sinking then decided to put both on the one board so I've a little more jiggling around to accommodate the heat-sinks then I'll try it out with a pair of LT1085s.
What size HS would the LT1085 require?
Hi Will,
GB on the 1085s would be good...................100 @ £3.18 plus vat....£3.82 sounds a lot better than....................single price £6.53 plus vat......£7.85.
Alan
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Post by jonclancy on Dec 5, 2011 17:56:42 GMT
Thanks Shaun!  |
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Post by Deleted on Dec 5, 2011 19:44:47 GMT
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Post by Deleted on Dec 5, 2011 20:25:18 GMT
Hi Alan If possible, mount them on a rear metal panel with a heatsink similar in size to the original article, or a couple of heatsinks with a similar total area. Alex Attachments:
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Post by Deleted on Dec 5, 2011 20:43:53 GMT
Hi Alan For me, that was a no-brainer. AU $10.76 EACH from Element 14, OR 4 from that U.S. ebay store for AU$13.50 inc. delivery ! Kind Regards Alex |
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Post by jeffc on Dec 5, 2011 21:18:28 GMT
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Post by Deleted on Dec 5, 2011 21:41:27 GMT
Hi Jeff
The LM333T certainly appears suitable. If I couldn't obtain the LT device I would use them.
If you chose to use all positive regulators you would need to come up with an alternative PCB design, as Alan is doing .
Again, I would have to query why manufacturers don't use this all positive regulator scenario when it would save them money.
There must be some minor drawback for them not to do so, especially when -VE regulators are often more expensive.
Alex
P.S.
Given the choice, I would always prefer a U.S. based seller to an Asian seller provided that the product is not a great deal more expensive.There is far too much counterfeiting in Asia, so there should be a better chance of a genuine product..
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Post by Deleted on Dec 6, 2011 1:30:06 GMT
Hi Jeff,
I've just laid out my Positive/Negative PSU using Two LT1085 Positive Regs. it's looking good to go so when the USA Regs arrive I'll try it out.
Alex has reservations as you will have read so I'm going to run it past Frans first for his opinion.
My thoughts on why manufacturers do not go down the dual positive reg road might be that you require to have a traffo with two separate windings and two bridges. You can't use a CT traffo. There is a Chinese manu' who has one on sale now.
Heading for bed now so tomorrow and I'll publish.
Regards,
Alan
PS that Taiwan supplier won't supply to the UK
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Post by Deleted on Dec 6, 2011 7:21:47 GMT
Alan
My reservations are mainly that the proven "earthing" method as used also in the Class A HA/preamp can no longer be used.
That involved NO connection with I.E.C. earth, except in the transformer case, and the centre taps of both transformer secondary windings being connected to the HA/preamp/15W Class A metalwork.
I have lingering doubts that the same low noise level may be achieved using dual rail supplies derived by this method using +VE regulators only, where neither side of either of the transformer secondary windings are connected to chassis.
I could be wrong, but it took a great deal of experimentation, involving similar phasing of both primary and secondary windings of both transformers to achieve the present results, which also resulted in improved channel separation as well.
Alex
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sorry for you having to repeat it. 
Hard to guess the sensitivity of my DML panels, but it must be pretty high so hopefully the high curent draw/Class AB issue won't arise.
