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Old 2nd November 2003, 11:26 AM   #431
Calebay is offline Calebay  Denmark
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Hello

nope 2 x 22 volt rail was not posible whit 2x 18 volt trafo, tested it last night.

what voltage will be optimal for me to those on a trafo if i want
2 x 22 volt rail whit the regulated power supply.

and how do i calculate the unregulated voltage volt from a trafo after diode bridge and caps?

Tnx
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Old 2nd November 2003, 01:54 PM   #432
Nisbeth is offline Nisbeth  Denmark
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Calebay, the voltage after diode bridge and caps is app. ((Vtransformer * 1,41) - 1,4V). The optimum voltage for 2*22 V would be 20V, since this provides the lowest voltage drop across the regulator. The power dissipated is your LM338 is the diffrence between the input and the output multiplied by the current you are drawing (i.e. if you have a 20V transformer, you'll get ~26,8 V after bridge and caps. If you've set your output voltage to 22V and you quiescent current to 2A, each regulator will dissipate ((26,8-22)*2) = 9,6W!!)

One option could be to lower the rail voltage to 20-21 Volts, Then you'll be able to use the 18V trafos without problems. Which JLH-version will you be building?

/U.
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Old 2nd November 2003, 02:18 PM   #433
Calebay is offline Calebay  Denmark
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tnx for the info.

but i dont understand 100% if i calculate ((18v*1,41)-1,4) i get 24volt but yesterday when i mesured it under load i got 22volt, after bridge and cap.

i want to build the 1996 updated version 15 watt
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Old 2nd November 2003, 04:15 PM   #434
Nisbeth is offline Nisbeth  Denmark
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The voltage drops when you load the supply. 22V from an 18V transformer sounds a little low, though. The output voltage is usually specified at full load. How big were the load? What does the transformer measure without the bridge and caps?


/U.

PS: Maybe you should take a look at Geoff's update of the Class-A circuit at:
http://www.tcaas.btinternet.co.uk/jlhupdate.htm. If I'm not mistaken that will run fine on +/- 20V or even +/-18V.
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Old 2nd November 2003, 04:26 PM   #435
Calebay is offline Calebay  Denmark
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the load was 4x 12v 20w spotlights in serie. 60watt i think
i didnt mesure the voltage from the trafo whitout bridge and caps. and the test setup is all desoldered now.

gues i just keep my trafos and run 2 x 20 volt tnx alot for the help.
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Old 3rd November 2003, 04:22 AM   #436
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Default MJ21194

Hi,

I have just finished with the amps today. Except I have to lift the ground on one amp, no other noise I can hear. No ocillation I hope since I have no scope to check it. Dead quiet.

CLC- PSU, cheapie surplus caps, 8 x MUR860, 400VA 22-0-22

All BC559, BD139, BD140, 4 x MJ21194 not matched, 4 x ohmite 25W 0R1 power resistors

C1 is 5 x 100n, yet to find a replacement.
Bias set at 150mV across R13, DC offset 1mV



Chris
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Old 3rd November 2003, 06:01 AM   #437
mikelm is offline mikelm  England
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great .... so how is it sounding ?
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Old 3rd November 2003, 04:57 PM   #438
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Default It sounds like...

It is very difficult to describe, that's why I haven't put it down with the previous post.
Well let me try. I can only compare it with my current JLH for ESL with MJ15003.

The low bass is definitely softer, mid-bass is about the same, the low bass tend to linger on just a bit more. The soundstage is a tad narrower or different. But it has something about the sound quality that is more musical. It is not as analytical. This new amp does not handle complex passage well it seems to get confused and muddle when there are lots of things going on. The background singers are more difficult to pick out from the mix. But for recordings of one female vocal and one guitar it sounds excellent. Male voice can be a little chesty sometimes.

Let me also find some excuses for it.
This amp has no proper input cap C1, using parallel 5 polypropylene of 100nf for now.
It uses surplus caps in PSU and badly assembled too, some caps might have been damaged by my butcher style using a high power butane gas blow torch to do the soldering.
Bias at 3A rather 4A.


My original pair uses
***********
PSU capacitors - 12 BHC Aerovox ALT22A 15,000uF 63V (339-7947) bypassed with
ACROTRONICS KP1.72 100nF polypropylene. (114-604)
The 470nF on the PSU (C13/C14) is a EVOX RIFA PHE428. (240-5413)
All electrolytics ELNA STARGET. (215-5742, 215-5764, 215-5720)
C1 2.2uF polypropylene by AMPOHM. (365-7479)
All bypass caps are 100nF polypropylene Vishay-Roederstein MKP1837.
(166-6487)
The 330pF on the input to amplifier (C2) is WIMA FKP2. (115-663)
R5,R9,R11,R10 and R12 are CADDOCK MP930 series mounted on biggish heatsinks.
All other resistors are WELWYN RC55C Series 0.25W ±0.5%, ±50ppm/°C.
***********

I am sure I can voice this new amp better with some help and suggestions from this forum.

Regards,
Chris
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Old 5th November 2003, 01:45 PM   #439
jccliu is offline jccliu  Hong Kong
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Hi Chris,

Similiar findings as mine, I prefer JLH for ESL(But mine is a PNP version without cap mult supply). Your findings strengthen my findings too. Perhaps the ccs Iq circuit result. Still thinking.......finding...........trying........

Regards

John
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Old 5th November 2003, 07:24 PM   #440
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Quote:
Originally posted by jccliu
Hi Chris,

Similiar findings as mine, I prefer JLH for ESL(But mine is a PNP version without cap mult supply). Your findings strengthen my findings too. Perhaps the ccs Iq circuit result. Still thinking.......finding...........trying........

Regards

John

Good to know that I am not alone
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