Balanced line stage, quistion's + unbalanced - diyAudio
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Old 19th December 2002, 06:13 PM   #1
lykkedk is offline lykkedk  Denmark
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Default Balanced line stage, quistion's + unbalanced

Hello out there.

I would like to have some schematics, howto use The Balanced Line Stage, with my Leach amp, which is not balanced.

Also i would like to know, where to put R18+R19 (221ohm), as a don't see them, on the PCB. (I know this quistion might be dumm...)

As a followup to my quistion last week, about howto use a different transformer, I just bought this torridal 2x0-55vac trafo. 120VA
I will use it with no modification's (7 Zener-diodes at 9.1v RIGHT, or just 6 ???)

If i plug in the Welleman-kit K4700 for loudspeaker protection, in my Leach-amp, I will not need to do anything at The Balanced Line Stage, turn on transient RIGHT ???

Just need to be sure, cause i just repaired my Audiovector 4 Laudspeaker's.

MERRY CHRISTMAS TO ALL OF YOU...
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Old 19th December 2002, 09:15 PM   #2
2Bak is offline 2Bak  Denmark
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Hi Jesper

R18 and R19:

Will you be using unbalanced in and unbalanced out only in your BoSoZ? If so, then you might find your answer here:
http://2bak.homepage.dk/mybosoz.gif

Will you be using pots at +input and -input or not?
If you use P1 connect R18 between line input (selector) and Pot in. Pot ground goes to ground on PCB and pot out goes to +IN on PCB.
The same wiring applies for the -IN if you use P2 for balanced input.

If you do not use pots at +IN or -IN or one of them then hook up like this:

+IN :
R18 between selector and +IN. This should do short between R18 and Z1, but someone correct me if I'm wrong here. Like the pot was full way up.

- IN (for balanced only):
R19 between selector and -IN. This should do short between R19 and Z3, but someone correct me if I'm wrong here. Like the pot was full way up.

Hope this help.
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Old 19th December 2002, 09:43 PM   #3
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Hmmm...this computer just ate my reply. Let me try this again.
Running an unbalanced amplifier from a balanced preamp is no problem at all...just don't use one of the preamp's outputs. If you want to get fancy, you can switch between the + and - outputs to give yourself control over absolute phase. Just be sure to leave ground connected at all times.
Since Nelson shows R18 & 19 as leading to pots, the easiest way to hook them up would be to solder them directly from the input jacks to the pots, rather than from the jacks to the boards, through the resistors, back out to the pots, and back to the boards. It's cleaner that way.
As far as power supplies go, I'm not clear on the transformer you bought. Is it 55-0-55V? If so, that's a little hot for the BOSOZ (30-0-30V, I believe). That's not to say it won't work, but you're going to have a lot of heat to dissipate in your regulator. Be sure to have plenty of heatsinking on hand. There are other ways to diddle the voltage, but let's get the transformer voltage clarified first.
The circuit itself will run on a wide range of voltages. The schematic shows 64V rails, but there's plenty of leeway. Yes, the regulator (as shown) uses seven 9.1V Zeners to set the reference voltage.
Loudpeaker protection is a subject that tends to start arguments. My view is this:
--If you're bi/tri/whatever-amping, they may be necessary to protect tweeters from turn-on thumps.
--If the amplifier has such a ferocious turn-on thump that it destroys speakers, you need to fix it or find a new design. Surely the Leach is better behaved than that.
--If you're clipping the amp by playing it too loud, then you need to either play at a lower volume or get a bigger amp. Clipping is the single biggest destroyer of speakers out there. This is a major point that a great number of people don't seem to understand. After they've bought new drivers (tweeters are the first to smoke), they're somewhat more likely to think before cranking the volume knob quite so far.
--If you're afraid the amp is going to fail, then dump the amp and go with a more conservative design. Again, surely the Leach behaves better than that. Any piece of equipment can fail (and will eventually), but if you're living on the edge of fear, you might want to consider another hobby.
--If it's the preamp turn-on you're afraid of, the solution is simple...turn on the preamp first, then the amp. Turn the amp off first, then the preamp.
Protection ciruits either don't work properly, degrade the sound of the amp, or trigger too easily. I avoid them like the plague, except for the first reason I gave above (multi-amping), in which case I go for a simple relay that engages after, say, five seconds.

Grey
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Old 19th December 2002, 11:20 PM   #4
2Bak is offline 2Bak  Denmark
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Grollins:
Quote:
Since Nelson shows R18 & 19 as leading to pots, the easiest way to hook them up would be to solder them directly from the input jacks to the pots, rather than from the jacks to the boards, through the resistors, back out to the pots, and back to the boards. It's cleaner that way.
That's also the way I did it, and what I meant above.
See R18's here going from selector to pots.
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Old 19th December 2002, 11:58 PM   #5
Mad_K is offline Mad_K  Norway
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Default Re: Balanced line stage, quistion's + unbalanced

Quote:
Originally posted by lykkedk



As a followup to my quistion last week, about howto use a different transformer, I just bought this torridal 2x0-55vac trafo. 120VA
I will use it with no modification's (7 Zener-diodes at 9.1v RIGHT, or just 6 ???)
-should be just perfect (assuming you are just using one 55-0-55), you're likely to end up with unreg. rails at +/- 80-85V. no modifications needed.
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