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Old 31st January 2002, 02:20 PM   #21
fcel is offline fcel  United States
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BOSOZ grounding question:

On the power supply board, one side of the thermistor is connected to chassis ground and the other side is connected to the earth ground but looking at the copper side of the board, this same side of the thermister is also connected to chassis ground (copper trace below the 2 screw hole opening).

1. I thought the earth ground and chassis ground should not be connected together. Am I right?

2. Should I open the trace and jump a wire from the thermistor to the earth ground so that the board does not have contact to the chassis ground?

3. Typically (I think), XLR and RCA jack has ground portion connected to chassis ground which will also be connected to earth ground as described in the first paragraph which could ....
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Old 31st January 2002, 04:16 PM   #22
grataku is offline grataku  United States
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fcel,
its fine as it is, it's a Nelson Pass design and I am pretty sure he is at a point in his career where he knows how to do grounds .
If the star audio ground is on the chassis then the AC ground should not go to the chassis. However, since all the audio grounds run on the two PCBs the thermistor becomes the element that separates the audio from the AC ground which is what you want. If for any reason you connected the star ground to the chassis in some other point you may have a problem and you should remove that connection.

maybe i see where your dilemma is, the jacks ground can be connected to the input ground line on the main board, that will in essence become the star ground point. That's what i did, signal grounds are separated from the capacitor grounds and everything is quiet.
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Old 1st February 2002, 02:05 AM   #23
fcel is offline fcel  United States
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Grataku,
After I post my question and after looking at the power supply board again, I can see that if one were to use NON-CONDUCTING "stand post" (don't know what is the exact term to describe it) to hold the board up and install a jumper wire from the earth ground socket to the earth ground on the power supply board (the 2 screw hole on one side of the power supply board), it would maintain the integrity of the earth ground. The potential problem I see is that most of the "stand post" and chassis are metal and if installed that way, essentially the earth ground is connected to chassis ground.
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Old 3rd February 2002, 12:27 AM   #24
Variac is offline Variac  United States
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Default 60w/60w transformer

I was planning to order a 60/60 V toroid from Plitron just as Grataku did, avoiding the 2 30/30 V transformers that NP uses.
Fortunatly for me he ordered first

So... what is the upshot here? The plitrons aren't as tightly speced as they claim? I should order lower voltage? Go with the dual Avel Lindbergs?

Sounds like a lot of his problems aren't related to the transformer?

I just wanna build it as designed, but the Plitron seemed a better,cheaper way to go.


Gotta finish the SOZ first anyway
MArk
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Old 3rd February 2002, 03:32 PM   #25
fcel is offline fcel  United States
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Just to let you guys know that I have recently completed building my first pre-amp, i.e. the BOSOZ and it sounds wonderful but this grounding thing is still bugging me as you can see from my previous post and below. I've read some more and I'm posting again to share my experience - grounding wise ...... and some more little questions. Note: I have built it with bal/unbal in and bal/unbal out but used it as unbal in and unbal out only.

The first grounding issue:
The power supply circuit as shown in Fig. 2 shows that the earth ground is isolated from the chassis ground but if you look at the second paragraph of the "safety note", it says that the earth ground should be tied to chassis ground. I guess I have answered my own question from my previous post.

The second grounding issue:
Currently, I have installed the RCA jacks to the metal chassis which means the RCA jack's ground is connected to the chassis ground. The second last paragraph under "construction notes" says otherwise. It says "...... these RCA grounds are isolated from chassis ground". Where can I buy those RCA jack that has some kind of insulation so that the jack's ground does not come in contact with the metal chassis? Can I buy them at Radio Shack? I guess I should replace my current RCA jacks installation even though I do not "hear" any problem.

The third grounding issue:
I have read quite a bit on this forum concerning whether to ground or not to ground the unused input leg if the pre-amp is going to be used as an unbalanced input with either balanced or unbalanced output. I could be mistaken but I did not see anywhere on the article that says to ground anything regarding to this. I'm looking at the circuit diagram as shown in Fig. 3 of the article ....... let's say the unbalanced input is connected to "+in" with "- in" not connected, the "G" of Q2 still sees a reference voltage to ground via R8 and R14, so why is it necessary to force the "- in" to ground? I say it's not necessary to ground the unused input. Comments?
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Old 3rd February 2002, 05:38 PM   #26
grataku is offline grataku  United States
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Fcel,
ah ah!!! That's where your problem is. Normally, the RCA should not be connnected to the chassis. In the good old days, I used to mount the full metal RCAs onto a piece of G10( basically green PCB fiberglass material without copper) and then attach the piece of g10 with the rca mounted on them on the chassis. Of course, prior to attaching anything holes were made in the chassis that were large enough to clear the RCA plugs.
Nowadays, I buy the gold RCA that have a nylon insulation ring and I can avoid the whole bloody mess.

Yeah, it's a good idea to ground the -In in SE mode.

MArk,
I am happy with the Plitron, although, if going with the 80VA, I would suggest a 50-0-50V or 55-0-55V rather than a 60-0-60V for the reason I stated previoulsy, unless you have room for HUGE heat sinks on the PS mosfets . If you use a lower power transformer the voltage will probably be lowered more quickly under load. By how much, I don't know.
There is no reason to go with 2 transformers just to get the 60V output. If it was for doing a dual mono PS it would make sense, as it is it doesn't.
The plitron secondaries are completely independent so the dual rectifier arrangment is maintained which is the only thing that matters.
According to my calcs, the preamp dissipates around 25W, including the PS. Ten of those watts from the 4 1500ohm current sources alone. All that heat has to go somewhere. I would be curious to hear form someone that has used the recommended heatsinks.
I solved all my cooling problems on the 750 Rs by going to heat sinked-thick metal film resistors TO-220 style. I also had to supersize all the mosfet heatsinks. Now is all running at a comfy (in my book) 45deg C.
The balancing problem was solved by more careful matching of the Mosfets and by matching the bias resistor values. Grey made a good point that mosfet should be allowed to come to temperature before taking the voltage reading. I wasn't doing that before.
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Old 3rd February 2002, 07:48 PM   #27
paulb is offline paulb  Canada
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Has anyone considered a voltage doubler arrangement a la the A75? I'm always trying to use up surplus transformers I've accumulated, and I've started thinking about the BLS oops I mean BOSOZ.
I was thinking a dual voltage doubler followed by a 60V linear regulator. Might make the preamp look like a battleship but what the heck.
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Old 3rd February 2002, 10:06 PM   #28
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A voltage doubler will work nicely, but the thing to watch there is your current draw. For a preamp circuit it should be fine, though.

Grey
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Old 3rd February 2002, 11:28 PM   #29
paulb is offline paulb  Canada
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Quote:
Originally posted by GRollins
For a preamp circuit it should be fine, though.
Exactly...(evil cackle ensues)...
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Old 6th February 2002, 10:31 PM   #30
fcel is offline fcel  United States
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Hi all,

I have completed building my BOSOZ as I've indicated on my previous posts and I'm ready for my next project which is to built a Aleph Power Amp. I have a Zen amp already and I want more power than SOZ and thus I choose Aleph.

My goal is to do the least amount of work with maximum enjoyment - listening - and be able to get parts easily in the least amount of time. Which Aleph Power Amp should I built accordingly to this criteria? I think I have read about Aleph 4 (Mark's Web Site from Australia) & 3(?) in the Passdiy site with quite detail description of construction and even a board layout. Recommendation please from those of you who have gone thru this process before or who has built several different models of Aleph Amps already.

I'm asking this power amp question here because I don't really know where I should post.
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