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PostPosted: 28 Oct 2010, 15:30 
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dtsup1 wrote:
As usual, pls write a review on the sound ;)
I think the jfet preamp designs are awesome.
Natural warmth. I see that you have mixed some carbon and metal film resistors.

Those Topcon caps were the same types I used in my first ever chip amp in Melbourne.
Well they exploded 1 feet from my face. (from inverted polarity) :mrgreen: :mrgreen:
Fun times...hahhaa...

PS: I still have a phobia whenever wiring up a chipamp.

Any electro will explode if inverted.

The carbons are only for the power. Not in the sig. path.

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PostPosted: 28 Oct 2010, 15:31 
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Dan wrote:
Where are the pics Mark ?

This post. Take a look.

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PostPosted: 30 Oct 2010, 07:46 
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Completed my BoZ today and had a very short listen. Not sure it is upto the B1 sonically but further listening will proof it one way or another. Lots of extended bass.

Images to follow. Draws about the same current as the Nelson Pass B1 buffer -> 20mA.

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PostPosted: 30 Oct 2010, 12:53 
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Nice clean build Mark. Do you have any underside photos of the strip board so members can see how simple these preamps are to build especially if used with a battery supply.
Cheers

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PostPosted: 30 Oct 2010, 17:24 
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Here is an image of the underside of the brd. The caps are 0.1uf snubbers for the 10uf output polies. Just a few straps are used and I like to keep them under the brd. for neatness. The heavy silver solder brings a lot of unused tracks to the negative or earth rail. This should help gather electrical noise away from the rest of the cct.

You will also notice in the previous images I built a symetric amp. So one side mirrors the other. Not sure weather this will make a difference but I thought it a good idea at the time. With the B1 I copied one side to the other - much easier.

The hook-up was all done with wire wrap wire (WWW). From info. I have learnt from the Cable Cook Book (soon to be reviewed) the use of ultra thin wire in hi-fi is better than heavy wiring. More to come on this matter.

I'm still to get a good listen to the preamp. Finished photos to come.
Attachment:
BoZBrd_IIss.jpg

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PostPosted: 31 Oct 2010, 03:19 
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mwhouston wrote:
I have learnt from the Cable Cook Book (soon to be reviewed) the use of ultra thin wire in hi-fi is better than heavy wiring. More to come on this matter.

Agree with that. I always use very thin multi stranded and flexible wires.

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PostPosted: 31 Oct 2010, 06:03 
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Finally some images of the completed BoZ. Sorry for the delay, life got in the way.

Once more the Hammond anodised Al cases. This one shorter than the B1. I upgraded the knob to a 4oz solid brass job. BUT down graded the rear RCAs. Still gold plated but no need to insulate from the case. Switch at the front is a mini on/off, switch on the rear selects between the two sets of inputs. Volts feed is meant to be 35V. Currently I'm running it on 34V of lithium batteries until I can get the hum out of one DC supply.

On an early listen bass may be weightier and just as extended as the B1.

I'm yet to get a decent listen but the day is comming.
Attachment:
BoZFinisSS.jpg
Attachment:
BoZRearSS.jpg


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PostPosted: 01 Nov 2010, 05:22 
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I have had a chance to compare the Nelson Pass B1 and BoZ, (simple form) both my builds. For absolute sound rawness and detail the B1 is supreme. But of course the B1 has no gain and even has negative gain. Its role is to drive.

Both preamps have the same metal film and carbon resistors from the same store. Both have exactly the same input cap (Russian military 1uf 40y-9, paper in oil (PIO)) and output caps, 100V polypropylene 10uf. With the BoZ this is snubbed by a 0.1uf poly. Hook-up wire varies from cotton coated tinned solid core copper to wire wrap wire (WWW) in BoZ. Both enclosures are Hammond anodised Al cases with the B1 having a slightly longer case. Both preamps have a single jFET the 2SK170 (BL).

The two preamps have been compared with different external power supplies. The B1 a 19V SMPS and BoZ 4 X 9V lithium batteries. You may rightfully argue that in the PS alone there is enough difference to make any sonic comparison redundant. If you do. bow out now, if not read on.

Let’s digress a little. The B1 worked first time it was powered up but BoZ gave me serious attitude. This was my fault due to the fact I added a input cap where there was none. Where I placed it blocked the critical bias voltage for the jFET. But it doesn’t stop there. A 1ohm resistor, in the PS, went open cct. And while re-assembling the case I caught the power wires which shorted the batteries.

Both preamps have good control over the bass. Both extend into low bass. BoZ has greater weight in the bottom end and excellent clarity and detail through the mid range and into treble. But B1 has a rawness of mid-range and treble which reveals a vulnerability in the music which draws you into it. You can’t turn away or stop listening. The B1 connects you with the performance where BoZ places the performance in your listening area.

In conclusion if you need gain and want a very natural, un-coloured sounding, simple preamp, BoZ is for you. If you have 200W of raw power in a power amp and a line driver will suit you better, take the B1 challenge. But you may find its rawness confronting and even distracting.

Remember both preamp invert the phase so if your power amp is non-phase inverting swap you speaker leads over.

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PostPosted: 01 Nov 2010, 11:52 
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Mark,

An excellent review.

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PostPosted: 01 Nov 2010, 16:52 
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One further comment. BoZ IS hard on power supplies. And is a real candidate for batteries. Any bit of noise, buzz or hum just comes straight through and amplified. As Nelson Pass says the B1 is easy on supplies. Both units draw just under 20mA.

See inside image with WWW hook-up wire.

The B1's rawness was not only my comment. This was commented on a a small pannel of hard core listeners.
Attachment:
BoZInsidess.jpg


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