Mezmerize DCB1 Building Thread - Page 39 - diyAudio
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Old 25th October 2011, 04:40 PM   #381
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I have finally got round to building my Mezmerize. Worked first time.

She is all light up and making music.

Using a 12v transformer which seems fine.

Thanks Salas and Mr Pass for a great preamp. Thanks also to Tea Bag.
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Old 25th October 2011, 04:45 PM   #382
Salas is offline Salas  Greece
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Picture of the fair maiden?
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Old 26th October 2011, 09:06 AM   #383
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Here she is:

Click the image to open in full size.

Some tidying still to do. I have bolted the IRF's onto an aluminium plate which is hardly getting above room temp after a few hours use. So I'm thinking of the hotrod. Is there much of an improvement?

Last edited by chalkandtalk; 26th October 2011 at 09:30 AM.
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Old 26th October 2011, 09:12 AM   #384
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There is, sounds somewhat ''bigger''. Aren't you gonna utilize the extra inputs?
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Old 26th October 2011, 09:29 AM   #385
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I have left space on the back plate to drill holes for more inputs. Two is enough for me at the moment. Most of my music is digital coming from a dac.

I will let the current configuration play for a while, before changing the resistor for the hotrod.

Thanks again!!
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Old 26th October 2011, 09:56 AM   #386
AndrewT is offline AndrewT  Scotland
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Chalk,
Is that red+ black through the 2pole terminal block to blue+ brown the mains feed to the transformer?

I would recommend two further and quite separate stages of improvement:

performance
1.) twist the leads together to minimise the loop area.
2.) move the cable and secure it further away from the audio circuits.

safety
3.) double insulate the mains cable. A wrap of sticky insulating tape would do. I go for 55% overlap in bright red for mains voltage cables. The ends of the tape should be mechanically secured (tiny tie-wrap), so that over the years they do not unwrap.

secondary winding leads
4.) the three feeds from transformer to PSU should be twisted as a triplet to minimise loop area.
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Last edited by AndrewT; 26th October 2011 at 09:58 AM.
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Old 26th October 2011, 01:50 PM   #387
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Thanks Andrew T. Your advice is appreciated. I'll get on to those improvements in the next few days.

I may aswell hot rod at the same time - which I think means changing two resistors. Have I got this right - changing the 2 x 68R to one 10R (5W), in two places?

Last edited by chalkandtalk; 26th October 2011 at 01:54 PM.
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Old 26th October 2011, 02:03 PM   #388
AndrewT is offline AndrewT  Scotland
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It is far easier to tack an extra resistor alongside the existing CCS resistor/s.

It also makes it much easier to predict the new CCS current.

If the CCS resistor have 1.9V across them and you have 68r//68r then adding 47r will reduce the Vr very slightly, I'll guess and suggest it drops by 10mV.

The original CCS current is 1.9/68r + 1.9/68r = 27.9+-1% +27.9+-1% = 55.9mA +-1%

New CCS current is approximately 1.89/68+1.89/68+1.89/47 = 27.8+-1% + 27.8+-1% + 40.2+-1% ~= 95.9mA +-1%

If you remove the 68r and replace with a 5W +-5% resistor you don't know how far the CCS voltage will drop. I can assure you it will be much more than 10mV.
The 10r current be be very approximately <1.89/10+-5% =~<189mA +-5%

BTW,
the original DCB1 PCB (both Hyp & Mes) has locations for upto 6 resistors in the CCS. For a 2.4Vdrop (the most that the stack up of tolerances will allow) you can use 47r to dissipate a maximum of 123mW (<25% of a half watt resistor).
6off 47r in parallel give ~7r8. That gives a very wide range of CCS resistor to experiment with.
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Last edited by AndrewT; 26th October 2011 at 02:12 PM.
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Old 26th October 2011, 02:11 PM   #389
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That's a good idea. I will only need a quarter watt 47R resistor too.
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Old 26th October 2011, 02:14 PM   #390
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Do not run any resistor @ Pmax.
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