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PostPosted: 22 Sep 2010, 11:09 
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Location: Christchurch, NZ
The P37 boards arrived (again :eek: ), and soldering took less than 10minutes. Worked perfectly and adjusted the trimmers to as close as 0V as possible. The board is housed in a small plastic case, and the PS module is kept 1m away, on the floor. All components were purchased from Farnell-Newark Malaysia.

Caps :

Electros are Panasonic low profile, high temperature caps. Bipolar 22uF used on the output.
MKP types are all WIMA film type.

Resistors : KOA 1%, 50ppm metal film.
Trimmer : Bourns 15 turns
Transistors : Fairchild semiconductors BC 559 and BC 549
Signal wiring = 30AWG solid silver core.
Power wiring : 30AWG silver, solid core, DIY shielded with alu foil. and heatshrunk.

The enclosure is shielded and damped with 5mm thick bitumen-alu foil. 3 way PCB computer type connector is used for the power supply connection. (15 - 0 - 15 V )

Sound : This version sounds noticeably clearer/brighter than my previous version. Midrange clarity is very good, Jim iHendrix really electrifies the air with his guitar work. Stereo imaging is up another notch, making the older point to point version sound duller and muffled. Bass is superb, and identical to the P2P(point to point) type. I think it has something to do with the metal film resistors giving a more aggressive, upfront and clearer sound. Transient attack is slightly sharper than the P2P. Oddly, noise is slightly higher with this version, and a slight hiss is coming through the tweeters, though only audible from 6 inches. Also, these Fairchild transistors are not available in local shops and are of much better quality.

Mark (mwhouston) is building me an identical type, P2P with his own specially selected Aussie parts specially to give a warm tone to the preamp.


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PostPosted: 22 Sep 2010, 12:11 
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Nice. Simple, clean and sounds good! :thumbsup: It will be interesting to see what Mark cooks up.
Cheers

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PostPosted: 06 Oct 2010, 13:03 
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Ok, I tried a bank of batteries and was surprised. Some of the harsh high freq toned down, bass was slightly more agile, less overhang. The photo shows a 4 banks of 24 alkaline AA batteries, of which 6 each are in a bank to form 9V. These banks are then wired to form +- 18V.

Performance is a step up again. Instrumental separation is more distinct.

I'm probably going to get 4800 hours on this battery bank. The issue with battery is that once the voltage drops, I have to readjust the bias again. Hopefully it won't cause problems if I forget to do so.


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PostPosted: 06 Oct 2010, 21:37 
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Hi Dinesh, how are you splitting the supply? Here is a great rundown on virtual ground circuits: http://tangentsoft.net/elec/vgrounds.html
Current draw is low so TLE2496 can work.
Cheers

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PostPosted: 06 Oct 2010, 23:20 
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Hi Gio,

Thanks. Good link. I have mine connected up like the one in the first pic of the link, but without the capacitors. Now I i finally see the problems with battery, no matter how clean they are! :cold:

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PostPosted: 07 Oct 2010, 11:51 
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Another idea would be to add some additional batteries and then use a low dropout regulator to get the voltage constant. This will allow you to keep the bias setting. But you want to do it efficiently so you don't eat up batteries. The battery supply could become more complicated than the preamp!
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PostPosted: 07 Oct 2010, 12:17 
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Hahah indeed. Gio, can you suggest how I can build the P3A amp? As an integrated amplifier with the P37A preamp (mark's board) or just build a power amp ?

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PostPosted: 07 Oct 2010, 19:53 
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You could share the power supply. But you may want to use regulators for the preamp portion. You have to watch the specs on the regulators as some may not work well with a very low current draw.

For the last while I have been building my amps as power amps using an external preamp. The reason being that I can swap the preamps and color the sound to my likings.

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PostPosted: 08 Oct 2010, 03:42 
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Guys,

The battery idea is not working out at all. The rails measure +16v and -17V after 2 days of non stop use. How is this possible that the batteries drained so fast ? I have enough amperage in the batteries to last 6X longer than a single 9V lithiums. :confused:

Back to the LM317/337 regulated power supply... :bawling:

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PostPosted: 08 Oct 2010, 17:01 
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A battery will work, but you need to use a better method for the virtual ground circuit.
Cheers

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