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Old 30th March 2009, 03:53 PM   #461
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I'm running a bias test on the LM4702 and Sanken STD03N STD03P:

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The LM4702 itself chews up about 23mA.

Here's a chart of idle current vs time:

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Old 21st June 2009, 04:51 PM   #462
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my lm4702
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Old 21st July 2009, 04:53 PM   #463
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hi,

how can ı find the matched sap15 ? And ı have lm4702BTA but generally use lm4702CTA.is thisimportant or ı can use BTA?

regards
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Old 21st July 2009, 05:03 PM   #464
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Quote:
Originally posted by yildiray
hi,

how can 1 find the matched sap15 ? And 1 have lm4702BTA but generally use lm4702CTA.is thisimportant or 1 can use BTA?

regards

SAP15N/P are obsolete -- new devices are STD03N/P -- the only difference seems to be the omission of connection to the emitter degeneration resistor in the older devices. You can get the Sankens from Profusion PLC.

I don't know whether Janneman used matched devices in his PAX amplifier (now also seen in August 2009 AudioXpress) -- Sanken suggests using a separate potentiometer between each of the diode strings in the p an n-channel devices.
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Old 31st October 2009, 07:00 PM   #465
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thanks jackinnj and i m so sorry for my late answer.i choosed 2sk1058 and 2sj162 groups.

so i searched for resistor.probably i will use riken or shinkoh.is there any idea from my dabhands about resistor
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Old 24th December 2009, 07:57 AM   #466
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Is there a known-good PCB design for the LM4702 I can use?
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Old 24th December 2009, 02:02 PM   #467
VLSI is offline VLSI  Australia
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Default LM4702 Boards

Hi Spasticteapot
Have a look at the P-4702H and P-4702I boards from CP Design (www.chip-pcb.cn) $8.00 and $10.00 USD.
I have built 5 amplifiers with earlier boards from them, mostly using the now obsolete SAP16 Darlington's and find them very good.
I like to keep the input impedance to 10k with no input or feedback capacitors, (dc protection circuit a must) bias 40-60ma range, Gain about 30 (10k/330R) DC +/- 50v is good for around 100w 8ohm with a single pair of Darlington's.
No pre-amp, input is direct from a Audio-gd "Reference One" DAC or a passively equalized LME49710HA phono pre-amp via a 5k stepped attenuator.
Tested on heaps of speakers but mostly Scan speak Revelatory designs from Zaph Audio and Troels Gravesen, The sound is magic.
I have had (on loan) a number of hi-end monster amps including Krell, Classe, and McCormack to compare with this little amp and apart from the lack of bass authority it hold its own in the mid and top.
Try and use the LM4702B, keep B+/- and speaker wires short and the same length, and if you can, try and make both channels as symmetrical as possible, experiment with your PS filtering capacitors and bypass them with good grade polypropylenes, also I use a separate shunt regulated PS just for the LM4702.
All the LM4702/SAP's amps I have built have a similar characteristic sound, despite very different power supplies and layouts.
Next amp is a 4702 with 6 pairs of BJT devices to see how this affects the bottom end.
As fun as it is to use crazy expensive parts the law of diminishing returns kicks in to hard and the money could be spent on say another power amp module.
One amp built with a good friend used the same chassis and PS but we built 3 LM4702 boards, one each with FET, BJT, and Sanken darlington outputs so we could quickly compare (btw the SAP Darlington's sounded best)
Good luck with your amp, look forward to seeing the finished product.
Kind Regards
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Old 13th January 2010, 10:42 AM   #468
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Default setting bias

Hi, I have built a 2ch amp based on LM4702 and SAP15's

To set the bias I can measure current in one supply rail but how much do I contribute to the LM4702 and can I assume the two SAP pairs draw the same current each ?

Another thought is if the built in resistors are accurate I could measure the voltage between two emitters to calculate bias ? I tried measuring them and my meter wasn't really that accurate ( same resistor gave varying readings ).

Pete
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Old 13th January 2010, 11:11 AM   #469
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Quote:
Originally Posted by Spasticteapot View Post
Is there a known-good PCB design for the LM4702 I can use?
If you like lateral MOSFET's you can use mine -- here's one fitted into my Pioneer SX-838:

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Old 14th April 2010, 01:37 AM   #470
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I have my LM4702 amp up and running after several hurdles. I would really like to thank jackinnj for all his wonderful help. This is using the AN4442 transformer and 58/60 lateral mosfet configuration. It has 4 analog single ended inputs, ipod dock, remote, front panel lcd that displays input and volume via AtMega128. The sound is amazing. I have it running two Polk Audio RTIA3 bookshelf speakers and couldn't be happier with the sound quality.
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