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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Simple High Performance DC Coupled Class A HPA with sub PPM THD
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Old 18th January 2019, 10:51 AM   #371
yourownbuzz is offline yourownbuzz  Australia
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Ok - rather inexplicably it works now. after checking for -16V I decided to swap out the BC857 as X suggested earlier. Put it on the transistor tester - it checked out. New one from the pack, also tested fine. Put in the new one and now voltages seem to be similar to the L channel (no sound test yet).
No idea why that did the trick - I did check the BJT for shorts before pulling it and it didn't seem like there were any.
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Old 18th January 2019, 12:51 PM   #372
xrk971 is online now xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Excellent news!
How do you like the sound?
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Old 18th January 2019, 08:42 PM   #373
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
I bet it was a cold solder joint on the BC857. Let us know what you think of the sound. For me, it’s one of the best headphone amps I have heard. Being DC coupled really gives it some amazing transparency and the depth of bass is very good.
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Old 20th January 2019, 02:15 AM   #374
yourownbuzz is offline yourownbuzz  Australia
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I actually killed my 7918 shortly after..I think the pins worked loose while testing and there was a spark.
Listening will have to wait until I get around to modifying the ldovr reg..
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Old 20th January 2019, 05:13 AM   #375
yourownbuzz is offline yourownbuzz  Australia
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Got the amp running with the ldovr regs (swapped the resistor as alexy said) and adjusted to within <0.1V on +ve and -ve rails.

My hardest to drive pair of headphones are Fostex T50rps. With a fraction of a turn of the volume knob its up to slightly higher than normal listening volume, and just for fun I turned it up higher (headphones on the desk of course). You weren't kidding when you said this thing has power!

Will have to get it mounted up for a more extensive listening session & comparison.

I'm kind of itching to build another to use as a speaker amp as you suggested
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Old 20th January 2019, 10:35 PM   #376
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
YOB,
Glad to hear that the sound is good so far. Please post detailed descriptions of which resistor you modified on the LDOVR to program the correct voltage.
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Old 21st January 2019, 01:02 AM   #377
yourownbuzz is offline yourownbuzz  Australia
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Quote:
Originally Posted by oxothuk View Post
replace R7 (1M5 resistor @ top right corner - 0.3V pad) with 105K (SMD 0603)
after modification 0.3V PAD will add 4V - you can configure from 3V to 22V with 1V step

for 20V - need to solder 8V, 4V, 1V and 0.3V (now 4V) pads
Vout = 3+8+4+1+4 =20V
Here. The modification is only required for the negative reg.

X - perhaps link this in the first post?
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Old 29th January 2019, 02:05 AM   #378
yourownbuzz is offline yourownbuzz  Australia
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Been listening and comparing this amp to a few others - mainly with Fostex T50rp mk3.
This amp is great, drives them well and brings out low lingering bass on the T50s.

Vs DCA - DCA doesn't give as much bass response
Vs Aksa Lender HPA - to my ears sounds quite similar
Vs O2 - O2 is positively anemic with the Fostex, and distorts as well. DCA much more worth it for the price O2s go for!
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Old 31st January 2019, 01:15 AM   #379
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
YOB,
Thanks for the listening impressions. I have heard similar comments about the O2 vs even the little Pocket Class A. The DCA has 125mA, more than double the bias current. This amp, is in another class because it has an active CCS that sort of makes it a push pull even though it is SE Class A. The DC coupling makes a difference too. The PSU in this amp is truly state of the art - you can’t get a quieter power supply that is wall powered.
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Old 31st January 2019, 03:32 AM   #380
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to be honest I don't really know how the BF862 stage in this amp works ha...
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