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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 offline 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
xrk971 is offline xrk971  United States
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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 Today, 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 Today, 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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