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My Krell:        

Got it cased.  Pretty standard.  I apologize for the power switch--I couldn't resist.  

I completed the full modification (output stage and front end) on both channels and listened to the amp briefly. The headphones were Grado GS1000 and Sennheiser HD595, the 8ohm speaker were B&W 60

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  • 2 weeks later...
3 hours ago, UFN said:

Nice. Although I'd have considered a red LED to match the switch cover and the Neutrik locking tab ^_^

 

//UFN 

Never thought of it.  I just got blue because all of my other stuff have blue LED's.  A red LED would definitely tie it all together.

Been binge listening to Cowboy Junkies.  Fell in love with Margo Timmins' voice all over again.

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Picked up a couple of red LED's and popped one in.  Looks much better.  Thanks UFN.

 

27883710805_ec69fd4cf8_h.jpg

 

I noted a 60 Hz hum with low impedance headphones with the music off and the volume turned all the way up.  Can't hear it with high impedance phones though.  The cables hooked up to the RCA input are 2 conductor, shielded, and I had grounded the shielding.  When I disconnected the shield ground, the hum went away.  I had also grounded the output cables, but disconnecting those did not make a difference.  For symmetry, I cut off all the ground wires to the shields.

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  • 2 months later...

Long time reader, first time poster...

Bought the boards from a member over at DIYA... this amp was going to be my first step into headphone listening. 

Starting by quoting Rod Elliot: most problems in circuits are due to incorrect parts... built the amp according to BOM, fired up the PSU (v2), checked voltages, all is fine. Hooked up amp (without OPAmps in place)... smoke in front of Q23 on the 2R Resistor... checked the PSU again: fried. Checking amp board... reverse installed Q24 and Q26...

I am waiting for the PSU replacement parts. Meanwhile I desoldered the incorrect installed MJF transistors and placed in new ones. 

Any idea what to replace before hooking up the repaired PSU? Or should I just do a power up and see?

Regards,

Fabian

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Thanks for the reply... was able to test the amp, working and sounding good... 

My PSU is making some... weird behavior... I exchanged all the semiconductors, tested the values of the resistors. At startup I get +24V / -4V... shorting legs 3 and 4 of the OP27 GP on the negativ side with a screwdriver for a glimpse of a second, the PSU shows +22 -22V... anybody an idea? 

 

 

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Thanks for the replies... gave up the rev2 PSU as I could not get it fixed. Just built the zener supply running perfect with +- 22V. 

Anybody tested different OPamps? Currently using OP27P... 

How much bias you would recommend maximum? Using the 63,5mm version and they barely get warm at 125mv (if I use Nelson Pass' of heatsink temperature analysis: less than "Blimey Hot", which means >10s hands on, so less or around 45°C).

What kind of headphones would you recommend for this amp? Thinking about DT-880-600. Should be at a reasonable price...

Thanks for all who helped to realize this project. A great sounding amp!

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The opamp is just a servo, so not much point in replacing the existing OP27s. 

As for headphones I believe this is intended for low-impedance phones so the 600ohm Beyers probably aren't the best choice.

//UFN

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  • 3 months later...
On 18/12/2016 at 9:54 PM, muskyhuntr said:

Well done.  Like that front panel!

Me3

 

On 18/12/2016 at 10:15 PM, ang728 said:

That engraving !  Well done~

 

Thanks you guys, actually that engraving and drill hole for audio jack (the volume pot hole come with the stock panel) cost me only 5$, incredible cheap!

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51 minutes ago, Thai Tao said:

 

 

Thanks you guys, actually that engraving and drill hole for audio jack (the volume pot hole come with the stock panel) cost me only 5$, incredible cheap!

super cheap ! I saw breeze audio's box in the background.Did the chasis and engraving make by breeze audio?

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  • 1 month later...

Hi All,

Got mine all up last night, or I should rather say, this morning...
Sounds terrific.
On my side, it was more an experiment, to see if it's any batter than the one I've been using for good few years, now rather than real need for an amp ...
Will give it some extended listening sessions over the course of next few days ...
I'm planing to try it with all the cans I got, HD800, K701, HD590 and K7xx,

I've tried to match all the transistor pairs, although still had some dc offset in range of 40-50mV for both channels, obviously after installing op-amps everything looks absolutely fine.
If I decide to keep it (read: case it) I will be putting some protection circuit (epsilon12) on top.

I would like to thank you all here, and Kevin for the great work.

DSC_7183.JPG

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  • 2 weeks later...

Hello 

First of all i would like to thank the authors for the awesome work done, to bring those devices available to us. I am starting my trip with building the ksa5 and using it as a line pre-amplifier. do you think this is a good idea or it is first of all a Headphone aplifier, and there are better solutions for the price when it comes to pre-amp.

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