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hackernap advice thread

hnapwiring.jpg
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these are the ones I spotted.

jo
 
Would it be possible to build this amp using lower voltage transformers? I have some excellent quality 350VA AST's with dual 25-025 secondaries and would like to use these if possible.If it's not possible I'll have to start saving.tia.
 
Marra said:
Would it be possible to build this amp using lower voltage transformers? I have some excellent quality 350VA AST's with dual 25-025 secondaries and would like to use these if possible.If it's not possible I'll have to start saving.tia.
Click to expand...

You will get slightly lower power output, but everything else should be fine. 25-0-25 should give about +/-- 35V rails - you might get 60 or 70W into 8 ohms.
 
Thanks PD. The AST's give 36vdc with the class A amp that they are currently used with.I would then need a transformer with 30/32 V secs for the front end?
 
Here is Hackernap no.3 of mine. Built into a 2U case. Full dual mono construction, transformers are Holden and Fisher 44-35-0-35-44 250VA per channel. Sulzer op-amp regs for the front-end, set to circa 51V output. I use 56V zeners to limit the op-amp input voltage. Op-amps are OPA551. Output stage is 6800uF -> L -> 6800uF -> L -> 22000uF and runs around 48V. 27uF MMK caps are on the output stage power supply rails and are under the PCB's, 56uF film feedback cap is bypassed by a 47nF polystyrene. As you can see the bias transistor is a TIP41C mounted on the output stage heatsink.

https://www.dropbox.com/s/28a6p3yvq3mf2hj/20140821_201233.jpg?dl=0

David.
 
I've only ran it for a few hours so far on test speakers, the system it was built for is running off a modded QED A270 at the minute as I am re-building the pre-amp into a new case. HackerNAP no.2 was built using the same front-end regs, the only real difference was the transformers used and it sounds noticeably better than the "standard" HackerNAP I built, detail and separation are improved.

The plan for this amp is to drive my Frugalhorn XL's with Mark Audio 10.3M drivers, I am about to start the build.
 
Does anyone have a wiring schematic for HackerNAPs with single transformers for front-end and power stages? I am using one H+F 250VA 45-35-0-35-45 per channel and getting some 50Hz hum from both channels, 5mV AC on one and 40mV AC on the other and am thinking my ground wiring scheme might not be quite correct. The 35V lines go to my HackerCAP boards and the 45V lines to my Sulzer regs.

Edit: this is the ground scheme I am using:

https://drive.google.com/file/d/0B5mNigTsST6ZVG42ckRuRU83LVU/view?usp=sharing
 
Hi, I am rebuilding my NCC200/Hackernap hybrid having had a failure of the rectifiers.
I have consumed a few pairs of output transistors but also found C3 to be shorted.
The other transistors, caps and resistors seem ok.
On the last power up with a low level signal from a function generator for 5 seconds or so led to another failure of the output transistors and loss of my cheap speaker load.
Today I have just rebuilt the amp and set the bias to the right point.
I have 70mv on the good board and 80mv on the difficult board offsets.
Is this ok??
I think this may be this board's last chance; the tracks and pads are past their best and won't stand another repair.
Strangely this board has been the one to cause problems repeatedly over the years.
New woofers aren't cheap and any concerns will have me onto Mr. W for a pair of his new NCC200 boards.
Cheers Andy.
 
Andrew did you try powering up the boards without the output transistors fitted and do the checks as per the manual first

Alan
 
Yes, I think I covered it all.
I have just powered up with no input and all seems fine.
I guess that if a signal causes a problem oscillation may be a reason for failure. All the components like the Zobel and polystyrene caps seem fine and dandy.
A bit of signal next.
I will be happier when my speaker protection boards arrive and are fitted.
Cheers Andy.
 
And a little bit of signal seems to work ok!
How far should I take the input voltage in a sine wave to be reasonably sure that it would stretch the amp sufficiently to replicate the output of a preamp?
Cheers Andy.
 
Hi guys i hope you can help.

i've got my hackernap on the test bench - i built it using all the recommended components in the BOM.

My Front end PSU is putting out +/-65v and this is +/-55v after the on-board regulation. My Output PSU is at +/-55v.

The problem: when i power it up with both supplies connected, i get MAGIC SMOKE from R19 (680R) and the Front end positive drops 5-6v (i.e. i get +49/-55v). It's fine when just one of the supplies is connected.

I've tried setting the bias trimpot at min and max but this does not effect the proliferation of magic smoke.

Any thoughts? I'm pretty lost here...
thanks so much
 
You could do worse than look at Rod Elliott's website. He seems to be full of common sense on many matters.
There is an Amplifier Troubleshooting and Repair Guide in the Beginners' Luck section.
Cheers Andy.
 
Thanks Andrew.

I found some good advice by digging back through this thread.

Turns out i have blown TR8, D3, R19 and R27 (at least).

I will update when appropriate...
cheers
 
andrewsutton said:
Yes, I think I covered it all.
I have just powered up with no input and all seems fine.
I guess that if a signal causes a problem oscillation may be a reason for failure. All the components like the Zobel and polystyrene caps seem fine and dandy.
A bit of signal next.
I will be happier when my speaker protection boards arrive and are fitted.
Cheers Andy.
Click to expand...

During the latest NEBO 5 bake off I was trying to connect a Croft pre amp to my Voyagers with the owners cables, one amp switched on ok but the other one wouldn't switch on and showed the red DC light from the Vellememn board, you could also hear a very faint HF oscillation, changing the phono lead fixed the problem and the amp switched on. It turns out the ground wasn't making good contact in the lead and would have resulted in the squeal of tweeter death if the amp had switched on so it shows that the vellemens are sensitive to oscillation as well :cool:

Alan
 
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