DIY Voyager power amp Build

[337alant]

Stuck a better speaker on it and played a bit of Keb Mo via my S3 phone :eyebrow




Alan

[Paul Lange]

Great build and looking good too as well. I have not so fond memories of that bum cheek flapping moment when the amp is switched on for the first time. Luckily I never had anything happen that caused me evacuate my bowels on an initial power up. All the best for number 2 amp.

[337alant]

Great build and looking good too as well. I have not so fond memories of that bum cheek flapping moment when the amp is switched on for the first time. Luckily I never had anything happen that caused me evacuate my bowels on an initial power up. All the best for number 2 amp.

Thanks Paul, I know what you mean about the switch on moment it really is quite a nerve racking moment.
On one of my first amplifier builds years ago I got the magic blue smoke from one of the output transistors and it was a massive anti climax. I just switched it off and walked away, I remember thinking WTF do I do now ?.
Anyway I got some good advice from PFM about testing the circuit and I managed to fix the problem which was a mistake by me on the build so it was happy days in the end.
Amp No2 drilling of case ongoing, watch this space

Alan

[337alant]

Getting pretty close with Amp No2 just the back panel to drill

Temp connected up the Front end supply and all was well
Connected up the NCC200 with just the output supply and jumper leads powering the whole board but the speaker protection circuit cut in immediately showing DC on the output from the board Damn
Weird thing is I checked this board a week ago and it was fine?

Removed the board and installed a known good working NCC200 and that worked ok so nothing wrong with the supply or wiring
De-soldered the output transistors from the sick board and they both tested OK ?
Started checking around the board and all resistors are ok but found the output diode on the neg channel was short so changed that
Fired the board back up without the ouput transistors and it adjusts ok to 1.7v across TP3-4 with the Bias pot but there is still rail voltage on the speaker output
I will remove the output drivers tomorrow and test them

Alan

[337alant]

Removed the output drivers TR7, TR8 and also TR6 but all tested perfectly ?
Strange that I have 45v on the output but it doesent blow the output transistors or the 0R22 resistors
As the rail voltage is 52V this leakage must be coming through the board through some resistors to be a lower voltage and the current flow must be low enough not to blow anything ?.
Checked around the board with a strong magnifier and light for shorts between tracks but all was ok.
I have tested all of the resistors and all are the same as the circuit diag or a known working board and all caps appear to be working properly and blocking the flow from the diode tester.
So I started testing around the front end and VAS transistors with a diode tester and noted TR1 has a reading of only 10ohms between the Collector and Emitter so removed that from the board and tested it with my Atlas comp tester and Bingo TR1 is faulty
TR1 by 337alant, on Flickr


removed TR2 and that tested ok so will match up a new pair of transistor's with the 10% offset and reinstall

This should be the fault that is causing the High DC offset and hopefully I can get this amp up and running this week end

Alan

[337alant]

its working now and I have it connected it up with just to output supply connected and the jumper leads to the front end so I can set the bias in the Avondale fashion
Set it to 34ma and leaving it with the lid on the case for half an hour then will reset as bias is climbing steadily as it is warming up
I still have a bit of wiring left to do on the back panel
Ok getting back to the Bias setting, the Bias settled down at a worshop temp of 22C / 38ma so I tweeked it back to 34ma.
I then disconnected the links to the front end and then connected up the VBE FE supply
the resulting readings on start up and again warm up were
Workshop temp 22 C
Front End Constant Current draw = 12.7ma
Output Bias Current = 24.4ma
This did rise to 25.8 as the temp rose to 23C but overall quite stable

IMG_1452 by alan.towell1, on Flickr

Off to the Caravan for a couple of days left the amp swiched on and cooking, hope it doesent burn the workshop down
Looking forward to giving them a blast next week
Alan

[Macca]

Alan I don't understand much of the electronics but nice work with the yellow and green LEDs

Was it some of your amps we heard at NEBO, with the aluminium fascias? They were pretty good.

[337alant]

Hi Martin
Yes the alloy fronted amps were a Hackernap Stereo power amp and a B4 buffer pre amp
They are a very good pre / power but I am hoping these mono blocks will be better, Im also thinking of a pre amp with a bit of gain to help with my phono stage as the B4 is virtually flat out to get that to sound good

Alan

[337alant]

Glad I listend to advice about using the Vellaman speaker protection as well
Never used these before but they work very well and cut in instantly when I got DC on amp2

There are a couple of things dont like though those pin connectors for speaker cable are usless IMO, I modified mine to take some spade connectors as shown in the attached photo, you have to scratch away some of the disused tracks to do this but its easy done

20140924_150312 by alan.towell1, on Flickr

20140924_150247 by alan.towell1, on Flickr

I think you could put better quality relays in there as well ?, I also wonder about that couple of inches of pcb track inbetween your speaked lead so not sure if that has an effect on sound quality?

The yellow and red LED indicator are usefull but you would never see them inside the amp with the lid on so I took the opertunity to remote wires using security wiring 6 core to the front panel so you can see if the DC indicator shows I also took a green LED off the output cap6 as a on off indicator
I used 2 x 5w 1.6K resistors which was a bit OTT but these resistors can get quite hot so this makes them run dead cool and they were just spare resisters I had in

20140924_150214 by alan.towell1, on Flickr

IMG_1401 by alan.towell1, on Flickr

IMG_1411 by alan.towell1, on Flickr

IMG_1413 by alan.towell1, on Flickr

Alan

[337alant]

F*ck these amps are good, got them installed in my main system now and have been giving them a good thrashing all afternoon, they haven't even broke sweat
A good friend of mine bought me a cracking album by Ray Stinnett called A fire somewhere just sitting enjoying it with a glass of red.


IMG_1501 by 337alant, on Flickr

IMG_1464 by 337alant, on Flickr

IMG_1462 by 337alant, on Flickr

Alan