diyAB Amp The "Honey Badger" build thread - Page 26 - diyAudio
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Old 17th March 2013, 10:18 AM   #251
bkevin is offline bkevin  United Kingdom
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Default Honeybadger build - observations, comments and advice

Well Ive nearly completed populating my HB boards and I thought it worth sharing my experiences thus far.
First off the DIYAudio boards are great quality! Dont even bother trying to etch your own unless youre a die-hard DIY enthusiast!
As noted earlier by others, some of the holes are too small and need to be drilled out a bit of a shame destroying those beautiful through hole plated pads. Im sure my experience will be different to others it will depend on where you are and your choice of components but maybe making some of those really small ones a little bigger in future production runs could make it easier for DIYers
C18 and C19 solder pads are unfortunately lacquered over. I had to scrape the laquer off in order to solder the components in place. Same for CRZ jumpers. Maybe this can be corrected in next production runs
Be patient, take your time and check, double check and check your work again its a bit of a mind-numbing job and so easy to mount some components the wrong way round. Ive had to de-solder and remount 1 or 2 components on the way, despite making sure I was putting them in the right way first time round! (or so I thought...)
Here in the UK Mouser seems to be the best source for most components, but they dont have everything. I sourced from a variety of places Farnell, HiFiCollective, ModulusAmplification and Toby Electronics covered everything I needed.
Im mounting the boards directly onto those big and beautiful (4U) HFi2000 heatsinks. Ive drilled and tapped my own heat sink mounting holes using a small hand drill and good quality M3 middle tap & holder (i.e ~ 15! - watch out for some of the Chinese rubbish floating around out there). This task proved to be easy and simple just make sure you use DIYAudios very useful universal mounting specification
Thats it for now I eagerly await supply of the PSU boards to become available in the meantime Im finishing off the amplifier boards, soft starts, speaker protection boards and also building a simple, programmable IR remote control receiver to manage power on/off for this baby.
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Old 28th March 2013, 09:11 PM   #252
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When building an amp, it's nominal impedance (4,6, or 8 ohm) is set right? So the honeybadger is for 8 ohm speakers, ideally, right? Are you able to build an amp where you can choose to send 4, 6, or 8 to your speakers?

When a amp says x watts at 8 ohms, and x watts at 4 ohms does the amp automatically adjust to what impedance the speaker is???
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Old 28th March 2013, 10:57 PM   #253
bkevin is offline bkevin  United Kingdom
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Default Help!

Just powered up my HB amplifier boards for the first time this evening. Board #1 is just fine, but board #2 immediately sent the sacrificial +V 10R resistor up in a cloud of smoke (and R53 with it). Strange thing is all is fine if I connect only +50VC and 0V, but as soon as I connect -50V as well, poof goes the +V 10R sacrificial resistor (and connecting only -50V and 0V is also OK). Ive checked and double checked the boards, components and their polarities and all is OK. A quick resistance test across 0V and -50V (and +50V and 0V) gives me about 600 ohms on each so theres definitely no short to cause such a high current drain. Its not the PSU because it works fine on the other board. I can only think I must have a duff output transistor somewhere. Any suggestions or thoughts, advice on how to proceed troubleshooting this would be most welcome....
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Old 28th March 2013, 10:59 PM   #254
AJT is offline AJT  Philippines
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check your biasing circuit...
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the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
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Old 28th March 2013, 11:14 PM   #255
bkevin is offline bkevin  United Kingdom
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the bias pot is trimmed to 500R as recommended....not sure what else there is to check?
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Old 29th March 2013, 01:05 AM   #256
bkevin is offline bkevin  United Kingdom
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Quote:
Originally Posted by Tony View Post
check your biasing circuit...
OK that was a good clue... I tracked it down to a tiny copper strand that I'd managed to solder across Q12 Collector - Emitter
could barely see it with a magnifying glass! hopefully that'll do the trick.
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Old 29th March 2013, 02:23 AM   #257
repeet is offline repeet  Australia
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A good tip that I've found for finding these sort faults is to take a high res digital photo of the PCB and then analyze on your computer.
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Old 29th March 2013, 02:25 PM   #258
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Quote:
Originally Posted by HiFi Rookie View Post
When building an amp, it's nominal impedance (4,6, or 8 ohm) is set right? So the honeybadger is for 8 ohm speakers, ideally, right? Are you able to build an amp where you can choose to send 4, 6, or 8 to your speakers?

When a amp says x watts at 8 ohms, and x watts at 4 ohms does the amp automatically adjust to what impedance the speaker is???

HiFi Rookie, I think you may be confusing transmission line theory with power distribution. In the former we are trying to minimise reflections by making the generator/amp source impedance equal to the load/speaker impedance.

Maybe somewhere along the way you read about the power transfer theorem, where the answer to the question, "How do I get the maximum power from a generator into a load? is"--By arranging the load impedance to equal the generator source impedance.

In audio, reflections and impedance matching are generally of no consequence. For reasons of electromagnetic damping we minimise the source impedance resulting in a voltage source. This is akin to the electricity supply to your house. Thus it does not much matter whether you have everything or nothing turned on, the voltage remains the same.

That is not quite the end of the story as we need to design our generator/amp to deliver current to some minimum value load while still having a constant output voltage. Having taken care of that lighter loads take care of themselves. Hope this helps get your mind around the subject.

Keith
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Old 30th March 2013, 01:07 PM   #259
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Thanks Keith!
With help from people like you I will get there... Someday.
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Old 31st March 2013, 09:09 AM   #260
bkevin is offline bkevin  United Kingdom
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Red face question about CSS and LTP current

Well Ive powered up both boards (only 1 at a time using a temporary, under capped PSU I knocked up still not clear when the Universal PSU boards will be available from the DIY store ), connected to my pre-amp and speakers and even with wiring lying in an untidy mess all I can say about the sound is WOW! This is shaping up to be good and I cant wait to finish it off so I can run both channels properly (just need those PSU boards ..... )
Something which has confused me a bit is the CCS and LTP current and how best to set that up... both boards measure ~6.7V across R14 with R7 adjusted to 85R (the build guide recommend ~8.25V with R7 at 85R, which gives a current of 3.75mA but I havent been able to achieve that). I left R7 at ~70R which measured ~7V across R14 - which I suppose should give about 3.2mA at the LTP? How critical is this setting should I up the current more to the recommended 3.75mA (which by my estimates is going to mean around 50-60R on R7)?
BTW the heatsink on Q10-12 (KSA1381 & KSC3503) is running fairly cool to the touch after about 20min of high volume listening if that helps
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