diyAB Amp The "Honey Badger" build thread - Page 119 - diyAudio
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Old 20th August 2014, 06:45 PM   #1181
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Mine is biased per spec. Sounds lovely.
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Old 20th August 2014, 11:52 PM   #1182
jdg123 is offline jdg123  United States
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Default adjustment and limits

I am Very impressed by the HB built to spec. No doubt about it.

It is just that there are inside it these little knobs one might adjust...I cannot help but wonder if I can make things a little bit better by adjustment...even if the adjustment is not in the build guide. I Do wonder though what are the limits to safe adjustment.

If turning up the bias is limited only by heat sink and common sense I see no harm in doubling it but I am new and may not see the pitfall...
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Old 21st August 2014, 12:16 AM   #1183
AJT is offline AJT  Philippines
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Quote:
Originally Posted by jdg123 View Post
I built to spec, no issues at all :-).

I'm just wondering if more bias, keeping it in class A longer, will make it even better ?
if your heatsinks are up to it, you can increase bias to increase idle output stage dissipation for wider class A window, you can do it in small steps and listen each time...
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Old 21st August 2014, 09:11 AM   #1184
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by jdg123 View Post
.......................but wonder if I can make things a little bit better by adjustment...even if the adjustment is not in the build guide. I Do wonder though what are the limits to safe adjustment.

If turning up the bias is limited only by heat sink and common sense I see no harm in doubling it but I am new and may not see the pitfall...
Doubling the output stage bias current adds 6dB to the ClassA output before transitioning to ClassAB.
That wil probably make a significant difference to the sound with certain types of speakers and for some specific types of listening levels.

If you find that you prefer the high bias version, then I suggest you look at adjusting the power supply to send much lower voltage to the amplifier.
A similar improvement can be had by doubling the number of output devices for the same doubling of output bias. This keeps the amplifier at the same bias per device.

A combination of doubled devices and reduced voltage would make a good ClassAB with 4 times the ClassA power capability (that +6dB).
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Old 21st August 2014, 02:23 PM   #1185
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I found the gain problem for the one channel. The signal and ground were swapped at the input to the terminal block. As far as bias is concerned I'm running at 50mv from TP1-2. That is around 114ma per pair. After an hour of low level listening the heatsinks were very warm but I could hold my hand on them continuosly without pulling back. My sinks are not that big but also have heavy aluminum angle bracket internal that they are bolted to. It's actually the chassis and power supply of an old Quartro 250 that works out well. Oh yeah this is with MJL21193/4 outputs and +/- 60 volt rails.
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Old 23rd August 2014, 02:13 PM   #1186
jdg123 is offline jdg123  United States
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Default Thanks for the input!

AndrewT: your responses are as always, informative and to the point. Thank you!

My only option for dropping rail voltage on this build is to cut it in half to 31VDC. That seemed too low when I put it forth to OS. This does not discount to possibility of a second build :-)

I'm in the process of building a Nelson Pass F5t v2. I'll compare the HB to the F5t and decide which way to jump: HB with maybe 40VDC rails and high bias for class A or a F5tv3. Or maybe a balanced Aleph...I wish I had the chance to visit other audio guys and hear what is going on with their builds. As it is, I am directed by chance to keep on building...not so bad an option :-)

Once again, I thank you as well as the many others lending me their knowledge making my builds possible! It is a good thing we have going here!

Cheers!
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Old 23rd August 2014, 02:58 PM   #1187
AndrewT is offline AndrewT  Scotland
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F5 and F5t are ClassAB amplifiers.
The difference is that the F5 & F5t use mosFETs and they don't have a optimal ClassAB bias current.

The crossover distortion just gets less as the bias current is increased.
There is no reason to run a F5, nor F5t, at low bias, except to save on heatsink and PSU.
Bias the mosFETs into high bias ClassAB, as high as the heat will allow.
That gets you into lots of ClassA before the amps transition into ClassAB.

A high bias ClassAB that never leaves ClassA should sound virtually the same whether it's a mosFET, or a BJT.
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Old 24th August 2014, 06:19 PM   #1188
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I've got hold of a pair of v2.2 HB pcbs. Can some one summarise the difference between v2.2 and the current version?

Any one in the UK or perhaps EU countries share their BOM ?

I'm collecting parts for my build.

Thanks
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Old 1st September 2014, 08:05 PM   #1189
jdg123 is offline jdg123  United States
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Default 101mV

Hello out there.

I thought I'd report that I have taken up the bias on my Honey Badger, TP1 to TP2, to 101mV and yes it does sound better!

Heat sink now gets pretty warm: 110F after an hour but on the Pass forums I get the impression that 130F (55C) is the practical limit. Am I wrong in this?



Cheers!
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Old 4th September 2014, 08:51 AM   #1190
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Hi guys, is it possible send this or another PCB from DIY shop to Europe?
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