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Old 10th September 2012, 07:52 PM   #101
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Default Smaller transformer doesn't save money.

Hey, be sure to do at least watts * 1.5 = VA for transformer. . . or even watts * 2 = VA if you're going to do heavy loads and/or CRC filtering. Why?

Slightly big transformer amperage capacity can use smaller power supply reservoir size and still have excellent bass,
-versus-
Slightly small transformer amperage capacity needs dramatically larger power supply reservoir size that adds much cost and still might not have excellent bass.

Basically, pepping up the transformer amperage capacity is a lower risk investment and its guarantee of good bass can save you a ton of cash on caps.

It is something to consider when purchasing transformers. Trying to save a little money on the transformer will be like shooting yourself in the wallet. See how that works? I didn't know it. But, there's a thread on this topic: Power Supply Resevoir Size See Tom's charts and see the big whammy of capacitance increase for even a slightly undersize transformer. Wallet say: "ouch!" Cheaper transformer increases costs, so don't risk that.
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Old 10th September 2012, 10:32 PM   #102
Struth is offline Struth  Canada
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Hi Guys

When amps are built for mass consumption, the designer has no real idea what load will be seen and has to allow for a certain degree of "crazy" impedance dipping. This is done with higher VA PT and increased capacitance in the supply - along with suitable silicon in the audio path to pass the current.

If you know what the load is, then specifying the supply and the entire amp becomes easier. If your speakers are actually 8R with no unusual dips, then you can use a straight W=VA for the PT, assuming split rails and single-ended drive of the speaker.

If you are doing balanced drive, then the PT should be 2W=VA

If the speaker has unusual dips or you wish to accommodate lower impedances, then 2W=VA is the minimum.

To size the filter caps, you have to look at the ripple current ratings. The convention is pretty light inasmuch as the cap ripple rating should equal the RMS audio load current. I like to follow IR's suggestion with a rating of 2.7 times the load current. The cap size won't be outrageous but reliability is improved.

There can be hazards with too high a filter value that ironically results in massive hum. So better to save you money and have better performance.

The Honey-Badger pretty much follows Doug Self's ideas with the addition of the Japanese-style common-mode referenced cascode for the front end. One thing that you can easily improve is the bias regulator. It is an irony that Doug does not like the CFP reg with its very low output resistance and hence better regulation than the single-BJT with resistive compensation shown, when later he advocates a very complex bias controller for his class-A amp! The latter was not original as others have used such circuits since the late 1970s.

Have fun
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Old 10th September 2012, 11:43 PM   #103
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Good memory Mark, those are used these days for the F5… I know, huge for that application.
The ones I will use on the Badger are similar, only smaller.
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Old 15th October 2012, 04:21 PM   #104
PKI is offline PKI  United States
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Guys, does this amp sound good? :-) Or its just "don't care" :-). How its compare to, lets say Adcom 545 amp? Sorry if my question is stupid. I just need to build an amp which can handle difficult speakers and sounds as close to class A (NP DIT amps) amp as possible :-)
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Old 17th October 2012, 03:29 AM   #105
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Quote:
Originally Posted by PKI View Post
Guys, does this amp sound good? :-) Or its just "don't care" :-). How its compare to, lets say Adcom 545 amp? Sorry if my question is stupid. I just need to build an amp which can handle difficult speakers and sounds as close to class A (NP DIT amps) amp as possible :-)
Tone1
In the builders guide (link at the bottom of the page in the diyaudio.com store) there is listed several different compensation options and that fine tunes the tone. It is Class A during low volume playback (the bias, you know). All of the options are highly linear, so mostly what matters is. . . whatever you put at the input.

Tone2
It is an excellent power amp, but it is not an integrated amp, and this will be an inconvenience that you can use to your advantage. For example, my computer can push a 20 watt amplifier to almost 20 watts. It can also push a 300 watt amplifier to almost 20 watts. My CD player can do almost twice as much, but still couldn't push a Honey Badger to maximum. Of course this needs a preamplifier. So, if you want Class A sound, just use a Class A preamp. You'll have a wonderful experience with both the dynamics and tone. If using computer source, try a buffered preamplifier. The computer would like a buffer if you would like an effortless presentation, but it will also need a preamplifier if you want to play quite loud. You can get all the Class A tone you want at the input of the power amp. The amplifier will amplify that very faithfully.

Driving speakers:
The output devices for Honey badger are all high end performance (albeit not all high end prices) and in triplicate the HFE doesn't fall low enough to burden the drivers. Crossing noise goes into the ballast resistors, not into your speakers. This OStripper amplifier was physically tested to withstand the load of a digital pipe organ and still play linear, even at high power. It will easily deliver all your transformer has to offer. It is possible to throttle any amplifier with the transformer too small, so if you have difficult speakers, go for watts*3=VA for an effortless presentation.
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Old 20th October 2012, 10:24 PM   #106
jimchan is offline jimchan  Norway
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Hi Daniel,

Thanks for your interesting comments about the sound. I would not expect to hear too much difference in the tone dependant upon the biasing, but am looking forward to trying.

Also interesting comments about the pre-amp. I expect the HB will reveal limitations in my source (DAC with opamp / passive pot) , but that will just be progress.


BR James.
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Old 21st October 2012, 04:32 AM   #107
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Originally Posted by jimchan View Post
Also interesting comments about the pre-amp. I expect the HB will reveal limitations in my source (DAC with opamp / passive pot), but that will just be progress. BR James.
That was fun--sent me right to the schematic too. The gain setting voltage divider is 33k feedback with 820R feedback shunt. Divide and then add 1. . . a gain setting of 41. In reference to the transformer selection discussion earlier on this thread, a lower voltage Honey Badger wouldn't need a preamp.

Discrete is nice because its adjustable and therefore, the spot to use a chip is the OnSemi MC7*** chip regulators, with excellent specs, and convenient for powering your discrete preamps and discrete buffers.

With a DAC of any sort, be it an on-board computer sound chip or something more elaborate, I'd be looking at discrete buffer projects, not because you need it but because you might like it. Flaws in your DAC are most likely to be power supply and drive, so clean power and buffered output should be really good enhancements.
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Old 21st October 2012, 01:59 PM   #108
jimchan is offline jimchan  Norway
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Agree with the comments about the DAC PS. I am building a Salas shunt to replace the regulators for the DAC chip and OPA827 Op Amp. Can swap out for a discrete buffer pre-amp project later down the line perhaps.

For the HB transformer selection, I was considering an identical 800VA Antek to Jojo...unless anyone has other suggestions (European shipper would be better)

For the components, I will start going through your BOM and mouser parts.... thanks for your efforts.
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Old 23rd October 2012, 07:12 AM   #109
Variac is offline Variac  United States
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Daniel,
I would appreciate it if you would mention when you write stuff that these are your personal theories, not necessarily the most commonly accepted ideas. Most people posting mention their observations and ideas are their personal observations, but you state your opinions and observations as audio fact. Please make it clear that you are only stating your opinions.

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Old 4th November 2012, 04:20 PM   #110
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Even simpler. Please point out any errors in these calculations.

The amplifier has a gain of 33K/820 = 40.2.

The power output is advertised as 150W into 8R, so 35Vrms. 35Vrms/40.2 = 0.87Vrms input.

0.87Vrms/24.8K = 35nA.

Even the most abysmal source will be able to drive this amp to clipping.
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