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Old 30th March 2011, 06:01 PM   #771
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Lineup -

I've been working with this schematic for the last few weeks and I intend to build a monster for driving 8 ohm loads in the next few weeks (transistors are arriving soon). Can you tell me why you decreased the emitter resistors in the output stage to 0.5 ohm when using 16V rails? I like the idea of getting (a little) more power out of the amp, but I don't want to run a bias of nearly 2 amps.

Others -

I bought some of the parts (output transistors, mostly) from MCM Electronics. It sounds like these certainly aren't the originals -- does anyone have experience with them working well anyway? I bought the JFET's and the cascode BJT's on Ebay.
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Old 30th March 2011, 08:49 PM   #772
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(I don't see an option to edit my post..)

Update:

I now see that the 0.5 ohm resistance increases the bias current in the output stage which is needed when driving a 4 ohm load to keep the amp in class A. So if I am to build this amp with 16v rails I should be able to still use 1 ohm emitter resistors with a bias of 800ma - 1000ma. Do people usually use pots for R1,R12 so that the bias is adjustable?
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Old 31st March 2011, 09:06 AM   #773
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Quote:
Originally Posted by ravix View Post
- Do people usually use pots for R1,R12 so that the bias is adjustable?
This is a good idea: Hiraga describes the amplifier as consisting of two halves.
The Hfe of the two sides never match perfectly. So adjusting the DC will also affect the amplification.

I observed that there is a slight preference for either the top side or bottom side to hit the power rail first when driven to almost full output. The difference is less than 100 mV RMS difference (seen on the scope) between sides in my implementation. A variable pot on R1/R12 would probably overcome this small inconvenience. In my Le Classe A I have done that, in an experiment.
I do have a distortion analyzer that allows me to see the effects.

Finding the right value though (this is implementation, not simulation) is going to take a long time I think as it involves iterations. I see it at this moment as just cosmetic though.
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Old 1st April 2011, 03:00 PM   #774
osscar is offline osscar  Latvia
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Hello jarinal !

Glad to hear that you like monster sound. Nice and big amp you built !
Congratulations!
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Old 1st April 2011, 04:12 PM   #775
lineup is offline lineup  Sweden
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Quote:
Originally Posted by ravix View Post
(I don't see an option to edit my post..)

Update:
I now see that the 0.5 ohm resistance increases the bias current in the output stage which is needed when driving a 4 ohm load to keep the amp in class A. So if I am to build this amp with 16v rails I should be able to still use 1 ohm emitter resistors with a bias of 800ma - 1000ma. Do people usually use pots for R1,R12 so that the bias is adjustable?
This is for 2x16 Volt operation.

For 4 Ohm I recommend 0.5 Ohm and 1.5 Ampere.

For 8 Ohm operation you need not the extra 1 Ohm resistors.
And you set bias to like 1.0-1.1 Ampere.

These figures is for pressing the amplifier max possible output.
Of course you can chose to run smooth on less current.
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Old 3rd April 2011, 07:35 AM   #776
WuYit is offline WuYit  Sweden
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lineup,
thatīs a very nice modification in post #767. Hopefully, the capacitor can be avoided.
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Old 4th April 2011, 03:53 AM   #777
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Quote:
Originally Posted by jarinal View Post
Good evening gentlemen.

I Thought I'd share a few pictures of my own build.
Click the image to open in full size.
Bildr.no
Here are the intestines of my monster. The power supply is as simple as it gets. Just two 220 000uF capacitors, a rectifier i found on the dump and a 300VA toroid. I'm currently working on making the transformer shield fit. The ground routes got a bit messy while trying to reduce the power supply noise, but it's nearly dead silent now.

Click the image to open in full size.
Bildr.no
The case is a bigger version of osscar's. The cooling is a bit over dimensioned, as the amplifier rarely gets hotter than 30-40 Celsius with a bias of 700mA

The main reason for the big case are the two capacitors.

I must say I'm impressed by the sound. The bass is so unbelievably tight. My NAD T744 doesn't have nearly as good sound.
glad you have the nice monstre sound excellent job
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Old 4th April 2011, 06:27 AM   #778
lineup is offline lineup  Sweden
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Quote:
Originally Posted by WuYit View Post
lineup,
thatīs a very nice modification in post #767. Hopefully, the capacitor can be avoided.
It is stable without caps.
For a prefect AC curve, use caps.
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Old 4th April 2011, 07:07 AM   #779
WuYit is offline WuYit  Sweden
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If only you knew just how devastating they are for the "AC curve", you probably would not say so.
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Old 5th April 2011, 06:51 AM   #780
vizion is offline vizion  United States
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Default Power Draw for Hiraga Bakamono (monster in japanese)

What is the power consumption of 8w Hiraga amps ? 8w x 2 channels = 16w , 25% of 64w = 16w. So I'm guessing just 64w power draw for Class A.

Pretty cool running.
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