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Old 26th October 2013, 02:19 PM   #511
Bigun is online now Bigun  Canada
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I've noticed that the Pioneer amplifier design for 2012 home theatre models which is traditional LTP - VAS - Sanken Darlington runs also a low bias current of around 8.5mA. It was obvious to me this was designed to reduce the thermal load for 7 channels sharing one heatsink but it didn't sound half bad which matches your observation too.
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Old 26th October 2013, 02:41 PM   #512
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Quote:
Originally Posted by Bigun View Post
I've noticed that the Pioneer amplifier design for 2012 home theatre models which is traditional LTP - VAS - Sanken Darlington runs also a low bias current of around 8.5mA. It was obvious to me this was designed to reduce the thermal load for 7 channels sharing one heatsink but it didn't sound half bad which matches your observation too.

I think the Sankens are designed to run at lower bias.
The smaller vintage amps have used C3856/A1492 for 25 years. This device
has superior SOA and much different Vsat/Ic-Vce charecteristics compared to
the typical ON/Fairchild offerings.
20-30ma bias is what the service manuals recommend as optimum.

MCM electronics has these MT-100's and the MT-200's for 2-4 usd $ apiece! Audio Output within Transistors - MCM Electronics Category

Seriously considering buying
20 of these for my 2 amps.

OS
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Old 26th October 2013, 02:57 PM   #513
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Quote:
Originally Posted by ostripper View Post
.......
20-30ma bias is what the service manuals recommend as optimum......
OS
Ah...ha...! This seems to be close to the 35mA that I tried. But then I guess I should check out 35 mA vs 100 mA also ? As everything is in place better to try it now as a 'later' might not take place any time soon!
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Old 26th October 2013, 05:24 PM   #514
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Quote:
Originally Posted by ostripper View Post
I think the Sankens are designed to run at lower bias.
The smaller vintage amps have used C3856/A1492 for 25 years. This device
has superior SOA and much different Vsat/Ic-Vce charecteristics compared to
the typical ON/Fairchild offerings.
20-30ma bias is what the service manuals recommend as optimum.



OS
The Pioneer amps of late use the Sanken 2SD2390/2SB1560 in TO-3 style packages. The service manual calls for 2mV across Re, which is a pair of 0R47's in parallel - hence 8.5mA. They don't use any Cdom, different compensation scheme. I have 7 pairs of these things which could be nice for Gabor's amp.
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Old 26th October 2013, 06:46 PM   #515
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You mean TO-3 (P)... alias MT100 ? I don't think they use the real metal packages
anymore.

Just looked at the 2SD2390 , thick film resistor is integrated ... local feedback from OP to internal driver.
This is another factor in the lower bias requirements.
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Last edited by ostripper; 26th October 2013 at 06:50 PM.
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Old 26th October 2013, 06:49 PM   #516
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Yup, them plastic with metal tab ones is the ones, not those big 2N3055-like things !
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Old 6th January 2014, 03:51 AM   #517
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Default Any more experimentation by anyone ?

I haven't had time to do anything more than I did earlier. However I tried the slightly different Acca version against a Bryston 3B power amp playing only one channel. I really couldn't make out any significant difference. Though I get some bass out of my speakers ( mission 701's ) I can't comment on LF control of the amplifiers. With the 701's I could not hear any diff in the bass.
My power transistors were TIP142/147.
I want to try out this circuit with discrete bipolar Darlington's so that I can raise the supply voltage. I think 100 W/8 ohms /200 watt/ 4ohms is doable. It might be a good idea to keep the number of power transistors down. I'm going by the often seen opinion that multiple power devices cause a loss of SQ though they enable more output power.
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Old 6th January 2014, 12:32 PM   #518
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Quote:
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I'm going by the often seen opinion that multiple power devices cause a loss of SQ though they enable more output power.
Look at my TGM8 for a possible solution - uses two pairs but one pair is run in Class C and doesn't impact sound quality during the first few watts.
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Old 6th January 2014, 04:16 PM   #519
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Hi Bigun,
In another post ( maybe on this thread....I don't remember !), I reported my test with a similar output pair run in class C. I called it augmented output stage. It came on only after the first power device provided some gain and worked something like a current dumper .
It did sound good and power was split between the devices. However I never compared them. Will probably do it some time.It's similar to some beefed up chip power amps. The sharing of the Re resistor is important which isn't possible in a chip power amp.
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Old 6th January 2014, 04:20 PM   #520
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In TGM8 you don't need emitter sharing resistors or any device matching. The Class C device won't runaway because it's normally biassed off and once the Class C device is turned on it limits the maximum current through the Class B device.

My feeling is that any impact on sound should be minimal and depends more on the driver than the output.

Edit: sorry, I see you meant 'sharing of Re' not using Re for current sharing.
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