more aleph 2 questions - Page 2

Mattyo5 · 18th February 2005, 05:36 PM

Great! now i'm set to fire it up (hehe, when i put the dang thing together!) ...hehe fire... gotta get that 2kva variac that i've got hooked up too

-Matthew K. Olson

Mattyo5 · 18th February 2005, 06:25 PM

Ah, one other thing i thought of. Does the bias setting of r19 effect the ac current gain settings?

I'd like to have perhaps 3 settings, summer winter etc. so, what if i set the bias to a switch, 3 different settings maybe 1,2,4A bias per side, then use that switch on those settings and set the ac current gain. Or do i need to set the bias on one setting, then set the ac current gain, then set the bias, then set the current gain, then set the bias on the last setting, then set the current gain? Sorry if this doesn't make sense, just trying to get an idea of procedure here. who knows, the amp my blow up and i may never get it running haha.

-Matthew K. Olson

Netlist · 18th February 2005, 06:59 PM

As far as I can see, R19 has no influence on the AC current gain.

/Hugo

Mattyo5 · 18th February 2005, 10:01 PM

exactly what i wanted to know...thanks

-Matthew K. Olson

Blues · 18th February 2005, 10:09 PM

The maximized setting of the A2 with 3A bias is as you see it in the schematic. Those values will yield 69% ACI gain and with 10Apk of current limit (R16=100ohms) the A2 will peak at 40V and 10A.

BTW, lower percentages of the ACIG will only yield earlier distortion setting in on the +V and +I part of the signal. It will not lower overall bias current...changing the Source resistors will.

Netlist · 18th February 2005, 10:13 PM

You are most welcome.

Keep in mind that the sound quality improves with higher bias.

/Hugo

Mattyo5 · 18th February 2005, 11:25 PM

Well, i added 4xtra fets per channel, effectively throwing off the stock value of r21. So, i'm sure i'll have to play with it a bit. I know 50% is ideal efficiency, and stock is 69%, so i will play with it in there. Perhaps when i chance to low bias setting i'll set ACIG to 50%, and when i use high bias i'll set it at 65-70%. Gotta love those DPDT switches

-Matthew K. Olson

wuffwaff · 19th February 2005, 09:27 AM

two things,

1. most multimeters don´t measure right above 400Hz so if it´s not a true RMS meter choose a lower value.

2. The bias setting does have influence on the ac-current-gain. When you set the bias higher, ac-current-gain will go down.
The amount of current added by the active current source will stay the same but since the bias is higher the percentage will go down.

William

Netlist · 19th February 2005, 09:31 AM

Thanks for the rectification William.

/Hugo

Billc · 19th February 2005, 12:51 PM

Also, as you adjust the bias the power supply voltage will change and that may make a difference too.

Here is what I did:

I used two potentiometers as temporary substitutes for the resistors that set the bias and the AC current gain. Then I set a bias point, ran the equations to determine what voltage drop to look for across the source resistors at my desired AC current gain, and then adjusted the AC current gain via the pot. Now I removed the pots and measured their values. I repeated the above for other bias points. Just plug the amp into a regular wall socket during the adjustments

The problem was that the amp sounded best at the higher bias point so I just left it at that, but at least my curiosity was satisfied.

Bill

19th February 2005, 09:27 AM	#18
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	two things, 1. most multimeters don´t measure right above 400Hz so if it´s not a true RMS meter choose a lower value. 2. The bias setting does have influence on the ac-current-gain. When you set the bias higher, ac-current-gain will go down. The amount of current added by the active current source will stay the same but since the bias is higher the percentage will go down. William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

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18th February 2005, 05:36 PM	#11
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	Great! now i'm set to fire it up (hehe, when i put the dang thing together!) ...hehe fire... gotta get that 2kva variac that i've got hooked up too -Matthew K. Olson

18th February 2005, 06:25 PM	#12
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	Ah, one other thing i thought of. Does the bias setting of r19 effect the ac current gain settings? I'd like to have perhaps 3 settings, summer winter etc. so, what if i set the bias to a switch, 3 different settings maybe 1,2,4A bias per side, then use that switch on those settings and set the ac current gain. Or do i need to set the bias on one setting, then set the ac current gain, then set the bias, then set the current gain, then set the bias on the last setting, then set the current gain? Sorry if this doesn't make sense, just trying to get an idea of procedure here. who knows, the amp my blow up and i may never get it running haha. -Matthew K. Olson

18th February 2005, 06:59 PM	#13
Netlist diyAudio Moderator Join Date: Jan 2003	As far as I can see, R19 has no influence on the AC current gain. /Hugo

18th February 2005, 10:01 PM	#14
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	exactly what i wanted to know...thanks -Matthew K. Olson

18th February 2005, 10:09 PM	#15
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: Bremerton, WA	The maximized setting of the A2 with 3A bias is as you see it in the schematic. Those values will yield 69% ACI gain and with 10Apk of current limit (R16=100ohms) the A2 will peak at 40V and 10A. BTW, lower percentages of the ACIG will only yield earlier distortion setting in on the +V and +I part of the signal. It will not lower overall bias current...changing the Source resistors will.

18th February 2005, 10:13 PM	#16
Netlist diyAudio Moderator Join Date: Jan 2003	You are most welcome. Keep in mind that the sound quality improves with higher bias. /Hugo

18th February 2005, 11:25 PM	#17
Mattyo5 diyAudio Member Join Date: Aug 2002 Location: Farmington, CT	Well, i added 4xtra fets per channel, effectively throwing off the stock value of r21. So, i'm sure i'll have to play with it a bit. I know 50% is ideal efficiency, and stock is 69%, so i will play with it in there. Perhaps when i chance to low bias setting i'll set ACIG to 50%, and when i use high bias i'll set it at 65-70%. Gotta love those DPDT switches -Matthew K. Olson

19th February 2005, 09:31 AM	#19
Netlist diyAudio Moderator Join Date: Jan 2003	Thanks for the rectification William. /Hugo

19th February 2005, 12:51 PM	#20
Billc diyAudio Member Join Date: Jun 2002 Location: CT	Also, as you adjust the bias the power supply voltage will change and that may make a difference too. Here is what I did: I used two potentiometers as temporary substitutes for the resistors that set the bias and the AC current gain. Then I set a bias point, ran the equations to determine what voltage drop to look for across the source resistors at my desired AC current gain, and then adjusted the AC current gain via the pot. Now I removed the pots and measured their values. I repeated the above for other bias points. Just plug the amp into a regular wall socket during the adjustments The problem was that the amp sounded best at the higher bias point so I just left it at that, but at least my curiosity was satisfied. Bill

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