some of your choices
alex, in your schematic you choose the 200 ohm resistor in the ouput feedback to + and - in. how did you come about this value. all of the national semi applications use a 20k approximate value for this purpose. learning here!!!! it seems by looking at your results that the overall result is quite impressive.
alex, in your schematic you choose the 200 ohm resistor in the ouput feedback to + and - in. how did you come about this value. all of the national semi applications use a 20k approximate value for this purpose. learning here!!!! it seems by looking at your results that the overall result is quite impressive.
tryonziess, I used 200k not 200ohm.
I used 200k/10k to set the gain because the in the inverted configuration, input impedance = Rin, i.e. 10k.
Noticed this is 3 LM3886s paralleled, the effective input impedance would be 10k/3 = 3.3k, which is a bit low if you don't have a active pre-amp. However in my case, I have a DRV134 to drive the inputs so it is ok.
I used 200k/10k to set the gain because the in the inverted configuration, input impedance = Rin, i.e. 10k.
Noticed this is 3 LM3886s paralleled, the effective input impedance would be 10k/3 = 3.3k, which is a bit low if you don't have a active pre-amp. However in my case, I have a DRV134 to drive the inputs so it is ok.
Since the second half of this thread was more or less a group buy, I split off that part of the thread to the Group Buys forum: http://www.diyaudio.com/forums/showthread.php?s=&threadid=103431
question concerning jrdg jensen trans
if you choose to install an input line transformer to balance the input for bridged configuration does that mean no input cap is needed. the transformer should not have any stray dc component so no input cap right?????? what about the amp gain with the trans. drv 134 adds gain to the circuit. will an input buffer be needed to boost gain. thanks
if you choose to install an input line transformer to balance the input for bridged configuration does that mean no input cap is needed. the transformer should not have any stray dc component so no input cap right?????? what about the amp gain with the trans. drv 134 adds gain to the circuit. will an input buffer be needed to boost gain. thanks
In that case I won't use the input cap.
If you use a passive pre amp (i.e. volume pot), the pot should be at 10k max. because the transformer want low source impedance.
If you concern about Amp gain, the simplest way is to change the gain setting resistors on the PA150. Default value is 10k/200k, you could change it to 10k/400k then you will double the gain.
Of course, adding a buffer before the transformer is also a good idea because transformer like low source impedance.
I may try the LL1545A later.
If you use a passive pre amp (i.e. volume pot), the pot should be at 10k max. because the transformer want low source impedance.
If you concern about Amp gain, the simplest way is to change the gain setting resistors on the PA150. Default value is 10k/200k, you could change it to 10k/400k then you will double the gain.
Of course, adding a buffer before the transformer is also a good idea because transformer like low source impedance.
I may try the LL1545A later.
Good work!
Is it possible for you to test the distortion at higher frequencies?
THD at 20 kHz is one standard measurement, for comparison purposes.
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
Is it possible for you to test the distortion at higher frequencies?
THD at 20 kHz is one standard measurement, for comparison purposes.
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
alex. in your amp project with 6- lm3886 chips you are using the drv 134 on input. what impedance is the drv putting out. does it provide gain to the overall circuit. and if you added the transformer would you still need a buffer or way to add gain. p.s. if anyone did not buy alex boards they really missed out. the 8 boards i bought are very well made. thanks
The DRV134 has a gain of 2 (6db).
From the data sheet : "Characterized by low differential-mode output
impedance (50 ohm) and high common-mode output impedance
(1.6k ohm), the DRV134 is ideal for audio applications."
If I use the transformer, I would first try without buffer. The gain of the BPA300 is high enough already, each PA150 has a gain of 20, total gain is 40.
BTW, my plan is to make a all balanced system. From my SA11 SACD player to a balanced passive preamp, to BPA300 with LL1545A at the input. The LL1545A will setup as 2:1 turn ratio to increase the input impedance of the BPA300 from 6.6k to about 26k.
From the data sheet : "Characterized by low differential-mode output
impedance (50 ohm) and high common-mode output impedance
(1.6k ohm), the DRV134 is ideal for audio applications."
If I use the transformer, I would first try without buffer. The gain of the BPA300 is high enough already, each PA150 has a gain of 20, total gain is 40.
BTW, my plan is to make a all balanced system. From my SA11 SACD player to a balanced passive preamp, to BPA300 with LL1545A at the input. The LL1545A will setup as 2:1 turn ratio to increase the input impedance of the BPA300 from 6.6k to about 26k.
my computer sound card has balanced and unbalanced inputs/outputs, it would seem that if i reworked the tuner and cd player to have balanced outputs then that would be the proper method. then you do not need transformer or drv. maybe a small buffer at the passive preamp. is that not the best solution having a total balance system.?????? and thanks again
