| 5150ed |
I just finished my inverted gainclone using OPA541AP, 16V-0-16V 5A tran and 100K TKD step. The sound is really impressive.
But I wondering I have to turn on the step around 1.00-3.00 o'clock to get the same loundness as 9.00-11.00 o'clock from my other int'amp. Is there anything wrong? [ I normally found gainclone with step is enough gain for int' amp]
My amp is truely humless, even connected to my 97db isophon fullrange. I measured DC at my bidingpost around .4 and .5 mV. And voltage +- 24V after diod.
Any suggestion :confused: ??? |
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| Nuuk |
| If you have followed the spec sheets then you will have set a much lower gain for your OPA541 GC than for a GC using one of the LM chips. I expect that's why you find you have lower volume levels. :att'n: |
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| 5150ed |
I use R1=10K, R2 and R3 = 220K.
Should I adjust anything? |
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| Nuuk |
| I'm not sure what R1, R2 and R3 refer to but it looks like you have set the gain to around 22. This is too high for the OPA541 and you should reduce it to around 10! :att'n: |
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| 5150ed |
Hmmmm....... You mean that I have to adjusted R2 adn R3 to 100K? And the gain will be much lower :eek:.
What should I do to keep to raise the gain ??? Do I need preamp??? |
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| Nuuk |
| Yes, if you need more gain then you will need a pre-amp with some gain. How about a valve pre? I tried one with my OPA541 GC and the combination was excellent! ;) |
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| 5150ed |
Ho in fact my chip is OPA541AM not AP. Is there anything difference?
Do u got schematic of ur tube pre amp?
Anyway, thank u so much |
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| Nuuk |
No it doesn't matter which version of the OPA541 that you use, the gain should be kept to around a maximum of 10.
Details of my preamp can be found
here and some 'simpler' (but very good) preamps can be found here . ;) |
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| theChris |
the opa541 is built to work. it has an excellent "phase margin" and is stable at any gain. but its gain-bandwidth product is low. basically, that term is just as you would expect: gain*bandwidth = GBP. high gains mean low bandwidth.
the lm chips have a high GBP, but are not unconditionally stable, and require a gain around 10 to function.
as for the low volume, i can't tell for sure, but maybe you have something wrong on the current limiting feature of the opa541. |
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| 5150ed |
Thank u so much Nuuk, but i still can not see the picture :bawling: .
Do u have the schematic for inverted OPA541 with 10X gain? |
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| Nuuk |
| quote: | | Thank u so much Nuuk, but i still can not see the picture |
Which picture? :xeye:
This is the circuit that I used although I can't remember where it came from!
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| 5150ed |
Do u have inverted schematic?
What would happen if I remove R***, R5 and C7? |
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| Nuuk |
| quote: | | Do u have inverted schematic? |
No I don't.
| quote: | | What would happen if I remove R***, R5 and C7? |
I would leave R*** in. R5, and I pesume that you maen C4, are the zobel network that you could leave out to begin with. |
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| theChris |
gain above is 33. non-inverting.
r5, c4 can almost certainly be remove. they are there to help prevent instability, but with the high gain and inherint stability of the opa541, they shouldn't be needed. if you have them, they won't affect things adversely though.
C1, R3 is the input highpass filter. R3 is required because the input needs some connection to ground.
R*** is the current limiting resistor. check the datasheet to find the appropriate value. IIRC it is permissable to short out the resistor, but check the datasheet first! |
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| franksmith |
I'm in the same situation with my lm3875 amplifier.
I have lowered the gain to 15 and it still too much with my active preamp and my 96db eff speakers.
Would it be possible to build a voltage divider at the input without compromising the sound quality ? |
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| Nuuk |
| quote: | | I have lowered the gain to 15 and it still too much with my active preamp and my 96db eff speakers. |
Can you lower the gain of your preamp? |
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