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Old 7th June 2003, 12:37 PM   #71
Mad_K is offline Mad_K  Norway
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547/8/9 have bipolar inputs. opa541 have fet input
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Old 7th June 2003, 07:19 PM   #72
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Default Re: Re: another question..

Quote:
Originally posted by Kuei Yang Wang
Koinichiwa,



Hey, I forgot, the OPA's are FET input I think, so you cannot null the offset the same way as on the LM3875/3886. Simply use 0.47/0.5R output resistors, ground the non-inverting input and hope for the best.

If they are not FET Input your Pot needs to be around twice the value of all the resistors that are not DC blocked on the inverting input in paralell, so in your case 6k2//220k*2 = 12k - NPV is 10k.

Sayonara

Quote:
Originally posted by Mad_K
547/8/9 have bipolar inputs. opa541 have fet input
i using opa541, what value should i use to zero the offset?
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Old 7th June 2003, 09:00 PM   #73
Cobra2 is offline Cobra2  Norway
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Maybe this can be used? :

Arne K

(BB - APPLICATION BULLETIN - sboa046.pdf)
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File Type: gif op-amp-offset.gif (9.3 KB, 1723 views)
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Old 7th June 2003, 11:24 PM   #74
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Koinichiwa,

Quote:
Originally posted by Cobra2
Maybe this can be used? :

Arne K

(BB - APPLICATION BULLETIN - sboa046.pdf)
Yeah, Sure. But it adds a load of components and potential noise sources. Other than that - it will work for any chip, J-Fet input or not.

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Old 30th June 2003, 03:08 AM   #75
wrl is offline wrl  United States
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Default Output:

Just wondering what kind of output values you are expecting to get out of these circuits.

I know that the app notes from national state ~100W out of the bridged and the paralleled versions, and ~200W out of the bridged/parallel version. Although I think that they specify +-40V for their power supply.




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Old 30th June 2003, 02:55 PM   #76
dorkus is offline dorkus  United States
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Default output

the output of a bridged cricuit into an 8 ohm load will be about 2x the rated output of the original non-bridged circuit into a 4 ohm load, generally speaking. so if your original circuit got 30wpc into 4ohms, it'll now put out 60wpc into 8 ohms. problem is that this rule applies to lower impedances as well, where you'll be more current limited than anything else.... so bridging is not recommended if you have low impedance speakers, unless you parallel devices to compensate.
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Old 3rd July 2003, 08:33 AM   #77
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Default Re: Re: Re: another question..

Quote:
Originally posted by Matttcattt
i using opa541, what value should i use to zero the offset?

as i havent had any feedback, i have ordered 2 5k 22-turn presets. if i have the non-inverting input connected to ground dirrectly now, why would a 200k+ preset be used? i would have thought that 5k was to much, and that i would not be able to zero offset accuratly. i will post the results of my test here.
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Old 28th July 2003, 05:52 AM   #78
dorkus is offline dorkus  United States
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Default bridgeclone impression - worth the trouble?

how're the bridgeclones going fellas? i'm going to build a quad-channel gainclone of some sort or other, partly for fun, partly for experimenting with biamping, mostly to use eventually for the rear speakers in my surround setup. like others i have been dabbling with the idea of a bridged version. the extra power into higher-impedance loads is an obvious benefit, but i'm more interested in improvements in quality than quantity. can anyone comment on how a "properly implemented" bridgeclone compares to a single-ended version (e.g. Peter's)?

my own idea is to use a "proper" input transformer to derive the balanced signal, followed by a two standard single-ended gainclone circuits in complementary (bridged) fashion. i hesitate to call this a "balanced" amplifier as it does not have any intrinsic CMRR (it's left to the final load - the speaker - to sort that out), but i have heard from a few people that this is the best sounding way to go anyway. does using gainclone in this manner have any implications for circuit stability or final sound quality? would be very interested in some opinions on the matter. i did search thru the various threads for such answers, but it seems that most people attempting "bridgeclone" had not reached the development stage Peter is at with his design. Kuei Yang Wang, any thoughts?

cheers,
dorkus
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Old 28th July 2003, 09:22 AM   #79
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Default Re: bridgeclone impression - worth the trouble?

Quote:
Originally posted by dorkus
how're the bridgeclones going fellas? i'm going to build a quad-channel gainclone of some sort or other, partly for fun, partly for experimenting with biamping, mostly to use eventually for the rear speakers in my surround setup. like others i have been dabbling with the idea of a bridged version. the extra power into higher-impedance loads is an obvious benefit, but i'm more interested in improvements in quality than quantity. can anyone comment on how a "properly implemented" bridgeclone compares to a single-ended version (e.g. Peter's)?

my own idea is to use a "proper" input transformer to derive the balanced signal, followed by a two standard single-ended gainclone circuits in complementary (bridged) fashion. i hesitate to call this a "balanced" amplifier as it does not have any intrinsic CMRR (it's left to the final load - the speaker - to sort that out), but i have heard from a few people that this is the best sounding way to go anyway. does using gainclone in this manner have any implications for circuit stability or final sound quality? would be very interested in some opinions on the matter. i did search thru the various threads for such answers, but it seems that most people attempting "bridgeclone" had not reached the development stage Peter is at with his design. Kuei Yang Wang, any thoughts?

cheers,
dorkus
i am in the construction stage of my proper amplifier, using bridged, and bridged and paralleled. i have tested bridged, and bridged and paralleled, using the DRV134 IC to get the balanced input. i am using the OPA541 and OPA549 (8 of each) to get 4x bridged (OPA541) and 2x bridged and paralleled (OPA549). it is documented (not very well ) on my website: http://www.freewebs.com/matttcatttweb/index.htm have a look
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Old 28th July 2003, 11:39 AM   #80
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....but how does it sound...?
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