| Alvin |
Hi! May I know about more about the "true" balanced gainclone circuit?
Where can I get the circuit?
Also, will it be better sound instead?
Thanks very much! |
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| Wes Marquenie |
| A non-inverted and an inverted gainclone... |
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| runebivrin |
Oh, no!:no:
That's a BridgeClone. A balanced clone is made up from two identical circuits with the loudspeaker connected between the outputs. The inputs are driven by a balanced output from a preamp.
Rune |
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| Faber |
I'm working on it.
It will be formed by a couple of 3 paralleled devices in non-inverting mode.
I'm using a +-24V at supply rails.
It will be drived by a Pass' Balanced Line Stage at aprox 60V supply voltage.
Actually it's not finished so I can't tell you if it's better or not than the BridgeClone :rolleyes:
I will use a 25dB feedback formed by high precision resistors so to avoid the use of servos, but I will also drill some additional vias to put one if needed.
HTH. Bye, Fabrizio |
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| GregGC |
| Isn't that what you meen? |
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| hitsware |
| quote: | Originally posted by GregGC
Isn't that what you meen? |
need to change R1 and R6 so their ratio is the same but the sum of their values is 10K (to match the input Z of the inverting side) |
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| theChris |
| the input imedance of both paths is not equal. this prevents it from being balenced. it is differenetial input, thoguh. notcie the input impedacne of Vin- is R1 + R0, where the input impedacne of Vin+ is dependent on signal presented to Vin-. |
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| GregGC |
I’m not exactly sure of the advantages/disadvantages of the two circuits I posted. Second one has matched + and – input impedance’s but the input DC biasing is not that good. Can anyone enlighten me on the subject. I guess the 3 opamp version will be the best of both worlds.
Greg |
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| hitsware |
| I'd dare say the 3 opamp one is purist for instrumentation, but I doubt it's veracity for audio because of the extra circuit involvement..............mike |
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| theChris |
| quote: | Originally posted by GregGC
I’m not exactly sure of the advantages/disadvantages of the two circuits I posted. Second one has matched + and – input impedance’s but the input DC biasing is not that good. Can anyone enlighten me on the subject. I guess the 3 opamp version will be the best of both worlds.
Greg |
it isn't at all balenced UNLESS one input is grounded (ignoring caps). even then the noise rejection is a function of the noise level. analyze the circut for a input of +V and -V for inputs. notice the constant 10k for the + input and the variable input impedacne of the - input. note that for a normal inverting amplifer the input impedance is 10k because the - terminal is at 0V. in this case it is at k/(k+1) V+. so is V+ is allowed to change, the input impedacne likewise changs. so if V+ is affected by noise, the noise rejection will decrease. if V+ is not grounded then the noise rejection will depend upon the input wave.
| quote: | Originally posted by hitsware
I'd dare say the 3 opamp one is purist for instrumentation, but I doubt it's veracity for audio because of the extra circuit involvement..............mike |
purist, no, but there are some practicle uses for balenced cables. the whole point is to elimanate enviromental EM and RF Noise. if neither exist you just raise the noise floor with extra active components. |
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| theChris |
| oh, there is a 2 opamp pseudo-balenced method, but there are problems because it either unbalences due to input impedance differences of the chip + opamp combo, or gets transconducatnce properties due to low input impedacne and the associated RL circut that is made.. |
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| platenspeler |
| quote: | Originally posted by GregGC
Another one. |
I would invert C11 too.
Maarten |
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| Alvin |
"I'd dare say the 3 opamp one is purist for instrumentation, but I doubt it's veracity for audio because of the extra circuit involvement..............mike"
May I know what is a 3 opamp one? |
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| theChris |
none, but he is refering to some incarnation of an instrumentation amplfier. you can either do a dual opamp inamp and then use an inverting or non-inverting amplifer after it, or use a more traditional 3 opamp implementation. i'd probably use 100k or maby 47k ohm as Rin. anything higher could increase noise, and lower adds a little transconductance, (the inductance of the wire creates a current which becomes a voltage output of the inamp).
http://www.national.com/ms/LB/LB-1.pdf - circuit 1 is a hihg impedance inamp.
you can also make a 2 opamp version with 2 opamps. each is a non-inverting amplifer. the gain of the one takeing Vin- is 2 (r1=r2) this becomes the "ground" for the feedback loop of other non-inverting amplifer. the result is k(V1 -V2), i think k > 2 is a condition. if input resistors are added, you can control the input impedance of both paths, so long as it is an order of magnitude less then the input impedance of the opamps. |
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| Squalish |
| Simply build two gainclones without input caps. |
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| theChris |
| quote: | Originally posted by Squalish
Simply build two gainclones without input caps. |
you mean to get a bridged output? |
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| Squalish |
Yes, that's what I mean.
Okay, he has a balanced source. He wants to use said source with an amp without the amp being inverted(which he calls 'bridged', balanced and bridged are the same thing, he simply wants the signal to be split at the preamp instead of the amp). Can't he just build four amplifiers, one for the + and one for the - of each channel? |
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| Dave Cigna |
| quote: | Originally posted by GregGC
Like that. |
Or even simpler.
gain = 1 + 2*R2/Rg |
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| theChris |
yeah, that works for a balenced signal with both signal polarities.
but if he has 4ohm speakers, it won't work that well. and it requires more gainclones. possibly he will make an amp that is bigger then necessary. but i guess he would also have a balenced signal to the speaker |
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| theChris |
| oh, if there's a lot of DC offset from source to amp, the thing will work oddly. the sound may still sound right at low volumes, but the clipping voltages would be lowered. |
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| GregGC |
| That would hapen if there are no input capacitor for each NIGC. If you have input caps DC on the input would not be that detremental IMO. |
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| agent.5 |
| Have any DIYers here build a gainclone driven by balanced signal yet? |
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| neutron7 |
| quote: | Originally posted by theChris
oh, if there's a lot of DC offset from source to amp, the thing will work oddly. the sound may still sound right at low volumes, but the clipping voltages would be lowered. |
if the DC offset was added deliberately and controlled the amps would be working in "class A" but without using more current or needing capacitor out.
the maximum power without clipping would be half with it in "pure fake class a" and more power, the less DC offset you added.
I have no idea how this would sound but i have been thinking of building one with adjustable offset to test it. |
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| gengcard |
| Invert Balanced GC version. :) |
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| squadra |
| quote: | Originally posted by gengcard
Invert Balanced GC version. :) |
The input resistance of this circuit is really low: < 1k.
Because pin 5 (- in) is virtual ground the input resistance is 1k // 47 k.
This will also affect the DC blocker at the input.
If the correct formula is: 1 / ( 2 * pi * R * C), the -3 dB point will be around 160Hz, which is a bit high :rolleyes:.
Change from inverting to non-inverting and the input resistance will go to 47k, and cut-off frequency will drop to 3.3Hz. |
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| gengcard |
| If I change R feedback from 20k ohm to be 1M ohm and all R 1k ohm to be 40k ohm, how about this solution? its low frequency cut off will be about 7 Hz. ;) From my opinion it'll be O.K.. |
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| theChris |
no, 1M will have implications with noise, biasing currents, and the ic amps input impedance.
you can do a T-clone. i made one -- a hi3gc (high input impedance invering gainclone). it uses a 100k input resistor and a network of 3 resistors instead of 1. this lends to more DC offset (70mV for my test).
the inverting output hooks to R2. R2 hooks to R3 and R4. R3 hooks to signal ground. R4 hooks to amp output. |
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| gengcard |
Hi theChris,
Could you post your schematic diagram to me? I will compare with my schematic diagram what are different from mine. |
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| gengcard |
| I tried to revise my design again and think that it maybe better that the old one. :D |
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| gengcard |
| I made a schematic diagram of difference amplifier. This design was added audio buffer. :) |
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| theChris |
| basically like this. i added some extra parts in for various things, but this was the design. |
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| gengcard |
| It's a good idea. Umm...Maybe I will try to design another GC by your idea. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by gengcard
I tried to revise my design again and think that it maybe better that the old one. :D |
You may wish to look for the "Chipamplifiers TNG" and various "Bridgeclone" Threads for extensive discussions of the topic....
Sayonara |
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| gengcard |
| Thanks for your suggestion :D |
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