Hi,
The Op-Amp's.
Once you show people that it can be done just passive they turn from Op-Amp fanatics into passive fanatics...
I think the Op-Amp Gyrators are a good compromise. A PCB could contain extra spaces for inductors, both better than those from Mouser I listed and for the LF, if they can be obtained.
For all of us who cannot, the Op-Amp gyrators would be a good choice. Horses for Course and all of that Jazz...
Ciao T
The Op-Amp's.
Once you show people that it can be done just passive they turn from Op-Amp fanatics into passive fanatics...
I think the Op-Amp Gyrators are a good compromise. A PCB could contain extra spaces for inductors, both better than those from Mouser I listed and for the LF, if they can be obtained.
For all of us who cannot, the Op-Amp gyrators would be a good choice. Horses for Course and all of that Jazz...
Ciao T
Hi,
Tina. The Fetlington (etc.) has enough extra output resistance to throw the circuit off quite substantially and there is no direct cure.
Ciao T
Tina. The Fetlington (etc.) has enough extra output resistance to throw the circuit off quite substantially and there is no direct cure.
Ciao T
An aspect often overlooked with SAB (Single Amplifier/buffer Biquads) gyrators that they eat a lot of headroom, the higher the Q the more so (easily 10dB and more). The amp's output follows a (high-Q) 2nd order highpass response. Also, you need lowish Zout and Gain exatly = 1, otherwise the second cap cant' fully bootstrap the resistor, that's why specs of the buffer must be excellent (wide bandwidth). Can be circumvented a little by some series R with the first cap.
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I realised that as the other guy was using highish value resistors.
Still, opamp (gyrator) is fine with me, for 15Hz and even 120Hz.
There are enough good sounding opamps when done right.
I am certainly not going for 50 GBP a piece 2H inductors however well made, especially I would need 4x to go 2 channel balanced.
And not exactly small either.
Inductors for audio EQ equalizers. Replacements for vintage recording gear.
Patrick
Still, opamp (gyrator) is fine with me, for 15Hz and even 120Hz.
There are enough good sounding opamps when done right.
I am certainly not going for 50 GBP a piece 2H inductors however well made, especially I would need 4x to go 2 channel balanced.
And not exactly small either.
Inductors for audio EQ equalizers. Replacements for vintage recording gear.
Patrick
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Okay. I contacted Cinemag and they can produce the inductors for about $20-25 apiece. They are indicating an initial order quantity of 25 is required, but apparently make exceptions for product components (not sure why this is).
Depending upon what bass bands you want, you might need 4-6 custom inductors (2-3 x 2 channels) total. Is there interest in a group purchase, and if so, what bands/inductor sizes would be most appealing?
Depending upon what bass bands you want, you might need 4-6 custom inductors (2-3 x 2 channels) total. Is there interest in a group purchase, and if so, what bands/inductor sizes would be most appealing?
Absolutely! Yes I'm interested. Same inductor sizes as in post #18.
Would it be worthwhile to enquire for the price of a complete set for all six channels (12 inductors total)? It will be more expensive than Mouser et al, but Cinemag makes a high quality product. I feel this project may justify the extra cost. And the price you quoted is reasonable compared to the only other alternative I've run across.
Pierre
Hi,
Do not attempt to make this circuit "balanced" the "HiFi" Way (I actually tend to call it something that starts with the name of my Friend "Stu" and finishes with something that rhymes with latin for foot). That is a recipe for disaster. I am not aware of anyone ever attempting anything like that for studio gear, making two channels match is hard enough work.
If you need balanced inputs (which for domstic situatio ns rarely have any benefit) use either a transformer or Nelson's Bal-SE Converter or just ignore the second signal phase.
The balanced outputs can be created with a minimal amount of extra circuitry, if needed.
Ciao T
Do not attempt to make this circuit "balanced" the "HiFi" Way (I actually tend to call it something that starts with the name of my Friend "Stu" and finishes with something that rhymes with latin for foot). That is a recipe for disaster. I am not aware of anyone ever attempting anything like that for studio gear, making two channels match is hard enough work.
If you need balanced inputs (which for domstic situatio ns rarely have any benefit) use either a transformer or Nelson's Bal-SE Converter or just ignore the second signal phase.
The balanced outputs can be created with a minimal amount of extra circuitry, if needed.
Ciao T
I wonder why that is the case.
Assuming I use switched attenuators, all resistors can be matched to 0.1%. Extra hand match if necessary.
Caps can be hand matched to well below 0.5%, and so can FETs (curve traced).
So the only culprit are the inductors.
If I now do not connect the RLC to Gnd, but with 2 of them in series across the +ve and -ve phase 10k pots (switched attenuators),
the slight difference in inductor values and DCR for the two Ls (and in fact also the 2 Cs) will average out and no longer matters.
Or have I missed anything ?
Patrick
Assuming I use switched attenuators, all resistors can be matched to 0.1%. Extra hand match if necessary.
Caps can be hand matched to well below 0.5%, and so can FETs (curve traced).
So the only culprit are the inductors.
If I now do not connect the RLC to Gnd, but with 2 of them in series across the +ve and -ve phase 10k pots (switched attenuators),
the slight difference in inductor values and DCR for the two Ls (and in fact also the 2 Cs) will average out and no longer matters.
Or have I missed anything ?
Patrick
Hi,
True, even inductors can if necessary be trimmed (with small series additions).
One question begs itself to be asked... Why?
I think you are better off designing something totally different if you must apply the approach of my Friend's Stu's foot to EQ for some reason (more odd order distortion?)
I guess if you use rotary switches and something like Nelson's differential circuitry with unity gain you can switch the same LC chain either between the drains (attenuate) or sources (boost).
That would be a better choice than what you consider now., though personally I would still not see any actual benefit.
Ciao T
True, even inductors can if necessary be trimmed (with small series additions).
One question begs itself to be asked... Why?
I think you are better off designing something totally different if you must apply the approach of my Friend's Stu's foot to EQ for some reason (more odd order distortion?)
I guess if you use rotary switches and something like Nelson's differential circuitry with unity gain you can switch the same LC chain either between the drains (attenuate) or sources (boost).
That would be a better choice than what you consider now., though personally I would still not see any actual benefit.
Ciao T
A relay switched linear taper potentiometer example can be found here, for those who might want to go digital.
http://www.edn.com/archives/1998/031398/06di.pdf
I personally am fine with rotary switches. Just a bit pricy.
Patrick
http://www.edn.com/archives/1998/031398/06di.pdf
I personally am fine with rotary switches. Just a bit pricy.
Patrick
I will be glad to join in a group buy for 1, 2 of more inductor values - starting with the large ones of course. Anyone else interested?
