kevin gilmore Posted November 29, 2017 Author Report Share Posted November 29, 2017 continuous improvement basically trading one opa445 for a opa551, 4 transistors, 5 resistors and 1 cap probably should do the same thing to the ss dynalo. Quote Link to comment Share on other sites More sharing options...
jose Posted November 29, 2017 Report Share Posted November 29, 2017 1 hour ago, kevin gilmore said: probably should do the same thing to the ss dynalo. Oh no! please Dr. Gilmore... I just finished doing it . 1 Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted November 29, 2017 Report Share Posted November 29, 2017 Guys( the ones that already built the amp) ,what do you think in comparison with ss dynalo? Quote Link to comment Share on other sites More sharing options...
Pars Posted November 30, 2017 Report Share Posted November 30, 2017 (edited) Yes Edited November 30, 2017 by Pars Quote Link to comment Share on other sites More sharing options...
mwl168 Posted November 30, 2017 Report Share Posted November 30, 2017 10 hours ago, kevin gilmore said: newest version of the current feedback amplifier with the servo not in the audio circuit so that you can use cheaper opamps. But if you run 30v, you still need 30v capable opamp. Like opa551. what the noise difference if any, I don't know yet. Hi Kevin: Other than removing the servo from the signal path, what other benefit does this added current mirror offer? And why would the SS Dynalo need it? Isn't the servo on the various Dynalo versions already out of the signal path? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted November 30, 2017 Author Report Share Posted November 30, 2017 ss dynalo has the servo's in the same place as the cfa amp. the audio signal is nowhere near as much as that in the ksa5, but still the quality of the servo opamp can have some slight effect. I can possibly measure the difference, but don't know if I can hear the difference. Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted December 1, 2017 Report Share Posted December 1, 2017 Guys can i use this https://pt.mouser.com/ProductDetail/Vishay-Dale/RN60D5600FB14/?qs=sGAEpiMZZMu61qfTUdNhG1jRaYe8f2sLpmQ2711SR7M%3d for the 560ohm resistors ? It only has 250mw of power rating..Is that ok? Thanks Quote Link to comment Share on other sites More sharing options...
Pars Posted December 1, 2017 Report Share Posted December 1, 2017 Yes. Dale RN60s are military rated, and will handle twice the power that they are rated for. Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted December 1, 2017 Report Share Posted December 1, 2017 Thanks Pars! Quote Link to comment Share on other sites More sharing options...
Pars Posted December 1, 2017 Report Share Posted December 1, 2017 Here's a revised ltspice model with the revisions made (I think, someone check this as it was done vs. the gerber file). The current mirrors get the offset down to ~10mV without the servo opamp connected. CFP2 v1.10.zip Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 1, 2017 Author Report Share Posted December 1, 2017 no that is not correct. here is the schematic, and I hope the board matches it cfa2cmirror.PDF Quote Link to comment Share on other sites More sharing options...
Pars Posted December 1, 2017 Report Share Posted December 1, 2017 Looks like you have the servo input going into the noninverting pin of the opamp? Is that right?Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 1, 2017 Author Report Share Posted December 1, 2017 (edited) current mirror flips the polarity, so you have to flip the polarity on the opamp. the difference between the 2 servo's is something like 1mv at 7 volts peak to peak output. so very little difference. Edited December 1, 2017 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
Pars Posted December 2, 2017 Report Share Posted December 2, 2017 Here is an updated spice file per Kevin's latest schematic (pls check). Still shows -51mV without the opamp. I guess the current mirrors purpose is just to take the servo out of the audio signal path, and not about offset without the servo? CFP2 1.10.zip Quote Link to comment Share on other sites More sharing options...
mwl168 Posted December 2, 2017 Report Share Posted December 2, 2017 (edited) I consulted with Kevin and there is an option to replace the servo with a trimpot similar to what was done on the original Dynalo. I use a 10K trimpot (10K - 20K should work for supply rails between 24VDC - 30VDC) with the wiper wired to pin 6 of the servo OP socket and the two outer legs to V+ and V-. With no input connected, I adjusted the output DC offset to 0V and it only drifts about 3mV from cold start to fully warmed up. Edited December 2, 2017 by mwl168 2 1 Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted December 2, 2017 Report Share Posted December 2, 2017 (edited) Nice! @mwl168 did you soldered directly a wire to the wiper pin? Edited December 2, 2017 by ti5002000 question Quote Link to comment Share on other sites More sharing options...
mwl168 Posted December 2, 2017 Report Share Posted December 2, 2017 (edited) On 12/2/2017 at 10:28 AM, ti5002000 said: Nice! @mwl168 did you soldered directly a wire to the wiper pin? No, take a closer look at the pic I posted; I soldered a 24AWG wire to one of the outer leg of the trimpot then plug the trimpot directly into pin 5 , 6 (out), 7 (V+) of the OP socket and insert the 24AWG wire into pin 4 (V-) of the socket. The socket holds the trimpot tight and it's totally reversible. Pin 5 of OP27 is NC but is offset trim for OPA445, it's not used for this amp so the pin 5 of the OP socket is not connected to anything on the PCB. Edited May 15, 2019 by mwl168 Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 2, 2017 Author Report Share Posted December 2, 2017 pin 5 on the opamp is not a NC, so if you want to do this and put a jumper from pin 4 to pin 5 on the back of the board cut off pin 5 of the opamp, or bend out of the way. the best servo of course is no servo at all as long as everything is stable with temperature Quote Link to comment Share on other sites More sharing options...
mwl168 Posted December 2, 2017 Report Share Posted December 2, 2017 4 minutes ago, kevin gilmore said: pin 5 on the opamp is not a NC, so if you want to do this and put a jumper from pin 4 to pin 5 on the back of the board cut off pin 5 of the opamp, or bend out of the way. the best servo of course is no servo at all as long as everything is stable with temperature Thanks Kevin. I posted my edit the same time you responded and I stand corrected. I got pin 5 as NC from the OP07 and OP27 datasheet but as you said, pin 5 is not NC on OPA445 and OPA551. Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted December 2, 2017 Report Share Posted December 2, 2017 12 minutes ago, mwl168 said: No, take a closer look at the pic I posted; I soldered a 24AWG wire to one of the outer leg of the trimpot then plug the trimpot directly into pin 5 (NC), 6 (out), 7 (V+) of the OP socket and insert the 24AWG wire into pin 4 (V-) of the socket. The socket holds the trimpot tight and it's totally reversible. Understood Thanks! 9 minutes ago, kevin gilmore said: pin 5 on the opamp is not a NC, so if you want to do this and put a jumper from pin 4 to pin 5 on the back of the board cut off pin 5 of the opamp, or bend out of the way. the best servo of course is no servo at all as long as everything is stable with temperature Yes, i will try this and see what is the result.Thanks Quote Link to comment Share on other sites More sharing options...
Pars Posted December 4, 2017 Report Share Posted December 4, 2017 (edited) I tried this myself yesterday, though I bent the leg on the trimpot and soldered a jumper wire to it, so nothing in pin 5 of the dip socket. Seems to work fine, offset drifts some but nothing bad at all, probably in the +/- 3-4mV range while I was watching it. Listened to a cd with protection circuit in place and no issues. BTW, Kevin, this is a very very nice amp! Congrats! Sent from my iPhone using Tapatalk Edited December 4, 2017 by Pars Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted December 4, 2017 Report Share Posted December 4, 2017 Will this work on a ss dynahi or dynalo? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 4, 2017 Author Report Share Posted December 4, 2017 (edited) ss dynalo already has the pot, just don't populate the opamps Edited December 4, 2017 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
ti5002000 Posted December 4, 2017 Report Share Posted December 4, 2017 Oh yes ,of course....Thanks Kevin...But my Dynahi without the opa445 is definitely a no go for me... Quote Link to comment Share on other sites More sharing options...
jose Posted December 7, 2017 Report Share Posted December 7, 2017 Guys... you're killing me! Quote Link to comment Share on other sites More sharing options...
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