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Dual Offest Sub-audio Test Signal

Started by Unknown May 23, 2014
"David Eather"
> Phil Allison >> "piglet" >> >> ** Confucius say: >> >> " Piglet cannot teach fool to sing " >> >> > > Phil, I don't normally comment about this (because we have a bit of > history) but most of the time you hand out *superb* advice - its only some > of the "other bits" that stop you from being an all-round super guy.
** Err ............... can I take it my tiny joke gave you a chuckle ? BTW: Did you write: "A Practical Approach to Amplifier Output Design", Silicon Chip, February 1991, .... Phil
On 25/05/2014 10:33, piglet wrote:
> Please have a look at the two sketches in the attached link > https://dl.dropboxusercontent.com/u/16764432/SED_JG_MAY14.pdf
Those two sketches should be regarded as semi-conceptual. If you were to actually build these then I suggest adding a few Rs and Cs to tame possible hf parasitics or instabilities. Link to revised sketches: https://dl.dropboxusercontent.com/u/16764432/SED_JG_MAY14_a1.pdf regards piglet
On Sun, 25 May 2014 02:33:44 -0700 (PDT), piglet
<erichpwagner@hotmail.com> wrote:


>Please have a look at the two sketches in the attached link > >https://dl.dropboxusercontent.com/u/16764432/SED_JG_MAY14.pdf > >they should help you get going. >
Many thanks for this. I have printed out your circuits and will build them up. Looks like good solid design, as opposed to my guesswork. John Gillmore
On Sun, 25 May 2014 01:18:15 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:


>> http://www.4shared.com/download/jKjCKu1aba/dual_current_driver_3.jpg?lgfp=3000 >> >The diagram indicates a 'synthetic ground' buffered by an op amp, which is never used. >
>How's this? ><http://www.digikey.com/schemeit/#u7g> >
Yes, I can now see what you are suggesting. I will build a circuit based upon all the helpful input so far, and see how it performs.
>I'm still not sure what's the goal... >
The object is to feed each coil with the same signal but at different potentials. It is for an experiment, which of course explains why it is never done:-) Thnaks again. John Gillmore
On Sun, 25 May 2014 03:23:49 -0500, John Fields
<jfields@austininstruments.com> wrote:


>I'm late into the fray. > >Is your supply's output: +6V 0V -6V or is it lacking a common? >
Hello John. To achieve the waveforms shown below, I believe the coils cannot be ground referenced. Maybe I am wrong, but so far I do not see any other suggestion that would do this. http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 I know this is not a conventional design, however some viewers have kindly sent in circuits that appear to address the problem, and correct my own flawed attempts. https://dl.dropboxusercontent.com/u/16764432/SED_JG_MAY14_a1.pdf http://www.digikey.com/schemeit/#u7g I know you are one of the long-time "experts" here, so if you have any comments they would be most appreciated. John Gallimore
On 25/05/2014 22:37, jgillmore@netscan.com wrote:
> ... I believe the coils cannot be ground referenced.
They can. The example circuit using split +6V and -6V supply does have one end of each coil connected to a common ground shared with the function generator and scope. piglet
On Sat, 24 May 2014 17:00:28 +1000, jgillmore@netscan.com wrote:

>On Sat, 24 May 2014 06:19:23 GMT, Jan Panteltje <panteltje@yahoo.com> >wrote: > > >>>This diagram shows it in detail: >>> >>>http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3D3=
000
>>> > >>Just use a transistor driven by an opamp on a 12V supply, >>and reverse the connections for once coil... >> >> >> +12 >> 10 Hz | >> +12 signal inductor2 (reverse connected) >> | | | >> [ ] =3D=3D=3D inductor1 (normal connected) >> | | \ | >> [ ] <------|+ \ c >> | bias | >--- b NPN >> /// --|- / e >> | / | >> -------------| >> | >> Rsense (1 Ohm?)=20 >> | >> /// >>? >>=20 > >Looks to me like two coils driven oppositely, or antiphase. > >Sorry, but I don't see how this would circuit provide the signal that >swings from -1V to -5V, as shown on my diagram. > >http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3D300=
0
> >Am I missing something? > >John Gallimore
Perhaps, inductors are biased with a current not a voltage. ?-) =20
On Sun, 25 May 2014 20:31:33 +1000, Phil Allison <phil_a@tpg.com.au> wrote:

> > "David Eather" >> Phil Allison >>> "piglet" >>> >>> ** Confucius say: >>> >>> " Piglet cannot teach fool to sing " >>> >>> >> >> Phil, I don't normally comment about this (because we have a bit of >> history) but most of the time you hand out *superb* advice - its only >> some >> of the "other bits" that stop you from being an all-round super guy. > > > ** Err ............... > > can I take it my tiny joke gave you a chuckle ?
While eastern wisdom is not widely enough appropriated in the west, no, I was enjoying reading your succinct and accurate posts.
> > > BTW: Did you write: > > "A Practical Approach to Amplifier Output Design", Silicon Chip, > February > 1991, > >
I am trying to disown that one. All my work up to then had been microprocessors and industrial control. The Roger Harrison and Graham Dicker put out "the best amp project ever!" - the Digi-125. From what I could find at the time Dicker has a reputation as being a bit of a valve amp guru (no guarantee there is any truth in that) but that Digi thing was (IMO) a travesty just waiting to turn into a house fire. I email or wrote to Harrison but he didn't care and just keep putting out glowing praise for it. I don't mind the first part of the article - except for compromises without giving reasons I wouldn't do it that way now, but I must have left the cellophane on my cigar while writing that stuff about filter caps. (its just carp - how do you choose cap size? Same way as everything else. Oui)
> > .... Phil >
"David Eather"
> Phil Allison >> ** Err ............... >> >> can I take it my tiny joke gave you a chuckle ? > > While eastern wisdom is not widely enough appropriated in the west, no, I > was enjoying reading your succinct and accurate posts. > >> >> BTW: Did you write: >> >> "A Practical Approach to Amplifier Output Design", Silicon Chip, >> February 1991, >> > > I am trying to disown that one.
** Good thing I never read it.....
> All my work up to then had been microprocessors and industrial control. > The Roger Harrison and Graham Dicker put out "the best amp project > ever!" - the Digi-125. From what I could find at the time Dicker has a > reputation as being a bit of a valve amp guru (no guarantee there is any > truth in that) but that Digi thing was (IMO) a travesty just waiting to > turn into a house fire. I email or wrote to Harrison but he didn't care > and just keep putting out glowing praise for it.
** Harrison ( editor of ETI magazine in the 1980s) was a ham radio guru - so knew little about electronics .... He was obliged to trust contributors and staff alike, having no way nor much interest in seeing through the smoke and mirrors game that was going on. There were a number of front page projects that simply did not work, but he was not interested in hearing about any of them nor the scam "TIC" brand, fake MJ15003/4 power transistors that DSE had imported thousands of. I know, cos I foolishly tried to inform him. .... Phil
On Wed, 28 May 2014 12:00:16 +1000, Phil Allison <phil_a@tpg.com.au> wrote:

> > "David Eather" >> Phil Allison >>> ** Err ............... >>> >>> can I take it my tiny joke gave you a chuckle ? >> >> While eastern wisdom is not widely enough appropriated in the west, >> no, I >> was enjoying reading your succinct and accurate posts. >> >>> >>> BTW: Did you write: >>> >>> "A Practical Approach to Amplifier Output Design", Silicon Chip, >>> February 1991, >>> >> >> I am trying to disown that one. > > ** Good thing I never read it..... > > >> All my work up to then had been microprocessors and industrial control. >> The Roger Harrison and Graham Dicker put out "the best amp project >> ever!" - the Digi-125. From what I could find at the time Dicker has a >> reputation as being a bit of a valve amp guru (no guarantee there is >> any >> truth in that) but that Digi thing was (IMO) a travesty just waiting to >> turn into a house fire. I email or wrote to Harrison but he didn't care >> and just keep putting out glowing praise for it. > > ** Harrison ( editor of ETI magazine in the 1980s) was a ham radio guru > - > so knew little about electronics .... > > He was obliged to trust contributors and staff alike, having no way nor > much > interest in seeing through the smoke and mirrors game that was going on. > There were a number of front page projects that simply did not work, but > he > was not interested in hearing about any of them nor the scam "TIC" brand, > fake MJ15003/4 power transistors that DSE had imported thousands of. >
I remember them. I had a job at DSE and they sent around memos (and a weekly video) claiming they were all kosher but a lot of people knew the truth.
> I know, cos I foolishly tried to inform him. > > > > .... Phil > > >