an audio question about impedance matching
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From: robert bristow-johnson on 30 Jul 2010 23:47 On Jul 30, 5:32 pm, spop...(a)speedymail.org (Steve Pope) wrote: > glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote: > > >The OP seems to be connecting a microphone to a guitar amp... > > I could swear the OP had talked about a guitar pickup, initially, > but my memory plays tricks on me these days. the memory score here is: Steve 1, Glen 0. i *did* say something about "a microphone going into a preamp or mix board, or an electric guitar going into a guitar amp," what i am wondering is, what is the deal, in either case, for why a transformer in between (in the guitar case, it might be because of a lower level, low impedance custom-wound pickup) the source and the load is necessary for *tone*? if i am putting any electronics (like a solid-state or op-amp preamp) in between source and input load, am i doing something detrimental to the *tone* if this electronic stage has very high input impedance and very low output impedance? levels can be adjusted for. maybe i have to make the (complex) input impedance (of the inserted electronics) look like a guitar amp input reflected through the transformer. r b-j
From: Jerry Avins on 31 Jul 2010 00:06 On 7/30/2010 11:47 PM, robert bristow-johnson wrote: > On Jul 30, 5:32 pm, spop...(a)speedymail.org (Steve Pope) wrote: >> glen herrmannsfeldt<g...(a)ugcs.caltech.edu> wrote: >> >>> The OP seems to be connecting a microphone to a guitar amp... >> >> I could swear the OP had talked about a guitar pickup, initially, >> but my memory plays tricks on me these days. > > the memory score here is: Steve 1, Glen 0. i *did* say something > about "a microphone going into a preamp or mix board, or an electric > guitar going into a guitar amp," > > what i am wondering is, what is the deal, in either case, for why a > transformer in between (in the guitar case, it might be because of a > lower level, low impedance custom-wound pickup) the source and the > load is necessary for *tone*? if i am putting any electronics (like a > solid-state or op-amp preamp) in between source and input load, am i > doing something detrimental to the *tone* if this electronic stage has > very high input impedance and very low output impedance? levels can > be adjusted for. > > maybe i have to make the (complex) input impedance (of the inserted > electronics) look like a guitar amp input reflected through the > transformer. Can A-B-X tests show that the effect is real? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: glen herrmannsfeldt on 31 Jul 2010 01:03
robert bristow-johnson <rbj(a)audioimagination.com> wrote: > On Jul 30, 5:32�pm, spop...(a)speedymail.org (Steve Pope) wrote: >> glen herrmannsfeldt �<g...(a)ugcs.caltech.edu> wrote: >> >The OP seems to be connecting a microphone to a guitar amp... >> I could swear the OP had talked about a guitar pickup, initially, >> but my memory plays tricks on me these days. > the memory score here is: Steve 1, Glen 0. i *did* say something > about "a microphone going into a preamp or mix board, or an electric > guitar going into a guitar amp," I thought someone mentioned guitar amps somewhere along the line, but it seems I didn't remember who. > what i am wondering is, what is the deal, in either case, for why a > transformer in between (in the guitar case, it might be because of a > lower level, low impedance custom-wound pickup) the source and the > load is necessary for *tone*? if i am putting any electronics (like a > solid-state or op-amp preamp) in between source and input load, am i > doing something detrimental to the *tone* if this electronic stage has > very high input impedance and very low output impedance? levels can > be adjusted for. In the case of a microphone I would have to say no. In other cases, it isn't so obvious. As mentioned, magnetic phono cartridges and guitar pickups depend on the load impedance to generate the appropriate response. (Flat, after RIAA equalization, in the case of phono inputs, I have no idea what response is expected of guitar amps.) > maybe i have to make the (complex) input impedance (of the inserted > electronics) look like a guitar amp input reflected through the > transformer. The convenience of the low impedance source is that it is fairly independent of load, assuming the load impedance is somewhat higher. Specifically, load input capacitance should not have much effect. A microphone with flat response connected to a phono preamp input or guitar input may result in a not so flat response. -- glen |