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From: jw on 13 May 2010 14:23 On Thu, 13 May 2010 10:38:40 -0400, Paul <nospam(a)needed.com> wrote: >jw(a)eldorado.com wrote: >> On Wed, 12 May 2010 21:03:57 -0400, Paul <nospam(a)needed.com> wrote: >> >> >>>> Did this, and the sound track from 'Top Gun' sounds great! >>>> Connecting the phono player to the preamp and the latter's output to >>>> same 'line in' on computer produced nothing, >>>> Now what? >>>> Duke >>> You could always record "Top Gun" :-) >>> >>> I would say the results you got, are great progress. It means >>> the computer end is working. Now, all you have to do, if figure >>> out whether the phono cartridge wiring is disconnected, some switch >>> on the turntable is in the wrong position, and so on. Or whether >>> the preamp has a bad power source, is muted, or has a blown fuse >>> inside. >>> >>> The phono amp is not strong enough to drive magnetic headphones >>> (like 32 ohm ones). It has an output impedance of 1000 ohms, which >>> is suitable for driving the computer Line In, or the line level >>> input of your stereo system. But that isn't enough to drive headphones. >>> >>> How is the cartridge connected to the cabling in the tone arm >>> of the phono gadget ? Is is soldered, or is a connector involved ? >>> Have you checked that everything is still intact ? All >>> wires secure ? >>> >>> You need to debug, stage by stage. >>> >>> For sensitive equipment, I might use the 60Hz hum from my >>> fingertip, as a test stimulus. If you disconnect the phonograph >>>from the preamp, then touch one of the input terminals on the >>> preamp, the 60Hz hum should be heard on the computer (output) >>> side. Always turn down the volume control, on the computer, >>> so you don't blow out any speakers. Then turn it up slowly and see >>> if your fingertip applies enough noise to make the preamp work. >>> With the RCA-style jacks, you'd need to touch the "center pin" >>> contact on each channel as a test. >>> >>> The TC750LC has a level knob on the front, which you have to >>> turn up to get sound on the output. If the front level knob is >>> set to zero, you get no output. >>> >>> http://www.phonopreamps.com/tc750lcpp.html >>> >>> Paul >> >> I tried connecting the phono player to the computer via the preamp. >> As I plug the RCA connectors together, I get a decided hum, which >> disappears once the plugs are fully connected. The audio from the >> phono vinyl record is still completely silent however. >> >> Duke > >I could be wrong, but it seems like the preamp has a problem. That is my thinking, and I fear that this might be the case. It seems unlikely since it is relatively new and used little and always worked fine. I know S... happens! > >(You really shouldn't have connected the VCR to the input of the >preamp, as that is about 500x more signal than it needs.) I only did that because (a) I got sound when I hooked the VCR directly up the computer's 'line in' and (b) it put the preamp in the circuit, I thought that this could indicate that the preamp indeed is bad, and it may have. > >If you have RCA cabling for this setup, you should be able to touch >the center pin of the RCA cable. Plug the RCA cable into the >preamp, and touch the exposed pin on the other end of the cable > _ _ > _____ cable cable > Hum <_____ ********** Preamp ********* Computer > _ _ The above diagram came through all messed up. Maybe you could say the diagram in words? I would appreciate it. My guess as to what you say is phono cable to preamp in---preamp out to computer in ---computer out to speaker. Would I try to touch the RCA connector going into the preamp? That cable is hard-wired to the phono. IOW since I think we are dealing with the female RCA plugs here. which one would I stick a pin in? The female RCA on the preamp? > >The claimed input impedance of the preamp, is 47K and 220pF. >The 47K is a relatively high input impedance, so the hum >test should work. > >If the hum isn't coming through, and the gain control on the >front of the preamp is at max, then the preamp must be >broken in some way. (Not getting power internally.) > >It is pretty hard to determine if any signal (2-3mV level) >is coming from the phono cartridge itself. You'd have to >rip the needle off the thing, to quiet the cartridge. And >you'd probably have noticed by now, if the cartridge isn't >quite right (physically damaged). Using a (working) preamp, >is about the only thing I can suggest, to monitor the cartridge. >It is pretty hard to get instruments to do that. > >I have had access to equipment, that could amplify the signal >enough. I had an oscilloscope in university, with a diff amp >on the front end, that was sensitive enough to pick up a >human heartbeat. We used to hold the test leads, one in each >hand, and the oscilloscope could display the heartbeat. So >they do make instruments with the required sensitivity, but >they're not common garden variety devices. At work, we never >had a setup quite as nice as that one at the university. > > Paul
From: Paul on 13 May 2010 15:28 jw(a)eldorado.com wrote: >> _ _ >> _____ cable cable >> Hum <_____ ********** Preamp ********* Computer >> _ _ > > The above diagram came through all messed up. Maybe you could say the > diagram in words? I would appreciate it. My guess as to what you > say is phono cable to preamp in---preamp out to computer in > ---computer out to speaker. Would I try to touch the RCA connector > going into the preamp? That cable is hard-wired to the phono. > IOW since I think we are dealing with the female RCA plugs here. > which one would I stick a pin in? The female RCA on the preamp? Plug a male to male cable, into the female RCA preamp input. Touch your finger to the end of the male cable. Listen for hum. Paul
From: jw on 13 May 2010 16:25 On Thu, 13 May 2010 15:28:42 -0400, Paul <nospam(a)needed.com> wrote: >Plug a male to male cable, into the female RCA preamp input. >Touch your finger to the end of the male cable. Listen for hum. > > Paul My preamp RCA input connection is female and is red and white (two). I have a cable of which one end's red and white are male and match the preamp's female red and white, the other end is single and is male. I touched the cable's male and did not hear a hum out of the preamp. Not even when I max'ed the knob. Thanks again Duke
From: Jon Danniken on 14 May 2010 09:05 jw(a)eldorado.com wrote: > On Thu, 13 May 2010 15:28:42 -0400, Paul <nospam(a)needed.com> wrote: > > >> Plug a male to male cable, into the female RCA preamp input. >> Touch your finger to the end of the male cable. Listen for hum. >> >> Paul > > My preamp RCA input connection is female and is red and white (two). > I have a cable of which one end's red and white are male and match the > preamp's female red and white, the other end is single and is male. > I touched the cable's male and did not hear a hum out of the preamp. > Not even when I max'ed the knob. Lick your finger and tap it (also while bridging the gap between the tip and the shield); you should hear *something*, a thumping, or static, or a hum. Jon
From: jw on 14 May 2010 11:44
On Fri, 14 May 2010 06:05:38 -0700, "Jon Danniken" <jonSPAMMENOTdanniken(a)yahSPAMhoo.com> wrote: >Lick your finger and tap it (also while bridging the gap between the tip and >the shield); you should hear *something*, a thumping, or static, or a hum. > >Jon > All these sounds i should be listening for - should come out of the preamp or out of the computer speakers? Bridging the male-female gap between either red or white link or the other? Sorry to be so dumb. Duke |