Have you used these combinations successfully before and this distortion is a new development?
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I have not changed tubes because I always thought that the phono stage provided RIAA reverse eq; and gain to be bring the signal to line level, and then the line stage provided additional gain to the signal to provide sufficient voltage for the amp. If I am wrong (which it seems I must be), then I stand corrected. I will have to disconnect the phone and then check the line stage tubes.
Happy Christmahanukwanzadan everyone.
Swampwalker: your description is right in how most preamps work, but as Tvad mentions, we aren't sure that's how this specific preamp works. His suggestion to disconnect the phono rig from the preamp ( interconnects, ground wire, power cord, etc... ) is where i would start. After that, it is a matter of tracking down the offending tube in the preamp, if there is one ( or two if dual mono ).
As a side note, the phono stage may not drive the line section as hard as your CD players do. As such, you might not hear as much distortion from the phono rig as you do the CD player. This would be due to the increased heardroom / lack of drive from the phono stage. This is just a guess though, so don't put too much faith in it. Sean
It is in both channels, and it is significant. You would have to be deaf not to hear it. Seems to be mostly in the mid-range (I'm running Merlins and they are 2 ways). But my new Teres still sounds fantastic. Perhaps the line stage of the VAC uses each half of a dual triode somewhere for each channel, before the phono stage feeds in? Nope, just checked web site
Tube complement: Line stage, 2 x 8416, 2 x 12AX7; Phono stage, 3 x 12AX7.
Still wrapping gifts, will check by removing phono and then tubes, when this is done. Many thanks to all, and to all.... nahh, too corny even for me.
Line stage almost never provides voltage gain; under most circumstances, attenuates signal. The voltage coming out of a linestage source component, if plugged dirtectly inot your amp, would be terribly loud, and therefore needs to be attenuated. I think the preamp may provide current gain (my term, probably not a correct electrical term), which is to say that if the amp requires more current than the source is capable of providing, the preamp will be able to provide it.
OK, there is a 0dB point in most pre attentuators, and attentuation below that point and gain above. the 0 dB pt IS pretty loud, so at most normal listening volumes, you are right, it is attentuation. However, the point is if the phono stage output feeds the line stage, just like any line level component, then a bad tube in the line stage should affect the phono and the cdp. I unplugged the phono as suggested and it cdp problem is the same, but it is intermittent in nature. Worked fine for an hour last night, then went sour. This am, bot about 15 minutes out of it. Will have to test the tubes, next.
OK, boys and girls. The answer you've been waiting for....My BAM was unplugged. No idea what that could have had the effect that it did. Plugged the sucker in, switched it over to AC/charge and away we went. Post christmas music tip, new Joan Osborne, "Pretty Little Stranger". Alt-rock meets country. Gift from my brother. Its great- go figure. Happy New Year to all.
I have no idea. Called VAC this am and they had a couple of troubleshooting ideas, including the balanced/se output switch being in the wrong position. When I rolled the rack to see the switch, I found the S-BAM dangling w/o a pc. If Sean or any or Bobby or any of our tech heads are hanging out and have any ideas, I would be happy to listen...Meanwhile I am one happy camper; the VAC tech said next step was a trip to FL. And many thanks for Brent at VAC who spent about 15 minutes w/me on the phono trying to trouble shoot.
The BAM module is basically an active equalizer with a high pass filter built into it. This reduces driver excursion below port resonance, lowers distortion, reduces power consumption and increases power handling.
Evidently, either your phono system isn't capable of very deep bass and / or the records that you were playing didn't have a lot of deep bass on them. Obviously, the CD's did, which is what caused the distortion that you heard. This is one of the drawbacks of using a vented design without some form of active equalization and / or a steep high pass filter. Now you've actually heard the distortion that i've mentioned many times before when discussing vented designs and the woofer(s) becoming "unloaded". Not pretty, is it?
Glad that you were able to figure things out without any real down-time or great expenditure on your part. Sometimes, as is the case here, the simple stuff is the easiest stuff to overlook. Sean
Sean- I could never disagree with your analysis because I have no knowledge in this area, but I will say that the distortion sounded like it was mostly in the vocal frequency range. and as far as I know, the BAMs (several generations ago) were optional with the VSM. The sound I got was very noticeable and totally unlistenable, even to my son who listens to MP3s played through his cell phone speaker!!!
Obviously, i wasn't there to hear what was going on, so i could be off in left field. Having said that, over-excursion of a mid-woofer can lend a distortion / vibrato effect to midrange and treble frequencies. Don't know if this is what you were hearing, etc... In severe cases of over-excursion, the driver will mechanically bottom out. This sounds VERY scary, as it should. Sean