2. amps-preamps
  3. 1258427381

Tape in + tape monitor = passive preamp?

If you plug a line-level source into a preamp's "tape in" jacks, then flip the "tape monitor" switch, do you essentially get a passive preamp?

I ran across a post on the AudioCircle Bryston forum claiming that the "best input" on a Bryston BP26 was the tape in (or, as Bryston calls it, "tape from"). Here's the url, and the claim appears in the two entries by "werd": http://www.audiocircle.com/index.php?topic=69427.0

I checked the schematic for my B60R on the Bryston website to see if the same would apply to its preamp section. Sure enough, it does (if I read the diagram correctly). From the "tape from" input, the signal goes almost directly to the balance and volume controls; while the signal from any of the four main inputs goes through the selector switch and a multi-step circuit (pre-amplification, I assume) before reaching the balance and volume controls.

I decided to hear for myself how using the "tape from" input would affect the sound of my system. My initial impressions are that the sound is more detailed, primarily in the upper frequencies, but that it lacks body and bass. Switching back to the CD input results in a loss of HF detail but a more balanced sound.

I'm going to try living with the system in the "tape from" set up for a while. I like the extra detail, and maybe I'll get used to the frequency balance.

Has anyone else experimented with this technique? Using other brands of gear? Any advice on reclaiming the bass?
jpbach

Showing 1 response by newbee

newbee
4,751 posts
 
I think not. The hall mark of a passive pre-amp is the obvious. It can attenuate a line level signal but it cannot amplify it. In your set up you still have a pre-amp amplification circuit between your source input and the amp.

An anp section of a pre-amp is always at full gain (as seen by the amp) and the signal from the source is attenuated from full gain to zero gain. So you may hear a 'cleaner' signal using a tape monitor input for the reasons you outlined but you would not have a passive line stage as the signal is still passing thru the pre-amp's amplyfing stage.

There are a few pre-amps out there that do allow you to switch the amp output from active to passive, but not many. I believe Adcom was one.

I don't have a reason for your perception of a loss of bass. Only WAG's. Perhaps someone else can comment on this.
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