2. amps-preamps
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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 jpbach

jpbach OP
25 posts
 
Thanks to everyone for your comments. Checking the B60R schematic again, I see that there is additional circuitry between the Balance and Volume knobs and the amplifier stage. (Doh! -- I should have seen that myself.) That clearly makes the "tape from" path more than passive.

I guess that werd's idea was that "tape from" is a more direct path than the main inputs: less circuitry = cleaner. But in this case the low impedance seems to alter the frequency balance.

I think Almarg might have the answer for that problem. My CDP is a Bryston BCD-1. According to the measurements in Stereophile, output impedence is 74 ohms at high and middle frequencies, rising to 106.5 ohms at 20 Hz. Almarg, would that change in impedance be enough to result in rolled-off lower frequencies?

I'm curious about Gregm's advice on using a high output source. I was using the single-ended outputs from the BCD-1, which Stereophile measured at 2.38 volts. If I switched to the balanced outputs, which measured at 4.76 volts (and "exactly twice" the impedances), would that produce better results?

As for perceived increase in detail, I was very careful not to adjust the volume when switching from one set up to the next. However that does not eliminate the possibility that the "tape from" path might produce more decibels at the same volume setting.
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