Think I just got Bias

[jwrosenthal]

In my brief time with open reel I have read alot about bias....and not really understood it. As a long time vinyl junkie, I know the quality of the recording is predicated mainly on the engineering and the pressing. I have heard sensational recordings on 120 gram "dynaflex" albums, and god-awful recordings on 200 gram virgin vinyl, hence the mastering and pressing rules.

When I got my Revox, I just listened to pre-recorded tapes that I had acquired over time and noticed that some sounded different from others and they tended to be characteristic of label, hence I thought the differences were solely the "house sound" of each label and the quality of the mastering. I got my hands on a nice stash of NOS BASF LP35 and NOS 3M 177 in 7" reels. Recordings I made on these tapes sound sensational and as close to the original source as I could possibly imagine (you could switch between monitor and source while recording and barely hear any difference). :yes:

I recently got my hands on a bunch of NOS Scotch 206 and 207 on 10.5" reels. I was very eager to record on this stuff, and today set about doing it by breaking the seal on a reel of the 207 (supposed to be one of 3M's best) . Once the tape started rolling, I noticed something disturbing. On monitor, the tape sounded dull with rolled off highs, recessed mids, and shallow bass. It didn't sound "bad", but not as dynamic and bright as the vinyl source. I switched back and forth through the recording and it was consistently dull. I checked my tone controls but they were flat as always. :thumbsdn:

Considering that every recording I have made to date on this machine sounds incredible (with the BASF and 177), I can only assume that the tape that I am using is not a good match for the settings on my Revox. Is that Bias? Can I easily adjust my machine to sound good with this tape (as I have about 10 NOS reels of it) or should I stick with the BASF as my tape of choice?:scratch2:

Attached are some pics of the beast in action. Nice to have it back home in full swing again!

 

[goldear]

Yes, this sounds like a significant bias, and record EQ mismatch. While this is possible to adjust, these settings are internal on your revox (my number one gripe with this machine), and the procedure requires both test equipment and a little experience to really get it right.

 

[jan_stevns]

Yes, this sounds like a significant bias, and record EQ mismatch. While this is possible to adjust, these settings are internal on your revox (my number one gripe with this machine), and the procedure requires both test equipment and a little experience to really get it right.

It does sound like a serious mismatch between tape type - yes - but honestly, i can't remember having experienced the amount of differences described - if it plays well with LP35, Scotch 207 should'nt be that different, what i read is allmost like the difference between Fe and Chrome casette tapes ......

found a note in a TEAC manual (X300) that lists following tapes as being the ones to use with that deck's LH1 setting

AGFA-PE36, PEM368
BASF-LP35, LPR-35LH
DENON-DX551
SCOTCH-177,207

And - on my own PR99, i use AGFA PEM368, BASF LPR35 and Scotch 207, without having to make adjustments - ok, there are small differences, but they are small - again i'm running 7,5 or 15Ips

 

[jwrosenthal]

The main difference was in the highs (and all recordings were at 7.5ips). The mid and bass characteristics weren't bad, just different that the LP35. It sounded like a blanket was over the speakers. Perhaps just that tape wasn't good (came with a batch of 4 other tapes, all of which were visibly moldy except this one). The other tapes I have are from a different batch so I guess I could test one of those, but I hate to cut the seal on NOS tape unless the recording is going to be a keeper.

James

 

[jwrosenthal]

One other question....when I finished recording on the second side, I had about 200ft of tape left. I stopped the record, and let the remainder of the blank tape "play" to maintain the pack. I could hear the very faint sound of the other side playing in reverse....is this common, or is this a problem with the alignment of my machine?

I just got it back from service and don't know think my tech played with the head alignment as that wasn't what it was in for, but I don't know.

James R.

 

[fortycoats]

I'd also like to know whether the other side coming through faintly is common as it happens on my Teac A-3440, when I'm playing out the end of a tape like you did. The service manual describes a crosstalk measurement but if that's what it is, I'm surprised I can't hear it on a cassette (I have done years ago on cheapo cassette decks but not on my 'good' one now). Another possibility in my mind is that, since my deck has 4 channels and they can't be switched off on playback, maybe it's some of the sound leaking through the output pots even though they're turned to 0.

 

[Ed in Tx]

I'd also like to know whether the other side coming through faintly is common as it happens on my Teac A-3440, when I'm playing out the end of a tape like you did. The service manual describes a crosstalk measurement but if that's what it is, I'm surprised I can't hear it on a cassette (I have done years ago on cheapo cassette decks but not on my 'good' one now). Another possibility in my mind is that, since my deck has 4 channels and they can't be switched off on playback, maybe it's some of the sound leaking through the output pots even though they're turned to 0.

On a cassette the L and R channels are paired together with a small guard band separating sides 1 from 2. On a 4 track stereo reel to reel, the tracks are 1 and 3 for one direction, the other direction would be tracks 2 and 4 on your 4 channel Teac, so there is much more chance while playing 1 and 3 to pickup a tiny bit of crosstalk from tracks 2 and 4. With a 4 track stereo tape those would be faintly heard playing backwards.

 

[fortycoats]

I thought they were spaced like that on R2R specifically to reduce the effect?

 

[Ed in Tx]

I thought they were spaced like that on R2R specifically to reduce the effect?

As I recall originally back in the late '50s early '60s when they came up with the 4 track stereo tape format, they used the tracks 1 and 3 because it was easier to manufacture the head and keep the poles isolated enough to get good stereo separation. On your 4 channel Teac there are 4 poles and coils packed into the head, and some intercoupling happens, along with some pickup of the adjacent tracks in reverse. I notice that too on my Teac A-2340.

 

[mcdan]

IMHO sounds like the playback head height is not adjusted correctly. There are guard bands with 1/4 track stereo as well. The low frequency noise should be nearly inaudible. As for the dull sound, It does sound like a bias and/or eq issue.