Recording to tape, should the low end sound like this?

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Beneficial
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Recording to tape, should the low end sound like this?

Post by Beneficial » Tue Nov 18, 2014 11:03 pm

I just finished calibrating my Sony/MCI JH110c 2 track 1/4" tape machine like I've done many times in the past. However, I noticed the low end sounds more distorted than I remembered. I thought it must have been a bias issue but overbiasing by various amounts doesn't seem to improve the sound. I'm recording at 15ips on ATR tape.

I created a wav file showing various test tones... digital tone followed by the tape version so you can hear the difference. If you listen in headphones you can hear it better. Is this low end distortion normal?

http://benefitofficial.com/up/GS/Digita ... tTones.wav

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JWL
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Post by JWL » Wed Nov 19, 2014 12:35 pm

Yeah sounds like something is off, you are definitely getting some distortion and noise in there that doesn't sound right to my ear.

Things like this are why I almost never miss tape. ;-)

Beneficial
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Post by Beneficial » Thu Nov 20, 2014 7:34 am

Anyone have any idea what would cause that type of low end distortion? Would it be bad tape, or something else? The example above shows the cleanest I can get it at pretty much any bias point.

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Nick Sevilla
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Post by Nick Sevilla » Thu Nov 20, 2014 8:34 am

Without going too much into speculation, I want to ask a few quesitons:

a. does your tape machine have separate amplifiers for recording / playback of low and high frequencies?

b. Does this distortion happen equally on all channels?

c. Does this type (kind, sort) of distortion occur the SAME across different frequencies? It sounds like it to me from your sample.

d. does your tape have both playback and sel/synch heads? If so, does this distortion occur on both?

Now, as to why I ask these 4 questions:

a. If it only happens on one channel, then you can isolate it to a component on that channel. Otherwise start looking at parts which affect all channels simultaneously.

b. If it does, then you might need to look at your source. Is it clean coming out of the actual output that you are feeding the tape machine? Are you sure? How do you know for sure?

c. Since the distortion is the SAME across all frequencies, I would start by looking at the PLAYBACK amplifiers on the tape machine. Can you swap amplifier cards / components on this machine?

d. Eliminating which tape head the distortion is coming from will help you pinpoint which amplifier(s) are the ones messing up, since on these kinds of machines, each head goes to a different amplifier circuit.

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Beneficial
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Post by Beneficial » Thu Nov 20, 2014 9:14 am

Thanks Nick. Here are my initial answers:

The machine has separate amplifiers for low and high freq on the repro cards, rec cards only high. The distortion happens equally on all channels (2 channel machine). The distortion sounds much more prominent on the low end. The tape has both repro and cue mode, distortion happens when playing the tape back on both. The distortion is recorded onto the tape.

It's clean coming out of the output. For the example wav above, I split the output signal and sent one to my tape machine, and one to my digital interface. You can hear the clean digital recording in the wav.

Considering the above, I'm wondering how likely it is that both reels of tape I'm using are the problem (an older reel I had laying around from a couple years ago unopened, and a new one I just bought... same company). Going to try a different tape brand and see what happens. Although, from the questions posted, it seems like this may be more a problem with the machine than with the tape type.

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Post by Beneficial » Thu Nov 20, 2014 10:19 pm

I tested it with another tape brand and the issue was still there. When I play low freq tones off of my MRL tape, I'm not hearing the problem, so I think it must be something on the recording side or something related to bias.

Any ideas out there as to what would cause just the low end to distort like this?

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Nick Sevilla
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Post by Nick Sevilla » Sun Nov 23, 2014 7:00 am

It's not the bias. As each channel has its own settings.

Since it is on both channels, and seems to be only on the record side (you say its on the tape... have you played the tape on a different machine?)

I would venture to say that it may be ground related, try to find in the schematics, where the ground is common between both channels, and if there are any common components between the two channels, also look there for bad capacitors, those usually get messed up before other components

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Realizing vibratory excursions from a paper widget.

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Post by Beneficial » Sun Nov 23, 2014 10:41 am

After all of the troubleshooting done so far, I'm about 90% sure there is something wrong with the circuitry.

A few years back I shipped all of the cards to Jim Williams to mod and supposedly improve... and for $600 my machine was rendered unusable. He replaced a bunch of stuff in the repro, rec, and in/out cards. When I got them back the audio was horrible... full of white noise and crackling. It turned out he didn't have a machine to test them in... he was just doing the mods and said they looked ok on the bench. I shipped all the cards back to him again to fix. He said he fixed them and sent them back. This time when I put them in and powered up the machine... the needles just slammed back and forth and the audio was bad, it basically turned my machine into a big oscillator. After a lot of back and forth and months unable to use my machine, I wrote it off as a big loss of money and time.

I then sent the whole audio drawer to Steve Sadler in hopes he could undo the mod or fix the problem, and for another $400 after shipping, he removed some of the stuff Jim had put in and put some of the old stuff back in... he got the audio working and got it aligning flat and in phase... however, I now believe the machine has had this low end distortion ever since then. It's something you don't notice unless you're listening closely to specific freq test tones, but aligning in the shop without critically listening at specific frequencies... you'd think the machine was good.

So I'm thinking the problem is having 80% new/different components in the cards with 20% old spec stuff put back in... maybe something about that combination is throwing stuff off?

Not sure what to do at this point. May have to call it quits with this machine. Not sure how much more money I can afford to spend trying to undo the expensive mod if that truly is the problem.

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Post by E.Bennett » Sun Nov 23, 2014 5:52 pm

I have seen complete audio drawers for this machine selling for about $100. Perhaps you can pick one up and see if that solves your issue.

Beneficial
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Post by Beneficial » Sun Nov 23, 2014 5:54 pm

I'd love to find a deal like that. Guess I'll keep my eye out.

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Post by Nick Sevilla » Mon Nov 24, 2014 11:29 pm

Realizing vibratory excursions from a paper widget.

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