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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 11th Nov 2019, 2:30 pm   #1
Michael Kay
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Default Akai 4000DB - Output level query

Hello,

I recently bought myself a very nice Akai 4000DB, my intention being to digitise a pile of tapes.

The guy I bought it from was using it in his hi-fi system and was happy to demonstrate it for me before I bought it. The only issue it had was the usual crackles from dirty pots, when operating the record level controls, etc. But I took its chassis out of the wooden case and squirted contact cleaner into those and indeed all the other switches including the SW1 (record/play) internal switch (then exercised them). It came with an Akai head de-magnetiser, which I have used and I have cleaned the heads several times too. No crackles at all now and everything seems to work perfectly bar one thing which, I think is an adjustment issue.

I am finding that tapes recorded at higher levels (briefly, but only briefly, going over 0dB on the VU meters) are distorting/clipping, when this happens. Because these tapes, which are factory recorded ones, recorded on EMI tape in the mid 1960s at 3.75 ips and in mono, I assume were recorded with the correct levels, so will not be over-saturated, Iím wondering if the output pre-amp settings inside are set too high, and that is the cause of the distortion/clipping. There is an exact match between the levels displayed on the VU meters and the corresponding levels on Audacity, when I digitise them. The distortion/clipping occurs pretty much when the VU meters exceed the 100% indication underneath the dB calibrations (so around +1.5dB). Below that there is no distortion and the sound is excellent.

Although this is all what might be expected, Iím assume the levels are correct on the tape as they were done commercially (being the predecessors of musicassettes).

Having downloaded a copy of the 4000DB Service manual and found the location of the playback output adjustment inside (LE-3506 circuit board, page 16/17/38 & p42, fig 10 part 114), I need to know 2 things. 1) if I lower the output levels will the same tapes playback without distortion/clipping and will the actual output level be displayed on the VU meters to reflect the lower output setting? And if so, how do I access the board with the output amp pots on because it seems to be inside the side section where you canít reach it. I donít want to have to unsoldering parts to get at it.

For the record, the EQ settings matched the speed (3.75ips) and the tape type is set to ĎLow noiseí which Iím sure matches this EMI mid brown (shiny outward facing side) tape type. The recordings are mono (2 track) commercially made ones (without Dolby, which is off). I have connected only the left channelís phono output and pulled out the right hand record level pot as it says Ďpull for mono useí (which shuts the right channel off). I think reducing the output levels by about 1.5/2dB would be enough to eliminate the clipping.

Can anyone advise please?
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Old 11th Nov 2019, 2:58 pm   #2
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Default Re: Akai 4000DB - Output level query

I suspect the output levels are fine but your computer soundcard is clipping at a standard line level. You don't say what this hardware is, but some of the onboard sound chipsets are pretty basic.

Can you just build an external attenuator? You only need a pot or a couple of resistors.
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Old 11th Nov 2019, 6:44 pm   #3
Michael Kay
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Default Re: Akai 4000DB - Output level query

Hello Paul,
Thanks for the reply. Iím outputting the left channel on the Akai via a phono lead into the left input (only) of a Behringer U-Phono UFO202 Analogue to digital converter, connected by its USB connection (there is only a USB output on the Behringer), to the USB input on my Apple iMac. Then using Audacity, set to its USB input option and 1 channel Mono record mode. The tapes which came with the Akai, so I assume were recorded on it, playback fine with normal levels on the VU meters. The pre-recorded ones are World Record Club recordings. Some of which have oddly high levels (going to +2 dB on the meters) and clipping in the process.
Regards,
Michael
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Old 12th Nov 2019, 7:42 am   #4
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Default Re: Akai 4000DB - Output level query

Michael, Paul is probably right: the levels are too high for your Berry converter.

Changing the internal playback reference levels is really a last resort. Much easier as Paul says to lower the signal level from after it exits the machine via a "pad".

Have you set the Berry switch to "line" rather than "phono"?

The little 202 converter is very inexpensive but should provide more than adequate results for what you are attempting. It should have a (self) noise floor well below that of your best pre recorded tapes.

The record meters in most digital recording software are not VU meters. They are peak reading. The maximum level really is absolute maximum. There is nothing above it but distortion. If that top bar is illuminating at all, even momentarily, we are recording too high. In practice we can record with peaks perhaps 10 db or more below that maximum.
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Old 12th Nov 2019, 8:40 am   #5
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Default Re: Akai 4000DB - Output level query

The interface may indeed be clipping, but also bear in mind that pre-recorded tapes, even from EMI, can sound pretty rough by modern standards. The tape was driven hard to keep the hiss down, and sometimes things went over the top. Even the legendary Stereosonics aren't free from quite severe peak distortion. This of course will be relatively soft clipping and intermodulation, so should be distinguishable from hard cipping caused by overloading the input.
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Old 12th Nov 2019, 11:28 am   #6
Michael Kay
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Default Re: Akai 4000DB - Output level query

Thanks guys for the replies.

I have decided not to attempt to change the levels inside my Akai. I've considered 3 options following your advice which you may be able to pass comment on please.

1) would the output from the DIN connecter on the Akai be any lower than the RCA phono I am using?

2) Although in the Sound settings on my Mac, it says 'The selected device has no input controls' in reference to the Behringer A/D converter, is there any mileage in looking to alter the Audio MIDI settings using the Applications/Utilities/Audio MIDI Set up options (they are greyed out at the moment though)?

3) would buying an in-line attenuator, like the Rothwell RCA In-Line Attenuators Pair [-10dB] (For Source), solve the problem? These are listed on Amazon and eBay. There is also a Harrison Labs 6dB RCA Line Level Attenuator Pair available from America which I assume does the same thing with perhaps a better (reduced) level of line input reduction? 10dB might be too much??

For the record, my Behringer is set to line output not phono. Also would there be anything in trying to take the output from the Akai via the headphone out socket with an adapter (the level is not adjustable as it has no volume control)?

Thanks again for your help.
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Old 12th Nov 2019, 12:04 pm   #7
Michael Maurice
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Default Re: Akai 4000DB - Output level query

I believe the DIN output is somewhat lower than the line out.

I cant help you with the MAC

Those attenuators seem an awful lot of money for a couple of connectors and four resistors, though it should solve your problem.

I wouldn't bother with the headphone output which is probably the same as the line out.
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Old 12th Nov 2019, 12:16 pm   #8
Michael Kay
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Default Re: Akai 4000DB - Output level query

Will try a DIN connecter next then. Many thanks Michael!
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Old 12th Nov 2019, 12:23 pm   #9
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Default Re: Akai 4000DB - Output level query

DIN levels are indeed lower, but only if the manufacturer followed the spec, and lots didn't. I don't know if the 4000 did or not - Japanese manufacturers did tend to be a bit cavalier about this, sometimes just connecting the line level RCA outputs to the DIN socket.

As Tim says, there is no point in letting the Audacity meters bang into the red when digitising. Keep the peaks at least 3dB down, and even lower levels won't really do any harm. You can always normalise the digital recording later.
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Old 12th Nov 2019, 12:29 pm   #10
Michael Kay
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Default Re: Akai 4000DB - Output level query

Thanks Paul. I've downloaded the service manual which has a DIN level at 0.5v and the RCA output is listed as 0.775v. Would that be enough to make a difference?
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Old 12th Nov 2019, 1:22 pm   #11
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Default Re: Akai 4000DB - Output level query

Quote:
Originally Posted by Michael Kay View Post
RCA output is listed as 0.775v.
A familiar figure. 1mW in 600 ohms.
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Old 12th Nov 2019, 2:05 pm   #12
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Default Re: Akai 4000DB - Output level query

The headphone output is adjustable if it's like the 4000D.
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Old 12th Nov 2019, 2:07 pm   #13
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Default Re: Akai 4000DB - Output level query

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Old 12th Nov 2019, 2:38 pm   #14
Michael Kay
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Default Re: Akai 4000DB - Output level query

Thank you but there is no volume control for the headphones on the 4000DB model.
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Old 12th Nov 2019, 2:56 pm   #15
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Default Re: Akai 4000DB - Output level query

That's the wrong way to go anyway. You need to sort out the line level outputs for the best quality. It really isn't difficult to attenuate the signal - a 10k resistor in series followed by a 2.2k resistor across the input is all you need. You can lash it up with a choc block connector if you can't solder, or even just twist the wires together.

The DIN output may be low enough to make the problem go away though.
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Old 12th Nov 2019, 2:59 pm   #16
Michael Kay
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Default Re: Akai 4000DB - Output level query

Hello again and thanks for the reply. I have just been and bought a 5 pin DIN to RCA Audio lead and am just about to try this instead of the RCA phono to phono as the output from the DIN is 0.5v instead of 0.775v via phono. Hoping this will solve the problem.
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Old 12th Nov 2019, 5:16 pm   #17
Michael Kay
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Thumbs up Re: Akai 4000DB - Output level query

Problem solved!! The DIN output doesn't clip as the level is lower going into Audacity! The sound now is free from distortion and clipping.

Thanks to all for their advice. £4.99 well spent on the 5 pin DIN to RCA Phono cable I think.

I have added thumbnail screenshots of the first (phono recorded) version and the new DIN version - both the same album/tape

Attached Thumbnails
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Name:	Recorded via RCA Phono Conection.jpg
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ID:	193627   Click image for larger version

Name:	Recorded via DIN Socket Conection.jpg
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Old 12th Nov 2019, 6:11 pm   #18
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Default Re: Akai 4000DB - Output level query

Good stuff, glad you have it sorted.
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Old 12th Nov 2019, 6:12 pm   #19
Michael Kay
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Default Re: Akai 4000DB - Output level query

Many thanks again!
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Old 12th Nov 2019, 9:33 pm   #20
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Default Re: Akai 4000DB - Output level query

Quote:
Originally Posted by Michael Kay View Post
Problem solved!! The DIN output doesn't clip as the level is lower going into Audacity! The sound now is free from distortion and clipping.
Perhaps Clipping is probably the most common mistake in both live audio and recording. Even professionally *. Levels simply too high. Peaks clipped, often right through the recording.

Your free Audacity programme may have a "peak search" or "peak check" function. It can automatically display the highest recorded peak in any given file as a value like - 12.2, -1, 0 etc. Obviously it cant display peaks over 0dbFS because by definition they've been clipped.

Audacity probably has a "Normalize" function which can automatically increase the recorded file's gain after it's been recorded, so the highest peak is now just short of clipping. I often peak normalize up to -1dbFS.

* Here's an example of serious clipping in a pro digitised compilation for a major performer.
https://youtu.be/uF5E0w2h6wM
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