UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Akai 4000DB

Michael Kay · 11th Nov 2019, 2:30 pm

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, I’m 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, I’m 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 can’t reach it. I don’t 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 ‘Low noise’ which I’m 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 channel’s phono output and pulled out the right hand record level pot as it says ‘pull for mono use’ (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?

11th Nov 2019, 2:30 pm	#1
Michael Kay Triode Join Date: Nov 2019 Location: Blackpool, Lancashire, UK. Posts: 15	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, I’m 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, I’m 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 can’t reach it. I don’t 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 ‘Low noise’ which I’m 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 channel’s phono output and pulled out the right hand record level pot as it says ‘pull for mono use’ (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?