Fixing a AKAI cr80dss (very technical stuff)

[winopener]

Here's a classic Akai cr80dss quad player-recorder with a strange behaviour: probablyit has been pushed too loud on the amplifier stages.
First, the line out level is waaaay over the top: my soundcard can be set at -10dB or +4db as a reference level, with a possible amplification ranging from 0 to +18dB.
In order to record from the akai to the soundcard *without clipping* i had to:
1) set the soundcard to +4dB reference
2) set the amplification to 0
3) place a 22Kohm resistor on all four plug from the Akai to the soundcard; with a 12Kohm it was still clipping.

At least to me it's clear it has been pushed too much - but that's not the real problem.

The real problem is that with this overamplification, the circuit board is working now outside linearity. To be precise, if i play a very hot-recorded q8 (rca), the positive sinewave is kinda limited (shaved peaks), while the negative has peaks and valleys as expected. If the tape is recorded at more normal levels, the waveforms are ok on both positive and negative side.

Problem is, *where* is possible to regulate the amplification without screwing out everything? There are several group of trimmers on the board, but i have no idea what are the right ones to turn down.

 

[quadsearcher]

I think I know what you are talking about, my CR-80D-SS is OK but loud on Q8 tapes so it has a lot of hiss. I don't have any RCAs, mostly Enoch Light. On some stereo tapes there is so much distortion I doubt it exists on the tape. I haven't scoped it but that is interesting that you padded the output and still had clipping. That tells me these things have one stage too hot as it hits the next stage. So, we have scopes and schematics and could check each stage. I don't know when I'll find time.

It also could be a sagging power supply on yours (and mine). If the positive or negative rail is weak, that side of the waveform will clip. I haven't checked or changed any electrolytic on my Akai and I would expect some bad caps by this time. It would be interesting to scope the + and - of the power supply while playing a "hot" tape and see if it dips.

 

[winopener]

Capacitors was the other open hypotesis, however it is nice to know my 80 is not the only deck which is too loud on the output.

 

[furui_suterioo]

I have cr80dss which sometimes has a similar problem. It plays fine but every once in a while, only when I use the REC button, the RL channel is way too loud even with the REC LEVEL knob all the way down. It usially goes back to normal after warming up awhile or after demagnetization but happening more often lately, although it been working hard, has churned out almost 40 Q8s in the last few months and they sound great. Did you end up fixing this problem? I've read that there are faulty transistors in these decks.

 

[quadsearcher]

The record/play switch might need a shot of contact cleaner. Doesn't look too fun to get to it though. Maybe from the top with a shaped nozzle.
This is from the era where transistors are known to develop black corrosion that supposedly goes throughout inside the package, mine look clean.

This is timely. I have my CR-80D stereo deck on the bench and finally am reading the manual. It is specified for +4dB output. This stereo deck performs about as well as my quad deck, which means usually at least some distortion on some tapes. However I had an HK stereo preamp and tapes sounded a lot cleaner with that in the signal path. I mean running a preamp into another preamp (or the HK out into a power amp), either way, it seems th HK is much more accomodating to the hotter level, or maybe it is a better impedance match. I'm looking for a known good reference alignment tape to check/set the output level. Also checking caps, the ones I can read without too much disassembly, so far checking fine.

 

[user 21078]

Capacitors was the other open hypotesis, however it is nice to know my 80 is not the only deck which is too loud on the output.

It is a problem on more Akai gear of the era! I owned this deck, and same era Akai R2R's amps and tuners etc you see. Especially before hifi Din norm this was a common issue. Line out and in voltages were way higher then nowadays post hifi norm years gear. And max line in voltages is since then also way lower. Example: One JVC series (black face., chrome knobs same design look) before my series silverface JVC had same line in or out incompatibilities with components of other brands or later hifi norm gear. Same with Marantz, Sansui, McIntosh etc. Industry cross brand standards harmonized line in and out voltages and amps years for the hifi norm. It can be reason for your issues, or at least part of it.

 

[par4ken]

It is a problem on more Akai gear of the era! Especially before hifi Din norm.

You should be able to turn down the level. Check out the manual! Service and owners manual are posted here.

https://www.hifiengine.com/manual_library/akai/cr-80d-ss.shtml