Akai X-201D weak bass during playback

[dariofon]

Hi

My Akai x-201D has very shallow bass during playback of self recorded or other tapes from Akai Gx-4000D which has very good bass. It drops a lot below 60Hz.

Recording function on Akai X-201D is working properly, tape plays on Akai GX-4000D with deep bass.

All electrolytic capacitors on amplifier board have been checked and suspects replaced but no change in bass reproduction.

Both channels behave the same way.

Because the same electronics perform recording an playback functions I am pretty puzzled. Probably there is something not quite right with RC elements involved in low frequency amplification during playback but I am not able to pin point it.

Link to service manual http://www.hifiengine.com/manual_library/akai/x-201d.shtml

Thank you in advance for your help.

 

[audiojones]

Since it's happening in both channels you might look to the power supply and ground paths. This deck uses plug in circuit boards so the connector socket prongs and board connection points sometimes get flakey. Maybe the ground path or power supply buss is dirty and not making contact? Also check the voltage coming out of the power supply, it might be out of spec. Clean the heck out of the record slide switch too, all signals in all modes pass through there. Loss of low frequency can also be caused by incorrect capacitor types being used in critical areas, but it sounds like this was happening before any caps were replaced.

 

[dariofon]

hi audojones and thank you for trying resolving my problem.

All the switches and contacts were cleaned many times, voltages are correct.
Would you show me please on the schematics, elements responsible for the low frequency gain during playback?

 

[audiojones]

Not sure about that, but some further troubeshooting may help. Does it sound tinny when listening to the line input or only when playing a tape back? If it's only when playing a tape back then your trouble may be magnetized or damaged heads, or possibly the head amp circuit that is just before the line amp IC. As a test you can unplug the head input to the amp section and run the heads from another deck through the 201's amp section with some temporary jumpers to rule the heads out. Also make sure you didn't lose your common ground from the heads to the amplifier (check the ground continuity on the plug that connects the deck to the amp).

If you find the problem is in the amp and not the heads after the above test then it's time for a scope and a signal tracer, or you could try replacing the components of the head amp. The electrolytic caps used in the head amp circuit likely need to be low leakage high impedance caps rather than run-of-the-mill power supply caps and they should be close to the original voltage ratings instead of way over. The transistors used there have modern replacements (you can use Fairchild KSC1854 for the two 2SC693 and also for the 2SC458 which you might as well do while you're in there).

It seems odd that both channels are doing the same thing which makes me think something happened to the heads or you lost a ground contact on the board somewhere. Even though you cleaned all the contacts you may still need to go over them all again. The head signal goes through so many contacts in this deck - the record switch, muting relay, head reversing switch, track selector switch, mechanism to amp connection plug, circuit board plug-in points, speed EQ board etc.

Hope this helps, the X201D is a very nice little deck (I really like my X201D and my M10).

 

[dariofon]

Not sure about that, but some further troubeshooting may help.

Does it sound tinny when listening to the line input or only when playing a tape back?
A: Signal coming out from line out during recording sounds great with deep bass.
Tape recorded on AKAI x-201D has proper deep bass on another Akai gx4000d.
Tape recorded on AKAI GX4000d with known deep bass has shallow bass on AKAI x-201d.

If it's only when playing a tape back then your trouble may be magnetized or damaged heads…
A: Heads are demagnetized.

Also make sure you didn't lose your common ground from the heads to the amplifier (check the ground continuity on the plug that connects the deck to the amp).
A: Done, looks OK

The transistors used there have modern replacements (you can use Fairchild KSC1854 for the two 2SC693 and also for the 2SC458 which you might as well do while you're in there).
AONE it already after noticing weak bass.

The electrolytic caps used in the head amp circuit likely need to be low leakage high impedance caps rather than run-of-the-mill power supply caps and they should be close to the original voltage ratings instead of way over.
A: Replaced capacitors are regular, nothing special and way over voltage, but if line out during recording sounds great it means that all of the electronics behave correctly as all of it is used in recording and playback excluding some nano, pico capacitors and some resistors I have not touched.

Even though you cleaned all the contacts you still may need to go over them all again. The head signal goes through so many contacts in this deck - the record switch, muting relay, head reversing switch, track selector switch, mechanism to amp connection plug, circuit board plug-in points, speed EQ board etc.
A: I am master cleaner now

It seems odd that both channels are doing the same thing which makes me think something happened to the heads or you lost a ground contact on the board somewhere.
A: GAIN below 60Hz is dropping quickly but 30Hz is possible to detect with 30dB drop.

This ground thing makes me wonder, if recording is good with deep bass (recorded tape checked on another Akai) I am assuming that the head is good and the ground is good during recording but maybe something is not right with the ground during playback or just simply Akai needs some extra boost for low frequencies in playback mode.

 

[audiojones]

Actually the head amp in this model (the portion before the line amp IC package) does not come into play when monitoring the recording. This unit uses a combination record/playback head so all you are hearing during record mode is the line amp. The head amp will only be heard during tape playback.

If you try connecting the head section from another deck to the head input or vice verse you can quickly determine which is at fault. You could also try the old "finger test" by first lowering the volume on your amp then touching the head connection with your finger and listening to the low frequency response compared to what it sounds like when touching the line input jack on your receiver or amp. Not a very accurate test but it might reveal a weakness in the electronics. I have come across heads that have gone bad and sound tinny but it's pretty rare. I've seen the same thing happen with phono cartridges too but again it's very rare.

 

[dariofon]

Some news on Akai x-201d troubleshooting.

Checked with ohmmeter signal path from the head to the amplifier board paying attention to the switches, cables. On both channels there is 1ohm in total so it is good. Traced playback amplifier signal with acoustic generator and digital scope. Both channels look similar. There is growing gain of low frequencies below 60Hz but because maybe of my particular head sample it is not enough.
Still missing punch and lows during playback so my next move will be trying to amplify low frequencies below 60Hz in EQ of the playback amplifier.

I am hoping for very direct suggestion what to change or adjust, which capacitor, resistor and what kind of range of values.

Holding my breath now.