Tascam DR 05 anomaly

I use a Tascam DR 05 to record my mates acoustic guitar and my bass in rehearsing some of his original material.I'm through an amp and hes playing and singing acoustically,My problem is that on playback,the playback sounds like it has an added 'tremolo' effect,emphasised at the bass end. We've tried different locations for the Tascam but that same effect is still there,I have discovered that the 'Tremolo' effect is only there when I use the 'headphone/line out' socket either into 'phones or straight into a stereo amp.If using the USB socket into my PC the recordings are 'clean' with no weird effects.What could be causing this?
 
what cable are you using to plug the line out into your stereo amp? do you have the same issue when plugging some other source into this stereo amp? also do i have it right that you'd heard this in a pair of headphones plugged straight into the DR-05? do you have a recording of this what this "tremolo" sounds like?

could be a bad line/headphone out on the DR-05, but impossible to provide definitive answers based on the info you've provided.
 
Not sure how long you've had your DR-05, but that's an older piece of gear and could be developing issues (the DR-05x is the newer model). The fact that the USB is working fine and the line out is problematic would suggest that you either have an issue with the circuit or a line level issue. I'm sure that you have tried the volume control. I always downloaded my music from the unit via the USB, but there are effects that can be applied during both recording and playback, this is from page 43 of the manual (see below).

Cheers...

FYI: My 10 year old DR-05 was a great asset for band practice and recently died. I replaced it with a DR-40x and I love it... it offers 4 channel recording so you can use the live mics and output from the sound board.

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I have a DR05. I've only ever used the headphone out to check what I've recorded afterwards, and that works fine. The device is only doing one thing at a time, recording, or playback.

I suspect when you ask it to do both at once, there's a voltage drop going on that causes the tremolo problem. It doesn't do it on USB because it provides the unit with additional power.

But I'm only guessing .