Pioneer SA-6300 issues

[cgme]

Hi there,

I'm very, very brand new to the world of vintage audio and last week purchased my first vintage amp; a good looking Pioneer SA-6300. I've also acquired a set of KEF Chorale bookshelf speakers. Both items I went to meet the buyer and had them demonstrate.

The Pioneer seller had the amp hooked up to a set of huge vintage Akai speakers and it sounded really nice, no distortion, nice and clear sound, and no crackling when using the dials and switches. He had replaced the (defective) power light with an LED light, cleaned it up a but, and resprayed the top cover as it had some scratches. If I recall right, he also replaced some (all?) capacitors, but I have to double-check that with him to be sure. Everything good so far.

The KEF seller had them hooked up to a big Sansui amp, no idea what type. Me being new to the audiophile world was easily impressed with the sound the Chorale speakers produced. Still everything good.

Now, at home I got myself a good quality speaker wire (6mm², might be slightly overkill?) and banana plugs, connected the speakers and hooked up my iPad (yeah, I know, not exactly top quality sound, I'm new to this ) with a quality jack-to-cinch cable to the aux input. Turning the Pioneer on I was disappointed to say the least; the right speaker had some crackling sound and distortion and the volume seemed a bit lower than the left channel too. The distortion is constant, regardles of operating any of the switches or dials. It also "scales" with the volume.

To rule out speaker and wire faults I've switched the speakers left and right, and after that the cables; still the same. The SA-6300 supports two sets of speakers, so tested on both outputs A and B. Used a different device as input, swapped the left and right plugs of the cinch input, switched input from aux to radio; still the same.
I've also tested with headphones which made it a bit weird for me. With the speakers connected to output A, output selector at A, I have the same distortion on the headphones as I hear over the speakers. Now, when I switch the selector to either OFF or B (essentially no sound via the speakers), the distortion disappears. This also works vice versa with the speakers connected to B.

I've already ordered a DeOxit kit (red and gold) to attempt cleaning the dials and switches, but some additional insight/advice would be appreciated.

 

[cgme]

I've been thinking since I've posted this thread...

Just thinking out loud here (mind you, I'm new to this), could it has to do something with the output inpedance?

Continuous power output for the SA-6300 is:

• 40 Hz-20kHz (Both channels driven): 20W + 20W (8 Ohms, Rated power) – 20W + 20W (4 Ohms)
• 1 kHz (Both channels driven) 22W + 22W (8 Ohms) – 24W + 24W (4 Ohms)

What confuses me here is the term 'both channels driven'. Could this mean that the SA-6300 only works with 8 Ohms speakers when both A + B channels are driven/connected? The KEF Chorale is specced at 8 Ohms.

 

[slimecity]

So you will need to do some testing to diagnose the Pioneer.

- Dont use your good speakers on this until its fixed,
- Run a DMM into the plus and minus speaker terminals of the Pioneer and measure the DC offset voltage in DC mV, tell us what you get,
- Use another lead to run your signal into the amp, there could be an issue with the RCA connections inside that or an issue with the 3.5mm socket in your ipad,
- Follow other posts here posted previously on cleaning all controls with deoxit, do this first,
- There are no "pre out, main in" RCA jacks on the back of this, so diagnosing the issue could be slow.

 

[cgme]

Thanks for your reply Slimecity.

• I don’t have a tone generator or something, but installed an app on my phone for that. With a 1kHz tone I measure 15 mV on the right channel (the bad one), and 40 mV on the left (the good one). On both channels there was some variation though, of about 0.5 mV, even with a constant tone.
• I’ll try with a different input lead tomorrow
• Hopefully tomorrow my DeOxit kit will be delivered so I can clean the controls. I’ve already found the thread on how to do that.

I also got a reply from the previous owner and the only thing he’s done was replacing the power indicator light. All other internals were untouched.

 

[slimecity]

Sure - you generally want to measure DC offset at the speaker terminals with volume set to 0 and no audio signal going thru the amp

 

[cgme]

Ok, second attempt. No audio input and volume set to 0.

Right after turning the amp on I measured 7.4 right and 37 left, but I noticed both channels fluctuating and slowly rising. After roughly 5 minutes I measured around 13.4 right and around 38.7 left, both bouncing +/- 0.3 mV.

I've also googled and downloaded the wire schematic for the SA-6300. I have a very basic understanding of wire schematics, so I can read the symbols but that's aobut it.