Sick pioneer SA6200

[pre65]

So the inputs are not AC grounded in any way then? Or are you actually playing music through it from something else?

No The amp is on the table no connections in or out the MM is connected to it monitoring the current

Are you going to try it with a dummy load ?

[colin.hepburn]

Well after running the sick pioneer SA-6200s /power amp with nad preamp and running the other pioneer SA-6200 it seems to sound different too sick pioneer SA-6200 After opening it up and checking I see the left channel has two different small single transistors and all drive and output transistors have been replaced but the numbers have faded will have to look again in day light but this amp does't sound as good

[colin.hepburn]

HO Dear I seem to have a problem with the Sick pioneer SA6200 I was running my headphone amp as a pre with some Sade sounding great then suddenly the amps sound brake up with a distorted cracking bass sound but oddly when switching off the SA6200 the sound come back OK for a few seconds with the capacitors discharging any ideas the amp is cap coupled to the speakers could it be a capacitor

[colin.hepburn]

HO Dear I seem to have a problem with the Sick pioneer SA6200 I was running my headphone amp as a pre with some Sade sounding great then suddenly the amps sound brake up with a distorted cracking bass sound but oddly when switching off the SA6200 the sound come back OK for a few seconds with the capacitors discharging any ideas the amp is cap coupled to the speakers could it be a capacitor

AH Breathing again
I over looked the fact there are two fuses in the speaker line strange thou any ideas what happened

[Mike H]

Without watching it do it with a 'scope or something can't really say.

Maybe a large slow DC offset on the input? Is the headphones amp loaded like it would be with headphones connected?

[colin.hepburn]

Without watching it do it with a 'scope or something can't really say.

Maybe a large slow DC offset on the input? Is the headphones amp loaded like it would be with headphones connected?

The Headphones were unplugged at the time Shunt pot is over sensitive there was a mains power Dip which may have contributed perhaps the pre out is 1uf polypropylene Caps and 1M resistors

[Mike H]

Looking at the diagram again, the power amp input impedance is about 50 kilohms, so 1uF should be about right for that. However is the headphones amp a valve circuit?

[colin.hepburn]

Looking at the diagram again, the power amp input impedance is about 50 kilohms, so 1uF should be about right for that. However is the headphones amp a valve circuit?

Yep its my 5757/12B4A

[Mike H]

Ah right so I'm guessing mains had a dip, BIG Voltage shift into the Pioneer. Probably drove it up to one supply rail or the other so no wonder it was clipping.

[colin.hepburn]

Ah right so I'm guessing mains had a dip, BIG Voltage shift into the Pioneer. Probably drove it up to one supply rail or the other so no wonder it was clipping.

\Ah OK thanks mike that hadn't occurred to me that
Next up is the over sensitive Shunt Alps pot 100k could do with a bit less gain
Pre out connected to 12B4A
See Page four
http://hollowstate.netfirms.com/mapletreebranches1.pdf

[Mike H]

Yes I see, though I think it probably wants a regulated HT supply.

That's the trouble with feeding valves outputs into tranny circuits, large Voltage shifts whenever the supply changes.

Can also be demonstrated on an oscilloscope, turn it up and the trace can disappear off the screen for a second or so next time the boiler thermostat goes on or off Viz, causes the mains to change a bit.