Hi and yes, I've cleaned those switches a couple of times already. I know muting and Line straight are sounding bad again. I'll see if that helps. Thanks Jakobsson. I hope you have found my troubleshooting and repair work here mildly entertaining
I have not made any adjustments, just changed the bulbs on power on/line straight.
EQ is working but i have only used line straight from sound card, never tested phono.
Amp is sitting in my storage unused at the moment.
I have used a HK670 at work with pretty good speakers and i took the Pioneer to work for cleaning and then tried it with the same speakers and it sounded better.
EQ is working but i have only used line straight from sound card, never tested phono.
Amp is sitting in my storage unused at the moment.
I have used a HK670 at work with pretty good speakers and i took the Pioneer to work for cleaning and then tried it with the same speakers and it sounded better.
Weak as in low volume or weak as in the tonal balance isn't correct ? It would be very odd to have a problem affecting both channels of the phono stage.
Both channels sound weak in tone at lower volumes. No depth. If I turn volume past half way then things seem better. When set to MC, tone is much better on lower volumes. It gets too loud at higher volumes. Liken it to the difference between having Loudness button on/off.
I'm suspecting those trim pots that are supposed to be set to 100mV according to service manual. They have to do with Phono stage, not other inputs. You seemed to think it was for setting bias on phono preamp. Mine don't want to stay put at 100 and seem to fluctuate all the time.
I'm suspecting those trim pots that are supposed to be set to 100mV according to service manual. They have to do with Phono stage, not other inputs. You seemed to think it was for setting bias on phono preamp. Mine don't want to stay put at 100 and seem to fluctuate all the time.
The 100mv will be the offset (haven't got the circuit in front of me) and what I think they are saying from memory is to set the voltage to at least -/+100 mv i.e. as close to zero as possible, but accepting the fact that the voltage will wander significantly with temperature variation.
You might like this as something to try with your scope, an inverse RIAA network.
You connect it to a signal generator (read CD player with a frequency sweep) and feed the output into the phono stage. The overall signal produced from the phono stage should be of equal level as the sweep goes from 20 to 20kHz.
You might like this as something to try with your scope, an inverse RIAA network.
You connect it to a signal generator (read CD player with a frequency sweep) and feed the output into the phono stage. The overall signal produced from the phono stage should be of equal level as the sweep goes from 20 to 20kHz.
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Yes, what they are saying is set for zero offset (but don't worry if it wanders).
A circuit like that can be built in a couple of minutes (honestly) just by wiring it between an 'open type' phono socket and phono plug.
The cap values are critical to it working correctly but the final values can be made up from any combination that gets to the desired value (caps in parallel add in value).
A circuit like that can be built in a couple of minutes (honestly) just by wiring it between an 'open type' phono socket and phono plug.
The cap values are critical to it working correctly but the final values can be made up from any combination that gets to the desired value (caps in parallel add in value).
Hi and yes, I've cleaned those switches a couple of times already. I know muting and Line straight are sounding bad again. I'll see if that helps. Thanks Jakobsson. I hope you have found my troubleshooting and repair work here mildly entertaining
I checked and reset the Phono/EQ adjustements last night (left was hovering around 200mV, right was around 30mV). But that did not improve turntable sound. What I did notice as Jakobsson mentioned was the switches. I noticed static when pressing Phono (CD seemed much better). Mashing Phono a couple of times did improve sound with MM selected. I'll pull face and give the switches another good cleaning over the weekend.
So I gave all the switches and pots a good cleaning with DeOxit and the sound seems much better (even set to MM). I'll check back here form time to time with an update as to how things are going with this amp. At some point I will consider an electrolytic recap, but am holding off on that for a bit. I want to again thank everyone for their help here. I could not have fixed it without the great support here at diyAudio! I have attached a pic of this A-88x's new home in our basement.
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