Pioneer Spec-2 - Unstable Bias

[ajohnnyz]

Last time I checked, postage isn't free. Packing materials and boxes/envelopes aren't free. The labor to pay some one to pull a part, pack it, someone else to QC it, and put it in a box and send it isn't free. Probably won't come in at a buck and a half anywhere outside of the third world.

I live in California I'm sure it's coming from my up the road. I'm just going by weight I mail stuff every day there should be $1.50.

 

[tarior]

You didn't read the part about the labor and packing materials? Price that stuff some time. Especially in California.

 

[ajohnnyz]

Yes. And that's why I usually don't buy anything from digikey. Mauser is my main choice. But that's OK I have the two I got an eBay with free shipping coming and the two coming from digikey that ripped me off with shipping.

I have three businesses of my own and I've always been fair was shipping I only charge people what it cost to ship I don't inflate the shipping cost.

They're a huge company they get excellent shipping rates way better than I can get and I could ship that to anybody in the US for three bucks.

 

[ajohnnyz]

So anyways I don't even know if that's the issue. I'm just gonna replace that read relay and see if the left channel starts working if not I'm going to need a lot more help to try to track down what the issue is. Like I said I've replaced pretty much every component in the spec 2 that needed to be replaced per instructions so we'll see.

 

[egellings]

There's a lot of possible causes, but I'm speaking about 'no' measurable bias current, or current that fluctuates from a normal value to something lower, and back again (or not).

The root of the problem is Pioneer's protection design, which is effective but horribly complex. The Spec-2 contains no less than eight (8!) relays, performing various functions ranging from a soft-start, to switching in an alternate set of resistors to change the current limiting curve when the amp is switched from 8 ohm to 4 ohm operation.

The relay I am speaking about at the moment interrupts the flow through the current mirror in the bias section of the main amp. The protection circuit of the amp does not allow bias current to flow until the last moment of operation. I'm not particularly crazy about the design, but it is what it is, and if you bypass the relay, you'll get nasty thumps as the protection circuit relinquishes control on power up.

What I have been finding with increasing frequency is that, once the protection has finished its power-up sequence, bias is unsteady, low, or non-existent. This will result in various levels of distortion in the affected channel - ranging from gritty highs and unbelievably flabby bass (think 'nearly unlistenable') to near total loss of signal.

The culprit is RL1 (as designated on the individual amp schematic and the foil pattern), or RL5 'a' and 'b', as designated on the large fold-out schematic. There is one on each driver board, and you can quickly see on the schematic that this relay is designed to interrupt the bias current. The stock Pioneer relay is, frankly, crap, and is likely the cause of a lot of crappy sounding Spec 2 amps.

Here is what the part looks like (circled in yellow):

Looks like a reed relay missing its metal cover, similar to the covered one right next to it.

 

[ajohnnyz]

Looks like a reed relay missing its metal cover, similar to the covered one right next to it.

Yes if you rewind and go back to the beginning of the of this post you'll see what the original pioneer relay looked like. I changed that one out years ago for one that was suggested and it's not the same one they're using here so I'm going to switch out to the one that they're using here and see if that resolves the dead channel issue and if not then I'm gonna have to move forward on my troubleshooting. This is not something I do for a living I do it for a hobby more or less to fix my pioneer equipment because it's getting harder and harder to find people to do this and they want too much money. I've never really paid to have anybody do anything for me in my life so I can do a better job myself for way less money. And in 2002 i spent about $3000 getting everything I need to do this properly I just need guidance. I'm a very quick learner just don't have anybody I can sit down with and show me anything so that's why I'm on this form.

And like we say on one of my channels be kind and rewind. That does save everybody a lot of time when you read the prior chats.

 

[ajohnnyz]

Yay, I won the part FINALLY came in from digikey took seven days for that $7.00 shipping! --that's nuts. Anyways soldered it in and it fixed my issue with the left channel. I went ahead and replace the one in the right channel also. Everything's good now, thank you for your help.

 

[plyzo]

Seems like the recommended relay is obsolete.

I found this one on mouser that seems to be same specs if anyone else down the road is interested.

https://www.mouser.com/en/ProductDetail/Coto-Technology/9007-24-00?qs=PSXJKkD%2FXAQiBDsGEoMUNA%3D%3D