Pioneer Spec-2 - Unstable Bias

EchoWars

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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):
 

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...and here's the replacement (sitting next to the removed original)...a US Relays 24V SPST relay. I looked for days to try and find a direct solder-in replacement, but finally gave up. At least this relay requires NO modifications to the existing circuitry, can handle 1A of current (many times what we need), and is rated for something like 5 million cycles. It'll last a while
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Mounting is odd but simple...with the original removed, there is space next to the original location. I mix up some epoxy, paint some on the flat surface that the relay happens to have on its top, and stick it 'top-down' just to the left of the 'dead-man' lines where the original relay sat.

The TO-220 transistor behind the relay gets hot...I install the relay with a small gap between the relay and the transistor heatsink. Close is fine, but touching is not.
 

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Lastly, I take some very small solid-core wire (actually it is wire stripped out of some Cat5 cable), and bend a 'C' into the end of the wire and solder it to the pins on top of the relay, then flip the board over and get the other side.

The two inner pins of the new relay are the coil...the outer pins are the contacts. Note the holes used...the two holes closest to the other relay are for the contacts (except on the left there's a dummy hole that the old relay used for support...don't use it, or the relay won't work). The two holes farthest from the other relay are the 24V for the coil.
 

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Knowing nothing regarding relays etc... would it be wise to replace all the crap relays?

Or would that be overkill and or expensive?
 
All in all, not the perfect solution, but this relay will last the life of the amp.

US Relays part #SD1A24D, Digikey part #Z535-ND. About $5 each.

Edit: You butted in before I finished. :butt1:

In your amp, there are now only three remaining original relays...the speaker relay, which is a good one, although old, and the relay that changes the current limit curve when switching from 8 to 4 ohm (one on each driver board, right next to the one we just replaced). This remaining reed relay is basically the same relay Pioneer and Kenwood used in millions and millions of tuners, receivers, amps, and preamps (my Kenny 700C uses one just like it, made by Hitachi, I believe). I've never seen one fail. The only 'crap' relay in the amp is this POS that Pioneer chose for the bias current interrupt. Both channels on your amp are now changed.

Edit #2: It appears that Digikey is dropping these small US Relays parts from their stock. Substitute the Hamlin HE3300 Series 24V SPST relay. Part #HE129-ND. Same layout as the original...inner pins are the coil, outer pins are the contacts
 
Excellent :thmbsp:

Would it be wise to bring down the other Spec 2 and have the relays replaced on it as well?
BTW Glenn I'll be down your way for a work conference on the 11th, thru the 14th. We'll have to tip a couple and listen to some tunes!
Scott
 
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Once again, a very detailed and informative post Glenn. All the sansui 8001/9001 quad receivers use that same relay to power the 4 channel synthesizer boards. It gets crappy and then you loose 4 channel functionality.

I agree that for the most part that hitachi relay doesn't really die much, but I guess it was just not designed for that particular application.
 
The Hitachi (and the Pioneer branded metal-enclosed relay such as the one next to the faulty ones replaced in this thread) seems to be quite reliable. But the one getting replaced here has essentially an open, unprotected coil, covered only with the brown paper. While troubleshooting this one, I was tapping the relay body, watching the bias change, and I guess I tapped too hard on the middle of the relay where the paper is and the coil opened up. Not much of a loss, as it had to be replaced anyway...I was just shocked that it was so easy to kill it.

I'm further amazed that they have worked for as long as they have. If anyone ever finds a direct solder-in replacement, I'd love to know about it. But for the meantime, the SPST US Relays replacement is a champ.
 
EchoWars said:
That's it...come down here for a visit, and ****in' put me to work. :tears:

You'll pay...:uzi:


:lmao: :lmao: :lmao: :lmao:


I'll bring plenty of :beer: and watch the Master hard at work :D
 
EchoWars said:
That's it...come down here for a visit, and ****in' put me to work. :tears:

You'll pay...:uzi:

Can you feel the love??? :D

Excellent work as usual Glenn! :yes: :thmbsp:

Scott
 
Would this cause the VU meters to climb or peg when no source is into the amplifier and no speakers hooked up to it . Simply plug it in and the left meter will peg all the way to the right and stay then start to bounce slowly the right meter will slowly climb and bounce . Protection light does go out, amp will work . Not that im going to be using it like this . I just picked this up yesterday $30.00 couldnt pass it up . This problem is not consistent though. The left yes but the right hit and miss. When the guy was showing me this yesterday he was flipping the 4-8 switch in the back , i didnt say anything to him as i wanted to get the amp out of there asap . But he did have it working and the sound was good and the meters was acting normal .
 
Sounds more like the meter driver transistors need replacing (Q1 ~ Q8 on the meter amp board). If you see the meters acting up AND the unit won't come out of protection, then the suspect is usually the pre-driver transistors (Q4 ~ Q7) on the amp board).
 
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Thanks EW , i ordered a couple Hemlin HE129-ND s that you have mentioned . Just thought i could start buying some replacement parts . These relays can they be replaced without having to adjust anything ?
 
In the Spec 2 (S M) the part #s are 2SC1312-G total of 4 and 2SA725-G total of 4. Would those be the ones ? For the meter drivers thanks
 
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