9001 flaw from factory

[Trnsfmr]

Hi all,
I discovered something new today about the 9001. And believe me, I thought I had figured out everything there was to figure out about this receiver. I've worked on so many of these things now, that you could tell me a symptom, and I could most likely tell you the exact part or problem and where it was.

Anyway, this is most likely wrong with every single 9001 ever shipped. It has to do with the 2X power mode. The 9001 has a function where you can get all 4 channels to drive just the two front stereo channels, in bridging mode, which gives you 2X as much power or 120 watts per channel instead of just 60. This is achieved by using a channel to drive each side of the speaker, with the negative side driving out of phase with the + side.

Bridging mode normally works really well, and actually gives you the peak power of 4X what a single channel does. It also doubles the slew rate, and spreads the heat load over the heat sinks for all 4 channels. So, in bridge mode you usually get the sensation of much more power, and effortless drive, and great sound, better than the single ch version.

Well, the 9001 bridge mode never sounded as good as I thought it should. But since the 9001 is about quad, and I, and most of my customers, don't usually run it in that mode, I didn't think much about it.

I had a customer who's unit developed a giant pop when switching to 2X. And then a unit on the bench that we had just recapped, did the same thing. I had to use the scope, pour over the schematics and actually think, to figure it out. Turns out that a cap that feeds the relay that switches to 2X mode has the cap marked backwards on the board. This cap only comes into play in 2X mode, but passes audio to the right channel, and is reverse biased by 8v (installed backwards). It's a 50v cap, and I guess most caps could handle the reverse bias. We just got a new bag of 2.2uf @50v caps in, and I guess they couldn't handle the reverse bias.

Well, a reversed biased cap doesn't sound very good, even if it doesn't fail. Now with that cap put in the right way, the 2X mode really shines. For a stereo receiver, it now sounds as good as the 9090, which to my ears always sounded a little better than the 9001 playing just stereo. Of course the 9001 always beat out the 9090 in quad mode, so I never thought much about it (that's a joke).

Anyway, if you have a 9001, and you care, it's C30 on the f2636 board. That is the board right behind the front panel with the bal and vol controls on it. You can get this board out without removing the front panel, if you remove the faceplate, and the bottom cover. It's tight, but it will come out.

I'd use a new cap. If you ever listen in 2X mode, it's worth the trouble.

Various 9001s I've seen in the past would pop to one degree or another when switched into 2X mode, uncharacteristic for this receiver, which generally does everything without any untoward noises. I guess that some had a problem with this cap being in various states of failure.

Once it is replaced and with proper polarity, the switch to 2X seems noiseless and gives the feeling of lots of power available. Indeed the peak power, calculated just from the total voltage swing of almost 90v, is around 250 watts.

Perhaps if this cap had not been misplaced from the factory, the 9001 would have been able to compete better with some of the high powered receivers of the day. Generally the 2x mode is a disappointment. But after this fix, it is pretty potent and sounds great, to boot.

 

[jefe1]

Wow, what a discovery! I'm going to ask you to fix this issue on my unit, which had the 2x disabled by quadbob as you can see.

 

[Trnsfmr]

Hi Jeff,
The 2X power position on your unit is completely disabled. In fact, your unit will not even go into stereo mode. The relays have been removed and hard wires put in their place. There are three relays involved in the switch from quad to stereo to 2X stereo. All three are missing from your 9001. Justin and I talked about putting it back, but only one of the relays is readily available today. If we had the parts, we could do it. Sorry.

 

[jefe1]

I don't know if I should blame quadbob for this. I knew stereo mode was being disabled but not that parts were being removed. He never told me and I didn't ask. Would have been nice if he disclosed that this would be irreversable. Great.

 

[JonUrban]

He did the same thing to my QRX-999. I haven't lit my 999 up in years. I'm almost afraid to. It may cause a power outage in the neighborhood.
I look at it now as a $1000+ QB nightmare, and a nice memory of my time in the Navy.

 

[Quadzilla]

I don't know if I should blame quadbob for this. I knew stereo mode was being disabled but not that parts were being removed. He never told me and I didn't ask. Would have been nice if he disclosed that this would be irreversable. Great.

With so many present-day speakers set up for bi-wire connection, I would suggest using the front and rear amplifiers to drive the high and low connections. That should give you better sound than bridging, and the F-R balance control would give you a bit of flexibility in terms of the bass and treble balance. Besides, isn't it heresy to think about using a quadraphonic receiver in stereo mode anyway?

 

[Quadzilla]

I sure dodged a bullet as far as that character is concerned. Cai Campbell talked me out of sending a couple of pieces to QB, and apparently he did me a huge favour. QB wasn't pleased about it though, but I got over it pretty quickly. I miss Cai.

 

[jefe1]

Thanks for the tip quadzilla! I know its heresy, just would have liked to try double power once in a while and have the neighbors complain.
Its too bad Hells Angels aren't into quad, I'd like to see qb pawn off a fake recapped sansui on one of them and watch while they do somethig about it, all 40 of them.....

 

[Quad Linda]

Double the power isn't as loud as it seems. Power works logarithmically. Double the power yields an increase of 3db, which is the smallest increment of change the human ear can perceive in most rooms. Double the power will give you twice the headroom. The neighbors won't complain with double the wattage. 10 times the power will yield double the volume level.

I don't mean to shoot holes in it. Don;t blame the messenger.

Thanks for the tip quadzilla! I know its heresy, just would have liked to try double power once in a while and have the neighbors complain.
Its too bad Hells Angels aren't into quad, I'd like to see qb pawn off a fake recapped sansui on one of them and watch while they do somethig about it, all 40 of them.....

 

[Quadzilla]

Doubling the power (e.g. going from 30 wpc to 60 wpc) will result in an additional 3dB of sound. Putting this into practical perspective, 1dB is the smallest incremental change in sound level that the human ear can detect. It is funny when you hear comparisions between 30 watts per channel and 40 ... really? Watts are not the whole story either, as anyone who enjoys Harman/Kardon will tell you.

 

[quadtrade]

Power from an amplifier will make a difference in how your speaker performs. The idea is to match up speakers with amplifiers that work for them. I run 4 JBL Jubal L65s and use a Fosgate Audionics Power Amp 4125, that only says 75 watts a channel in 4 channel mode. The low end with this amp is ten times what i can get out of a modern receiver. Amazing dynamics. Great imaging also. Much of an amp depends on the build. Each one does have it's own sound and performance. These old JBLs require lots of power and can even be harmed by not enough power. The magnet for the woofer in these JBLs weighs more than many speakers people listen to these days. Many older speakers will sound much better with a lot of power, not a lot louder but a hell of lot better bottom end and usually a good amp will have better transparency. Speakers can have a huge varience. The L65s are said to be better played loud. Fine by me.
A set of preamps out on the 9001 would have been a nice feature.

I found this which gives a sort of amp basic.
The main areas in which amps vary are: timing, dynamics, stereo imaging and transparency. Timing is the ability to -present the attack and decay of each note precisely; amps with strong timing have a snap and coherence that is very appealing.

Dynamics is a general term for the ability to portray variations in level between -individual notes and is different to dynamic range (the difference between the loudest and softest notes). Dynamically strong amps tend to have more life and energy.

Stereo imaging is how solid or three-dimensional an instrument or voice sounds. The point of having two rather than one speaker is to make it possible to recreate the soundstage of the original recording, thus amps that have strong imaging skills can create a sonic space that seems to extend the room.

Transparency of detail is the most -obvious difference between amps. One amp will present more subtlety than another, but the drawback with using this as your main criterion is that a forward or ‘bright' sounding amplifier will emphasise detail at the expense of overall musical coherence.

 

[Trnsfmr]

IMPORTANT, READ THIS POST


Well, I'm sorry to say, cause I hate this kind of stuff myself, but there are more variables to this problem. I have six 9001's in the shop right now, plus an 8001, which has the same board. The caps appear mounted correctly in one unit, but most of the time wrong, AND the solder mask, the printing on the board, got corrected, I would imagine, on later boards. I wish I could tell you a serial number, after which you can trust the print on the board, but I can't.

So here is the correct way to deal with this. As you look down from above at the board, f2636, C30 should have its positive side toward the BACK of the receiver, negative to the front. With a flashlight, you can check without removing anything but the wooden cabinet. You have to push some wires aside so you can see, but it's relatively easy to do.

You can also change out the cap, if it's wrong, without removing the board. You just need to remove the bottom plate. It's hard to figure out which two pads are the cap, but you can desolder, pull the cap out, and replace it with some forceps or long needle nose.

Sorry to make this even more complicated, and I hope no one got fooled by the changes. This is the right way to deal with it.


And incidentally, the 2X mode does indeed give twice the power, but because of the afore mentioned dynamics and the fact that peak power has been increased by 4X, the perceived difference in available power will be 6 db, an appreciable difference. That, coupled with the doubling of the slew rate, and you will really hear the difference.