[minivan]

just fired up my ss version last night, very good detail with good extension on both end.

anyone live near me wish to audition the amp before their build can pm me for time arrangmement

 

[BoilermakerFan]

OK, I cleared up the schematic for the PVA preamp attenuator:

LMK if there will be issues since it has a gain of 2 for preamp use to my F5s. The 4PDT on the Balanced/SE will be before the primaries and the 4PDT for the eXStata/Preamp will be after the RK27, I just didn't draw them in and the SE drawing I forgot to label the two series resistors as 5K, but they're the same...

EDIT: Have to thank cetoole for the idea and all the help getting the wiring correct.

The 1:2 PVA transformers are $55 each from E-P. So for under $150 I have a pretty nice preamp attenuator.

 

[n_maher]

Quote:

Originally Posted by minivan /img/forum/go_quote.gif just fired up my ss version last night, very good detail with good extension on both end. ]Imageshack - estatass - Uploaded by triseven

Interesting use of the Neutrik D housing to hold the Stax jack. Does that actually work out ok?

 

[digger945]

Quote:

Originally Posted by BoilermakerFan /img/forum/go_quote.gif OK, I cleared up the schematic for the PVA preamp attenuator:

Are the 5k's really necessary? The reason I ask is because I dunno

I was thinking we would see something where the only resistance was in the shunt element of the circuit.
I'll be trying this soon to listen for meself. Already have some transformers, just need some time.




Quote:

The 1:2 PVA transformers are $55 each from E-P. So for under $150 I have a pretty nice preamp attenuator.

I like the price.

 

[BoilermakerFan]

.

 

[BoilermakerFan]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif Are the 5k's really necessary? The reason I ask is because I dunno I was thinking we would see something where the only resistance was in the shunt element of the circuit. I'll be trying this soon to listen for meself. Already have some transformers, just need some time.

Without the series resistors in place, mimicking the schematic from the E-P site and only using the single 10K pot while bringing the secondary's grounded point high as IN- with the wiper going to IN+; the signal is only balanced at full volume, with no attenuation going on at all. Turn it down a bit though, and you have a resistor divider on the + phase, but nothing on the - phase. This still provides a constant 10k load to the transformer, because the transformer just sees the impedance across the whole conductive track of the pot, but not the amp's signals are unbalanced as soon as the pot is turned down.

Now, with the schematic I posted, the one with the series resistors and the pot used as just a variable resistor, we have a fixed series element on both phases, but the shunt varies. When the pot is at 10k (all the way up), we get 6dB attenuation. As we turn the pot down, the shunt element gets smaller, so the attenuation increases equally for both phases and we stay in balance.

And we get to use a single ALPS or Nobel stereo pot instead of quad.

 

[pabbi1]

Ok, found my psu faux pas... well, at least the symptoms - its r16:

While it would give off a whisk every now and then, it never failed with the psu running for 20 minutes - and where the left rail would drop a few mv, and I'd crank it back up... where the led was dying. All making more sense. I was almost convinced the wisps were cat hair or some stray saw dust (hey, it happens - at least it wasn't stray aluminum shavings).

Well, except for what the root cause might be?

And, an obligatory money shot:

 

[les_garten]

Nice Looking Build AL! Can't wait to hear your thoughts on the Sound.

 

[gilency]

Al's SS prototype sounds wonderful with my Sigma Pros. There is plenty of volume . I can't listen if I turn the know all the way up. I have to remove the SP's from my ears. There is zero distortion at max volume.
It sounds energetic with lots of bass and plenty of detail.
Kudos to Alex, Al and Nick.

 

[runeight]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Ok, found my psu faux pas... well, at least the symptoms - its r16: While it would give off a whisk every now and then, it never failed with the psu running for 20 minutes - and where the left rail would drop a few mv, and I'd crank it back up... where the led was dying. All making more sense. I was almost convinced the wisps were cat hair or some stray saw dust (hey, it happens - at least it wasn't stray aluminum shavings). Well, except for what the root cause might be? And, an obligatory money shot:

This is hard to diagnose. Since the LED does light there is current in Q7/Q8. But for this resistor to burn also means that too much current has passed through it which means that during power up something is awry.

I think you have to check all of the transistors in the shunt portion of the negative (edit) rail. Make sure they are the right polarity. And check the zener string too.

This would be Q7,Q8,Q11,Q12. And then if everything checks out you might have to replace the CRD (R14). Is the CRD in the right orientation? If you don't have one handy for replacement you can temporarily run with 4k7 resistor in this spot.

EDIT: I meant to say negative rail and I've edited the post.

 

[n_maher]

That resistor doesn't look cooked in the traditional sense, looks more like it was damaged by force or perhaps just flawed to begin with? As a first try I'd remove it and replace it in kind and monitor the voltage drop across it during the initial power up. That is of course after checking the parts that Alex suggested to make sure it isn't simply a current over-load situation.

 

[runeight]

Good catch Nate. You might very well be right and it would save Al mucho work.

 

[pabbi1]

Saving Al mucho work is a good thing...

IIRC, that resistor looked funky from the get go, so I'll replace it to see if I get lucky. The zeners are all oriented correctly, and I'll recheck everything else. That said, it wouldn't dial in right otherwise - or am I just being, well, optimistic?

Oh, and are there any other points to measure to see if something else is awry? And, maybe a higher value resistor, say .5 or .75w - or is that just squeezing the baloon?

 

[runeight]

Measure R12. Should be near 150V. Higher wattage is not needed. If everything is working properly 1/8W is 10X more than required.

 

[luvdunhill]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Measure R12. Should be near 150V. Higher wattage is not needed. If everything is working properly 1/8W is 10X more than required.

It's hard to tell from the picture, but it seems that that resistor is too big to fit. Perhaps using a properly sized resistor would help prevent this, as I agree, it seems that the damage was done before power-up.