[Ampersand]

As I can't get my hands on any 627/637's, I was thinking of using AD797 on L/R/G. Anyone try this? Or see some glaring problem with using these?

 

[Ikon]

Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif As I can't get my hands on any 627/637's, I was thinking of using AD797 on L/R/G. Anyone try this? Or see some glaring problem with using these?

I don't think AD797 is unity gain stable, so it probably won't work in the ground channel. In the L/R channels, it will likely cause a dangerous amount of DC offset (depending on the set gain) as it is a bipolar input chip.

In the PPA, you need FET input op-amps for the L/R channels unless you add extra input caps. In the ground channel, a bipolar input chip should also work, but it has to be unity gain stable. OPA132, for example, should work flawlessly in all channels (tangent has more examples on his op-amp page).

It's not entirely impossible to adapt the PPA design to make AD797 work, but I'll leave that to the gurus.

 

[Soymilk]

Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif As I can't get my hands on any 627/637's, I was thinking of using AD797 on L/R/G. Anyone try this? Or see some glaring problem with using these?

i believe the AD8610 should work in L/R/G, unless you had some reason to not use them.

edit - they dont come in a dip-8 package though, so you'll need to get an adapter for each one. tangent has them for sale on his site.

 

[Ampersand]

Quote:

Originally Posted by Soymilk /img/forum/go_quote.gif i believe the AD8610 should work in L/R/G, unless you had some reason to not use them. edit - they dont come in a dip-8 package though, so you'll need to get an adapter for each one. tangent has them for sale on his site.

I've used the AD8610 in a pimeta before and didn't really care for them.

Any word on when the 627/637 will be available again?

 

[Ikon]

I finally finished assembling my PPAv2 and a quick test with cheap earphones even revealed that it basically plays music, BUT my working voltages are seriously off. Measured at the C5 caps (which feed the op-amps), I get +/-5V und +/-6.5V on the left and right channels and, most strangely, +2/-0.6V on the ground channel. I guess it's pretty obvious that there is something quite wrong with the ground channel, but even the other voltages appear rather low given the fact that I'm feeding the amp 20V.

Heat-wise, things stay pretty cool. The op-amps are hardly warming at all and the output transistors get just a little hot. I use OPA134s on all channels and also tried a LT1122 on the ground channel to check if that would change anything (it didn't). FYI, I had to pick some alternatives for a few of the transistors that should theoretically work (please ask if you need more info). Oh yeah, and I also added every optional cap that tangent has made room for on the board, just to be safe.

Can you help me, please?

 

[n_maher]

Check for a short between V+ and ground.

 

[tangent]

Quote:

Originally Posted by Ikon /img/forum/go_quote.gif Measured at the C5 caps

Why not measure right at the op-amp power pins? They're a lot easier to get to, and it's more certain you're measuring the right thing.

Also, are you measuring against IG or OG? It should be IG, for this measurement.

Quote:

Heat-wise, things stay pretty cool.

What about current draw?

Quote:

alternatives for a few of the transistors that should theoretically work (please ask if you need more info)

We can only decide if this is relevant if you give the part numbers.

 

[dbfreak]

In Tangent's "Parts Selection Guide," what exactly is meant by Single Voltage or Dual Voltage Power Supply?

 

[MisterX]

Single or dual is just a reference to polarity.

Single power supply = positive voltage and ground.
Dual power supply = positive voltage, ground, negative voltage

Single voltage AC adapter -----> http://www.alliedelec.com/Cart/Produ...p?SKU=879-1080

 

[luvdunhill]

so, i'm finally getting around to tweaking my first real DIY project, my PPAv2. I recently added a AC wall-wart and a TREAD to my existing PPAv2, which sports crossfeed, battery pack, and bass boost.

I think my TREAD is dropping out of regulation, or I don't really understand what regulation means properly. Here are the numbers.

I'm using a Triad 24 VAC @ 200mA which measures 26.81VAC unloaded (and unconnected). I did a bunch of research using Tangent's psu estimator to try and reduce the amount of heat dissipated by the TREAD, hence the above wall wart choice. Before, I was using a 24V Elpac DC power supply. Also, I wanted to be able to tweak the supply voltage via the TREAD to optimize the charger circuit, per Tangent's site. I don't have the exact battery pack specs, but it's fairly conservative and is one of the stock "recipes".

So, when I hook up the TREAD, I get 26.50VAC at the wall wart and 25.00 VDC output and I get 33.3VDC across TP1-TP3, which represents the voltage after rectification.

Now, when I hook it up to the PPAv2, and turn the power switch off, the charger starts working. Now I get 22.94 VAC at the wall wart and 22.77 VDC at the TREAD output. Now, when I turn on the amp I get 21.56 VAC at the wall wart and 20.71 VDC at the TREAD. I believe I'm using 30mA biasing (the battery pack is kinda pointless when using the OPA627/OPA637 *and* 30mA biasing, but anyways)... the deal is, I don't think my battery pack is getting enough voltage to fully charge.

So, can I crank up the TREAD? Anyways, should it be regulating the voltage better than this?

Thanks!

 

[n_maher]

You should try and measure the current draw of the PPA, it may be that you're trying to extract more than the wallwart has to offer. I don't think you should be drawing more than 200mA but that's just based on a rough approximation in my head and shouldn't be trusted. And you could certainly try dialing up the TREAD to see if the otuput voltage comes back up but I'm concerned about the drop in AC voltage output at the trafo, that doesn't seem right to me at all unless you're overloading it.

 

[luvdunhill]

Quote:

Originally Posted by n_maher /img/forum/go_quote.gif You should try and measure the current draw of the PPA, it may be that you're trying to extract more than the wallwart has to offer. I don't think you should be drawing more than 200mA but that's just based on a rough approximation in my head and shouldn't be trusted. And you could certainly try dialing up the TREAD to see if the otuput voltage comes back up but I'm concerned about the drop in AC voltage output at the trafo, that doesn't seem right to me at all unless you're overloading it.

so, I think I figured it out... well, I did indeed measure and allow at least an extra 20% headroom for the current draw of the PPAv2, I forgot to figure in the charger

So, without the charger hooked up, I get 24.000 VDC turned off and 24.002 VDC turned on

With the charger hooked up, and the PPAv2 off, I get 25.46 VDC after the rectifier and 23.16 VDC after the regulator. Once I turn the amp on (with the charger) I get 20.82 VDC after the regulator and 27.52 VDC before. So, yeah, the charger is pulling too much current...

so, next question is, how do I calculate this? Wouldn't this be 1.25 / R2, or 1.25V / 4.7 Ω = 266mA ?

 

[tangent]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Wouldn't this be 1.25 / R2, or 1.25V / 4.7 Ω = 266mA ?

Yes.

 

[applegd]

Just found one interesting thing on my PPAv2. I have two sets of Cardas RCA jacks for two independent inputs(INPUT#1, INPUT#2) and I put one NKK DPDT switch between them as Input signal selector before the input signal goes to PPAv2 circuit board. There is tiny "cross-talk" between my 2 sets of Cardas RCA Jacks, cross-talk between INPUT#1_L_channel and INPUT#2_L_channel, same thing happened between INPUT#1_R_channel and INPUT#2_R_Channel. But no cross-talk between L and R.

Practically above cross-talk is not a big problem. When I am playing music on INPUT#1 while INPUT#2 has no signal input, then change NKK switch position from INPUT#1 to INPUT#2, I can not hear the music from INPUT#1 at this moment. Then I change the ALPS RK27 voulme pot to maximum volume position, I can hear the music playing at INPUT#1 but its volume is tiny.

I checked the resistance between INPUT#1_L and INPUT#2_L, between INPUT#1_R and INPUT#2_R, the reading on my B+K 2706A DMM is OL(range is 20M Ohms). I think the problem might be in the NKK switch(Insulation Resistance is 1000M Ohms min @ 500V DC) or the RF effect.

Anyone saw this kind of problem before? I will run more testing to isolate the root cause.

 

[amb]

applegd, if one set of inputs is open (no source connected) then it's not unusual to have the sort of crosstalk you describe when you switch to the unused input. A floating input will pick up all kind of stuff, including crosstalk from nearby wires, RFI, hum, and other garbage. As soon as you short it to ground, or connect a source, the problem should go away.