[silvalis]

I'm getting a thump through the L/R channels when I switch on/off. I'm currently using a transformer type 24V/1A reg supply.
Could anyone speculate on the possible causes of this thump, if it will damage my headphones if i leave it connected when I turn on/off and how I can fix the problem?

 

[tangent]

Quote:

Originally Posted by silvalis I'm getting a thump through the L/R channels when I switch on/off.

This is probably normal. If you have access to a DSO, you can capture it. If it's just a volt or two, it's harmless.

 

[ceRon]

Quote:

Originally Posted by tangent This is probably normal. If you have access to a DSO, you can capture it. If it's just a volt or two, it's harmless.

but can it be avoided? though it is harmless to the headphone, i dont want to be shock whenever i switch it on or off

 

[steinchen]

it's depending from the opamp you're using, some pop very loud (especially opa637), some hardly at all (ad744).

if you don't want to plug/unplug your cans every time you power on/off your amp you may consider building a muting delay, there are several designs out there in various boards. The latest one, the ε12 from amb, additionally incoporates an offset protection -> http://www5.head-fi.org/forums/showthread.php?t=119066

 

[groovy2]

delete meee

 

[rhooper]

So far the following setup seems to be stable:

AD8610 x 3 and all other "default" parts available from Digikey or Tangent's audio shop, excluding the class a bias parts -- 5 x 470uF cerafine 25V.

Power source: TREAD @ 24 VDC from a 24 VAC 200mA wall transformer that puts out 27 VAC unloaded.

The regulator on the TREAD is running hot w/o a heatsink, but is still just barely touchable. Ouput voltage drops briefly when the PPAv2 is first powered up (and the TREAD LED dims), but otherwise it remains at constant brightness. (I assume that the high initial draw is the caps charging?)

If I do my math right, 24V @ 200mA is 4.8 Watts, which is plenty for a PPAv2 driving Grado SR-80s, right?

The PPAv2 sounds significantly better than my CMoy with the Grados. Right away I noticed considerbaly more fullness to the bass without the bass boost circuit installed.

Is that because of the discrete buffers? If I have it right, the buffer is there to provide the current the headphones need, and the opamps are there to provide the appropriate voltage?

PS - Thanks to everyone who worked on the PPA design and its predecessors and successors (especially tangent and his detailled webpages)!

 

[tangent]

Quote:

Originally Posted by rhooper The regulator on the TREAD is running hot w/o a heatsink

I coulda told ya that.

Or you could have found out for yourself in advance.

Quote:

Ouput voltage drops briefly when the PPAv2 is first powered up (and the TREAD LED dims)

Absolutely normal. The regulator is dealing with a massive capacitive load during that period. Many regulators will completely fail to cope with your ~2500uF rail.

Quote:

If I do my math right, 24V @ 200mA is 4.8 Watts, which is plenty for a PPAv2 driving Grado SR-80s, right?

That's misleading. There's no way you can deliver 4.8W to the headphones. The correct way to calculate wattage to the headphones deals in sinusoidal RMS output voltages from the amp, and takes into account clipping, and current limits in the amp's output stage.

Quote:

Is that because of the discrete buffers?

That gives you the slam. The tightness in the bass is because of improved channel separation, lower supply impedance, etc. There are lots of things that make the PPA the PPA, not just the buffers. A PPA with BUF634s sounds better than a similarly-configured PIMETA.

Quote:

the opamps are there to provide the appropriate voltage?

More or less. The pot is an attenuator, and the op-amp provides gain. Between the two, you adjust to overall amp gain to be what the phones need. If you knew the proper system gain in advance, you could do without the pot, and just set the gain appropriately.

 

[Buzzerbro]

I don’t know if this has been asked before and I can’t find the answer when doing a search. I am planning on building a PPAv2. For the bass boost pot, the 50k Alps Rk27 is suggested. I would like to know if a 100k pot would work for bass boost. Would anything on the PCB need to be changed to accommodate a 100k pot for bass boost?

Regards,
Buzzerbro

 

[Clutz]

Quote:

Originally Posted by Buzzerbro I don’t know if this has been asked before and I can’t find the answer when doing a search. I am planning on building a PPAv2. For the bass boost pot, the 50k Alps Rk27 is suggested. I would like to know if a 100k pot would work for bass boost. Would anything on the PCB need to be changed to accommodate a 100k pot for bass boost? Regards, Buzzerbro

AFAIK it should be fine. All the pot does is take the place of R7 in the circuit, and there is no specific reason it couldn't be set to a value of 100k.

 

[tangent]

Quote:

Originally Posted by Buzzerbro Would anything on the PCB need to be changed to accommodate a 100k pot for bass boost?

No, it will just give you a wider boost adjustment range. Maybe too wide to be useful, but that's for you to decide.

 

[Buzzerbro]

I almost have my PPA V2 put together. I am still waiting for my OPA627 chips to arrive which I will use on all 3 channels.

Is there some way to test the board with out the Opamps? Can I jumper the socket? Which pins would I connect in the diagram below?

Thanks

OPA627 pin configuration

Attachment 6886

 

[jagrifen]

I recently built the PPA v2 following tangent's guide. I've left the opamps out and left out the parts to bias into class A. I have also cleaned off all flux and trimmed the leads cleanly from the bottom. When I flip the power switch, the LED does not turn on, and I get about 2 volts at the supplies to the opamps. It seems there is a short somewhere, but I am not sure how to track it down efficiently. I have doen a visual inspection a number of times and can not locate any misplaced parts. I have also tried doing an in-circuit continuity test at each capacitor. One of the many transistors may be fried, but I hate to have to take them out one-by-one to track down the problem. Does anyone have any good troubleshooting methods? Any good ways to isolate the bad section?

 

[Clutz]

Is the protection diode in backwards?

Take some pictures of it wioth a digital camera and post them. Get nice and close up, and pretty good resolution, so that we can look at it.

 

[jagrifen]

The diode is in correctly and functions properly. With the psu plugged in and switch off, i get 24V in all places up to the switch. When the switch is turned on, voltage drops to about 2 volts. I measured the current throught the diode to be .33 amps, which is the limit of the psu. I have tried another psu, and the same occurs.
I am using four 470mF cerfine caps for C1. All are in correct polarity. The caps for C2 are not polarised. Do you think it matters that I do not have the opamps installed for this step? Does R12 need to be turned to a halfway point or something like that? Does the amplifier need a load?
I am not sure how to post pictures on this website. I am told I am limited to a filesize of 25kb, which is not nearly large enough for a detailed picture. I can send the files via email unless someone has a better idea.

 

[Clutz]

How much capacitance do you have on the rails (C1)?
How do you have the switch wired up - is S1- jumpered, and S1+ is going to a SPST switch?


When you're trying to measure the voltage on the PPA board, have you tried measuring the voltage between the V- and V+ pads? What about measuring the voltage between the + and - pads on the capacitors?