Please help me with my PPA

[kramer5150]

Relatively new around this forum, Ive lurked before but thats chnging now.

Looking to OP amp roll my PPA.

Its running with a 24V ELPAC.

Would it benefit from a better P/S?

What are some BASSY, open sounding OP amps for it? I have some OPA2107s, can those just drop in?

thanks!!

Garrett

[tkam]

So your looking to improve bass? Getting a STEPS or similar power supply upgrade would get you significant improvements there.

[kramer5150]

Is that a DIY?

Where do I purchase one

Bass is always welcome in my book. I just want to get the most out of the amp really.

Thanks!!

[n_maher]

1. Yes it will benefit from a better PS, I'm not aware of a commercially produced alternative though.

2. You might try shooting a friendly PM to MisterX and see if he'd build you a STEPS. Ask nicely and be willing to work with him on schedule and I'd guess he'd hook you up proper.

Quick question, what version PPA do you have? If it's V1 do you have chip or diamond buffers? Also, what opamps are in there now? I'll have a look at the 2107 and see if I see anything to discourage using them.

Nate

[dc]

sorry to dig up an old thread, but I believe the OPA2107 is a dual opamp so won't work in the PPA

I do however need some help with my PPAv2 that just landed

At the moment there are 3 x AD8610 opamps in there. I've got a few combos I plan on using: 2 x OPA637 + OPA627, 3 x AD843 and 2 x AD744 + AD829

Now, my understanding of this amp is limited atm but I believe there are trimpots on the board for biasing 1. opamps 2. output buffers

I've got a digital multimetre and I can manage to pull things apart and put them back together if need be, but how the amp works and what all the parts do is out of my scope.

I've had a quick look around and bookmarked a few links but just wondering if anyone can point me in the right direction for where to measure the current draws for 1. opamps 2. output buffers

I am of the understanding the opamps should be given between 1-2mA and the output buffers anywhere up to 50mA

So far I haven't touched anything except adjust the STEPS so it's outputting exactly 24v

I'm going try to familiarise myself with the amp's sound so I have a benchmark for tweaking but already this amp is sounding very good.

[n_maher]

I do however need some help with my PPAv2 that just landed

Here we go. Congrats on what is a great amp, brutally revealing but very rewarding when coupled with a proper source.

At the moment there are 3 x AD8610 opamps in there. I've got a few combos I plan on using: 2 x OPA637 + OPA627, 3 x AD843 and 2 x AD744 + AD829

Careful, some those combinations are in no way guaranteed to play nice with your PPA depending on how it's configured. Specifically if the gain setting could mean very bad things for the 637s, not too sure about the others.

Now, my understanding of this amp is limited atm but I believe there are trimpots on the board for biasing 1. opamps 2. output buffers

I've got a digital multimetre and I can manage to pull things apart and put them back together if need be, but how the amp works and what all the parts do is out of my scope.

I've had a quick look around and bookmarked a few links but just wondering if anyone can point me in the right direction for where to measure the current draws for 1. opamps 2. output buffers

Unless you have reason to believe that something is setup incorrectly I'd leave well enough alone. Take it from someone who has rebuilt PPAs after people have blown them up trying to adjust the buffer bias, you DON'T want to find yourself in that situation. It took 3 rebuilds to get one of them working again. And it's really easy to have a probe slip and short the buffer while trying to adjust the bias and then all your amp will do is smoke components (how I got my custom title at head-fi) which is not nearly as much fun as listening to music.

So far I haven't touched anything except adjust the STEPS so it's outputting exactly 24v

I'd highly suggest leaving it that way (see below).

I'm going try to familiarise myself with the amp's sound so I have a benchmark for tweaking but already this amp is sounding very good.

http://www.tangentsoft.net/audio/ppa/amp2/ - read all of that, then re-read it, then go read this - http://www.head-fi.org/forums/f6/ppa-v2-help-smoking-output-resistor-long-124880/.

[dc]

how did I know n_maher be one of the first to respond =)

I'm very impressed with it at the moment considering I've only had so little time with it - a very good sign. But it could be new toy syndrome...

I'm aware the minimum recommended gain for the OPA 637 is 5, i believe the amp is at a gain of 8, I will be using the OPA627 for ground so should be ok.

the AD744 (comp pin out) + AD829 is similar to that of the LISA III

thanks for the links, i've already put the tangent page on my list of to-reads before fooling around. resistor smoking sounds interesting though

i'll report back if i've killed the thing =\

[dc]

Your logic does seem right about not fiddling, apparently this amp is 2 years old and hasn't had any issues so might be a case of "if it ain't broke..."

The soldering on it is very good too, it almost look like it was machine manufactured. Casework and wiring leaves a bit to be desired for though, but that's ok - hammonds anyway.

[dc]

Well I took all the essential measurements

Gain: ~9

Output buffer bias: 45mV

Opamp bias: 1mV

However I experienced some strange things.

Only when using my DT880s I got some wierd funky as distortion/white noise when I turned up the volume knob and it got to a loud part of the a song it would go out of control and then even if I turned down the knob the crazy noise stayed. Is this oscillation?

It happened in a couple of opamp combinations:

2 x OPA637 + 1 x OPA627

and

3 x AD843

It only happened with the above opamps and with the 250 ohm DT880, does anyone know what's happening?

Other headphones/opamps used were K501, K701, DT531, 3 x AD8610, 3 x OPA627, 2 x AD744 + AD829.

I've ruled out oscillation due to low gain, unless I'm reading/mesuring the gain resistors wrong (possibly) what else might cause oscillation or whatever's happening?

[n_maher]

Are you getting any DC offset? Measure DC volts for the following w/ no phones or source connected - OL to IG, OR to IG and OG to IG.

[dc]

yeah one of the first things i checked actually, but i just checked on the outputs between left and ground and right and ground - all stayed <10mV until about 80% of the pot at which point it quickly shot up to like 45mV but there's no way i'd ever go past half way on the pot

OL to IG = 1.5mV

OR to IG = 2.5mV

OG to IG = 0.1mV

With a little help over @ H-F I think I solved the problem with the OPA637/OPA627 opamp combo doing freaky deaky things. it turns out i mis-intepreted my previous readings (i'm a newb)

I measured 45mV across the output resistors but forgot that that is voltage NOT current, and are supposed to divide that by the value of the resistor to calculate current which in this case is 2.2ohm which works out to be just 20mA - which was not enough juice for the DT880 and making the OPA637 cranky

I've now adjusted it so I measure 65mV which equates to about 29.5mA and works just fine now with any of my headphones

the AD843 combo still isn't happy in the PPAv2. AD744 comp pin out with AD829 in ground is still my favourite, and even better with the higher bias on the output transistors.

[n_maher]

You might want to pose the question on head-fi about the variable offset you're getting with the different pot settings. Personally I don't like the sound of that. 45mV is certainly fine and not likely to do anything bad to your cans but the behavior seems strange.

[dc]

Yeah I might do that.

I appreciate the link to your resistor burning thread btw.

Before each measurement of the resistors near the buffer transistors I took a deep breath in and then out and measured on the side away from the transistor legs for extra good measure

Decided not to risk adjusting the trimmer while measuring so I measured, got out, adjusted the trimmer, got back in and measured and repeated until I got where I wanted to be. Took a few goes but it's at least there's no smoke

[n_maher]

Decided not to risk adjusting the trimmer while measuring so I measured, got out, adjusted the trimmer, got back in and measured and repeated until I got where I wanted to be. Took a few goes but it's at least there's no smoke

That was a very wise decision. The smoking resistor would be the least of your problems had it happened.

[dc]

Replaced the unmatched, uncomplimentary BD139/MJE253 output transistors with matched and complementary 2SA1930/2SC5171

DC offset never goes above 5mV even at the highest point on the volume pot.

Sound is a lot smoother and resolving, doesn't have the treble sizzle that it did previously. I don't know if that's a good or bad thing, but it doesn't seem to have lost any detail, just a lot smoother sounding.

with 4.7ohm resistors and biased to 25mA the heat is very reasonable too. all good for now =)

thanks for everything Nate!

[n_maher]

Glad to hear that everything seems sorted out but I'm not sure that I had all that much to do with it. The PPA is a great amp, don't be fooled into thinking otherwise.

[en480c4]

The PPA is a great amp, don't be fooled into thinking otherwise.

Just figured I'd x2 this sentiment.

I bought my PPA v2 back a few months ago, but it had gotten little use since picking it back up. So I decided to upgrade my amp at work, setting the PPA v2 with my 2nd DA-500 today. It required reconfiguring my entire workspace, but it's definitely worth it. It definitely seems like overkill to have a stack of full-size components for a pair of AT clip-ons, but it doesn't bother me. And it sounds great with the DAC and headphones with its 637-627-637 opamp configuration.

[luvdunhill]

I'm going to have my PPAv2 up and running again real soon and up with me at work... wonderful little amp, and best opamp-based amp I've heard period. If you build one, feel free to ignore all part recommendations and just tweak until it sounds good. For example, I'm using some Xicon polypropylene caps that I haven't seen anyone mention round these parts... but they sound fantastic in the PPAv2. Same with the yellow ERO axial capacitors I'm using.

Perhaps I'll post pics when it's all said and done!

[en480c4]

I'm amazed at what a difference the PPA has made with the EW9s. With the mini3, there was always a bit of an upper-midrange glare that could be fatiguing, even with the warm-ish DA-500. But that glare is gone and I'm left with a sound that while lacking some weight in the low end, is fairly balanced and very good with almost Grado like mids. It should be noted I'm running some EQ in foobar to boost the bottom end of the the EW9s.