[Koen]

Hi vgjako,
 
Congratulations on your decision to build a PPA! You will not regret that decision.
 
I have no experience with the opamps you are asking question about. However, I do have experience with deciding on an opamp when I built my PPA.
 
Which specification(s) of the opamps you mention make you believe they are THE choice for your PPA?
 
If you can't answer that question for yourself, I'd say go with an AD8610 or OPA627/37 set. Maybe save the money (if relevant at all) for your source, power options.
 
Just my $0.02.
 
(btw, I have AD8610 in my PPA, based on Tangent's opamp reviews on his website).

 

[Spacehead]

I can provide you pair of OPA637 at a nice price, if you are interested , PM me. I have 8 left.
 
OPA637 doesn't work in ground channel. So only two OPA637 needed for left and right, because it needs gain of 5 to be stable. With my headphones and PPAv2 there isn't much background hiss at gain of 5 and OPA637 works fine. Usually I use OPA827 or ADA4627-1 on ground channel, those are unity gain stable.

 

[tangent]

I know nothing about those op-amps, but can tell you you'll need to use three of the singles for a PPA.

 

[vgjako]

I haven't been able to find a datasheet of the Burson Audio op-amp, so I haven't any good reason to choose this op-amp. The specs I have found on this op-amp is:
 
Working voltage: +/-12-25v DC
Current Draw: 19mA (each module)
THD: Less than 0.0007%
Dimensions: 39mm × 10mm × 29mm, (single) 39mm × 23mm × 29mm (double)
Weight: 19g
 
But according to the people who have reviewed this op-amp, they where very pleased with the results, follow this link: http://bursonaudioblog.blogspot.com/search/label/HD%20Audio%20Opamp%20(Review)

 

[vgjako]

Hi again
 
I have a few questions listed below:
1. What is the highest voltage I can use on OPA637/27 op-amps? The datasheet says plus-minus 18 V, can I use lets say 24 V? If not, what would you suggest as an appropriate voltage level?
2. Is the resistor R4G supposed to be the same value as R1G if you tune the gain? I have chosen to go for a gain at 7, just changing R4L/R. To put the question in another way: Do I have to change the value of R4G to tune the gain, I guess not.
3. The input called B+ on the high-current power section is there if you are going for battery power, right? Or am I wrong?
 
Thanks 
vgjako

 

[FallenAngel]

1) Well, if you can use +/- 18V, that's 36V rail-rail, you can use anything below that, including 24V.
2) Ground channel is running with gain of 1x, R4G stays = R1G.
3) Yes, B+ is battery contact.

 

[Koen]

Quote:

(..)
I surely will return here in about a month or so.
 

Hi, I'm back!
 
Built my DAC, see this post for details.
 
I am convinced that with my DAC, the 'issue' of not noticing bass boost effect is not at the source (still can't hear a difference when flipping bass boost switch). Will have to open up my PPA to put in the 3PST switch across R10 tangent suggested a few posts ago. This is probably an error on my side: this amp is still incredible!

 

[tangent]

While in there, you might just want to increase the boost's strength.  No point in having an audio filter that's too subtle to hear.

 

[phishhead92]

I accidentally got 6 BD139's insead of 3 of those and 3 of the 140, can i use the 139s in place of the 140s? or should i try and find the 140s (currently out of stock on mouser and i dont want to order just 3 little chips and pay like 3$ for shipping)

 

[FallenAngel]

I'd send you some, but it would take some time to arrive.

 

[phishhead92]

slow and having some is better than paying more for shipping than what the 3 parts cost 

 
im down, PM me if you actually want to do this
 
 
Quote:

I'd send you some, but it would take some time to arrive.

 

[FallenAngel]

PM address, I'll drop them in the mail for you.

 

[phishhead92]

Also, i want to use a RLED, but i cannot figure out which resistor i need, i will be using a 12V supply, and i want somewhere around 10mA or less going through the led, can someone help me out in figuring out the "Vf"?
 

 

[tangent]

As I said in my PM reply to you, you will find the Vf figure in your chosen LED's datasheet.

 

[phishhead92]

OH, for a sec i thought you ment something else, like on the site. sorry i was really tired when i first read it (got back from a long bike rid

---

so here is what i have so far, not completely done but pretty close, just waiting for some parts from mouser

 


that  PCM2707 is crooked, oops! oh well, its all on the right pads it looks like
 
 

 
the upsampling chip was being difficult, and so was desoldering the bridges, looks messy now