AD8065 mix w/ OPA627 in PPA?
Mar 9, 2005 at 10:45 PM Thread Starter Post #1 of 6

Juergen

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I currently run my PPA w/ OPA637's L&R and 627 on G. I ordered some sample AD8065's but they only ship a max of two samples so I ordered the 3rd one. The samples came in two days but it's going to take a week or so for the 3rd one. Could I use the 2 8065's for L&R and use an OPA627 or 637 for G? Just curious.
 
Mar 9, 2005 at 11:03 PM Post #2 of 6

Sovkiller

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Quote:

Originally Posted by Juergen
I currently run my PPA w/ OPA627's L&R and 637 on G. I ordered some sample AD8065's but they only ship a max of two samples so I ordered the 3rd one. The samples came in two days but it's going to take a week or so for the 3rd one. Could I use the 2 8065's for L&R and use an OPA627 or 637 for G? Just curious.


The OPA637 is not stable in the ground channel as it is not unity gain stable...be careful...try to use the AD8065 in all three channels, order two more samples next month and you will love it....
 
Mar 10, 2005 at 12:00 AM Post #3 of 6

Juergen

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Quote:

Originally Posted by Sovkiller
The OPA637 is not stable in the ground channel as it is not unity gain stable...


You are correct. I was on my way out of the office when I quickly posted. I had it backwards. I always have a 627 in the G channel and alternate between the 627 and 637 on L&R. I am still working on getting my Larocco Dyno Bias Diamond Buffer stable. I started a thread on that earlier (I believe you participated in the thread). It looked like with Larry & Phil's help I got it stable. At that point I had almost no spare time to enjoy my newly modded amp. I later got a little time to do some critical listening. I am unfortunately getting some static and distortion when the volume pot is adjusted past 12:00 for low level recordings. I heard it first on Peter Gabriel: Security, track 1, The Rythm of the Heat. I expect to hear from Larry shortly for the magical cure
icon10.gif
I decided to check out the 8065 on your recommendation and possibly cure my stability issue at the same time. Anyway, I guess I'm still wondering if I can plop in my two 8065's with a OPA627 in G without damaging anything. (I have no patience
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)
 
Mar 10, 2005 at 12:05 AM Post #4 of 6

Sovkiller

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Quote:

Originally Posted by Juergen
You are correct. I was on my way out of the office when I quickly posted. I had it backwards. I always have a 627 in the G channel and alternate between the 627 and 637 on L&R. I am still working on getting my Larocco Dyno Bias Diamond Buffer stable. I started a thread on that earlier (I believe you participated in the thread). It looked like with Larry & Phil's help I got it stable. At that point I had almost no spare time to enjoy my newly modded amp. I later got a little time to do some critical listening. I am unfortunately getting some static and distortion when the volume pot is adjusted past 12:00 for low level recordings. I heard it first on Peter Gabriel: Security, track 1, The Rythm of the Heat. I expect to hear from Larry shortly for the magical cure
icon10.gif
I decided to check out the 8065 on your recommendation and possibly cure my stability issue at the same time. Anyway, I guess I'm still wondering if I can plop in my two 8065's with a OPA627 in G without damaging anything. (I have no patience
wink.gif
)



Yep I have tried that and there is no problem, also you could try the OPA627 on all three channels, it will be even more stable than the 8065 (this has a higher bandwith, though more chances of oscillation at high freqs than the 627)
 
Mar 10, 2005 at 12:52 AM Post #5 of 6

ppl

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Sorry you’re having issues yes you can put the AD8065 in the rt and left channels also perhaps increase the value of the 10ohm load resistor to 47 ohms or 100 ohms to present a lighter load however distortion and premature clipping are indicative of instability still lurking some where in your system
try making sure the Bias on the output stage stays good and you should have no issues< However Disclaimer this is the Dyno-Bias circuit and must be in a perfect situation or gets unhappy kind of like some people.

You will be pleased to know as have others that have the Dyno-Bias that i have found the situation the Dyno~Bias likes and soon to be posted is my new mod that will detail this however it will probably be after the PPA 2.0 is released. PPA 2.0 is not Dyno-Biased however it can be modded as such as well as this configuration is also very good with the standard biased buffer also.

Unlike the previous mod this includes the output stage within the multi-loop just as a normal PPA and dose not require ferrite beads however dose require load resistors and strict adherence to posted component values including one op-amp no rolling allowed.

Disclaimer,
(1) Since the PPA gooses through subtle layout change without notice except for a letter change as in V 1.0,1.0a, 1.0b, 1.1,1.1a. And such a change could have an unexpected impact upon stability this mod may at any time need adjustment to account for subtitle changes in the PPA layout.

(2) Since the Dyno~Bias is so sensitive, it also requires proper assembly on the part of the amp builder. Things like insulators on the RCA jacks and then having no ground or a flaky ground via one thin wire or something far worse is inviting problems so proper assembly methods are required so this is not for the novice or faint of heart.

(3) In no way is this any acknowledgement of you being able to get a functioning Dyno~Bias circuit as only myself seem to be able to assemble a ppa with a properly functioning Dyno~Bias circuit you are on your own hear and while I can offer support as needed I don’t have the time to spend with everyone having issues with the Dyno~Bias. It is thus my recommendation that unless your willing to bearer any pain anguish or loss of sanity to obtain the sonic improvement of the Dyno~Bias over the standard buffers that you forgo the Dyno~Bias goodness and use the standard buffer it works and sounds great and is soon going DIY in PPA v 2.0 so more of the head-fi community can enjoy the improvements of the Descrete component TRIAD over the HA5002 IC buffers without buying anything extra and at the same time provide a cost savings as the separate transistors cost alot less than the HA-5002's however there are like 9 transistors per channel so money saved in parts cost is spent in assembly time, Althought this is the atraction of DIY so i think (Shall i say Hope) this is not an issue with the DIY crowd.
 
Mar 15, 2005 at 7:04 PM Post #6 of 6

Juergen

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Quote:

Originally Posted by ppl
...You will be pleased to know as have others that have the Dyno-Bias that i have found the situation the Dyno~Bias likes and soon to be posted is my new mod that will detail this however it will probably be after the PPA 2.0 is released. ...


Ok Phil, PPA 2.0 is out
wink.gif


Seriously, your site does warn that this mod is not for the faint of heart. I dove in anyway realizing I could easily convert my dyno buffer to a non-dyno. Lord knows you and Larry have spent enough time babysitting my attempt at stabilization
biggrin.gif
I eagerly await your posting of the stabilization mod.
 

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