The Opamp thread

[leeperry]

good point, I only tried them as final buffer...I'll try them as AK4396 LPF whenever I'll get those adapters from HK, that are supposedly better than the browndogs..

but the ability to put 4*single DIP8 on my soundcard has made me kinda lazy w/ soldering...especially w/ the AD797BN/LT1028ACN8 still pending a try

 

[12Bass]

Quote:

Originally Posted by ROBSCIX /img/forum/go_quote.gif Do you not like the OPA827's?

Nah.... haven't you read my posts?

Just curious to know what others think about how it sounds. I like it in most applications where I've tried it. Haven't noticed a lack of bass either.... though I do think that the LM/LME family sounds a bit thin at times. OPA827 seems to have most everything covered, IMO, although it isn't quite as open/transparent as some of the high speed op amps. AD825 might have a bit more of a colored, "scooped", sound with boosted bass and treble, for those with that sort of preference.

 

[ROBSCIX]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif Well, I really think it depends on the application and of course what you are listening through. I can tell you that I am using these In a P3+ with Hi-C Buf634's in the buffer section & LME49710HA's in ground/Vground with my JH13 IEM's and these are anything but shy of lower frequencies . In fact they are not shy of any frequencies, this set up was a match made in heaven I have had some real late nights recently because I can't stop listening with this set up and I've had the same set up for quite a few weeks now, it still gives me goose bumps

Yes and it would also have to do with what your listening with. Some use headphones that are more bass heavy or birghter..etc. The circuits is the major factor also though.

 

[ROBSCIX]

Quote:

Originally Posted by 12Bass /img/forum/go_quote.gif Nah.... haven't you read my posts? Just curious to know what others think about how it sounds. I like it in most applications where I've tried it. Haven't noticed a lack of bass either.... though I do think that the LM/LME family sounds a bit thin at times. OPA827 seems to have most everything covered, IMO, although it isn't quite as open/transparent as some of the high speed op amps. AD825 might have a bit more of a colored, "scooped", sound with boosted bass and treble, for those with that sort of preference.

They are good but I like many opamps.

 

[majkel]

The 1-8-7 mod is to increase bias currents of the input stage. Just short the pins all together, or feed B+ to 1 and 8, just like it's done to pin 7. I'm not sure it improves the LT1028 while the change is obvious but it surely improves the already great OPA228.

 

[SpudHarris]

Could you post a picture at all? I'm struggling with the finite detail..... Do you leave all the pins as they are so they all insert or do you bend all or some out before shorting them together.

I tried what I thought was right but didn't like the sound.

 

[majkel]

Use a piece of wire and solder it from pin 1 to between pins 7 and 8. Just make a bridge over the chip and solder the wire to the wider part of the pins so that you can still insert them properly. This mod doesn't apply to many other op-amps or might even damage them. OPA228 and LT1028 are OK. Something equivalent for the AD797 is shorting pins 1,4 and 5 but you need to surround the chip with the wire. Sound gets cleaner and softer.

 

[SpudHarris]

Quote:

Originally Posted by majkel /img/forum/go_quote.gif Use a piece of wire and solder it from pin 1 to between pins 7 and 8. Just make a bridge over the chip and solder the wire to the wider part of the pins so that you can still insert them properly. This mod doesn't apply to many other op-amps or might even damage them. OPA228 and LT1028 are OK. Something equivalent for the AD797 is shorting pins 1,4 and 5 but you need to surround the chip with the wire. Sound gets cleaner and softer.

Ahhh right, so no need to snipp off any pins then? That's where I went wrong

 

[ROBSCIX]

Will have to give that a try when I get time.

 

[SpudHarris]

Done it and yes I have to say it does make a difference. It will take me a while to put it into words but I like it so far.

 

[diditmyself]

Quote:

Originally Posted by majkel /img/forum/go_quote.gif Something equivalent for the AD797 is shorting pins 1,4 and 5 but you need to surround the chip with the wire. Sound gets cleaner and softer.

I don't think there's a detailed official AD797 schematic, but the above is said to be the real deal. I think the offset trim probably is at R5/R7 - at the emitters of the VAS current mirror. By connecting the current mirrors directly to V- you bypass the floating current mirror concept, and the opamp will not be an AD797 anymore. You definately wont get higher bias to the input stage nor the VAS. I don't think it can operate this way at all.

The above picture seems to have bene censored, or just lost. This is the official simplified schematic:

The offset trim is probably at the emitters of Q5 and Q6, the VAS current mirrors. In this simplified schematic it's clear to see that you can't just connect those emitters to V-. Even if the current mirror wasn't floating, there would be nothing to gain from bypassing the emitter resistors. It would just make the current mirror less balanced.

 

[diditmyself]

Regarding the LT1028 mod. By connecting the trim pins to V+ you change the LTP load resistors from 3130 to 3000 Ohm. This wont increase the input stage (LTP) bias. This bias is set by the CCS (Q3/R7/Q15/R8).

 

[leeperry]

hehe, since reading majkel saying that the new burson is the exact same as Moon(which is utter bs), that AD797B doesn't exist in DIP8 and more funny judgments about discrete op-amps....I've learned to take his words w/ a grain of salt

I suggest modders to do so as well, better be dubious than sorry...you can find some simplified schematics for the AD797 there: AD797BN pdf ::: ALLDATASHEET :::

 

[ROBSCIX]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif Done it and yes I have to say it does make a difference. It will take me a while to put it into words but I like it so far.

with the 228's?
What are you hearing?

 

[ecclesand]

Got the ADA4627s earlier today and soldered them on some adapters. Anymore it takes longer for the iron to heat up than to actually solder them. I'm liking them so far...very clean sound with a black background. I'm using them in conjunction with some Hi-C BUF634s as a headphone amp driver.