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The Opamp thread - Page 278

post #4156 of 4812
Quote:
Originally Posted by wakibaki View Post

 

Is it? It doesn't say so anywhere in the datasheet.

 

Jfet opamps are usually characterised by an input bias current in the picoamp range. The LME49990 has an input bias current in the range 30-1000nA which is more typical of a bjt input.

 

See page 190 of Horowitz & Hill.

 

http://books.google.co.uk/books?id=bkOMDgwFA28C&pg=PA190&lpg=PA190&dq=typical+bjt+input+opamp+bias+current&source=bl&ots=F3cnVDc0Yw&sig=u90V9iQ3wq7nAJFZvfiSi9mnRkw&hl=en&sa=X&ei=MUFiUMSGJoiWhQfmz4H4Cw&redir_esc=y#v=onepage&q=typical%20bjt%20input%20opamp%20bias%20current&f=false

 

w

 

Hi wakibaki,

 

You're probably right.  I don't remember where I had heard that, and having just spent about 10 minutes looking, all I could find was a reference indicating that the 49880 (not the 49990) is a jfet dual.

 

Thanks!

 

Mike

post #4157 of 4812

@ WiR3D Hi thanks for the reply :D, I was considering the LME49990 too, but as i've seen, they're a SOIC-8 type is it?

 

so I was wondering if i need 1 per dip-8 adapter? or 2? I've seen someone on the forum selling one to europe, and they linked a ebay page someone selling 2 of them soldered on top and on the underside of a PCB adapter?

 

Can I just get 2 and solder them onto 2 separate adapters? Are there even adpaters that doesn't require soldering at all?

Quote:
Originally Posted by WiR3D View Post

AD797 (could be unstable and eventually fail, but the best clarity), LME49990 - not a single complaint, almost equal to the AD797, and then the THS4032 - a smoother sound, with probably the best imaging, but SLIGHTLY smaller soundstage compared to the AD797.

 

The entire LME49720 based range is a compromised design.

 

Quote:
Originally Posted by PurpleAngel View Post

The LM4652 (STX's buffer op-amp), LME49720NA & LME49860NA are the same op-amp, the LME49860NA is just the cherry pick (tested with better voltage range).

@PurpleAngel thanks for your quick reply too man, is the LM4652 the stock buffer op-amp? I've read on here that changing the buffer on my Essence STX wouldn't really do much for my headphone but I'm guessing they might for my speaker outlet?

 

so in that case if i was to choose LME 49990 as the I/V right... what would be a logical ideal choice to use as buffer to compliment the 49990? 49860NA perhaps or even another model of brand even?

 

 

Once again guys, thanks so much for all these quick responses, you guys are saving lives here lol.

post #4158 of 4812
Quote:
Originally Posted by Edifier12 View Post

@ WiR3D Hi thanks for the reply :D, I was considering the LME49990 too, but as i've seen, they're a SOIC-8 type is it?

 

so I was wondering if i need 1 per dip-8 adapter? or 2? I've seen someone on the forum selling one to europe, and they linked a ebay page someone selling 2 of them soldered on top and on the underside of a PCB adapter?

 

Can I just get 2 and solder them onto 2 separate adapters? Are there even adpaters that doesn't require soldering at all?

 

@PurpleAngel thanks for your quick reply too man, is the LM4652 the stock buffer op-amp? I've read on here that changing the buffer on my Essence STX wouldn't really do much for my headphone but I'm guessing they might for my speaker outlet?

 

so in that case if i was to choose LME 49990 as the I/V right... what would be a logical ideal choice to use as buffer to compliment the 49990? 49860NA perhaps or even another model of brand even?

 

 

Once again guys, thanks so much for all these quick responses, you guys are saving lives here lol.

you need x2 per adapter, check ebay, they make it for you. There are a few sellers. 

 

also the 49860 is based on the 49720, which is flawed. they are cheap upgrades though. but not in the LME49990, AD797, THS4032 range.

post #4159 of 4812
Quote:
Originally Posted by WiR3D View Post

you need x2 per adapter, check ebay, they make it for you. There are a few sellers. 

 

also the 49860 is based on the 49720, which is flawed. they are cheap upgrades though. but not in the LME49990, AD797, THS4032 range.

Thanks! So basically, I just need 3 x 49990 or I can experiment the buffer with others you've mentioned? Would the buffer affect my speakers output? Currenctly using Edifier s730 speakers

 

 

 

This looks about right WiR3D? http://www.ebay.com/itm/2PCS-LME49990MA-on-SOIC-DIP-adapter-DIP8-Socket-/320863638478?pt=US_Amplifier_Parts_Components&hash=item4ab4f693ce


Edited by Edifier12 - 9/26/12 at 3:10am
post #4160 of 4812
Quote:
Originally Posted by Edifier12 View Post

Thanks! So basically, I just need 3 x 49990 or I can experiment the buffer with others you've mentioned? Would the buffer affect my speakers output? Currenctly using Edifier s730 speakers

 

 

 

This looks about right WiR3D? http://www.ebay.com/itm/2PCS-LME49990MA-on-SOIC-DIP-adapter-DIP8-Socket-/320863638478?pt=US_Amplifier_Parts_Components&hash=item4ab4f693ce

yes, the buffer is for the speakers only. 

 

And lol thats the seller I use. They package stuff very well. And yes its the right one.

post #4161 of 4812
Quote:
Originally Posted by WiR3D View Post

yes, the buffer is for the speakers only. 

 

And lol thats the seller I use. They package stuff very well. And yes its the right one.

sweeeet man lol, I'm going for it! thanks a lot for the help!!

post #4162 of 4812
Quote:
Originally Posted by Edifier12 View Post

sweeeet man lol, I'm going for it! thanks a lot for the help!!

WAIT!!! I was wrong - I hate their naming scheme.

 

http://www.ebay.com/itm/1PCS-Dual-Mono-LME49990MA-replace-OPA2604-NE5532-TL072-/320863640326?pt=US_Amplifier_Parts_Components&hash=item4ab4f69b06

 

thats the correct one

post #4163 of 4812
Quote:
Originally Posted by WiR3D View Post

WAIT!!! I was wrong - I hate their naming scheme.

 

http://www.ebay.com/itm/1PCS-Dual-Mono-LME49990MA-replace-OPA2604-NE5532-TL072-/320863640326?pt=US_Amplifier_Parts_Components&hash=item4ab4f69b06

 

thats the correct one

haha dude, lucky I messaged him to double check, i thought the name was a little off, well since you replied now and are sure I'm gonna just go ahead and buy it haha, cheers man, thanks for the help

 

haha damn, these things are a bit dear for 3 aren't they :P

post #4164 of 4812

Hey peeps,

 

I'm struggling to decide which opamps I should get for my titanium HD, was leaning towards the LME49990 until I got these 2 responses in a thread I made.

 

As the stock opamps are known to be kind of a let-down, I was wondering what else there is to choose, maybe OPA627 or OPA827?

 

I have to note I did a LOT of searching but on this card speficifially I can't seem to find any common recommendations.

 

Another thing I was wondering, what if I decide to take SOIC opamps for my titanium HD, would I have to use a dual to single adapters for both the two I/V slots and the two buffer slots?

I can't imagine I'd need 8 opamps in total for one card.

 

By the way I'll connect the RCA outputs to a headphone amp so the buffer opamps will not be bypassed if I'm not mistaken.


Edited by kazaakas - 9/26/12 at 12:12pm
post #4165 of 4812
Quote:
Originally Posted by kazaakas View Post

Another thing I was wondering, what if I decide to take SOIC opamps for my titanium HD, would I have to use a dual to single adapters for both the two I/V slots and the two buffer slots?

I can't imagine I'd need 8 opamps in total for one card.

SOIC op-amps need to be soldered to something, the DIP-8 sockets (like in the Titamium HD) are designed for removeable op-amps.

If you used all SOIC single channel op-amps, you would need 6 op-amps, with 4 op-amps soldered on to 2 dual SOIC to DIP-8 adapters and the last 2 op-amps soldered on to 2 single SOIC to DIP-8 adapters

post #4166 of 4812
Quote:
Originally Posted by PurpleAngel View Post

SOIC op-amps need to be soldered to something, the DIP-8 sockets (like in the Titamium HD) are designed for removeable op-amps.

If you used all SOIC single channel op-amps, you would need 6 op-amps, with 4 op-amps soldered on to 2 dual SOIC to DIP-8 adapters and the last 2 op-amps soldered on to 2 single SOIC to DIP-8 adapters

Thanks!

 

So the opamps in the buffer stage only need one channel?

 

ie: 2 of these for I/V: http://www.ebay.com/itm/1PCS-Dual-to-Mono-LME49990MA-replace-OPA2604-NE5532-TL072-/320863640326

and one order of these (2 adapters) for buffers: http://www.ebay.com/itm/2PCS-LME49990MA-on-SOIC-DIP-adapter-DIP8-Socket-/320863638478

 

Also, does anyone else has some intel about how these perform on the Titanium HD?

post #4167 of 4812
Quote:
Originally Posted by kazaakas View Post

So the opamps in the buffer stage only need one channel?

ie: 2 of these for I/V: http://www.ebay.com/itm/1PCS-Dual-to-Mono-LME49990MA-replace-OPA2604-NE5532-TL072-/320863640326

and one order of these (2 adapters) for buffers: http://www.ebay.com/itm/2PCS-LME49990MA-on-SOIC-DIP-adapter-DIP8-Socket-/320863638478

Also, does anyone else has some intel about how these perform on the Titanium HD?

The buffer is a dual channel, but uses one single channel op-amp in each of the two separate buffer DIP-8 sockets.

Those are the correct op-amp packages to get.

I have no idea on how well they work in the TiHD.

post #4168 of 4812

Thanks, I got that, though I still wonder why the I/V section would have the need for two dual channel opamps? That makes a total of four channels... I'm confused!

post #4169 of 4812
it needs 4 channels in the IV section because its a balanced dac and thus needs Left +/- and Right +/-.

lme49990 isnt the greatest chip for IV, or buffer. it'll work and its a great chip, but its not really fast enough for IV in modern dacs IMO. its pretty current limited for buffering, but it depends on your reason for the buffer, if they will be driving headphones directly then I would choose another opamp. I love them, but I would be more likely to use a current feedback opamp (would require other mods), or perhaps an opa827 for IV followed by a line stage with 4999 and a buffer wrapped in the lme49990 feedback loop.
Edited by qusp - 9/28/12 at 1:40am
post #4170 of 4812

qusp,

 

Not wanting to interrupt, but as a side question, a couple of days ago I replaced the 4x HA5002 buffers in my iBasso PB2 with 4x AD797 as buffers, still using 4x LME49990 singles in L/R.  Everything seems to be running cool, with no evidence of oscillation.  The sound is warmer yet more detailed than with the HA5002 buffers.  

 

Have you ever tried this combination (and/or do you have any comments that come to mind)?

 

Thanks!

 

Mike

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