[SpudHarris]

Got my P3+ yesterday and firstly I'd like to say it's real nice. Looks and sounds better than the P3. However, I do have a problem......

One of my favourite chip combo's in my P3 was/is OPA637BP's in 1/2 - Ibasso Buffers & AD8066 in Ground. Gain on low.

a) With the P3+ I have to use the combo without buffers as it just hisses with them. (not really a problem but different to the P3)

b) Can't use the 637's on low gain, period.

c) Can only use this combo with the mains adapter as it just hisses with the batteries in use. The hiss is really loud but goes as soon as the adapter is plugged in. The hiss changes if you touch the case.

Just so you are aware the 637's are genuine, bought from Farnell and have been my weapon of choice for some time in almost any amp I roll with. OpAmps are not touching anything they shouldn't be.

I thought the P3+ would offer me more flexibility and better SQ over the P3 and that's partly true but I feel that I've been short changed if I can't use it with my favorite chips.

Any advice guys would be appreciated. Thanks in advance.

Nigel

 

[SpudHarris]

Anyone?

 

[hopeless]

It appears that the OPA637 hisses audibly when supplied with too low supply voltage.

I wouldn't use it with less than 15V total


...and at a gain of 5 minimum, because it's only stable from that up.

Let go the OPA637, try the LT1469 (single LT1468) or the TLE2142 (dual).


From BB also try the OPA211, which is superior to every other BB specified for audio.

 

[SpudHarris]

Hear what you are saying but the 637's work with my P3 even on low gain....

I can't let go as they are my joint favourite OpAmps with AD744 OBCA.

I've e-mailed Ibasso but don't suppose I'll see a response until Monday. HiFlight tried this combo in his and had no problems so I'm assuming mine is duff.

Still, if I'm missing something please shout out.

Nigel

 

[TzeYang]

I've tried to fix an Ibasso before and I realized that the design itself isnt made to cope with high input bias bipolar type opamps. Nor it was made to work well with fast opamps.

BE 100% SURE that the input bias is balanced. I don't know about the new P3+ but if it is not made for bipolar opamps you will get high dc offset at higher volumes (exceeding 100mV)

EDIT: I would also like to take this opportunity to lambast most/some people who don't "ask" before doing things like swapping opamps and think that it's making an improvement while the reality is that it's more damaging than it seems to be. Ibasso does not seem to warn people about those either. I have not yet once see a clear explanation of the noise issues with certain opamps officially from them.

 

[SpudHarris]

I've never once had issue with my P3 with any Opamp (and I've a vast sellection) so can't agree wholly with what you've said there. However I do have an issue with this particular combo and the P3+ which is why I started this thread.

Any constructive help would be appreciated.....

Nigel

 

[HiFlight]

I have experienced no instances of instability with any opamps that I have tested in the P3 and P3+, regardless of whether they are FET or bipolar. Nor have I had issues running non-unity gain opamps at low gain. I have observed no scope artifacts when running signal generator inputs thruout the audio spectrum.

As there is no method of adjusting bias or balance on the iBasso amps, that is a dead-end issue.

If all the other opamp combinations work normally in the new P3+, I would suspect the 637s might be bogus, as this exact combination worked perfectly in my P3+ with no audible hiss at all. It was a very nice-sounding combination.

I left these opamps in my P3+ and will listen until the batteries are exhaused and see if I can duplicate this problem. Although the 637s are being operation below the usual voltage range, the still appear to be functioning normally, although it is likely that they would not meet all of the datasheet specifications at this reduced voltage.

In the final analysis, datasheet specs are not always an indicator of quality sound...If an opamp sounds good you your ears, USE IT!!

 

[jamato8]

There are no blocking caps on the P3+ so you don't want anything that is putting out DC, which can happen.

On the 637, I have those and the 627 and will try them later on in mine but I trust Ron's ears so I would think that for some reason there might be an issue with the 637.

 

[TzeYang]

Quote:

Originally Posted by HiFlight /img/forum/go_quote.gif I have experienced no instances of instability with any opamps that I have tested in the P3 and P3+, regardless of whether they are FET or bipolar. Nor have I had issues running non-unity gain opamps at low gain. I have observed no scope artifacts when running signal generator inputs thruout the audio spectrum. As there is no method of adjusting bias or balance on the iBasso amps, that is a dead-end issue. If all the other opamp combinations work normally in the new P3+, I would suspect the 637s might be bogus, as this exact combination worked perfectly in my P3+ with no audible hiss at all. It was a very nice-sounding combination. I left these opamps in my P3+ and will listen until the batteries are exhaused and see if I can duplicate this problem. Although the 637s are being operation below the usual voltage range, the still appear to be functioning normally, although it is likely that they would not meet all of the datasheet specifications at this reduced voltage. In the final analysis, datasheet specs are not always an indicator of quality sound...If an opamp sounds good you your ears, USE IT!!

I don't have experience with the P3 versions (i've fixed the D2s) so I'd really hope they have sorted the issues I had with the D2s in the past.

Almost every single head-fi recommended LT and National opamps oscillated with the D2 and had terrible DC offsets at the output.

 

[SpudHarris]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif There are no blocking caps on the P3+ so you don't want anything that is putting out DC, which can happen. On the 637, I have those and the 627 and will try them later on in mine but I trust Ron's ears so I would think that for some reason there might be an issue with the 637.

They work no problem in my P3 though....Why wouldn't they work with the P3+??

Oh man those things cost me dearly, I can't afford another £60 for 637's at the moment. Does anyone know how much they cost over there? Ron? Jamato?

 

[hopeless]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif Hear what you are saying but the 637's work with my P3 even on low gain.... I can't let go as they are my joint favourite OpAmps with AD744 OBCA. I've e-mailed Ibasso but don't suppose I'll see a response until Monday. HiFlight tried this combo in his and had no problems so I'm assuming mine is duff. Still, if I'm missing something please shout out. Nigel

Well, it's you who said that when you connect the external adapter the hiss disappears... Probably more voltage makes it (OPA637) stable.

'Cause if the hiss changes when you touch the case on battery power, then definitely the OPA637 is not working stable, at least at that (which is very low for it, at or below its specified min. supply voltage threshold) supply voltage.


Try the OPA211, it's better sounding and works from 4.5V up.

 

[SpudHarris]

On Farnell there are loads of different OPA211's, with varying bandwidths. Which should I order?

Browse for Products | Farnell United Kingdom

Thanks

 

[hopeless]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif On Farnell there are loads of different OPA211's, with varying bandwidths. Which should I order? Browse for Products | Farnell United Kingdom Thanks

OPA211AID ... You'll need the Browndogs, too (SOIC->DIP).

 

[SpudHarris]

Thanks Hopeless. The one you recommend is not available in the UK, can I get the OPA211AIDG4? I notice that the band width is the difference.

Is this really as nice as the 637?

I suspect as you guys have said that my 637's are the issue. Mine are the expensive BP's will I notice any difference if I get the AP's or AU's (SOIC)?

Nigel

 

[hopeless]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif Thanks Hopeless. The one you recommend is not available in the UK, can I get the OPA211AIDG4? I notice that the band width is the difference. Is this really as nice as the 637?

It is technically superior, and better throughout... IMO.



Yes you can get the AIDG4, but there's no difference at all. The datasheets mentions no bandwidth differences among the different variants...