[PinkFloyd]

Quote:

Originally Posted by biovizier Ah sorry its 6 nV/root hz. This is only "noisy" as far as the phono first stage is concerned. Its still not too bad though. Its still much quieter than the lm6171. Just not as quiet as the ad797. I find the extra dynamics offset the extra noise to a certain degree. The quietest opamp I have found is the ad811. The CFB operation means the overall noise is lower for an MC cartridge than the ad797 even though the voltage noise figure is similiar.

My apologies I thought you were referring to "audible" noise.

 

[12796]

Sorry I should have been more precise.

I have a low o/p moving coil - 0.2 mV so 6-8 nZ is audible at high volume but not intrusive. Ideally I would like a low noise CFB version of the ad8067 to make things absolutely perfect! Such chips exist but the phono is +/- 12v and the XFCB ad chips with low noise only operate +/-5V.

Will keep you posted!

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Will keep you posted!

Please do

 

[FritzS]

Quote:

Originally Posted by FritzS So I will use a (fuse)resistor, value between 8 ... 22 ohm, momentary it will limit the current. For my Sennheiser HD 600 industry standard 120 ohm output resistor is not recommended. It gives another way - to use diodes to limit the voltages between B and E+resistor of the output transistors and so limit the outgoing current. This is standard in the most amplifiers but discussed controversial.

Walt Jung describe a flexible Class A buffer in
http://www.elecdesign.com/Globals/Pl...tent/2800.html
http://www.elecdesign.com/globals/pl...mages/2801.gif
and a protection
Quote:

Walt Jung .... Protection of this circuit is provided by several means. Without D3 and D4, the upper current limit for Q3-Q4 is set either by the limited-drive current (5 mA) times the gain (50 to 250), or by the R6-R8 values and the supplies. This current can easily reach several hundred mA, so active current limiting is very useful. The optional Red LEDs D3 (D4) provide this, clamping the drive to Q3 (Q4) when the emitter current reaches about 1.2/R6, or ~240 mA as shown. For lower levels, the LEDs don't conduct and signals pass normally. The LEDs are Panasonic types as noted.

I mean this design

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Already tried the ad797 - it was pretty good. But the lm6181, ad811, ad829 and ad8021 were better in the first stage. The ad847, ad843, lm6171 were better in the 2nd and 3rd. The ad8067 beats all of them in every position but is a bit noisy. Bizarrely the ad8067 is more stable than the ad8065 in the phono which just didnt work at all - which is odd as it is just a decompensated AD8065. The ad8067 needs a gain of 8 or a few tweaks to be stable lower than that. It has a compensation pin and you can also try cap in the FB loop or a load resistor. Apparently the sound is rock solid and crystal clear - cant wait to hear it take on the lm6171 in the headamp. Dont take the lm6171 name in vain - David might hear you!

Have you tried any of the single TI chips apart from the 134 and 627 Nick? I've just ordered up some 227, 228, 604 and 637 to give them a whirl under the bonnet.

I know from past experience that the 2227 / 2228 / 2604 duals are very nice sounding chips so the same should be the case with the singles.... I'll keep you posted and may well even get serious and do a shootout and write up of all the chips I have at my disposal...... It's about time I put my extra 150mb of web space to good use and September is always the time I get excited about all things "audio" so I'll don my listening cap, arm myself with a notepad and get down to some serious listening and will then update this seriously lame page

Obviously the page will be renamed "WNA grand op-amp test" or I may even dedicate a brand new page to the WNA opamp grand shootout

You can send me your opamp impressions and I'll add them also, always best to have a second unbiased opinion.

Yeeeeeeeehaw! My audio juices are starting to flow again

Mike.

 

[12796]

Yes I tried the opa637 - better than opa627 but still didnt like it much. It seems I just like the AD sound.

I will get a mop ready!

 

[PinkFloyd]

Quote:

Originally Posted by biovizier I will get a mop ready!

You better make it a supermop! I will have spare opa227 and opa228 if you want to try them Nick. As I say, we can both take notes on lots of opamps and I can publish our (independent) findings along with scores (out of ten) on a webpage for all to see...... It's up to you, if you'd like to take part in the WNA grand opamp shootout then let me know and we can organise some reference listening material, a selection of opamps to be compared and headphones we will listen with...... I propose to do this sometime in September.

Mike.


For starters I have the following at my disposal:

OPA227
OPA228
OPA627
OPA637
OPA134
OPA604
AD843
AD797
LM6171
LM6181
AD811
AD8610
AD8065

and a few others......

 

[12796]

Sounds great!

Taking the caps out makes a difference for the ad chips as well - the ad8065 sounds fab in the headamp without them.

I have a pair of spare ad8067 if you want them.

I have tried quite a few opa chips now and didnt like any of them so will pass on that offer.

I suggest we wait until I have ad8067 fitted in the headamp along with BGs and vishays. My headamp is running on battery power now so I can compare that with psu.

I am using akg k340, beyer dt231 and akg k271.

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Sounds great! Taking the caps out makes a difference for the ad chips as well - the ad8065 sounds fab in the headamp without them. I have a pair of spare ad8067 if you want them. I have tried quite a few opa chips now and didnt like any of them so will pass on that offer. I suggest we wait until I have ad8067 fitted in the headamp along with BGs and vishays. My headamp is running on battery power now so I can compare that with psu. I am using akg k340, beyer dt231 and akg k271.

I'd love to try the 8067 Nick. From my experience the WNA is not too good at driving the K-340, I actually sold my K-340 as the WNA didn't provide them with the necessary "grunt" required to bring the best out of them.... the old X-Can V2 and Chiarra did a better job with them but that's another story. It could also be the case that my K-340's had lost their charge (AKG technician reckons they start to lose charge after about 15 years)

Tried the 271 but found them very honky, closed and rubbery sounding so I will be testing with HD-600 and K-501 (again, the WNA doesn't do a great job of driving the K-501 but it's good enough to test opamps with) I may buy the 50 ohm HD-595 and give them a go too but for the test I'll probably use the HD-600 as the main reference 'phones s they are a good jack of all trades headphone.

You've removed the output caps but have you fitted the 10M resistor and 100K trimpot? This is pretty essential to get the DC offset down to 0.00mV. If you read through the MKl thread you'll see that the 8065 was my second favourite to the LM6171 and that was "with" output caps so I imagine they'll sound even better without them...... must give them another shot!

Going to try the AD843 again later today, the last time I tried them was with output caps and they sounded bloody great in the headamp so let's see how they fare without output caps and 0.00mV DC offset.

Just out of interest Nick, what position on the volco do you listen to the K-340's at? IIRC I had to crank the WNA up to 2 o'clock to get anything decent out of them and, even then, they sounded thin compared to the X-Can V2 which would drive them beautifully (and the K-501) at any level and really make them shine (specially in the bass department) K-340 are superb 'phones Nick (the first proper pair I bought many many years ago) but they really need an amp with "grunt" to bring the best out of them IMO.... how do you find them with the WNA <be honest!>

PS: here's a few pics of my trusty old K-340's

Mike.

 

[12796]

I use the akg271 in the gym - they are great for that.

I find the akg 340 is fine - however there are numerous different versions. I whack it up to about 2pm as well. I am not using caps or trimpots with the ad8065. If you fitted the 100M resistor then I think it is still on there. Where should I look? Maybe David tweaked it for the akg when isent it to him.

I have a bare pair of ad8067 - they are sot23-5 so you need a custom adapter from wilmslow adaptics. About a fiver each. I dont have any spare ones.

I look forward to hearing about ad843 and ad8065 without the caps - the ad8067 is sure to be better even than that!

 

[PinkFloyd]

Quote:

Originally Posted by biovizier I use the akg271 in the gym - they are great for that. I find the akg 340 is fine - however there are numerous different versions. I whack it up to about 2pm as well. I am not using caps or trimpots with the ad8065. If you fitted the 100M resistor then I think it is still on there. Where should I look? Maybe David tweaked it for the akg when isent it to him. I have a bare pair of ad8067 - they are sot23-5 so you need a custom adapter from wilmslow adaptics. About a fiver each. I dont have any spare ones. I look forward to hearing about ad843 and ad8065 without the caps - the ad8067 is sure to be better even than that!

Hi Nick,

NO, you don't have the 10M and 100K trimpots fitted but if you send your amp to me I'll fit them FOC for you.... you really "must" listen to the LM6171 / LM6181 without output caps and the only way you can do that is with the trimpots fitted so you can zero the offset..... even with the other opamps you're trying it's best to have the trimpots in place in order that you can adjust the offset to 0.00mV on both channels.

Basically you trim the offset by turning the screws on the trimpots and check between sleeve and ring and sleeve and tip using a Multimeter set to the 200mV (DC) range...... It's easy to do and I recommend you get this done so you can trim the DC offset to 0.00mV.

Here's what the trimpots look like..... if you have them in your amp you'll notice them:

Trimpots are the blue things with R & L written on them (denotes each channel)

Mike.

 

[12796]

Thanks! I have to send the amp back to wna to get the ad8067 and Bg vishay fitted so I had planned to sort the trim pots at the same time. Where is the 10M resistor? i will take a look. Did you find any issue with the ad8065 stabilty or any tips for tweaking it?

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Thanks! I have to send the amp back to wna to get the ad8067 and Bg vishay fitted so I had planned to sort the trim pots at the same time. Where is the 10M resistor? i will take a look. Did you find any issue with the ad8065 stabilty or any tips for tweaking it?

10M is in series with the wiper of the trimpot thus:

You won't have the 10M on your amp Nick. Only if you remove the output caps and use the Lm6171 is it really necessary to fit the 10M & 100K trimpot though it's also handy for reducing the offset with some other opamps.

Didn't find any stability issues with the 8065 but I was using output caps..... will try the 8065 without the output caps and let you know.

 

[FritzS]

Has anyone tested other output transistors in place of BD138/139?
Toshiba's 2SC2238 / 2SA968 have a higher ft - about 100 MHz

 

[FritzS]

Quote:

Originally Posted by PinkFloyd Here's what the trimpots look like..... if you have them in your amp you'll notice them: Trimpots are the blue things with R & L written on them (denotes each channel) Mike.

What case use you? I search for a little bit greater - for place for a headphone protection circuit kit.