Opamp Comparisons

[LNeilB2]

Hello all,

I picked up a link DACIII on the cheap. Sounds ok, midrange seems slightly hard and glassy. I'm planning to pick up the powerbase to see if that helps, but I also figured an opamp swap might be in order.

Many reference the LT 1364, but I've seen comments that this sounds a bit lean, which is the opposite of what I'm looking for. That said, any opinions on the AD or BB options? I'd be happier with warm, or even bloated sounding opamps (as opposed to the current sound I'm getting).

Thanks in advance,

Neil

 

[gootee]

Please remember that the circuitry around the opamp (and before and after it) is often at least as important as the opamp itself, and is often tailored, by the original designer, for a specific opamp. So it often wouldn't make sense to just blindly substitute another opamp. Similarly, judging the sound of such a circuit when a different opamp is substituted is not a valid test of the opamp. Having said that, if you can find another opamp that sounds better to you, and can operate within its specifications in your circuit, then go for it.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

 

[georgehifi]

Hello all,

I picked up a link DACIII on the cheap. Sounds ok, midrange seems slightly hard and glassy. I'm planning to pick up the powerbase to see if that helps, but I also figured an opamp swap might be in order.

Many reference the LT 1364, but I've seen comments that this sounds a bit lean, which is the opposite of what I'm looking for. That said, any opinions on the AD or BB options? I'd be happier with warm, or even bloated sounding opamps (as opposed to the current sound I'm getting).

Thanks in advance,

Neil

I too thought the LT1364 lean and hard, in the DACIII, you will love the Analog Devices OP275 very smooth big and generous, sort of like a good tube amp. And the DAC3 needs an opamp like that because with any of the super dynamic up front opamps it will sound fatiguing, even with better power supplies or as I did total battery power.
Also the OP275 has almost zero dc offset which aloud me to cut out the dc servo from the output stage, and keep it dc coupled, which maybe helped the sound a little more as well I think. (somebody once said dc servo can sound bad) anyway I was able to cut it out by using the OP275.

Cheers George

 

[LNeilB2]

Re: Re: Opamp Comparisons

I too thought the LT1364 lean and hard, in the DACIII, you will love the Analog Devices OP275 very smooth big and generous, sort of like a good tube amp. And the DAC3 needs an opamp like that because with any of the super dynamic up front opamps it will sound fatiguing, even with better power supplies or as I did total battery power.
Also the OP275 has almost zero dc offset which aloud me to cut out the dc servo from the output stage, and keep it dc coupled, which maybe helped the sound a little more as well I think. (somebody once said dc servo can sound bad) anyway I was able to cut it out by using the OP275.

Cheers George

Now this sounds like a plan! Did you have to mod the opamp circuits in order to accomplish the above?

Thank you very much for your reply!

Neil

 

[georgehifi]

Re: Re: Re: Opamp Comparisons

Now this sounds like a plan! Did you have to mod the opamp circuits in order to accomplish the above?

Thank you very much for your reply!

Neil

Not at all, but you will need the circuit diagram to do it, and here it is.
And if you want something more dynamic and detailed and more etched than the OP275 use the AD825 on brown dog boards.

I did this (below) over 3 years ago .

Note: one half of the opamp is the dc servo, just cut it out and set up what's left, +input (pin 3) to deck (earth)
I think for memory that's all I had to do to get rid of the dc servo, but just to be safe for now, just change out the opamp you have for the OP275 or the AD825's on brown dogs and listen with the dc servo.


Cheers George

 

[munosmario]

musical fidelity A3 24 DAC

Sorry for interjecting off-topic. Wanted to get feedback (or up-date) from Georgehifi regarding latest mod recommendations for the MF A3 24: Op amps, clock etc. I have just seen his postings on subject from a couple of years ago and I was wondering if he still owns that unit and has continued modifying it. I would have send him a PM but I just registered and the system does not allow me to do that until I have made several postings. Perhaps some one can forward this query to him on my behalf (will be most appreciated).

Munosmario

 

[georgehifi]

Munosmario hi, the MF A3.24 was almost maxed out with these mods
http://www.diyaudio.com/forums/showthread.php?postid=649154#post649154
and should get a better again with the Tent XO2 @ 45.1584 MHz + Tent XO power supply
http://www.diyaudio.com/forums/showthread.php?postid=1186195#post1186195

I have since then found a cheap ($499aud) Harman Kardon HD970 cd player (AD1955 dac chip), which can also be used as a separate dac.
It moded with a discrete Transimpedance I/V stage and discrete class A output stage, beat the A3.24 handily, the A3.24 would still be with me though if not for this stunning HK HD970.

Then I made up an AD1955 Eval board it too is there with the HD970 but a little more laid back
http://www.diyaudio.com/forums/showthread.php?postid=1297060#post1297060

Cheers George

 

[munosmario]

Georgehifi, many thanks. From your reply and your other posts it appears that you did not get to implement the clock (and its PSU) upgrade in your MF A3 24 (you don’t mention at all having done it and/or evaluated it). So, all the mods you actually implemented (and stayed with until you encounter the HK HD970) were the direct coupling and the replacement of the NE 5532’s with the AD825’s mounted on Brown dogs. Accordingly, a direct aural experience with a Tent’s clock moded MF A3 24 is actually an unknown commodity to you—your know about its sonic effect mainly by reference from Guido Tent who has done it for a client. Is my understanding correct? In any event (putting aside the temptation to somehow get my hands on a HK HD970, not available in the US) I am contemplating carrying your suggested mods all the way including upgrading the clock. However, I am thinking more towards using the Audiocom Superclock IV (not the Tent’s clock set you mention). It appears to work very well in applications where the AD 825’s are present (including several of the recent MF players and DACs). Any words of wisdom?

As you experiment with boards, rather than putting them in metal cases, perhaps, you may be interested on the way Altmann of Altmann Micro Machines mounts his Kilo-Euro creations on slabs of lacquered white spruce (legs are just little wood knobs). Mother-of-tone is his theme and the domain for his website…interesting stuff there.

http://www.mother-of-tone.com/creation.htm

Cheers……Munosmario

 

[georgehifi]

If I kept the A3.24 I would of ended up instaling a Tent XODAC and power supply, and slaving the transport to the dac, even better than just re-clocking the dac with an XO2.

http://www.tentlabs.com/Products/DACupgrades/XODAC/index.html

Cheers George

 

[munosmario]

Thanks, Georgehifi. Question, does the TentsLink mode described in the Tent's site accomplishes the same as the slave/master mod you suggest?

http://www.tentlabs.com/InfoSupport/page25/page25.html

Cheers....Munosmario

 

[Filburt]

I'd be happier with warm, or even bloated sounding opamps (as opposed to the current sound I'm getting).

OPA2134?

 

[georgehifi]

Thanks, Georgehifi. Question, does the TentsLink mode described in the Tent's site accomplishes the same as the slave/master mod you suggest?

http://www.tentlabs.com/InfoSupport/page25/page25.html

Cheers....Munosmario

Go back to the XO2 and XO Supply as this is the answer I got from Guido when I asked him about the XO-DAC for the A3.24

"Hi george
The 3.24 has a sample rate converter, no use for XO DAC
best"

Cheers George

 

[kevinkr]

Re: Re: Re: Re: Opamp Comparisons

Not at all, but you will need the circuit diagram to do it, and here it is.
And if you want something more dynamic and detailed and more etched than the OP275 use the AD825 on brown dog boards.

I did this (below) over 3 years ago .

Note: one half of the opamp is the dc servo, just cut it out and set up what's left, +input (pin 3) to deck (earth)
I think for memory that's all I had to do to get rid of the dc servo, but just to be safe for now, just change out the opamp you have for the OP275 or the AD825's on brown dogs and listen with the dc servo.


Cheers George

You might also want to consider the LM4562 as a potential candidate for this mod. You can defeat the dc servo using this op-amp as well. All you need to do is short C48/58 (right pn hopefully, schematic is a bit hard to read) to ground and jumper C47/57 to keep the servo from going open loop and slamming to the rail. (Op-amp behavior can be unpredictable depending on type when this is allowed to happen.)

I would also reconfigure the relay if the inputs are not used such that the signal does not go through those contacts on the way out.
To retain the mute function you can connect it such that when the dac mutes the closed contacts short the output.

 

[pmkap]

I'll second Kevin's recommendation of the LM4562/LME49720. IMO, its a lovely (if such adjectives apply to opamps) chip, lacking grain, with extended, resolving, controlled treble and bass. Its also one of the few bipolar input chips that might function well sans servo, given its unusually low input bias current demands.

That being said, tonally, its not that different from the LT1364, albeit with far less propensity for that solid state 'grit' and hardness. You might well find those tonal characteristics far more to your liking with the removal of those nasties you described.

As George mentioned, the OP275 is also a very nice, 'warmer' chip. If you are looking for a bit of 'tube warmth', without the stereotypical (but when well implemented oftimes undeserved) charaterisation of mushiness, you might also consider the OPA2107. A di-fet input dual, IMO, it does everything 'mo betta' than the typical BB fet input duals. These are pretty much unobtainium from the distributors, but are available on FleaBay -
http://cgi.ebay.com/OPA2107-dual-Lo...eZWD1VQQtrksidZp1638.m118.l1247QQcmdZViewItem
I really like this chip, as much as those Nationals, but a different flavor.

The LT1364 is substatially faster and wider bandwidth than the other opamps suggested by everyone on this thread, so their choice sholdn't be problematic as a replacement.

FWIW

 

[munosmario]

Go back to the XO2 and XO Supply as this is the answer I got from Guido when I asked him about the XO-DAC for the A3.24

Thanks, Georgehifi. Since you have planted the seeds of temptation, could you tell me if the HK HD970 can work with US voltages 110-120V. Looking at pictures of the rear panel, it does not seem to have any external user adjustable settings but it could well be that there is an internal switch or a transformer circuit with an easy alternative wiring arrangement for the transformer to work within a 110-250V (50/60Hz) range.

cheers...................munosmario

 

[georgehifi]

Thanks, Georgehifi. Since you have planted the seeds of temptation, could you tell me if the HK HD970 can work with US voltages 110-120V. Looking at pictures of the rear panel, it does not seem to have any external user adjustable settings but it could well be that there is an internal switch or a transformer circuit with an easy alternative wiring arrangement for the transformer to work within a 110-250V (50/60Hz) range.

cheers...................munosmario

They were never made for the US market, pitty then it really would have taken off, and HK never made them in 110v only 220v-240V, it has what looks like a Sony R-Core mains transformer in it, no switch mode rubbish in this unit.
But all is not lost I have from a good source who is doing it in the US, they can be used by using a 240v to 110v (1amp) step down transformer in "reverse", it also then doubles as an isolation transformer and sound even better as well as uping the 110v mains to 240v.

Cheers George

 

[munosmario]

Georgehifi, brilliant. Thanks

 

[munosmario]

Georgehifi, do you happen to remember if the signal at the coaxial digital output of the MFA3 24 is the upsampled digital signal corresponding to that entering the analog conversion stage, or is it the same as the original digital signal fed into whatever of the two digital inputs that has been selected?

Cheers.......................munosmario

 

[georgehifi]

I think it maybe just a pass through, maybe someone else can answer better than me. Here's that part of the circuit.

Question: Will the spidf digital OUTPUT be upsampled to 192khz as well when the 192khz upsample switch SW1 is turned on.

Cheeres George

BTW
munosmario, did you know the HK HD970 upsamples to 384khz!!

 

[munosmario]

Georgehifi., I talked to Musical Fidelty and the answer is no. The digital output of the A324 is just a buffered passthrough and presents the original signal fed to the unit, not the upsampled digital signal that is converted to analog by the A324's internal DAC. This means that the A324 cannot double as an external upsampler. Regarding the HK HD970, it is interesting that the manual refer to 384Khz "oversampling," not "upsampling." 384Khz oversampling is the same as 8X Oversampling which has been around for quite a while. It appears that mathematically the two processes are the same, the diference beeing in the implementation of the algorithms in the filters used. If you Google the two words --upsampling oversampling--you will get several entries on the subject, one of the the best (ironically?) from Stereophile's John Atkinson.

Cheers....................Munosmario