What, the ha5002 isn’t a direct swap with the BUF634!
I have the BUF634A it’s great if you need extra oomph but sound wise I found it overpowering. Maybe it’s great for high impedance headphone (80 Ohms or more??)
Was really looking forward to swapping the Buf634A with the ha5002!
There might be a adapter that re-circuits the pins of the Ha5002 to be a direct replacement for the BUF634?!
Will do some digging!
Sidenote: Taking a “break” to learn more about testing both hardware and software analytics for audio so to eliminate my “guess work”. Found this nifty little audio software from a German company called “Musicscope” that checks the overall health of your entire music collection so that it makes it easier to spot if there are hardware issue with op amps, etc. or not!
The best part is it’s dirt cheap 11 euros German Vat included)
I am convinced that many audiophiles don’t really pay enough attention to issues they may be having with their music collection and are op amp rolling and make alterations that they may not be necessary!
In regards to Opa1622 I did some digging and there are some pretty rad designs out there for stand alone headphone Amps where the Opa1622 is properly baked into the IC that have been developed by the DIYERS (who know what they are doing ie sound engineers who know the ins and outs of all audio production turned hardware engineers) and Pros that are definitely worth look into if you want to invest in some high impedience headphones for home usage and as portable amps (Caveat: the really good portable headphone amps with Opa1622 can be über expensive)
In order to properly assess high impedience with large capacity loads for the Opa1622. Three things must be true high voltage proportional to the resistance. (I suspect algebra is involved to make this true).
The high current 145mah in the Opa1622 is to offset a lost in current due to resistance.
I’m guessing that the output Vrms on a dap must be lower than 0 and anything lower will be better to reap the benefits.
However, this requires HIGH VOLTAGE output with resistance that allows current to pass through. I would also imagine that low ripple current is better for audio??? I have seen Film Caps used around op amps so there is certainly more than one way to get a cleaner signal.
If you have low voltage portable dap with no dedicated headphone amplification and believe by simply lowering resistance in for being surprise when it becomes unstable. Moreover it is doubtful if you can get the full effects sans testing your results by making arbitrary guesswork choices.
The opa1622 requires 0603 resistor (it’s in the datasheet) however, John the engineer who worked on the project stated that the larger the resistor the less power it draws. (Nothing to do with “Johnson’s” recommendation that some DIYERs like to regurgitate on threads) I’d also imagine that using the correct +ppms and % of accuracy plays a huge role in selected the best resistor for the job.
Principles involved for high impedience
Ohm’s law states that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance (R). Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change
Which means that if resistance is high current is low and if resistance is low current is high. Then we can see that current flow around a circuit is directly proportional ( ∝ ) to voltage, ( V↑ causes I↑ ) but inversely proportional ( 1/∝ ) to resistance as, ( R↑ causes I↓ ).
Updated: DIYER:
“Zishan DSD AK4497 version has a discrete transistor output buffer (voltage follower), so there's no point to put OPA1622 into DSD UNLESS you bridge opamp's output all the way past output resistors to the output relay inputs (or bypass discrete buffer and put OPA1622 between DIP8 opamp output and HP out, I did it on one of my DSDs).“
OY! This entire paragraph is an oxymoron. The first clause contradicts the second statement as it isn’t as simple as creating a bridge and also admitting state it’s unless-ness. You will have DC off issues if the OPA1622 isn’t properly tested for performance error when you do this. Hence, the “pop” and “crack” described in the adapted soic could be a clear sign of DC offset. It may be “ok” on floating 24-32 bit PCM files & firmware supports floating but in Dc offsets you will have issues with DSD files since it’s ONLY on one bit which already makes it unstable to begin with especially when it’s played natively with the modification. DoP may be able to meta the floating on 24-32 floating but must be baked in a sophisticated algorithm software playback! (Oh, Geez)
Digital DC Offset
In digital-land, there are two main ways DC offset can get into a signal.
More commonly, inaccuracies in the A/D converter or conversion subsystem that produce a slight output offset voltage.
As with analog circuits, a processor that provides lots of gain (like a distortion plug-in) can turn a small amount of offset into something major.
Do not attempt this if you like to play DSD files especially on a dedicated DSD player! The 1622 isn’t intended to be used as universal buffer as well nor to be put on an adapter. If it was, TI would have made on and until then mod at your own risk!
You MUST throughly read through this jargon (one of many). There is very little regard for making absolute statements nor zero accountability in testing this modifications for accuracy nor this claim “you bridge opamp's output all the way past output resistors to the output relay inputs (or bypass discrete buffer and put OPA1622 between DIP8 opamp output and HP out, I did it on one of my DSDs)”
DIYER:
“John mentioned something like 3-6dB noise increase in noise above 10kHz if using this arrangement, which is negligible (and probably would still be below many opamp's noise anyway).“
Except John is talking about the Opa1622 in its true element- that is on IC circuit in a VSSON package.
Moreover, sitting below “many” opamp noise is not ignore that fact of what it’s intended to be used for ie Headphone Amps and to drive high impedience headphones. Therefore, you can’t just lump in all or many into the topic of Op amp since Buffer Amps are designed for Buffer amps and MUX amps are designed for multichannel, etc. I would agree that some are capable of general audio usage (provided that you know what you are doing otherwise you are turn an op amp into an oscillator, lol)
Now, speaking about OPA1622 on a DIP8 adaptor in HP output stage again...
There's few potential issues indeed:
1. Ground connection
2. Power on/off click
3. Bypass caps some distance away from the supply pins
I still believe these issues are not really significant enough to discard using OPA1622 on a DIP8 adapter PCB in output stage.
Specifically, re: #1:
in response to this comment:
Some people made an attempt in this regard but since OPA1622 requires GND pin connection for best performance it is impossible to use standard DIP-8 layout unless a compromise is made by connecting the GND pin of the OPA1622 to negative supply.
Please understand that by "compromise" we're talking about a 3-6dB increase in distortion at 10kHz, it's still quite good performance and I use DIP adapters in the lab at TI for quick results if I'm not testing for absolute best performance.
I note that cheap ebay version creates a virtual ground by splitting rails, and that ground pin is used for enable and a compensation capacitor, so as long as the rails are not totally out of whack I doubt performance will take even a small hit that it does when the ground pin is connected to negative supply.
I also note that Johnc has no issues with PCB DIP adapter
and while it does not provide "absolute best performance", I agree that it is very, very good (and actually better compared to many general use or otherwise repurposed for HP output stage opamps).
#2 is tricky as it is possible to easily create a voltage divider for enable pin so that it is on only after rails ramped up completely (I tried that), but even using it properly (say using delayed GPIO signal and I tried that too) still produces low-level pop (this has been noted on diyaudio as well), which is still well below what some other opamps produce anyway so no real issue here IMO.
#3 bypass caps are mounted on the PCB and while the ground is virtual, it is not uncommon to bypass power supply by hooking up a x2 value cap between rails, but having them on PCB is still far better than not having them at all or some distance away.
Finally, opamps have never been designed to work as HP drivers (so ANY opamp driving headphones directly is not used for intended purpose, unless it has been specifically designed for this purpose, but only few were e.g. OPA1622, TPA1620 I actually struggle to come up with any other examples here), and the way their pins are arranged is not very good for low noise/distortion performance (one of the reasons for OPA1622 form-factor by the way). So from my point of view (I'd like to believe that it is a well informed one too) retrofitting ANY device that offers DIP8 socket for opamp as the output stage (aka CMOY) with DIP8 socketed OPA1622 is a no-brainer, and I am not aware of any characteristic that matters where OPA1622 is not superior to any other opamp (or at least on par), even when using DIP8 adaptor (well, except maybe output impedance as there are some opamps that offer lower Z and are still capable of driving capacitive loads e.g. AD826 if memory serves me right here but it does not sound as good unfortunately).
I don't get a cut from OPA1622 on DIP8 PCB ebay sellers
Finally, opamps have never been designed to work as HP drivers (so ANY opamp driving headphones directly is not used for intended purpose, unless it has been specifically designed for this purpose, but only few were e.g. OPA1622, TPA1620 I actually struggle to come up with any other examples here)
Some of the JRC/NJM opamps are designed with audio use including driving headphones in mind, same for the TI variant of the RC4580. AD8397 and a couple more like that are designed for the kind of loads that you'd get from headphones as part of their audio considerations. There are 2-3 more that I can't name off the top of my head that are designed with driving 16-600ohm headphone model loads.
It is true of a lot of opamps though - especially some can as I've mentioned have implementations designed for things like the demands of DSL drivers that are sub-optimal for headphone use.
Some of the JRC/NJM opamps are designed with audio use including driving headphones in mind, same for the TI variant of the RC4580. AD8397 and a couple more like that are designed for the kind of loads that you'd get from headphones as part of their audio considerations. There are 2-3 more that I can't name off the top of my head that are designed with driving 16-600ohm headphone model loads.
It is true of a lot of opamps though - especially some can as I've mentioned have implementations designed for things like the demands of DSL drivers that are sub-optimal for headphone use.
Generally it’s either repurposing ADSL drivers or opamps designed for LCD monitors (e.g. LM7332 which is actually quite good and easy to implement, especially compared to AD8397) and these are a bit better at driving capacitive loads too.
But among opamps dedicated specifically to driving HPs OPA1622 is the newest and addresses issues older designs had (e.g. stability issues of TPA1620 requiring use of output resistors).
Well, there’s also INA1620 which is even better than 1622 (EMI/RFI hardened input stage, integrated high precision resistors), but it’s unlikely to appear on DIP8 adapter (I have it on a bigger DIP PCB but did not have time to test it yet).
Some of the JRC/NJM opamps are designed with audio use including driving headphones in mind, same for the TI variant of the RC4580. AD8397 and a couple more like that are designed for the kind of loads that you'd get from headphones as part of their audio considerations. There are 2-3 more that I can't name off the top of my head that are designed with driving 16-600ohm headphone model loads.
The JRC/NJM engineers were some bada** Audio op amp engineers with all encompassing op amps that hold merit to present day!
Funny thing all this talk and research made me really wanna get a killer portable headphone amp designed to drive low impedience headphones.
Anyone have an recommendation Holla at ya boy!
Oh, is there a headphone with an amp build inside of it that’s powered by rechargeable battery! It would be pretttty rad if a company would make it with a op amp like the 1622.
I don’t know...Grados is family owned a located in BK May have to take a trip and present my idea to say what they say haha
Generally it’s either repurposing ADSL drivers or opamps designed for LCD monitors (e.g. LM7332 which is actually quite good and easy to implement, especially compared to AD8397) and these are a bit better at driving capacitive loads too.
But among opamps dedicated specifically to driving HPs OPA1622 is the newest and addresses issues older designs had (e.g. stability issues TPA1620 has).
Well, there’s also INA1620 which is even better than 1622 (EMI/RFI hardened input stage, integrated high precision resistors), but it’s unlikely to appear on DIP8 adapter (I have it on a bigger DIP PCB but did not have time to test it yet).
Analog Devices have recently pushed out some new opamps in the LTC range I think that are designed with driving headphones in mind but I've not kept upto date on developments like that.
Analog Devices have recently pushed out some new opamps in the LTC range I think that are designed with driving headphones in mind but I've not kept upto date on developments like that.
I’m think with a combo of high current op amps and higher voltage along with volume control op amp you get there too. The biggest challenge is how to keep it stable!
“The PGA2311 device is a high-performance, stereo audio volume control designed for professional and high-end consumer audio systems. The PGA2311 uses an internal high-performance operational amplifier to yield low noise and distortion. The PGA2311 also provides the capability to drive 660-Ω loads directly without buffering. The 3-wire serial control interface allows for connection to a wide variety of host controllers, in addition to support for daisy-chaining of multiple PGA2311 devices.”
The PGA2311 is a smash hit on arrow.com and operates only a 5 volts. It’s in their top searched. It’s a 16pin soic op amp that can function on a dap volume control and gain.
That said Opa1622 is a pretty rad innovation for its package and intended using in a IC for headphone amplifiers
Analog Devices have recently pushed out some new opamps in the LTC range I think that are designed with driving headphones in mind but I've not kept upto date on developments like that.
On paper, whether it is noticeable to the ear or not is another matter, the 2210 is much improved for things like noise, though the 2111 still has some tricks up its sleeve in that context. There are a fair few differences in "architecture" approach as well. I've never sat down and tested them side by side but from what I recall the 2111 is quite bright compared to the 2209 which tends to sit in a half-way point between the 1612 and 2228 having a more 2228 like organic sound than the 1612 but not the touch of warmth that gives a richer sound to the 2228.
Shame they didn't put a bit more design focus into the 2210 in driving headphones with a bit of attention to those kind of loads and slightly extend the current output a bit as otherwise it looks excellent for that use - they do look like a solid choice on paper for the IV stage though.
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