[ctm]

Dear members,

I was referred to this sub-forum as in case some of you have extensive experience with opamps...

The topic recently got my attention when a fellow member and experienced and successful DIY builder of a number of different types of amps commented on the op-amp TL074 from Texas Instruments. He noted that this could be replaced with an OPA1604, an audio op-amp having over 100X less distortion than the TL074. He further went on to say that there are also other possibilities for op-amps such as these 4 channel versions: OPA1664, OPA1644, OPA1654, OPA4134, OPA4227, AD8273, and OPA4172. However, he admitted he has never done any rolling of opamps so cannot comment on the subjective sound differences.

The TL074 is the one used in my HEV70, which may be refurbished by said builder. If this proceeds as planned, he may also be swapping out some electrolytic caps and, if warranted, may also look into building a robust external power supply.

We would greatly appreciate whatever comments and recommendations you have on the opamp alternatives listed above or any others worthy of consideration. Also, if you know any others who have extensive and long time experience with a wide range of opamps, but does not frequent the DIY community on this site, then please let us know.

Thanks & best regards!

 

[ctm]

Bump... any assistance from members with some experience rolling opamps would be greatly appreciated. TIA

 

[E8ArmyDiver]

Burson "Vivid or Classic"...

 

[jamato8]

Dear members,

I was referred to this sub-forum as in case some of you have extensive experience with opamps...

The topic recently got my attention when a fellow member and experienced and successful DIY builder of a number of different types of amps commented on the op-amp TL074 from Texas Instruments. He noted that this could be replaced with an OPA1604, an audio op-amp having over 100X less distortion than the TL074. He further went on to say that there are also other possibilities for op-amps such as these 4 channel versions: OPA1664, OPA1644, OPA1654, OPA4134, OPA4227, AD8273, and OPA4172. However, he admitted he has never done any rolling of opamps so cannot comment on the subjective sound differences.

The TL074 is the one used in my HEV70, which may be refurbished by said builder. If this proceeds as planned, he may also be swapping out some electrolytic caps and, if warranted, may also look into building a robust external power supply.

We would greatly appreciate whatever comments and recommendations you have on the opamp alternatives listed above or any others worthy of consideration. Also, if you know any others who have extensive and long time experience with a wide range of opamps, but does not frequent the DIY community on this site, then please let us know.

Thanks & best regards!

There are many good op amps. There are also many that have a wide operating range. Of course if you use a dual op amp, then you have modify the board so I would stick with single, if that is what you are working with. Also the best measuring is not always the best sounding. A good slew factor is always good. I would use op amp sockets to facilitate easy changing and then you can have fun trying different op amps, as long as they use the same pin out and are within their operating points.

The power supply is the most important. If you don't have a good supply of current and clean current, there is no reason to do anything.

 

[ctm]

E8ArmyDiver - If your suggestions are compatible and will fit in the opamp sockets as suggested by jamato8, then we look forward trying them.

 

[ctm]

jamato8 - all great points and considerations. thank you!

 

[tomb]

Dear members,

I was referred to this sub-forum as in case some of you have extensive experience with opamps...

The topic recently got my attention when a fellow member and experienced and successful DIY builder of a number of different types of amps commented on the op-amp TL074 from Texas Instruments. He noted that this could be replaced with an OPA1604, an audio op-amp having over 100X less distortion than the TL074. He further went on to say that there are also other possibilities for op-amps such as these 4 channel versions: OPA1664, OPA1644, OPA1654, OPA4134, OPA4227, AD8273, and OPA4172. However, he admitted he has never done any rolling of opamps so cannot comment on the subjective sound differences.

The TL074 is the one used in my HEV70, which may be refurbished by said builder. If this proceeds as planned, he may also be swapping out some electrolytic caps and, if warranted, may also look into building a robust external power supply.

We would greatly appreciate whatever comments and recommendations you have on the opamp alternatives listed above or any others worthy of consideration. Also, if you know any others who have extensive and long time experience with a wide range of opamps, but does not frequent the DIY community on this site, then please let us know.

Thanks & best regards!

He's right. The TL074 is basically a jelly bean chip, meaning cheap and convenient, but not a great performer. The OPA 227 is fairly popular and the OPA 134 or OPA 132 (almost identical) formed the basis of the famous CMoy headphone-amp-in-a-mint-tin. Note that for Burr-Brown chips (OPA designation, but also owned by TI), a "2" in front of the last 3 numbers means it's a two-channel chip, a "4" in front of the last 3 numbers means it's a quad-channel chip. According to the schematic for the HEV70, it uses quad versions of the TL074. That's going to limit what you can find. Quad opamps are not as common as two-channel or single-channel opamps.

You should probably read through this:
https://tangentsoft.net/audio/opamps.html
Head-Fi user "Tangent" probably knows as much about opamps as anyone and as can be seen by that link - he's done a lot of actual testing, too.

The comments about the power supply you've received are valid, but I'm not exactly sure you'll notice the difference. Quite frankly, messing with the power supply of an electrostatic amplifier would not be my first choice of things to do. You're talking about a different realm of voltage (600V) compared to the typical operating voltages of dynamic headphone amplifiers. If it's the voltage supply for the signal input (+or- 10V), that's different, but I don't know enough about how the HEV70 operates to offer additional advice.

Assuming the schematic I found is valid for the HEV70, the biggest, noticeable change would probably occur from swapping out the C31, C32, C33, and C34 output capacitors. Depending on the room you might have inside that device (not much from the pics), high-quality audiophile film caps in those positions would probably reap the most reward in sound improvement. Those caps are directly in the signal path, more or less the last thing before the headphone, except for a few resistors.

 

[ctm]

tomb - Such good stuff you've provided there!!! Also, really appreciate your referring us to fellow member Tangent!

In one Sunday afternoon swoop you've managed to not only uncover, but also outline AND prioritize how we're going to tackle the HEV70 amp. I mean... it's chilling how you approach things so similarly!!!

Your post could easily have come from him. I look forward to introducing him to you!

 

[ctm]

Tomb: Meet fellow member A2029! He is the one assisting me to see just how much the performance of a stock HEV70 amp can be improved when powering the HE60.

Thanks again to you and others for providing some very helpful info. I will be officially in A2029's job cue the moment the HEV70 is in his hands. Will report back with any significant updates.

 

[Harry Manback]

TI opa1622. hands down the best I've heard.

 

[ctm]

Harry Manback - Really appreciate you submitting a reply. Also, love the quotes in your signature! Thank you.

Can you please provide more info in order to get a better perspective and clearer context on your experience with the TI opamp you are suggesting.

For example:
1. How did you come across TI OPA1622 and In what piece of audio gear did you use it? Please also detail what other gear were part of the signal chain?
2. Is the OPA1622 the stock opamp for that unit? If not, then...
3. Please detail what was the stock opamp AND what specific issue(s) did you have that prompted you to use the OPA1622 instead?
4. Did you try any other opamps before settling on the OPA1622? If, so then...
5. Please list them and for each, tell us what it was about them that made you continue your search?
6. It would also be great to know what specific tracks you use to evaluate ANY piece of audio gear you are looking to add to your system?

Thanks in advance and best regards.

 

[ctm]

An update:

As stated in my OP, we are looking to potentially replace the stock opamp (TL074 by Texas Instruments), in an amp that was designed to be used only for a specific set of electrostatic headphones.

According to our very capable fellow member and DIY contact, A2029, come of our limitations include:
a. the stock TL074 opamp involves a surface mount (SOIC-14) that is not compatible with through hole version of some opamps of intertest -- like those made by Burson Audio for example
b. the stock opamp is a 4 channel type
c. A2029 is looking to come up with an adapter to convert (or make compatible) the surface mount SOIC-14 to the through hole opamps from Burson and perhaps others from Burr Brown(TI), but for such an adapter to not limit us to just using only 4 channel opamps, but to be flexible enough to allow the use 1 or 2 channel opamps.

Having the ability to directly compare different type of opamps is the goal. Too bad it's not in a widely used and currently available piece of audio gear, but so be it. It's a start.

Who knows, after this project we may be tempted enough to roll opamps in some carefully selected piece of hifi equipment that is:
1. currently in production and
2. is well known to have superb playback capability.

 

[tomb]

Remember that this is the DIY section of Head-Fi. I think if you do a bit more research, you'll find some famous DIY designs having easily switchable opamps. Some are currently in production and all of them are known to have superb playback capability: There's been literally a couple of decades now of headphone amplifier development that in many cases, offer DIP--8 sockets for opamp rolling.

AMB Labs M3 opamp-MOSFET amplifer (easily purchased and readily available)
Tangent's PIMETA
Tangent/Morsel/PPL's PPA - either V1 or V2.

The PPAV2 and M3 are still competitive as world-class headphone amplifiers.

There are many others, I'm sure - including the lowly CMoy, which has always offered a DIP-8 socket for opamp rolling.