The Opamp thread

[carlmart]

Have you guys played around with RIAA preamps? What chips worked best and on what specific circuits?

 

[raoultrifan]

Not personally, but any audio opamp should do; I would start with the opamps presented here: http://sound.whsites.net/project06.htm.

RIAA curve is tested by preamp’s manufacturer and swapping opamps might change that (we don’t want that); as there are not test vinyls to do RMAA tests, you might want to share here your preamp’s design/schematic and find together a better replacement (if any).

However, the only improvement you might get would be an opamp with similar specs but lower internal noise. Also, given the high gain used in RIAA preamps a scope to test for possible oscillations mighf be needed (or at least check for opamp overheating).

 

[CoiL]

By I/V stage You meant that I`m ok to swap OPA2134 with AD8599ARZ ? I`m thinking it will be best by specs for DAC differential opamp and provide OPA1612 with cleaner, more detailed signal and pair up nicely with OPA1612 sound signature.
Just to be sure, are ADA4084-2ARZ and OPA2228PA also compatible to try out in that spot? Don`t wish to buy any more opamps since upgrade isn`t very noticeable so far. I guess upgraded caps are doing their work very well.


So far havent noticed any problems with OPA1612 and AD8599ARZ in that place. No click with gain switch, no noise/hiss with vol control, no power-on pops (audio chain won`t switch on before tube has warmed up, so it isn`t audible anyway).

OPA2228 isn't a drop in replacement if you don't know the circuit - it is optimised for gains of 5 and above and fussy about capacitors around it and load capacitance - pay attention to the section in the datasheet "Using the OPAx228 in Low Gains" as it is also helpful for using it in wider application. Very good opamp when supported properly but I've seen some fairly experienced people dismissive of it with their subjective evaluation of how it "sounds" showing it plainly wasn't stable in their use.

One of my favourites for "easy listening" as it is quite forgiving on the quality i.e. if you are feeding it with a so-so quality MP3 without ever sounding like it is lacking in detail with a nice smooth low fatiguing presentation.

Woah! Didn`t expect this out of OPA2228 used as HO opamp with Aune T1!
Very organic, natural and open sounding! And seems to deliver quite good amount of details.
Soundstage seems VERY open and airy but not sounding distant/laid-back with Siemens E88CC tube.
Bass & percussion hits hard, tight and clean. Vocals/mids seem very natural. Guitars full and weighty.
Seems 45mA per channel output does its work better than stock 38mA.
I`m suspecting this will be best for my ears out of NE5532P, AD8599ARZ, OPA1612AID but will let it "burn-in" for week and do more proper comparing along with ADA4084-2ARZ which I will receive in few days.
Initial impressions - OPA2228PA put a BIG smile on my face and head bangin! ;P

 

[FritzS]

Woah! Didn`t expect this out of OPA2228 used as HO opamp with Aune T1!
Very organic, natural and open sounding! And seems to deliver quite good amount of details.
Soundstage seems VERY open and airy but not sounding distant/laid-back with Siemens E88CC tube.
Bass & percussion hits hard, tight and clean. Vocals/mids seem very natural. Guitars full and weighty.
Seems 45mA per channel output does its work better than stock 38mA.
I`m suspecting this will be best for my ears out of NE5532P, AD8599ARZ, OPA1612AID but will let it "burn-in" for week and do more proper comparing along with ADA4084-2ARZ which I will receive in few days.
Initial impressions - OPA2228PA put a BIG smile on my face and head bangin! ;P

If OPA2227 are better for low gain amps? Needs OPA2228 a compensation in low gain amps?
What are the difference between OPA2227/OPA2228 and the FET OPA LT1057 (and ‘family‘)?
I want to upgrade an Solo headphone amp. Solo use original AD823.

 

[CoiL]

If OPA2227 are better for low gain amps? Needs OPA2228 a compensation in low gain amps?
What are the difference between OPA2227/OPA2228 and the FET OPA LT1057 (and ‘family‘)?
I want to upgrade an Solo headphone amp. Solo use original AD823.

For those questions, someone with more knowledge here should answer You.
I`m just doing simple opamp swap in pretty simple headphone amp board (basically c-moy type with gain switches).
In different applications results may vary. But with Aune T1 - OPA2228 sounds crazy good and seems to bring Siemens E88CC goldpin tube to its maximum potential.

 

[Rroff]

If OPA2227 are better for low gain amps? Needs OPA2228 a compensation in low gain amps?
What are the difference between OPA2227/OPA2228 and the FET OPA LT1057 (and ‘family‘)?
I want to upgrade an Solo headphone amp. Solo use original AD823.

You'd have to check really, with an oscilloscope, on a case by case basis whether the OPA2228 was stable in a low gain amp - there is a section in the datasheet about it. My subjective impression is that the OPA2227 is a bit different to the OPA2228 though they both have that so called "burr-brown" sound the 2228 is just a bit more organic - the OPA2227 IMO is a great replacement for the OPA2132/2134 which personally I find somehow sound uninvolved in the music even though they are generally pretty close to transparent. If you want an alternative to the OPA2228 that is stable in low gain amps then there is the OPA2209 but AFAIK it isn't available in DIP8 format so you'd have to mount it to an adaptor - though it doesn't have quite the bass of the 2228.

I'm not personally very familiar with the LT1xxx family.

 

[FritzS]

Now I searched in my old archive and found an old Austrian Praktiker DIY project from 1983 (!) which use some 5534 OPAs. 5534 is one of the longest standing OPAs too.
The output stage from 5534 could be easy drive to decrease Crossover Distortion with an 68 Ohm resistor between pin 6 and pin 5, in my opinion this knowledge may have been lost. Which I don't know if this will increase the idle current in the output transistors. It would be more effective to simply measure that. At the moment I lack the tools to do it.

.... der Widerstand R4 hat einbe besondere Aufgabe: bei kleinen Signalpegeln wird die Übernahmeregion des Ausgangsverstärkers in U1 (5534) überbrückt - die Verzerrungen bei kleinen Signalpegeln werden dadurch reduziert.

..... the resistor R4 has a special task: at low signal levels the crossover region of the output amplifier in U1 (5534) is bridged - this reduces the distortions at low signal levels.

 

[carlmart]

The big problem with 5534s is that you always have an output DC offset, so you need to put a blocking capacitor.

Only by using a DC servo do you get to eliminate the cap.

 

[FritzS]

The big problem with 5534s is that you always have an output DC offset, so you need to put a blocking capacitor.

Only by using a DC servo do you get to eliminate the cap.

Does this offset change strongly or can it be permanently minimized with offset correction?

In this old DIY project, there are some caps in signal path for blocking DC.

Some manufacturers still use 5534/5532 in the analog filter stage of CD/SACD players today,
detto 5534/5532 is still used in professional audio equipment.

 

[carlmart]

Almost all manufacturers put capacitors inter stages or at the output, so you don't have to consider their uses as the best for quality audio.

They will say that nobody can listen differences with cap or no cap. It's imagination when somebody say they do. They belong to the "objective" school, where if it can't be measured it doesn't exist. So they are not to be trusted.

High quality single chips, like the 5534 or LT1028, have null pins, where you can zero the offset. But on chips like the 5534 it drifts from zero all the time, so you can't trust the null: cap or DC Servo.

The LT1028 or AD797 are more drift-free, and you can trust them to remain close to zero offset. You just need to check the datasheet of the IC you are planning to use and see what's their offset without any null. Most modern chips can be used without any caps..

The 5534 is still a very good sounding chip, much better than the 5532. It does always deserve a listen, with cap or servo. The other problem is that the cap has to be large, usually an electrolytic type.

In any case, I always follow Ben Duncan's advice: do not use any interstage caps, and put just one high quality film cap at the last stage, before the power amp or headphone amo.

 

[FritzS]

In any case, I always follow Ben Duncan's advice: do not use any interstage caps, and put just one high quality film cap at the last stage, before the power amp or headphone amo.

Pity that the best electrolytic capacitors in my opinion, the nonpolarized Black Gate electrolytic capacitors, are no longer produced!

I use BlackGate NX 1000 uF 25V at the output of my headphone amplifier too. Till today I don't found similar nonpolarized electrolytic capacitors!

 

[carlmart]

There was a research article, some years ago, that the best choice, both measured and on listening tests, was two bipolars in series, no bias in between.

You can find the article in Linear Audio's site.

 

[raoultrifan]

[...]
They will say that nobody can listen differences with cap or no cap. It's imagination when somebody say they do. They belong to the "objective" school, where if it can't be measured it doesn't exist. So they are not to be trusted.[...]

I this a contradiction or am I misunderstanding?
I think subjective people assumes that a cap might be better than another cap, of course...without providing any evidence or measurement. Usually, if on scope measurements across audio-bandwidth there is no phase-shift nor phase-delay then that cap should be good for use inside audio equipment. It actually quite simple to measure this...just need to use a scope and see the phase; of course, RMAA or ARTA will help too.

Also, the plain-old "best cap is no cap" or "wire with gain opamp" etc. are usually to be on the safe side, so yes...it's more technically advanced to use DC-servo or DC protection instead of a cap to block the DC, but it's always cheaper and good enough for audio equipments to use a decent MKP cap.

 

[raoultrifan]

[...]

I use BlackGate NX 1000 uF 25V at the output of my headphone amplifier too. Till today I don't found similar nonpolarized electrolytic capacitors!

It's all about proper calculation of the output low-pass filter, nothing else: http://sim.okawa-denshi.jp/en/CRlowkeisan.htm. And if you have a scope around (preferable a frequency generator too, if not already built into the scope), you can actually check for any phase shift or phase delay for any audible frequency you might want (usually 20Hz, 50Hz, 100Hz, 1KHz, 5KHz, 10KHz, 15KHz, 20KHz).

For the input caps here's an example of what a cap in signal path can do:

Original HPA-3B with 2.2uF input caps
https://cdn.head-fi.org/a/10082789.png

vs.

Audio signal applied after the input caps (or short-circuit input caps)
https://cdn.head-fi.org/a/10082797.png

With square waves it might look nasty, but in real life it's a roll-off at 20Hz of about 0.3dB, so nothing to worry about. I was unable to actually feel any difference on my headphones when doing a short-circuit on the audio caps. Maybe if the difference would be 0.5dB or higher, then it would cause an audible concern, but for less than 0.3dB that I was able to measure, I really care not.

TL;DR: From https://www.v-cap.com/coupling-capacitor-calculator.php we can calculate the output capacitor values for our audio equipment, we should simply choose 2Hz for the frequency and 10...50 KOhms for the input impedance of the connected equipment, to be on the safe side (for DAC's or preamps only, not for speaker amps!).
For power amps instead, we should understand why some of them are not perfectly flat, especially on the low-end (-1dB at 20Hz), because if we calculate the output filter capacitor for a 3-dB roll-off @ 2Hz and need to connect 4 Ohms speakers that are actually 3 Ohms in real measurements, then we might need a 26525uF capacitor on outputs (quite expensive and bulky design)!
So again, based on the design, sometimes indeed best cap is no cap, unless we're happy with a -3dB roll-off @8Hz instead of 2Hz and we'll never connect 4 Ohms speakers, only 8 Ohms, that actually measures around 6 Ohms on the bass department (I'm speaking about impedance @ 20-30Hz), so a 4700 uF will do very well here. Of course, sometimes a cheap cap will simply work very well, it's all within the design and calculations.

 

[FritzS]

It's only for headphone amps - AKG K812/872 have 36 Ohm, Denon AH-D7000 have 25 Ohm.