SPL Volume 2 preamp mod

Discussion in 'The Projects Forum' started by Thraex, Oct 29, 2012.

  1. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    Hello to all of you!

    My first post is to ask help a newbie like me do the hardware mods to upgrade the SPL Volume 2 balanced preamp.
    The inside pic is from 6moons review here http://www.6moons.com/audioreviews/spl/open_big.jpg .

    The only thing that I can do now is to swap TL071CP input JFET op-amps in DIP8 connector, but even here I'm uncertain which upgraded type will work.
    I've already contacted SPL and they confirm me the OPA134 will work but they like the sound of the stock TL071 better, they tell me the OPA627 isn't compatible.
    I really don't understand why or which are the real alternatives or specs to look at for upgrading.

    I'm also ready to change capacitors and anything is considered an upgrade.

    Any suggestion and step by step guide will be greately appreciated.

    Thanks
     
  2. BillO

    Well-Known Member

    Nov 24, 2008
    985
    136
    What would be the aim of this? Just to change something?

    Just changing one op-amp for another will not accomplish anything unless the new op-amp is significantly lower noise or some other spec is vastly improved in such a way that the overall effect is better performance.

    So, what does the OPA134 offer that the TL071CP can't?
     
  3. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    I want to upgrade the SPL Volume 2.
    I don't understand if you think the SPL Volume 2 is perfect as is or if you consider the op-amp change useless.

    From specs the OPA134 seems much better than TL071CP and a lot of reports stated the sonic differences between op-amps.

    Since I'm a novice I was just asking help for upgrade it.
    Is it impossible?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The TL071 has distortion that is 0.003%. If its distortion is 30 times higher then you might hear it. It has a tiny amount of noise (hiss).

    The OPA134 has distortion that is 0.00008%. Its extremely low noise level is difficult to measure.

    Replacing the opamp will make identical sound but the numbers will look better.
     
  5. BillO

    Well-Known Member

    Nov 24, 2008
    985
    136
    While I agree the OPA134 is a better chip, like Audioguru says, you won't hear a difference, and that is doubly so since the back end will not be upgraded.

    However, I guess the exercise might be okay for the exercise itself. I've always been a tinkerer and have done stuff like this to keep myself occupied and interested. Do you have a way of measuring the overall noise and THD? It might be interesting to see if the change actually makes a real world difference.

    As for impossible, not if the pin-out and supply requirements between the two chips are compatible. Then it should be a simple pop and replace. 2 minutes and your done.
     
  6. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    Ok thank you.

    I've already ordered OPA134, OPA604, TLE2071 (TL071 upgraded) and OPA627.
    Unfortunately SPL told me the OPA134 could work but not the OPA627, I'll resell the latter or may I try it anyway?

    If those chips will have the same sound, where do I have to upgrade the capacitors given the inside picture?

    Thanks
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Without seeing the schematic, we don't know if the electrolytic and ceramic capacitors
    are simply filters for the power supply or if they are in the signal path causing distortion.
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    I've been building audio devices for about 45 years now. It always made me scratch my head when audiophiles seem to be obsessed with changing something, even though they have no actual improvement in mind, they are just convinced that changing something will surely improve it. Monster cable convinced the world that pure sound could only be obtained with speaker cables as thick as telephone poles. Later, I saw audio nuts buying "braided" audio ribbon cables to connect to their speakers to fix the "standing wave" problem. Oh, well.

    As to your pre amp: any aluminum electrolytics which are in the signal path may be changed out simple because they degrade with age. I am not sure there are any, but maybe. Good polyester/polypropolene film caps are generally "audiophile blessed" for this usage.

    As for op amps: the TLO74 type devices are excellent for general pre amps since the signal levels are about 500 mV (RMS) @ 0dB, so any noise the op amp has is about 80 dB below that. In other words, YOU CAN'T HEAR IT. For very low level signals like a magnetic head amp or a mag phono cartridge amp, you need a super low noise amp like maybe an NE5532. But for your pre amp, the TLO74 op amp you have is excellent.

    At the risk of stating heresy: it's possible the person who designed and built the pre amp circuit knew what he was doing and it's OK as it is.

    Let me help stoke the hysteria about the evils of capacitors just for fun:

    http://www.bext.com/replace.htm

    http://sound.westhost.com/articles/capacitors.htm

    http://www.nutshellhifi.com/library/capacitor.html


    http://www.reliablecapacitors.com/pickcap.htm


    http://conradhoffman.com/cap_measurements_100606.html
     
    Last edited: Oct 30, 2012
  9. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    With the pic here http://www.6moons.com/audioreviews/spl/open_big.jpg no idea? If not I'll not try out anything.
     
  10. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    Thanks for the info, the op-amp is the TL071CP not the TL074 you mentioned.
     
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    They are identical. The last number just denotes whether they are single, dual, or quad. The TLO71 is single, the TLO74 is the exact same part in quad version. The "CP" suffix denotes temp range and type of package.

    http://www.ti.com/lit/ds/symlink/tl071a.pdf


    TL071, TL071A, TL071B, TL072
    TL072A, TL072B, TL074, TL074A, TL074B
    LOW-NOISE JFET-INPUT OPERATIONAL AMPLIFIERS

    description/ordering information

    The JFET-input operational amplifiers in the TL07x series are similar to the TL08x series, with low input bias
    and offset currents and fast slew rate. The low harmonic distortion and low noise make the TL07x series ideally
    suited for high-fidelity and audio preamplifier applications.
     
    Last edited: Oct 30, 2012
  12. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    OK thank you.

    I've read the new enhanced replacement of the TL071 is the TLE2071 but reading the specs it's stated :

    "Because BiFET operational amplifiers are designed for use with dual power supplies, care must be taken to
    observe common-mode input voltage limits and output swing when operating from a single supply. DC biasing
    of the input signal is required and loads should be terminated to a virtual ground node at mid-supply. Texas
    Instruments TLE2426 integrated virtual ground generator is useful when operating BiFET amplifiers from single
    supplies."

    Given the inside of the SPL Volume 2 do you think I've already the dual supply so to safely try the TLE2071?
     
  13. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Why bother with the TLE2071 when its distortion is more than double the low distortion of the TL071?
    Its typical noise level is the same. But it amplifies well up to radio frequencies (woopee).
    It costs more than 3 times more.

    Of course your circuit has proper biasing for the opamp or it will be a severely distorted rectifier. ANY opamp will work in that circuit.

    Texas instruments sells ICs so of course they tell you to use their expensive TLE2426 virtual ground generator instead of you using 2 resistors and 1 capacitor.
     
  14. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    Since I've already the OPA627 do you think I could try it without damaging my preamp?

    SPL told me OPA627 is not compatible, maybe for its higher bandwidth which can influence the following circuit?
     
  15. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The OPA627 opamp has spec's that are slightly better than the TL071 that sounds identical. But it costs 42 times as much!

    It works at frequencies as high as AM radio transmitters so it might oscillate if the pcb is not layed out for a radio circuit. If it oscillates then it will get hot.

    Try it. It will not damage the circuit.
     
  16. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    OK thanks, I'll try it tomorrow and report back.
    How can I understand if it's oscillating or has some other problems?
     
  17. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    When an opamp oscillates then its output switches on and off and on and off at a very high frequency that causes it to get hot. Audio will sound very distorted when it is modulated by the high frequency that causes clipping.

    Some young people can hear as high as 20kHz. The inexpensive TL071 goes very well up to 100kHz. Why use an expensive opamp that goes up to 1200kHz?

    Some people can hear distortion as low as 0.1%. Audio opamps are at least 30 times better then the distortion cannot be heard by anybody. Why use an expensive opamp with distortion so low that it is difficult to measure?

    Some people buy the very best of anything. The best cars also cost a lot more than ordinary cars. But a very expensive car drives down the street the same as an inexpensive car.
     
  18. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
  19. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Did you notice that the distortion of all the opamps listed is so low that nobody can hear it?
     
  20. Thraex

    Thread Starter New Member

    Oct 29, 2012
    20
    0
    About hearing something and measurements, I'm convinced the ear can measure a lot of things equipment can't and the body feels what the ear can't, it's a fact.
     
Loading...