Gutting a commercial amp to improve it

  1. ginetto61
    Hi ! sorry for the weird question.
    But i see many cheap amps that seem to have a great potential not fully expressed.
    This is perfectly understandable. They are made at a budget. Therefore they use cheap pots, wimpy mains transformers, weak connections, wiring etc.
    I wonder if anyone has thought about using the internals of a commercial amp and adding higher quality parts to improve its performance.
    For instance imhe a good stepped attenuator is always a great addition.
    I like this thing of freeing the hidden potential of already promising units a lot indeed. Don't you ?
    Thanks a lot, gino
     
    Last edited: Nov 3, 2017
  2. randytsuch
    Sure, I've modded a bunch of stuff over the years. Sometimes because cheap parts were used, and sometimes because mistakes were made, or maybe they simply cut corners to save costs.

    For instance, I'm currently using an older Ming Da headphone amp. I've made changes to the power supply section because the heater voltage was too high, and put in better coupling caps. Also rewired it to use different tubes, mostly so I could roll some tubes in it lol.

    Depending on the amp, design, parts used, etc, there may be the potential for good bang for buck changes.
    But, you need to know what your doing. Tube amps in particular as they have potentially lethal voltages. I almost always add a bleeder resistor on the high voltage of my tube amps, because many don't have them.

    Randy
     
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  3. ginetto61
    Hi thanks a lot for the very kind and valuable advice. Speaking of tubes i am both fascinated and worried for the high voltage involved. So i am more inclined to ss units even if some sonic qualities of tubes make them unique.
     
  4. ginetto61
    Sorry but i am writing in difficult conditions but i would like to explain my idea on how to set up a system. I have already got a lot of criticism but anyway.
    I see a very good headphone like the stetoscope of the doctor. The good ones can be extremely revealing of the quality of what is upstream. And they are also very convenient to test and evaluate different sources preamps without having to bother for the listening room. The all process is much simplified i mean.
    So my idea would be to optimize the sound up to the headphone level and then make a resistors divider to reduce the output when i want to use a power amp plus speakers.
    I have bought already some amps and HPs but i am still confused about which of the two elements should be picked up first. What did you do ? Did you choose first the Headphone or the amp ? Thanks a lot gino
     
    Last edited: Nov 4, 2017
  5. Speedskater
    I was just reading a post from a guy who did repairs of modded units. You are more likely to damage the component that to improve it.
    Stick to electrolytic capacitors, switches and capacitors.
    But damaging the printed circuit board is a common problem.
     
    ginetto61 likes this.
  6. ginetto61
    Hi and thanks for the helpful advice
    I was thinking about the volume pot Power supply connectors and of course Electrolytic caps.
    I have indeed already ruined a pcb time ago Usually the copper traces are thin and delicate Moreover recent units sport smd parts. Some kits look better than commercial units
     
  7. randytsuch
    It is easy to damage stuff when you mod it, especially when they use cheap pcb's. But you can also repair boards that you damage. More than once, I've scrapped solder mask from a pcb so I could add a wire to repair a board. Like many things, once you get the hang of it, its not that hard. But I've also broken gear modding it. You have to learn to live with that, but it is depressing.

    Guys do use resistor dividers to use speaker amps with headphones, but it may not be optimal. You are generating all of this gain, and then throwing it away. And with tube amps, you have to be careful with impedance matching between the load and transformer. I was thinking about doing it but will likely get a output transformer made for higher impedance loads (headphones) at some point.

    I've been at this a while, so I've had both headphones and amps for some time. But I guess I usually pick up a set of cans, and then find an amp that can drive them properly. I think it easier that way, find cans with the strengths you want, and weaknesses you can live with. Then figure out what amp that's within budget that can drive them.

    Randy
     
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  8. ginetto61
    Hi again ! this is comforting. I have been doing some work on cheap things and i found that 1st it is absolutely mandatory to have the right tools and be able to use them properly, like for desoldering for instance, a very delicate work on some units with copper traces think like a hair (actually i do not understand this thing. Just make some thicker and wider traces. Really i do not understand. I tend to like the more complex wiring with wires much better).

    as i said before i would like to take profit of the extremely revealing abilities of some nice headphones. They let almost everything to pass through, the bad and the good. And the test can be done without having to set up speakers in a treated listening room. These advantages are immense.
    I understand that gain in an headphone amp is much more that what is needed for a line stage (sometimes it has just to buffer the signal and no gain is required). Nevertheless is much less that the gain of a integrated amp for speakers. I guess an average voltage gain in a headphone amp should be around 5 to 10 times ? in a line stage a voltage of 2-3 is enough.
    Not a big reduction. The idea of course is to use two very high quality resistors that summed equal the resistance of the headphone and select their value depending how much reduction in gain is wanted. It could work ... maybe.
    Regarding soundstaging ability of course this cannot be evaluate with HPs. But in my mind a good soundstage depends a lot on the listening environment. A bad room can devastate the soundstage whatever system is used, even a very expensive and good one. This will be coped with at a later stage.

    This is a very important point and thank you very much for your valuable advice. i will forget electrostatic ones because the amp cannot be used as a line stage.
    Big choice. I will pick up the one i like best. Kind regards, gino
     
  9. randytsuch
    I misunderstood that you want basically a combined preamp/headphone amp.
    You may not even need resistors for this.

    One consideration is the impedance of the cans. Low impedance, like grados at 32 ohms, need more current to drive them. High impedance, like senns at maybe 300 ohms, need higher voltages to drive them. And then planars are harder to drive in general. My planars are lowish impedance, around 50 ohms. But my amp has taps for low, med and high impedance cans.
    Preamps usually don't need much current or voltage since they just need to drive the amp's input.

    I don't even use a traditional preamp, I usually go direct from my dac to my amp, although I am looking at adding a buffer in the path. Buffer would have no gain, just for driving the signal.
     
  10. ginetto61
    Hello again ! Exactly ! the idea is to optimize the audio chain up to the HPs and then "adjust" the HPamp output reducing is Vout in order to drive properly a power amp or a pair of powered speakers, adding a pair of RCAs on the back of the HPamp.
    The DIY approach sounds very good to me.
    Of course the selected HP amp must be quite good in itself and usable for this purpose.
    A good pair of HPs can be extremely revealing and therefore an excellent tool to evaluate what there is upstream, sources and headphone amps.
    And it is also extremely convenient. I do not need to set up different speakers in a listening room.
    Swapping sources and HPamps is much easier that to swap speakers of course.
    Moreover most of my listening is actually through HPs during evening and night hours. But i like also the opportunity to listen through speakers when possible.

    If i understand right should i aim at high sensitivity HPs and usually these are also low impedance ? i would like to use normal HPs and not earspeakers. I do not bear them.
    as you say current is not an issue with power amps but V out is. Clearly the HP amp out must be reduced a lot ... at least 5 times i guess.

    then how do you set the volume ? your dac has a variable output maybe ?

    As an aside i really do not understand why they make the power amps so sentitive.
    I was looking at some lab reports of line preamps, both tube and SS, on the Stereophile site.
    A preamp has no problem at all to output even 10V with very low THD+noise.
    Then why to place so much voltage gain in power amps ? Why not design them to have 10V of sensitivity ? in this way it would be possible to use just one high gain preamp for HPs and power amps. Less gain implies also simpler circuits i think.
    However i will start to look at high sensitivity HPs of decent quality. Not an easy task i guess.
    If you have any recommendation of specific HPs of good quality and high sensitivity i would be grateful.
    Thanks again and kind regards. gino :smile_phones:

    P.S. it seems that in ear speakers are indeed the best options to do what i have in mind
    Reading here https://www.innerfidelity.com/images/SonyMDREX1000.pdf they require very little Voltage to produce good dB levels.
    I do not like the idea of use in ear speakers ... but if it is the only way ....
     
    Last edited: Nov 6, 2017

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