Hello everyody !
I've built my new TQWT speakers based on Fostex FX120 for one month now , http://www.diyaudio.com/forums/showthread.php?s=&threadid=55505
and people on this forum ,
as well as a sound engineer who heard my system suggested me the amplifier could be replaced by a Gainclone for better results.
I searched for hours on the net and I found these solutions to be the best :
- non inverting circuit
- LM3875 chip
- not so high voltages for the supply rails (18v ~ and around 25V = )
Now, I have some little (novice maybe, sorry) questions :
- Are there several non-inverting circuits, because I'm not sure to have seen exactly the same schematics
- Why not use multiple capacitors in parallel (such as 10*1000mfd) to avoid inductance issues with high capacitance ? I were also very interested in the snubber trials by carlosfm but it seems not to always work
- people use BlackGate capacitors as input decouplers, but they seem to be polarized, contrary to film capacitors. What is the best, and are some film capacitors better than others ? Is it truly useful to put 6$ input caps ?
- is a 225VA transformer enough ?
- Does the circuit integrates a preamp ? Is it possible to enhance it or to replace it with another simple and cheap circuit ?
- Is the pot really important in the sound quality ?
I've built my new TQWT speakers based on Fostex FX120 for one month now , http://www.diyaudio.com/forums/showthread.php?s=&threadid=55505
and people on this forum ,
as well as a sound engineer who heard my system suggested me the amplifier could be replaced by a Gainclone for better results.
I searched for hours on the net and I found these solutions to be the best :
- non inverting circuit
- LM3875 chip
- not so high voltages for the supply rails (18v ~ and around 25V = )
Now, I have some little (novice maybe, sorry) questions :
- Are there several non-inverting circuits, because I'm not sure to have seen exactly the same schematics
- Why not use multiple capacitors in parallel (such as 10*1000mfd) to avoid inductance issues with high capacitance ? I were also very interested in the snubber trials by carlosfm but it seems not to always work
- people use BlackGate capacitors as input decouplers, but they seem to be polarized, contrary to film capacitors. What is the best, and are some film capacitors better than others ? Is it truly useful to put 6$ input caps ?
- is a 225VA transformer enough ?
- Does the circuit integrates a preamp ? Is it possible to enhance it or to replace it with another simple and cheap circuit ?
- Is the pot really important in the sound quality ?
Everyone has there own preferences... but any of these give good bang for the buck.
more variations on the theme... VBIGC my favorite.
There are probably more variations in the power supplies than in the actual amp. Start with the basic amp and experiment from there.
Caps probably add more "colour" to a circuit than any other part... and which one sounds best can be very dependent on the rest of the build.
yes
With a volume pot the basic chip amp can be an integrated... sometimes a buffer helps (the buffer can be considered a pre-amp in some senses..
sure
a fixed R instead should have sonic benefits over a pot (althou you are going to have a volume control somewhere in the chain.
dave
Thanks for your answer Planet10
I heard about the "buffer" but don't really understand what it is. Does it replace the chip preamp ?
I have some ideas to build a multiple stage volume control, instead of a pot, but I'm afraid it may cost me more than a stereo Alps pot !!
How are calculated the values of the different resistors ? Does it depends on the chip or the input impedance resistor ?
I saw on decibel dungeon that carbon resistors sounded better for line in than metal resistors, though they come in larger tolerances (5%,which is anyway better than a pot). Is it true ?
Question for everybody : what are your favorite input capacitors ? Is it a problem if they are polarized ?
And last question, will I be able to get an very good Gainclone, though not the best, with 80 - 100 euros ?
I heard about the "buffer" but don't really understand what it is. Does it replace the chip preamp ?
I have some ideas to build a multiple stage volume control, instead of a pot, but I'm afraid it may cost me more than a stereo Alps pot !!
How are calculated the values of the different resistors ? Does it depends on the chip or the input impedance resistor ?
I saw on decibel dungeon that carbon resistors sounded better for line in than metal resistors, though they come in larger tolerances (5%,which is anyway better than a pot). Is it true ?
Question for everybody : what are your favorite input capacitors ? Is it a problem if they are polarized ?
And last question, will I be able to get an very good Gainclone, though not the best, with 80 - 100 euros ?
Banned
Joined 2002
Banned
Joined 2002
http://www.chipamp.com/nigc_kit-users_guide.pdf
http://www.decdun.fsnet.co.uk/gainclone4.html
I found these two circuits for a non-inverting GC. There are subtle differences between them but I cannot really predict which one would be the best.
I will not add a buffer at first because it may increase the total price, and people seem to say that they remove a little bit transparence.
But I will use Carlosfm regulated PSU which seems excellent, and I suppose it will be a more intersting inmprovement than a buffer. He says to add 1000mfd capacitors to the supply pins, snubberized too. Are these snubber capas integrated in the circuit or aren't they shown on the PSU circuit ?
My last problem is input capacitor : is it possible to use a polarized capacitor such as a BlackGate or do I need a non polarized cap like a MKT cap ?
http://www.decdun.fsnet.co.uk/gainclone4.html
I found these two circuits for a non-inverting GC. There are subtle differences between them but I cannot really predict which one would be the best.
I will not add a buffer at first because it may increase the total price, and people seem to say that they remove a little bit transparence.
But I will use Carlosfm regulated PSU which seems excellent, and I suppose it will be a more intersting inmprovement than a buffer. He says to add 1000mfd capacitors to the supply pins, snubberized too. Are these snubber capas integrated in the circuit or aren't they shown on the PSU circuit ?
My last problem is input capacitor : is it possible to use a polarized capacitor such as a BlackGate or do I need a non polarized cap like a MKT cap ?
youyoung21147 said:
I am not Planet10 but can share my experience.
1). Type of res depends on your system and type of music you listen as well. There is no 'ideal best' res for every one. For fullrange speaker, one might prefer the carbon res but it might too soft for moden music The mix of metal film (e.g. 22K) and carbon (680) res on the feedback should compromize.
To me, I prefer the compact panasonic (metal film 1/4w, ero series) than RN60D as it make me more enjoyable with music.
2. Also depend on your taste and system, I had tried many 4.7UF cap: BG, anti-parallel BG (as Fedde's), SCR, Illinois cap, Cerafine, WIMA MKP10. To me, I prefer WIMA MKP10 most though I know it add some 'color' in the sound.
Note, it's not easy to differentiate the sound of expensive BG vs much-cheaper red Cerafine for general use.
3. "will I be able to get an very good Gainclone, though not the best, with 80 - 100 euros ?" <-- depend on your definition of 'very good GC'
Cheers,
Just a couple of suggestions.
I would try building a basic GC (inverted or non-inverted as there is very little difference). Use just 1000 ufd on the pins for now.
This keeps things very simple and ensures that you have a successful amp to listen to.
Then add the snubbered PSU and listen again.
And if you like, you can try a buffer later as well. The three transistor buffer shown on my site is simple to build and works well. Or you can go for Pedja's excellent Jfet buffer, or one using an opamp. The fun is in comparing them all!
Don't worry about differences between the various circuits that you find. Other factors like choice of chassis will have more influence on the sound than the addition or removal of an extra component like a cap or resistor.
If you want the best sound, use a polypropylene film cap for the DC blocker. You will not find a better electrolytic cap even if it is a Black Gate (and I have compared the NX against a polyprop).
And don't worry about your English, it is very good.
I would try building a basic GC (inverted or non-inverted as there is very little difference). Use just 1000 ufd on the pins for now.
This keeps things very simple and ensures that you have a successful amp to listen to.
Then add the snubbered PSU and listen again.
And if you like, you can try a buffer later as well. The three transistor buffer shown on my site is simple to build and works well. Or you can go for Pedja's excellent Jfet buffer, or one using an opamp. The fun is in comparing them all!
Don't worry about differences between the various circuits that you find. Other factors like choice of chassis will have more influence on the sound than the addition or removal of an extra component like a cap or resistor.
If you want the best sound, use a polypropylene film cap for the DC blocker. You will not find a better electrolytic cap even if it is a Black Gate (and I have compared the NX against a polyprop).
And don't worry about your English, it is very good.
Thanks for all your nice replies !
As you suggested it, I will begin with the simple non inverted GC, and just 2200mfd on the pins, snubberized like Carlosfm suggests it, but w/o the regulated PSU.
I used succesfully some 2.2mfd MKT caps in my High-end measurement microphone, but as couldn't compare with anything else I'm just able to say that they work fine
I made some calculations this morning, it may cost me more than 100€ with regulated PSU and BG caps. Not nice
The only thing I will do is to build my own multiple stage volume control instead of an ALPS pot. Concernig this, I will then just have an input and the output after the resistors. How do you cable this kind of thing ?
Right now, the only thing I need is money, but I have a little, and time because I'll soon have exams
As you suggested it, I will begin with the simple non inverted GC, and just 2200mfd on the pins, snubberized like Carlosfm suggests it, but w/o the regulated PSU.
I used succesfully some 2.2mfd MKT caps in my High-end measurement microphone, but as couldn't compare with anything else I'm just able to say that they work fine
I made some calculations this morning, it may cost me more than 100€ with regulated PSU and BG caps. Not nice
The only thing I will do is to build my own multiple stage volume control instead of an ALPS pot. Concernig this, I will then just have an input and the output after the resistors. How do you cable this kind of thing ?
Right now, the only thing I need is money, but I have a little, and time because I'll soon have exams
I suppose the multistage volume control replaces the pot, so it's placed before the input cap. The only thing is that it has 2 pins, unlike a pot which has 3.
Should it be connected like this (excluding the input-to-mass resistor and the cap) ?
|-> multistage controler -> ground
|->------------------------------------------> lm3875 input
or like this
-> multistage controler -> lm 3875 input
Should it be connected like this (excluding the input-to-mass resistor and the cap) ?
|-> multistage controler -> ground
|->------------------------------------------> lm3875 input
or like this
-> multistage controler -> lm 3875 input
Yes I plan to build a stepped atenuator :
There will be two rotary switches (2*6poles) : one for a first level setting, and the other for a fine level setting, and with this, I'll get 36 volume control positions (6*6) by associating all the positions of the two switches.
It means there will always be two resistors in serie : one on the first switch which leads to another resistor on the second switch, and then leads to the output.
My problem with this is that you get only two "pins" : the input and the output, whereas a pot has 3 pins, so I don't know how to connect this thing in order to replace a pot (I'm not a crack in electronics )
Concerning input capacitors, I found a nice MKP serie of polypropylene capacitors. The 3.9mfd is rated at 5% and 160V and costs 4 euros, which seems quite interesting for input purposes. They are quite big but I don't mind, place is not my problem.
There will be two rotary switches (2*6poles) : one for a first level setting, and the other for a fine level setting, and with this, I'll get 36 volume control positions (6*6) by associating all the positions of the two switches.
It means there will always be two resistors in serie : one on the first switch which leads to another resistor on the second switch, and then leads to the output.
My problem with this is that you get only two "pins" : the input and the output, whereas a pot has 3 pins, so I don't know how to connect this thing in order to replace a pot (I'm not a crack in electronics
)Concerning input capacitors, I found a nice MKP serie of polypropylene capacitors. The 3.9mfd is rated at 5% and 160V and costs 4 euros, which seems quite interesting for input purposes. They are quite big but I don't mind, place is not my problem.
Unless there is a type of attenuator that I have not yet seen, you must have a way of shunting the 'unwanted' volume to ground.
A resistor in series does not attenuate the signal on its own. You can use two rotary switches to give a first and fine setting but one must also include resistors to ground.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.