2Bak said:
Peter would you mind giving some more details on the sound qualities of the Gainclone?
I'm standing here on a crossroad and I can't decide if I should extend my GC 4-channel cinema-add-on amp to a full 5-channel amp, to be used for both stereo and cinema.
If the sound is really good, like you say (haven't heard it in action yet, I must admit), then only a few more positive statements will convince me that it's time to say goodbye to my 20 years old stereoamp...
My future setup will be this: After this amp project has finished, next project are new front and center loudspeakers, small enclosures for a small room. I guess the Gainclone performs best if speakers are efficient type...?
/Jan
If you use the schematic below: 50k log pot at the input, 4.7BG N coupling cap, standard BG caps for PS filtering (4,000u in total), 400VA toroid (double 22v secondaries) with 8 discreet hexfred diodes (separate bridge per rail, both channels share rails, separate wires from PS to amp, 8 total), no bypas, no filtering in PS. Resistors - Riken 1W for 10K input and 220k, 0.5W Holco for feedback (Holco worked well here, Riken might be good too, but I didn't check it yet). Chassis should be solidly built as well. Check my example here: http://www.diyaudio.com/forums/showthread.php?s=&threadid=9112&perpage=15&pagenumber=35.
If you built the amp with those parts, I can almost guarantee that it will equal or better most other commercial offerings, regardless of price. How's that?
As to the sound, here's a quote from an e-mail I received recently (not my amp):
The sound keeps getting better, and keeps getting 'meatier' and smoother. You are correct in saying that this is an incredible sounding amp, I am in love with it. It has such a 'grab you' factor, that I really have never heard before, and the soundstage is UNBELIEVABLE.
That's the best I can do for you.
Attachments
You know, some of us heathens are still getting along with 800 x 600 screen resolutions and the way this place formats the page with the big strip down the left side, bitmaps with 800 pixel widths spill over the right side of the screen.
If you don't mind, I took the liberty of redoing your schematic in a width that'll allow the entire schematic to be viewed on an 800 x 600 screen.
Oh, I did add some polarity indicators at the loudspeaker so folks will be sure and wire them up right to preserve polarity.
You're free to download it to your system and use it however you like.
<center>
<img src="http://www.q-audio.com/images/pd-gainklone.jpg">
</center>
se
If you don't mind, I took the liberty of redoing your schematic in a width that'll allow the entire schematic to be viewed on an 800 x 600 screen.
Oh, I did add some polarity indicators at the loudspeaker so folks will be sure and wire them up right to preserve polarity.
You're free to download it to your system and use it however you like.
<center>
<img src="http://www.q-audio.com/images/pd-gainklone.jpg">
</center>
se
2Bak said:
I used this circuit with 18 v transformer and there was more bass then. Also, take into account regulation factor. My transformer, although rated 22V was actually making 24V. With big power transformer rated 25V, you might be actually getting 27 or more volts. One way is to just unwind secondary wire and get lower voltage. That's what I actually did to get 18V. Even with higher voltage, the parts stay the same.
It's perfect now Steve.
Peter Daniel said:
Thanks for all the help. I will not use pots, only fixed resistor at input, cause this will be a poweramp. In fact I have bought all the parts for making the Thorsten version as multi-channel, even Caddocks 0,2R for output.
However this minimized PD klone looks really cool...
Looking forward to plugging in this amp!
Moving DC Blocking Cap?
Hello Peter,
I’ve finally decided to jump on the gainclone bandwagon. I noticed in your schematic that the 4.7 uF DC blocking capacitor is between the 50 Kohm potentiometer and the 10 Kohm resistor. Have you tried to move the capacitor to the point just before the potentiometer for a lower DC offset? As it is now, the only DC path from the inverting input of the op amp (pin 8) is through the 220 Kohm resistor, which will produce a fairly large voltage drop even with a small input current. Assuming 0.2 uA input bias current, the output offset voltage will be 0.2 uA * 220 Kohm = 44 mV. This is not too bad, but it can be reduced by moving the capacitor to the input side of the potentiometer. With this change, there is a DC path through the 10 Kohm resistor and the 50 Kohm potentiometer to ground (probably much lower resistance to ground for a typical listening level), and the resulting output offset voltage due to the input bias current will be less than 10 mV. Just a thought.
JSKang
Hello Peter,
I’ve finally decided to jump on the gainclone bandwagon. I noticed in your schematic that the 4.7 uF DC blocking capacitor is between the 50 Kohm potentiometer and the 10 Kohm resistor. Have you tried to move the capacitor to the point just before the potentiometer for a lower DC offset? As it is now, the only DC path from the inverting input of the op amp (pin 8) is through the 220 Kohm resistor, which will produce a fairly large voltage drop even with a small input current. Assuming 0.2 uA input bias current, the output offset voltage will be 0.2 uA * 220 Kohm = 44 mV. This is not too bad, but it can be reduced by moving the capacitor to the input side of the potentiometer. With this change, there is a DC path through the 10 Kohm resistor and the 50 Kohm potentiometer to ground (probably much lower resistance to ground for a typical listening level), and the resulting output offset voltage due to the input bias current will be less than 10 mV. Just a thought.
JSKang
Re: Moving DC Blocking Cap?
Either that or you could just put a 220k resistor from the inverting input to ground and you could lower it even further.
Thorsten's original schematic included that 200k resistor, though Peter wasn't too concerned with offset so he left it out.
However another advantage of moving the cap to the input of the pot would be a wee bit better low frequency response at less than full rotation of the pot.
Of course some components will either have negligible output offset or be capacitively coupled in which case you can do away with the cap entirely. Or you could add a switch to short across the cap when you're using capacitively coupled source components.
Just some more thoughts.
se
JSKang said:
Either that or you could just put a 220k resistor from the inverting input to ground and you could lower it even further.
Thorsten's original schematic included that 200k resistor, though Peter wasn't too concerned with offset so he left it out.
However another advantage of moving the cap to the input of the pot would be a wee bit better low frequency response at less than full rotation of the pot.
Of course some components will either have negligible output offset or be capacitively coupled in which case you can do away with the cap entirely. Or you could add a switch to short across the cap when you're using capacitively coupled source components.
Just some more thoughts.
se
JDeV said:
It doesn't really matter. What Steve is trying to indicate is that since the amp inverts phase, by wiring the speaker as shown phase is restored. But this assumes that the pre-amp is delivering a signal in the correct absolute phase. Now because the actual CDs or LPs don't all do absolute phase the same way (and some will change song to song*) you can never know before hand whether your pre will deliver abs phase correctly.
So it doesn't really matter... you should have a switch somewhere that allows you to flip the phase either way.
* i am ignoring songs where abs phase is not maintained track-to-track
dave
JDeV said:
Well, both speakers must have the same polarity, not phase.
The reason I made note of wiring of the speaker (or rather the wiring of the speaker terminals on the amp) is because that circuit uses the opamp in inverting mode, so it will invert the polarity of the signal being fed to it.
So in order to have the speaker cones move outward for a positive input voltage, and rearward for a negative input voltage, you need to wire the speaker terminals at the amp opposite of what they would be otherwise.
If the amp were non-inverting, then you'd wire the output of the amp to the red terminal and ground to the black terminal. In this case you wire the output of the amp to the black terminal and ground to the red terminal.
Then when you wire up your speakers to the amp, going red to red and black to black, the cones will move the way they're supposed to as per the polarity color coding.
Some feel it's important to preserve the absolute polarity of the acoustic waveform of the actual event. For example, a kick drum will give you a really big initial positive going pulse, compressing the air.
If you invert absolute polarity, then when you play it back on your loudspeakers, that initial pulse will be a rarefaction rather than compression and this can change the sound.
However if absolute polarity isn't important to you, it doesn't matter how you wire up the output terminals as long as they're consistent from one channel to the other.
Hope this helps.
se
JDeV said:
Oh crap. Did I forget the scuffy comments? *sigh* And I'd just got a new batch of 'em back from the cleaners.
Sorry about that. What can I say, it's late. I promise I'll have some scuffy comments for you first thing in the morning.
Thanx Dave and Steve, really appreciate.
You're welcome.
se
Re: Moving DC Blocking Cap?
In my setup the offset is never more than 30mV. I will try and see how it works with a cap at the input, but I have a feeling that moving the cap directly to the input will change the sound. I noticed that with Aleph X, when placing resistors to ground right before the cap, improved the sonics somewhat.
The reason I removed the 220k resistor from positive input to ground was also in order to achieve better sound and I was not that much concerned with a bit of offset.
JSKang said:
In my setup the offset is never more than 30mV. I will try and see how it works with a cap at the input, but I have a feeling that moving the cap directly to the input will change the sound. I noticed that with Aleph X, when placing resistors to ground right before the cap, improved the sonics somewhat.
The reason I removed the 220k resistor from positive input to ground was also in order to achieve better sound and I was not that much concerned with a bit of offset.
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