Well it took me longer than I expected but today I listened to my GC with a buffer and LPF.
And I am quite impressed at the sound, on first audition a clear improvement over the basic IGC.
The buffer that I used is contructed around an OPA627 and you can read full details HERE
A big thank you to Pedja Rogic for help and encouragement with the project!
BTW - I forgot to put it on the site but the LPF consists of a 695R carbon film resistor and 6N8nF polystyrene cap.
And I am quite impressed at the sound, on first audition a clear improvement over the basic IGC.
The buffer that I used is contructed around an OPA627 and you can read full details HERE
A big thank you to Pedja Rogic for help and encouragement with the project!
BTW - I forgot to put it on the site but the LPF consists of a 695R carbon film resistor and 6N8nF polystyrene cap.
That's the plan Frank.
Another reason I wanted to do the OPA627 buffer was that I feel it much easier for less experienced constructors to try that type of buffer than dive straight in with a valve buffer!
And the important thing is to hear the difference the buffer makes, which will help confirm the idea that it is worth doing the valve buffer.
Nuuk said:
That's the plan Frank.
Another reason I wanted to do the OPA627 buffer was that I feel it much easier for less experienced constructors to try that type of buffer than dive straight in with a valve buffer!
And the important thing is to hear the difference the buffer makes, which will help confirm the idea that it is worth doing the valve buffer.
Good on ya Nick. We have another convert!!!!
You've got the general idea... when Pedja decided to go the jfet route I did not pooh pooh the idea. While an IC would be my last option, then at least I reckon you chose a good chip. Expensive but quite good. I would have thought Pedja's jfet approach just as easy? But now we at least know it can work with IC as well.
If I was to recommend a less expensive chip, I'd say OPA-134 could work nicely as well. In fact, if you had an IC socket, you could go and get a whole bunch of UGS ICs and listen to the lot. In fact it occurs to me this would be a good tool to audition different ICs.
I read you audition comments on your web site with great interest. IC or not, would you still describe the plusses, that we would expect to be there?
And sure enough your description is right in the ball-park as to what you'd expect. In fact spot on!
It might be worth pointing out just how important that LPF is, in fact no Gainclone should be without it IMHO.
But it is the buffer that makes the LPF possible!
Also, this is a good way for new kids on the block to cut their teeth on tubes. Use 6922 or equavalents, and you don't need any lethal voltages... so now go for broke and show us what you come up with!
Joe R.
Joe Rasmussen wrote:
I don't know how you come to this conclusion. Adding an LPF without input buffer is just a question of dimensioning.
See my post #15 within the following thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9852
Regards
Charles
I don't know how you come to this conclusion. Adding an LPF without input buffer is just a question of dimensioning.
See my post #15 within the following thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9852
Regards
Charles
before signal cable?
i've been listening to IGCs with 2-way active-XO for quite a while and being pretty satisfied with their performance. Would like to try the buffer for IGC, but it's much easier to build my buffer in the active-XO side since its' power is built for opamps. So is it ok to put the buffer before the signal cable? and how about a BUF634 to do this job?
i've been listening to IGCs with 2-way active-XO for quite a while and being pretty satisfied with their performance. Would like to try the buffer for IGC, but it's much easier to build my buffer in the active-XO side since its' power is built for opamps. So is it ok to put the buffer before the signal cable? and how about a BUF634 to do this job?
Luke said:
Of course.
You could make an LPF directly on the power op-amp chip (LM3875 in this case).
Nuuk, if you're happy with the sound (I'm sure you are
), then I would not attribute so much of the merits to the LPF.The fact is that now you have a higher input impedance on your power amps, and a buffer.
You use a passive pot on an external box.
And, most important, you picked one of the (if not THE) best op-amps for audio applications.
I'm very happy with my pre too.
OPA627 + BUF634 is explosive.
It's finished, photos soon.
phase_accurate said:
You state that any LPF should be well above audio... yet if you calculate what we're talking about here, it does cut into audio. Indeed typically -1.3dB @ 20KHz.
That requires a buffer.
This is a case of: Don't ask questions, just do it! Then you too will experience what this is about. This LPF was determined purely by ear. In fact, the beauty of it that anyone can vary the LPF to their hearts content. But so far this final preferred value has now been independantly verified as the desired one.
The starting point here is the standard IGC, and how we can improve it. Whatever the theory...
Luke said:
With great difficulty. Click on below link to my "The Tube Gainclone for DIY Buffs" web site and goto 'sans tube' - and the difficulties are explained in detail.
The buffer makes it straight forward as it defines a Lo-Z source that is needed to drive the LPF, otherwise its time constant is over all the place, ergo... don't use a pot. Use the pot before the buffer.
On the other hand, if you have a Lo-Z source already, for example the output of a preamp (tube preferably, sorry but I am biased) then you already have a ready made buffer. Still not ideal but usable.
Joe R.
Oh yes Joe - but is it the influence of having drunk a lot of Kalgoorlie Stout many years ago?
Let me just reiterate that this choice of buffer and opamp was purely based on the fact that I had the buffers already here. I agree, some of the other opamps that would do the job here will probably produce excellent results too.
The PSU for the buffer was another 'already have' item and I didn't have time yesterday evening to write up full details but will later.
It is a fairly standard job, 18-0-18 torroid, rectifer bridge with Schottkeys if I remember correctly, 2 x 4700uF with smaller bypass caps and one stage of regulation (317/337) in one box, then another stage of regulation (317/337) for each channel closer to the buffers.
Without wishing to get on my soapbox, may I second what Joe says. There are a lot of people on these forums expressing opinions about matters like the buffer and LPF when they have not actually tried it! I only built my GCs in the first place because I could not decide who was right - those saying they were brilliant or those saying that they couldn't be. Sometimes you just have to hear it for yourself and then you can talk with some authority!
Listening again today, I notice that the chips seem to get slightly warmer with the buffer. Is there any reason for this or am I just playing it louder because it sounds so good?
Nuuk said:
Oh yes Joe - but is it the influence of having drunk a lot of Kalgoorlie Stout many years ago?
You lucky sod! The rest must wonder where a place like Kalgoorlie is? Like places called Wagga Wagga or Woy Woy (where Spike Milligan's brother still lives to this day) - it's in the land of Oz, the place Down Under, the land of Tassie Devils, Platypusses, Wallabies, Koalas and Kangaroos. If they haven't cotton on... then we can't help you!
Hey, no sweat! We got interesting feedback!
Without wishing to get on my soapbox, may I second what Joe says. There are a lot of people on these forums expressing opinions about matters like the buffer and LPF when they have not actually tried it! I only built my GCs in the first place because I could not decide who was right - those saying they were brilliant or those saying that they couldn't be. Sometimes you just have to hear it for yourself and then you can talk with some authority!
Hear, hear!
Hey, only you can answer that!
Mind you, if it got very warm with no music playing, then I'd worry. But if it gets hotter as you crank the volume up, then I'd consider that normal. Stereophile did a half-rated-power continous test on their original Gaincard and it got uncomfortably hot, even to touch.
Joe R.
Medical help
Actually some of my friends say I need medical help.
Then I show them some of the things I've done and then THEY need medical help.
The last one who almost called the doctor was my brother.
My ultra-small GC (pictures soon) blowed his big Vincent amp into dust. At his room, with his speakers.
BTW, that ultra-small GC (world record?) I made with OPA548s.
I'm impressed.
They're very good too.
Oh, this week I'm gonna test my Pre and GC power amp seriously.
A friend of mine who works with high-end is going to prepare a room for us.
Let me just tell you that the source will be a LINN CD12!!!
Speakers will be several, from the same cathegory.
Hahahahaha!
Seriously!
That guy has been at my home a week ago and got out needing medical help.
Nuuk said:Good day to you Carlos. If you let me have your wife's email address, I will write to her and ask if you talk about OPA627's in your sleep.
Actually some of my friends say I need medical help.
Then I show them some of the things I've done and then THEY need medical help.
The last one who almost called the doctor was my brother.
My ultra-small GC (pictures soon) blowed his big Vincent amp into dust. At his room, with his speakers.
BTW, that ultra-small GC (world record?) I made with OPA548s.
I'm impressed.
They're very good too.
Oh, this week I'm gonna test my Pre and GC power amp seriously.
A friend of mine who works with high-end is going to prepare a room for us.
Let me just tell you that the source will be a LINN CD12!!!
Speakers will be several, from the same cathegory.
Hahahahaha!
Seriously!
That guy has been at my home a week ago and got out needing medical help.
Joe R wrote:
Back then when I mentioned this LPF thingie in the other thread, my intent was different from what you are doing now.
I just want to point out the possibility of having an LPF without any buffer, which should be a piece of cake.
I don't want to claim that it sounds the same (and I don't want to try it out by now, but maybe someone else wants to do so) but the LTF would be the same if you had the 10k resistor first and the 680 Ohms resistor second with still the same capacitor from the node between them to ground.
Regards
Charles
BTW: AFAIK I was the first one mentioning the use of an LPF at the input of a GC.
Back then when I mentioned this LPF thingie in the other thread, my intent was different from what you are doing now.
I just want to point out the possibility of having an LPF without any buffer, which should be a piece of cake.
I don't want to claim that it sounds the same (and I don't want to try it out by now, but maybe someone else wants to do so) but the LTF would be the same if you had the 10k resistor first and the 680 Ohms resistor second with still the same capacitor from the node between them to ground.
Regards
Charles
BTW: AFAIK I was the first one mentioning the use of an LPF at the input of a GC.
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