Hi Manfred,
if you use R=1k the B1 will see an Impedance of (approx) 3k in parallel with the input Impedance of the next stage, means less than 3k.
That's much too low! The B1 is en excellent buffer, but it isn't an opamp driving 600R without misbehaving.
Im my experinece (no measurements), the impedance to be driven by a B1 should not be lower than 10k, assuming the impedance of the next stage is higher than 20k, 20k for R+2R should be sufficient. In this approximation, I would consider R=7k as minimum.
Regards
Flo
Hi,
I finished my second filter yesterday: -ECdesigns'- JFET "differential amplifier" used as input buffer (it receives balanced signal from a TVC) which feeds the two way third order filter with 1000Hz as XO point. It sounds good but I have a wrong wiring somewhere and I suffer from significant hum and buzz, which depends on the source. My speakers are Beyma KX15 coaxials mounted on Autograph enclosures, so around 100db sensitivity for bass and 106db sens. for the tweeter...the input buffer and XO are "modular", shall I want to try another input buffer like the Treshold's one...
I had the opportunity to listen a couple of hours from a blue-ray player (which was the less noisy) and it sounds much more fullbodied than my previous active XO: an Ampslab XO with upgrades on PS, regulators, opamps and a balanced output made of THAT balanced driver chips. I'm happy, if were not by the ground loop, because it worked at first attemp and I had to mod the "diff amp" to behave as a buffer (I think it may have *2 gain, actually). I have no scope to check out the behaviour...
Well, I have to re-wire my TVC... and read again Bill Whitlock papers about Ground Loops. I remember one of them ends saying something like: "If all of the above fails to thame the problem, then start praying your local god of hum"
Cheers,
M
I finished my second filter yesterday: -ECdesigns'- JFET "differential amplifier" used as input buffer (it receives balanced signal from a TVC) which feeds the two way third order filter with 1000Hz as XO point. It sounds good but I have a wrong wiring somewhere and I suffer from significant hum and buzz, which depends on the source. My speakers are Beyma KX15 coaxials mounted on Autograph enclosures, so around 100db sensitivity for bass and 106db sens. for the tweeter...the input buffer and XO are "modular", shall I want to try another input buffer like the Treshold's one...
I had the opportunity to listen a couple of hours from a blue-ray player (which was the less noisy) and it sounds much more fullbodied than my previous active XO: an Ampslab XO with upgrades on PS, regulators, opamps and a balanced output made of THAT balanced driver chips. I'm happy, if were not by the ground loop, because it worked at first attemp and I had to mod the "diff amp" to behave as a buffer (I think it may have *2 gain, actually). I have no scope to check out the behaviour...
Well, I have to re-wire my TVC...
and read again Bill Whitlock papers about Ground Loops. I remember one of them ends saying something like: "If all of the above fails to thame the problem, then start praying your local god of hum" Cheers,
M
Hi Guys,
All the bad weather we have had here lately gave me a little time to fix things. Blew the reg in doing so and had to make 2 sets of 7812/7912 regulators, one for each channel.
The main thing was that I rewired the drivers, used test tones from different sources:
Subwoofer Test - Bass Test mp3 - Subwoofer Test mp3
Stereo Polarity Sound Test
Disconnected the tweeters and made sure the woofers were in phase.
Then without the woofer, got the tweeters into phase and finally made sure the woofer and tweeters were in phase. Verified this with the THX Optimizer from CARS dvd.
Getting everything into phase without the test tones is difficult. Now the imaging is good, it centers nicely, has good bass and sounds great. This does not produce killer images, but is good enough. However, I think my speakers have their own difficiencies and would be better not to blame the active crossover. I am very happy with what I have. Played the Terminator Salvation on Bluray, boy the experience was immersive. With this sound on my 54" Panasonic Plasma S1, made this otherwise forgettable/bad movie an enjoyable experience. Terminator series has surely jumped the shark, but I digress...
In conclusion, this experiment has now reached a logical milestone. Very happy with the control and authority my system over the sound. Substantial level of detail, and no fatigue. It took sometime for me to get used to the control actively crossed over systems have. It eliminated the grain and flabbyness the passive crossovers had. The next phase can probably be re doing this on a nice PCB with better supply, so I await for the PCBs this thread will bring us.
Finally, Mr. Pass,
Thank You Very Much for giving us this gem The B1. Your generosity knows no bounds.
All the bad weather we have had here lately gave me a little time to fix things. Blew the reg in doing so and had to make 2 sets of 7812/7912 regulators, one for each channel.
The main thing was that I rewired the drivers, used test tones from different sources:
Subwoofer Test - Bass Test mp3 - Subwoofer Test mp3
Stereo Polarity Sound Test
Disconnected the tweeters and made sure the woofers were in phase.
Then without the woofer, got the tweeters into phase and finally made sure the woofer and tweeters were in phase. Verified this with the THX Optimizer from CARS dvd.
Getting everything into phase without the test tones is difficult. Now the imaging is good, it centers nicely, has good bass and sounds great. This does not produce killer images, but is good enough. However, I think my speakers have their own difficiencies and would be better not to blame the active crossover. I am very happy with what I have. Played the Terminator Salvation on Bluray, boy the experience was immersive. With this sound on my 54" Panasonic Plasma S1, made this otherwise forgettable/bad movie an enjoyable experience. Terminator series has surely jumped the shark, but I digress...
In conclusion, this experiment has now reached a logical milestone. Very happy with the control and authority my system over the sound. Substantial level of detail, and no fatigue. It took sometime for me to get used to the control actively crossed over systems have. It eliminated the grain and flabbyness the passive crossovers had. The next phase can probably be re doing this on a nice PCB with better supply, so I await for the PCBs this thread will bring us.
Finally, Mr. Pass,
Thank You Very Much for giving us this gem The B1. Your generosity knows no bounds.
Picks from my second XO.
Hi
Thanks to my ground loop problem I had to study again the Rane and other papers about the subject and now I am a wiser person... I love when things go wrong because I learn so much!
Moderators should advice every novice to start reading about grounding equipment.
I re-wired the whole system and found that the cable TV was the culprit of the most noise. Even with these measures I can't get rid of all the noise but I have to get close to the very sensitive speakers to hear it..."I can live with that" as the ground loops articles begin with...
Now, I took some picks if you like to see them:
XO board.
Picasa Web Albums - mauricio
Another:
Picasa Web Albums - mauricio
Picasa Web Albums - mauricio
Installed, with -ECdesigns-' diffamp as input buffer.
Another, which shows THAT's balanced line drivers:
Picasa Web Albums - mauricio
I hope you like them.
I have a question: though this XO is much enjoyable (more dynamics, sweeter tone and warmth) than my previous one, based on opamps, I find it is less clean. Would it need adding some bypass caps on the rails next to the active units or is the PSRR high enough not to need them???
Thanks,
M.
Hi
Thanks to my ground loop problem I had to study again the Rane and other papers about the subject and now I am a wiser person...
I love when things go wrong because I learn so much! Moderators should advice every novice to start reading about grounding equipment.
I re-wired the whole system and found that the cable TV was the culprit of the most noise. Even with these measures I can't get rid of all the noise but I have to get close to the very sensitive speakers to hear it..."I can live with that" as the ground loops articles begin with...
Now, I took some picks if you like to see them:
XO board.
Picasa Web Albums - mauricio
Another:
Picasa Web Albums - mauricio
Picasa Web Albums - mauricio
Installed, with -ECdesigns-' diffamp as input buffer.
Another, which shows THAT's balanced line drivers:
Picasa Web Albums - mauricio
I hope you like them.
I have a question: though this XO is much enjoyable (more dynamics, sweeter tone and warmth) than my previous one, based on opamps, I find it is less clean. Would it need adding some bypass caps on the rails next to the active units or is the PSRR high enough not to need them???
Thanks,
M.
This is crazy!
You know how my vote was always a little less than vehiment. Well, on one level, you could see the sound was very clear, crisp and nice. Lacked any grain, grunge or other gremlins... How I felt a little odd that something was missing, could'nt quite put my finger on it. The image that kept coming back to my mind was that it was too clean, and too crisp, a little like a hospital ICU. A little soul was missing. Showed it to a friend of mine, and he said, yaa, it' nice. I was disappointed that it was not a Yeah!, this is Great!.
I kept wondering what was missing. Recently one of the old threads was dredged up linking to Humble Homemade Hifi
I re-read that famous page and then it stuck me. I have 16 pin DIP sockets in the filters. There I had empty pins and a bunch of Vishay Roederstein MKP1837 10nf caps burning a hole in my parts bin. On a lark, I bypassed the Vishay MKP caps I had in the low pass filters. The difference it made was startling. Vishay MKPs are not slouches, but this was crazy. Well, can one stop there? So, I went ahead bypassed the hipass filter caps as well. It shifted the frequency a bit, if it was just that or the micro-details coming through that made the difference, I can't be too sure. Opened up the power amp and bypasssed the input coupling caps as well.
Here I am sitting with a smile ear to ear. Like we don't have enough of a capacitor fetish among us the audiophools, I am now falling deeper into it. What's next, Gold Foil Teflons?
It's only a habit, I can break it anyday....
You know how my vote was always a little less than vehiment. Well, on one level, you could see the sound was very clear, crisp and nice. Lacked any grain, grunge or other gremlins... How I felt a little odd that something was missing, could'nt quite put my finger on it. The image that kept coming back to my mind was that it was too clean, and too crisp, a little like a hospital ICU. A little soul was missing. Showed it to a friend of mine, and he said, yaa, it' nice. I was disappointed that it was not a Yeah!, this is Great!.
I kept wondering what was missing. Recently one of the old threads was dredged up linking to Humble Homemade Hifi
I re-read that famous page and then it stuck me. I have 16 pin DIP sockets in the filters. There I had empty pins and a bunch of Vishay Roederstein MKP1837 10nf caps burning a hole in my parts bin. On a lark, I bypassed the Vishay MKP caps I had in the low pass filters. The difference it made was startling. Vishay MKPs are not slouches, but this was crazy. Well, can one stop there? So, I went ahead bypassed the hipass filter caps as well. It shifted the frequency a bit, if it was just that or the micro-details coming through that made the difference, I can't be too sure. Opened up the power amp and bypasssed the input coupling caps as well.
Here I am sitting with a smile ear to ear. Like we don't have enough of a capacitor fetish among us the audiophools, I am now falling deeper into it. What's next, Gold Foil Teflons?
It's only a habit, I can break it anyday....
Max,
I got to agree with you, this is not very quite. My system is even more worse because I made too many changes to the supply for my LM4780 based amps. I wen from on board single bridge rectifier and capacitor to a off-board, MUR1520 based, dual bridges with snubber caps followed by CLCLC filters. In doing so, I have introduced that bugaboo Ground Loop, obviously because it lacks a star ground. The hum/hiss/noise is small enough that I am tolerating it. Hoping to start a new project sometime later on to design a PCB with a proper ground.
The PCBs for this active crossover too need to be carefully designed with large ground planes and provide ample bypass caps.
I got to agree with you, this is not very quite. My system is even more worse because I made too many changes to the supply for my LM4780 based amps. I wen from on board single bridge rectifier and capacitor to a off-board, MUR1520 based, dual bridges with snubber caps followed by CLCLC filters. In doing so, I have introduced that bugaboo Ground Loop, obviously because it lacks a star ground. The hum/hiss/noise is small enough that I am tolerating it. Hoping to start a new project sometime later on to design a PCB with a proper ground.
The PCBs for this active crossover too need to be carefully designed with large ground planes and provide ample bypass caps.
the filter should see near zero ohms feeding the input and near infinity ohms as load on the output.
A standard B1 gets close if you don't hang anything else on the B1's input/output.
Unfortunately B1 needs some resistance on it's output to be stable. some have reduced the 1k0 to 220r and find that works. Maybe a bit of experimentation on that to find what works. But whatever, the next R, of a low pass filter, must take the source resistance into account when assembling the active filter.
Not so easy with a high pass that starts with a cap. This is now preceded with the B1 output impedance + the resistance of that stabilising resistor.
A filter feeding into B1 should not have anything between the filter output and the very high input impedance of the B1. Do not add any of the Rin setting components and/or band limiting filters that are used in a standard pre-amp/buffer.
A standard B1 gets close if you don't hang anything else on the B1's input/output.
Unfortunately B1 needs some resistance on it's output to be stable. some have reduced the 1k0 to 220r and find that works. Maybe a bit of experimentation on that to find what works. But whatever, the next R, of a low pass filter, must take the source resistance into account when assembling the active filter.
Not so easy with a high pass that starts with a cap. This is now preceded with the B1 output impedance + the resistance of that stabilising resistor.
A filter feeding into B1 should not have anything between the filter output and the very high input impedance of the B1. Do not add any of the Rin setting components and/or band limiting filters that are used in a standard pre-amp/buffer.
Hi,
Last week I had the (nasty) visit of my (very snob) little brother
who insisted on listening my second main system with only my humble Paradigm Monitor 3 bookshelf speakers (avoiding active amplification, hence no B1 crossover) and with the said speakers positioned much lower and in front, on axis with respect to the big Eminence 15" woofers. Very well. This week, after some tweaks to my NOS DAC (-ECdesigns-' M1 USB DAC) I'm having very good sound and monster bass! I know it can be all coming from the Paradigm and I feel more cone movement from the 15" woofer (more than when the bookshelf were mounted on them) so I believe I am having a "passive radiator" effect, with an acoustic crossover based on the physical relation between the two speakers (bookshelf and woofer) and the own response of the woofer.
I can say this makes me wonder if I need here two more channel of amplification plus an active crossover plus a ground loop at all!
Picasa Web Albums - mauricio
Imagine the bookshelf just in front of the woofers...
First time that I find this effect. Wonder why it is not recomended more...
Cheers,
M
Last week I had the (nasty) visit of my (very snob) little brother
who insisted on listening my second main system with only my humble Paradigm Monitor 3 bookshelf speakers (avoiding active amplification, hence no B1 crossover) and with the said speakers positioned much lower and in front, on axis with respect to the big Eminence 15" woofers. Very well. This week, after some tweaks to my NOS DAC (-ECdesigns-' M1 USB DAC) I'm having very good sound and monster bass!
I know it can be all coming from the Paradigm and I feel more cone movement from the 15" woofer (more than when the bookshelf were mounted on them) so I believe I am having a "passive radiator" effect, with an acoustic crossover based on the physical relation between the two speakers (bookshelf and woofer) and the own response of the woofer.I can say this makes me wonder if I need here two more channel of amplification plus an active crossover plus a ground loop at all!
Picasa Web Albums - mauricio
Imagine the bookshelf just in front of the woofers...
First time that I find this effect. Wonder why it is not recomended more...
Cheers,
M
OK well a slightly different (I think) question to what has been asked. I'm a bit challenged when it comes to input and output impedance's, so have hit a bit of a roadblock.
I want to make the high pass part of my B1 active crossover (yet to be built) using a gyrator circuit like SY's one linked to early in the thread. To do this I can't use the standard sallen key equations to work out my filter component values.
I need to (as far as I can tell) work out the values of the passive equivalent of a 2nd order LC filter so I can get the value I need for L.
in order to do that I (think I) need to know the input impedance of the next B1 (as the load for the LC network) so I can plug it into the equations.
I think once I have the values for a passive realisation of L and C I can then derive the values for the Gyrator circuit and get on with it, but as you can probably tell, I'm a little confused.
Any help would be greatly appreciated, even if it is only of the form of "read this excellent article that explains input and output impedance's" something that I really should never have got this far in DIY'ing without knowing.... I guess that's the difference between building a proven design and making your own though.. the knowledge required for the latter is massively greater
Tony.
I want to make the high pass part of my B1 active crossover (yet to be built) using a gyrator circuit like SY's one linked to early in the thread. To do this I can't use the standard sallen key equations to work out my filter component values.
I need to (as far as I can tell) work out the values of the passive equivalent of a 2nd order LC filter so I can get the value I need for L.
in order to do that I (think I) need to know the input impedance of the next B1 (as the load for the LC network) so I can plug it into the equations.
I think once I have the values for a passive realisation of L and C I can then derive the values for the Gyrator circuit and get on with it, but as you can probably tell, I'm a little confused.
Any help would be greatly appreciated, even if it is only of the form of "read this excellent article that explains input and output impedance's" something that I really should never have got this far in DIY'ing without knowing.... I guess that's the difference between building a proven design and making your own though.. the knowledge required for the latter is massively greater
Tony.
OK well I'm feeling a little silly now.... re-read the B1 article and note that the volume control sets the input impedance, so I guess all I really need to do for the buffer after the gyrator circuit is either put in a trimpot (for adjusting the level) I note Jaques used a 22K in this position in his circuit, howerver I'm not sure why he then has a 220K after that... , or just put in a fixed resistor to ground in the same position and use that value in my calculations. I'll try and model it in spice and see what happens
Tony.
Tony.
Thanks Bill good to know!
I've run into my next hurdle though The gyrator circuits that use an op-amp has the input fed to both the +ve and -ve inputs.. struggling at the moment to work out how I could do this with a B1 (the sallen key isn't a problem because the -ve on the opamp is only used to make it unity gain)...
Might need to employ an opamp for the gyrator (from what I've read the single transistor versions should be avoided)... I've been doing some spice modelling to get comfortable with the gyrator circuit, once I'm happy with that I guess I'll get a bit more adventurous.
Tony.
good to know! I've run into my next hurdle though
The gyrator circuits that use an op-amp has the input fed to both the +ve and -ve inputs.. struggling at the moment to work out how I could do this with a B1 (the sallen key isn't a problem because the -ve on the opamp is only used to make it unity gain)... Might need to employ an opamp for the gyrator (from what I've read the single transistor versions should be avoided)... I've been doing some spice modelling to get comfortable with the gyrator circuit, once I'm happy with that I guess I'll get a bit more adventurous.
Tony.
Hi Tony,
I use this gyrator circuit with the B1 (R=10k) and it works great.
Forssell Technologies
Manfred
I use this gyrator circuit with the B1 (R=10k) and it works great.
Forssell Technologies
Manfred
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