Hi Charles, I agree with what you are saying.
There are such variances between recordings and the systems used to produce them, a tool like the Palette is essential to get the most from your music library.
I think program eq is where the Palette excels not for room eq per-se.
Thanks for the detailed info about the Palette. I was very impressed the times I heard what it could do.
I know that unlike most eq system the Palette used very low eq filters and had a lot of overlap, could you comment on that if you have the info?
Back to(at) you Kevin
The Palette uses pretty simple bandpass filtering that I believe was first published (discovered???) by Peter Baxandall. I found some good (simple?) info here: HeadWize - Project: Designing A Pocket Equalizer For Headphone Listening (A HeadWize Design Series Paper), which appears to include a lot of that found in the wonderful National Semiconductor Audio booklet. Filters are low Q and the maximum boost/cut amounts are determined by the ratio of the potentiometer value to the resistors attached to both ends of it - again you don't need anywhere as much boost/cut in the middle frequencies as at the extremes.
Burwen seems/seemed to embrace the basic "program" equalizing concept rather than the more modern "parametric" concept. I'll define "program" to mean filters where most of the parameters (slope, Q and perhaps rolloff characteristics - Butterworth, Chebychef(sp?)) are fixed (by design) instead of (user) variable as in the "parametric" design. I believe approach may have been chosen to minimize the "audible artifacts" of the filter - which is supposedly what we are after in this wacky hobby.
Cheers
Charles
The Palette uses pretty simple bandpass filtering that I believe was first published (discovered???) by Peter Baxandall. I found some good (simple?) info here: HeadWize - Project: Designing A Pocket Equalizer For Headphone Listening (A HeadWize Design Series Paper), which appears to include a lot of that found in the wonderful National Semiconductor Audio booklet. Filters are low Q and the maximum boost/cut amounts are determined by the ratio of the potentiometer value to the resistors attached to both ends of it - again you don't need anywhere as much boost/cut in the middle frequencies as at the extremes.
Burwen seems/seemed to embrace the basic "program" equalizing concept rather than the more modern "parametric" concept. I'll define "program" to mean filters where most of the parameters (slope, Q and perhaps rolloff characteristics - Butterworth, Chebychef(sp?)) are fixed (by design) instead of (user) variable as in the "parametric" design. I believe approach may have been chosen to minimize the "audible artifacts" of the filter - which is supposedly what we are after in this wacky hobby.
Cheers
Charles
It appears Burwen is using the same philosophy with his current software based eq system.
Hey Kevin, I understand he is doing a whole lot more than just EQ based on comments from two friends who attended the BAS sponsored demo at Dick Burwen's house a couple of Sundays ago.. I heard the original prototype at his house about 23yrs ago which was in itself an interesting experience. (I'm not a member of BAS, and it's moments like this that make me wonder why..
)Hey Kevin, I understand he is doing a whole lot more than just EQ based on comments from two friends who attended the BAS sponsored demo at Dick Burwen's house a couple of Sundays ago.. I heard the original prototype at his house about 23yrs ago which was in itself an interesting experience. (I'm not a member of BAS, and it's moments like this that make me wonder why..
Yeah, I originally went to the web site because of the thread wanted to comment on the original Palette I heard many years ago. In addition to the Palette functionality, it adds a small amt of Hi Freq Reverb which he says will get rid of the screechy sound of digital, he also can do up-sampling of standard CD, and can synthesis up to 7.1 from stereo signals. One appealing feature of the software is that the eq for a recording can be stored as metadata so you only have to set it once for a system unlike the original Hardware Palette,
What did you friends think of the software?
I am thinking of buying it. I appreciate the input from people who have heard what the software can do.
Stereophile's review of the Palette Preamplifier
can be found here: Cello Palette Preamplifier | Stereophile.com
Charles
can be found here: Cello Palette Preamplifier | Stereophile.com
Charles
Folks,
A while back i was working on a concept for a "Zero Feedback Tube Palette". The thoughts applied may also suit some here...
One may use a single triode section in a circuit like the classic "concertina" phasesplitter together with either series LC circuits or modern Gyrators.
Essentially the pots or switches are connected between the two phasesplitter outputs, as we need extra series resistors to handle the reduced ranges in the middle bands there is not as bad a load as may seem.
The output is then taken from the anode and is inverted.
If the pot/switch is advanced towards the cathode node we get boost, if we advance towards the anode node we get cut, equal in level.
One may need to add a cathode follower to buffer the output and perhaps a single stage of amplification ahead of the concertina to get a Preamplifier, however the whole circuit can be made easily in all tube, single ended and zero looped feedback manner which may appeal to some.
For true purists, i would use real chokes for all but the lowest two bands.
In this case a total five dual triodes plus a suitable tube rectified and LCRCRCRC filtered supply can make our "ZerO Looped Feedback All Tube Palette Preamplifier", or ZOLFATPPA as it is known to the cognescenti.
Ciao T
A while back i was working on a concept for a "Zero Feedback Tube Palette". The thoughts applied may also suit some here...
One may use a single triode section in a circuit like the classic "concertina" phasesplitter together with either series LC circuits or modern Gyrators.
Essentially the pots or switches are connected between the two phasesplitter outputs, as we need extra series resistors to handle the reduced ranges in the middle bands there is not as bad a load as may seem.
The output is then taken from the anode and is inverted.
If the pot/switch is advanced towards the cathode node we get boost, if we advance towards the anode node we get cut, equal in level.
One may need to add a cathode follower to buffer the output and perhaps a single stage of amplification ahead of the concertina to get a Preamplifier, however the whole circuit can be made easily in all tube, single ended and zero looped feedback manner which may appeal to some.
For true purists, i would use real chokes for all but the lowest two bands.
In this case a total five dual triodes plus a suitable tube rectified and LCRCRCRC filtered supply can make our "ZerO Looped Feedback All Tube Palette Preamplifier", or ZOLFATPPA as it is known to the cognescenti.
Ciao T
Tube Equalizer
Hi, and Thanks Thorsten.
Maybe 8 years ago, Glass Audio published an article on a tube equalizer - which I ended up building. I have asked them if "we" could have the rights to reprint it and they said OK.
They will be sending me a PDF of the article (along with another article on building a VERY nice -relatively simple- IM analyzer) and I'll post it/them as soon as I get them.
Cheers
Charles
Hi, and Thanks Thorsten.
Maybe 8 years ago, Glass Audio published an article on a tube equalizer - which I ended up building. I have asked them if "we" could have the rights to reprint it and they said OK.
They will be sending me a PDF of the article (along with another article on building a VERY nice -relatively simple- IM analyzer) and I'll post it/them as soon as I get them.
Cheers
Charles
Hey guys
Sorry for not checking this thread for some time.
Great to see and hear about your projects too.
6L6: Schematic ?... I used this one, with a Q = 0.7 for all bands. This was chosen based on the image of the measured frequency maniapulation of the audio palette, however I do not know for certain what the real Audio Palette used.( ...maybe Stellvox knows?)
Whenever I get to make the final circuitry ( endless projects - you all know it I am sure), I am thinking of doing simple 1.order filters with buffers between for the bandpass filters, so that I can get rid of the opamps.
The part which Rod Elliot calls "input/output stage" (figure 2 in the link) I would like to make with disrcete opamps somehow.
Anyway: I have put some more text - but not all - on the frontpanel, but I will ofcourse give an update when I have made some real progress.
Thanx
Sorry for not checking this thread for some time.
Great to see and hear about your projects too.
6L6: Schematic ?... I used this one, with a Q = 0.7 for all bands. This was chosen based on the image of the measured frequency maniapulation of the audio palette, however I do not know for certain what the real Audio Palette used.( ...maybe Stellvox knows?)
Whenever I get to make the final circuitry ( endless projects - you all know it I am sure), I am thinking of doing simple 1.order filters with buffers between for the bandpass filters, so that I can get rid of the opamps.
The part which Rod Elliot calls "input/output stage" (figure 2 in the link) I would like to make with disrcete opamps somehow.
Anyway: I have put some more text - but not all - on the frontpanel, but I will ofcourse give an update when I have made some real progress.
Thanx
Original schematic of Cello Audio Palette!
Wow, I just found the original schematic of the Cello Audio Palette!
The original design used NE5532AN op amps. In the actual Cello Audio Palette they replaced the op amps with discrete components.
INITIAL DESIGN OF THE CELLO AUDIO PALETTE
Richard S. Burwen, March 3, 1984
The accompanying schematic, description, and tentative specifications and features were submitted to Mark Levinson’s Cello Ltd. and became the basis of the Cello Audio Palette tone control system. This design used a large number of integrated circuit op amps. Cello wanted to achieve the best possible performance and avoid any possible criticism of its op amps. They replaced the important signal processing op amps with their own proprietary
discrete component opamps, greatly increasing the manufacturing cost. The final production circuit, aside from the op amp design, was simplified somewhat in order to use fewer op amps. Cello’s Audio Palette was a remarkable success and manufactured for many years.
http://www.burwenaudio.com/images/CELLO_AUDIO_PALETTE.pdf
Wow, I just found the original schematic of the Cello Audio Palette!
The original design used NE5532AN op amps. In the actual Cello Audio Palette they replaced the op amps with discrete components.
INITIAL DESIGN OF THE CELLO AUDIO PALETTE
Richard S. Burwen, March 3, 1984
The accompanying schematic, description, and tentative specifications and features were submitted to Mark Levinson’s Cello Ltd. and became the basis of the Cello Audio Palette tone control system. This design used a large number of integrated circuit op amps. Cello wanted to achieve the best possible performance and avoid any possible criticism of its op amps. They replaced the important signal processing op amps with their own proprietary
discrete component opamps, greatly increasing the manufacturing cost. The final production circuit, aside from the op amp design, was simplified somewhat in order to use fewer op amps. Cello’s Audio Palette was a remarkable success and manufactured for many years.
http://www.burwenaudio.com/images/CELLO_AUDIO_PALETTE.pdf
It is really 'just' made from Rod Elliots discription of Ranes constant-Q EQ circuit
Link
Diff-amps are using OPA2134 dual opamps, where as filters, gain stages (notice there is 3 different gain levels to be used) and buffers are using TL084 quad opamps.
Of course the circuit complexity adds up with 6 frequencies and two channels, and I also had to cure some oscillations when the 20Khz section was in +20dB boost.
Then I added the rest of a 'normal' preamp with input selector, balance control, volume control, phase inverter and a switch to choose from internal EQ - external EQ - both of these - or direct mode.
The result is to my ears really good with neutral and dynamic sound, and actually it is not even possible to hear if the EQ part is coupled in, if all the dials are in zero.
If ever I get to the task of rebuilding with homegrown 'audiophile quality' circuitry, I will gladly share the schematics of that too.
I realized quite some time has passed now, but hey - you probably all know this, many on-going projects and this unit actually works everyday so it can wait a little longer.
And thanx to Henrico11 who localized the schematic!
I have spend countless ( literally hundreds of) hours trying to find just snippets of it, and the trick was just to see what images Mr. Burwen had uploaded on his webpage folder !
However: that circuitry is quite complex, even with op-amps. Though before I go one-transistor-simple with that ( I will not, but at least a little more purist-like) I will definitely look into the exact frequency manipulating sections. There is definitely some genuine engineering-magic in those, and it is especially interesting that Mr. Burwen made the effort and took the time to describe it in detail - that shall not be forgotten in the honor of the project!
I couldn't agree more.
Nrik - Thanks again for the info, I'm very glad you followed up, it is such an interesting project that any information is valuable!
Basing it on a Rod Elliott project is genius - the amount of information on his website is always great, and his stuff is always based in great engineering... I think if I were making one I would use good opamps for the EQ and a discrete output buffer.
However, the Rod Ellott P37a Minimalist Discrete Hi-Fi Preamp might be the discrete op-amp you could use. If it has enough gain for this.
Again, thanks for the info!
Basing it on a Rod Elliott project is genius - the amount of information on his website is always great, and his stuff is always based in great engineering... I think if I were making one I would use good opamps for the EQ and a discrete output buffer.
However, the Rod Ellott P37a Minimalist Discrete Hi-Fi Preamp might be the discrete op-amp you could use. If it has enough gain for this.
Again, thanks for the info!
I've been intensely studying the circuit schematic of the original Cello EQ. Holy crap! Our good friend Mr Burwen was clearly not afraid of using too many Op Amps in his designs. Surely a new and simplified version of this classic design could be done with same or better performance. I would like to see the details of Nrik's version.
I am sure you know what Thorsten posted a while ago :
http://www.diyaudio.com/forums/anal...te-style-eq-design-high-end-tone-control.html
Patrick
http://www.diyaudio.com/forums/anal...te-style-eq-design-high-end-tone-control.html
Patrick
Carl_Huff: yes indeed. I have also studied the schematics closely (I think I even spotted a mistake... R153 should probably go to the positive input of A112B instead of the negative).
However as you can read in Burwens text he is delibaratly using 'low' impedance pots etc to keep noise level low, and also taking care not to overload the opapms outputs.
Anyway: So we know that in the "Audio Palette" (not to be mistaken with the cheaper "Audio Palette Preamp" which features opamps) they used discretely built modules instead of all those opamps. When you look at images of the inside of the Audio Palette you can count : 3 opamp modules on the left, six OTA pcb's, six buffers, and finally 3 opamp modules on the right. ( note that you only see one channel from the top, the other channel is mirrored and can be seen from the bottom).
Now this must mean that they made most of the buffers redundant, and that they probably incorporated all of the frequency 'arms' in one opamp feedback loop instead of two. Now it starts to look exactly like the RANE constant Q EQ from Rod Elliots site, the only difference being, that in the Audio Palette the potmeter feeds the input of all the filters, whose outputs are summed into the feedback loop, whereas RANEs approach sends the output of the filtersections into the potmeter. It will probably not make a big difference anyway.
By looking at images from the internet I have managed to reverse-engineer all these modules topology. Note that ofcourse there can be mistakes, and I dont have all the component values, but you can certainly get an image of what is going on. Notice that in many other Cello products the same kind of modules are used, however there are more versions of each module.
The OTA circuit (output transconductance amplifier) is most definately used as the filter, but I don't actually know for sure where the buffers are used ( before or after the filter, or as buffers for the feedback loop lines). The output impedance of the OTAs must be quite low, since it is running with huge standingcurrent, so I am guessing the buffers are use to isolate the filters from the potmeter. The discrete opamp circuit might also have a very low output impedance, so that is why many of the NE5532s that Burwen used are redundant.
The opamp circuit I didn't reverse engineer from pictures of the pcs in the Cello Audio Palette ( since I could not find any pictures of them detailled enough to see) but it is from the linestage in Mark Levinson ML7 which Tom Colangelo appearantly made right before the Cello Audio Palette, and that looks very much as the same BOM and topology judging from the pictures of the Cello. I regard this as 'close enough' to judge the topology of the circuit.
enjoy:
However as you can read in Burwens text he is delibaratly using 'low' impedance pots etc to keep noise level low, and also taking care not to overload the opapms outputs.
Anyway: So we know that in the "Audio Palette" (not to be mistaken with the cheaper "Audio Palette Preamp" which features opamps) they used discretely built modules instead of all those opamps. When you look at images of the inside of the Audio Palette you can count : 3 opamp modules on the left, six OTA pcb's, six buffers, and finally 3 opamp modules on the right. ( note that you only see one channel from the top, the other channel is mirrored and can be seen from the bottom).
Now this must mean that they made most of the buffers redundant, and that they probably incorporated all of the frequency 'arms' in one opamp feedback loop instead of two. Now it starts to look exactly like the RANE constant Q EQ from Rod Elliots site, the only difference being, that in the Audio Palette the potmeter feeds the input of all the filters, whose outputs are summed into the feedback loop, whereas RANEs approach sends the output of the filtersections into the potmeter. It will probably not make a big difference anyway.
By looking at images from the internet I have managed to reverse-engineer all these modules topology. Note that ofcourse there can be mistakes, and I dont have all the component values, but you can certainly get an image of what is going on. Notice that in many other Cello products the same kind of modules are used, however there are more versions of each module.
The OTA circuit (output transconductance amplifier) is most definately used as the filter, but I don't actually know for sure where the buffers are used ( before or after the filter, or as buffers for the feedback loop lines). The output impedance of the OTAs must be quite low, since it is running with huge standingcurrent, so I am guessing the buffers are use to isolate the filters from the potmeter. The discrete opamp circuit might also have a very low output impedance, so that is why many of the NE5532s that Burwen used are redundant.
The opamp circuit I didn't reverse engineer from pictures of the pcs in the Cello Audio Palette ( since I could not find any pictures of them detailled enough to see) but it is from the linestage in Mark Levinson ML7 which Tom Colangelo appearantly made right before the Cello Audio Palette, and that looks very much as the same BOM and topology judging from the pictures of the Cello. I regard this as 'close enough' to judge the topology of the circuit.
enjoy:
Attachments
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Carl_Huff:
Just to clarify: So the above post is my research of the original Audio Palette, obviously I only built the Rod Elliot version.
EUVL: Yes I did see that ( if you go a couple of posts back in that thread you can even see I tried to advertise THIS thread ) and the topolgy of the EQ circuit is very similar. However the usage of passive components including huge coils and only a single bipolar transistor is obviously SLIGHTLY different from the Audio Palettes approach, and will only appeal to some people.
I am not these people, but I do respect them so I let them have it their way.
Just to clarify: So the above post is my research of the original Audio Palette, obviously I only built the Rod Elliot version.
EUVL: Yes I did see that ( if you go a couple of posts back in that thread you can even see I tried to advertise THIS thread
) and the topolgy of the EQ circuit is very similar. However the usage of passive components including huge coils and only a single bipolar transistor is obviously SLIGHTLY different from the Audio Palettes approach, and will only appeal to some people. I am not these people, but I do respect them so I let them have it their way.
Anyway - low output impedance is might not key, when the outputs just are summed together through voltage dividers. Not that it doesn't matter, but it is possible to calculate. It still looks like the buffers are placed before the filters physically.
The high Idle current in the OTA is probably chosen to get low distortion and high speed.
The high Idle current in the OTA is probably chosen to get low distortion and high speed.