TREBLE BOOST for PPA, Pimeta, MMM!

[zxc]

This is my first post. Thanks to all who've worked on Pimeta, PPA and MMM. I have just puilt my first Pimeta and I enjoy it a lot. Than I decided that my Senns really need tone controls. I noticed that I could implement the bass-boost circuit on PPA directly to Pimeta.

Then I searched for treble boost; but all I could find was a thread started by doobooloo, a reference to equilizer circuits and a useful but short reply by PPL. What I'd like to see was the right and easy way to implement a treble boost to Pimeta, PPA and MMM.

So all I could do was start a "begging thread from people who could do this (Tangent, PPL, Morsel, ABM, anyone, please...), but despite my total lack of knowledge, I studied all the previous posts and references and here's what I came up with (which might be a total disaster):

Here's where it goes on Pimeta (similar on PPA):

Now all I need is your opinions;
1. Will this work, if not, how I can we modify it to work...
2. If it works, is it like to degrade the sound, or create noise, how can we optimize it?
3. What should be the values on R* and C*?

 

[zxc]

Although it would be great to see someone knowledgable to it; I am willing to modify the schematics, add values according to your replies, and at the end, build, test and report the results here. Thanks!!!

 

[doobooloo]

Awesome. I hope this thread picks up and a nice solution is found.

I really think Head-Fi needs to do a high quality inline passive/active equalizer-ish thing group project.

Anyway...

I can't contribute much in terms of EE knowledge but I'll be keeping up with this thread and help out whenever I can.

 

[amb]

zxc, what you've drawn up is at best a variable treble-cut function, not treble boost. If you want to implement a simplistic treble boost circuit in the feedback loop you'd need an inductor instead of a capacitor, but that's rather inelegant. An alternative is to use a resistor/capacitor network inline with the input, but that again is kludgy.

A more full-fledged tone control with bass and treble boost/cut will involve a lot more parts than that.

 

[zxc]

Thanks a lot for your reply ABM. I was trying to imitate the following but apperantly it's no good. Isn't there a way to implement the following design into Pimeta/PPA/MMM?

Or any of the designs at
http://www.headwize.com/projects/sho...=equal_prj.htm

I was thinking that it wouldn't be so hard because of PPL's following comment about the shematic above:
Quote:

you can add the tone controll circuit showen on headwize where the bass boost is now but all other components in the feedback loop would also have to be changed. basicaly you remove that 1uF cap on the Tone controlls input and connect the outpout of the Tone to the output side of the Bass Boost and the Input side to the inverting input side of the bass boost and ground the tone controll as marked. as far as what component values need to be changed to make this work is somthing you have to figure out.

PPL's description was a bit dense, so I couldn't clearly understand what exactly to do. Any ideas, comments, suggestions would be greatly appreciated.

 

[amb]

zxc, ask and you shall receive!

in the figure 1b diagram, notice that both opamps are configured to operate in inverted mode. The Baxandall tone control network is actually in both the input and the feedback portion of the second stage. Since the M³, PPA and Pimeta all operate in a non-inverting mode there you can't apply that tone control network in quite the same way.

Figure 1 is an all-passive control but it is lossy (i.e., there is a 20dB loss at flat setting).

Shown below is an example implementaion of the Baxandall circuit in a non-inverting topology. The "opamp" could be a cmoy-style amp, or it could be representative of the entire amp block of the M³, PPA, Pimeta including the buffer, or even a Gilmore amp. The gain is 11 when flat, and there is a defeat switch to give you truely flat response (better than what might be achieved by simply setting to bass/treble pots to the center positions). That switch has to be a shorting type (make before break) to prevent switching transients. It is shown in "defeat" position. If you change the gain of the amp you'll have to alter the values of all other tone control parts.

Note that PCB modifications are required in order to integrate this into an existing amp.

Have fun.

 

[zxc]

Amazing. Thanks a lot amb. This is exactly what I wanted. Now, before I go ahead build it:

1. Would it be possible to use 50K potentiometer instead of the 100K one, so that we can use the ALPS or the Panasonic EVJ; would it require a change on the values of the other resistors or caps? (what would be the changes.) I couldn't find a 100K EVJ on digikey. Or is there a descent 100K pot that we can use?

2. Do we still keep the R6 (1M) between (1) and (2)?

3. Do we keep the Buffer and the Jfet cascode between (2) and (3), or do we move them between (3) and the output?

Thanks again...

 

[amb]

zxc, you need linear taper (not log or audio taper) pots for the bass and treble, or else in the "center" setting you will not get anything near a "flat" response. The pot values can be changed to 50K if you wish, but I suggest you keep the values as they are, because they're based on an actual preamp that I built (long ago) and it works well. The 316 ohm and 499 ohm resistors are there to fine-tune things and you may experiment with the values there. When I built this circuit I used special pots for tone control use, that has a detent in the center position, and I wanted to get the response as flat as possible there.

The diagram I drew does not include the inner loop of a Jung multiloop setup, but for those amps that have it, leave them in just as they were.

As I said, the "opamp" symbol in the schematic I drew is representative of the whole amp, so the jfet cascode and buffer is all part of that. The tone control stuff is all part of the global feedback loop, taken from the output of the final stage of the amp.

 

[Sovkiller]

Nevermind!!!

 

[amb]

sovkiller, I think zxc wanted to add tone control capability to one of the diy amps rather than buying a commercial product.

 

[Sovkiller]

Quote:

Originally Posted by amb sovkiller, I think zxc wanted to add tone control capability to one of the diy amps rather than buying a commercial product.

Sorry for my suggestion, you are absolutelly right....

 

[SDA]

Quote:

Sometimes a commercial product is a lot cheaper and the easiest way to get what you want, instead of trying a DIY complicated, and at the end, less satisfactory product. Don't forget that you are "adding" to a final product, that was not intended to have this circuit inside. OTOH while you design from scratch having those requirements in mind since the beginning, it is easier to get a better and easiest solution....Just my two cents, unfortunatelly the audiphile world has nothing to do with tone controls, equalization, and real world problems....

And sometimes at the end having something you built, understand, and are able to maintain yourself is much more satisfying than buying a possibly inferior complete product out of laziness. Besides, what makes you say that the amplifier you've linked to is automatically a "better" solution? Do you speak from experience, or are you guessing based on the opinions of others with no relevant (applicable to this situation) experience? And lastly, what's wrong with adding to an existing circuit in such a way that doesn't interfere with what's already in place (especially when doing so will let you utilize the advantages of the existing amplifier and/or save you the cost of buying a new one)?

In fact, I can summarize that paragraph with a single question: how is buying an inexpensive (and likely inferior) amplifier with the feature that you want to have better in any way (with the obvious exception of effort expended) than developing a design that allows you to add aforementioned feature to one of many popular established DIY amps?

I'm not saying that DIY is always a better approach, of course, merely pointing out that going commercial is actually not an obviously superior route in this situation. More specifically, I'm pointing out that your proposal is based on flawed assumptions (that the finished product is better; that the DIY product will definitely be less satisfactory; that you gain nothing for the extra effort spent; I could go on, but then the Semicolon Police would arrest me), and that there are reasons beyond curiosity (reasons beyond wanting to learn, even!) for wanting to make a treble boost instead of buying an amplifier with that feature built in.

I do agree with the last part, though. Equalizers are something of a guilty pleasure for me, and I wish they'd get more mention. I'm really happy to see a thread like this, I just wish there were more...

 

[Sovkiller]

Quote:

Originally Posted by SDA And sometimes at the end having something you built, understand, and are able to maintain yourself is much more satisfying than buying a possibly inferior complete product out of laziness. Besides, what makes you say that the amplifier you've linked to is automatically a "better" solution? Do you speak from experience, or are you guessing based on the opinions of others with no relevant (applicable to this situation) experience? And lastly, what's wrong with adding to an existing circuit in such a way that doesn't interfere with what's already in place (especially when doing so will let you utilize the advantages of the existing amplifier and/or save you the cost of buying a new one)? In fact, I can summarize that paragraph with a single question: how is buying an inexpensive (and likely inferior) amplifier with the feature that you want to have better in any way (with the obvious exception of effort expended) than developing a design that allows you to add aforementioned feature to one of many popular established DIY amps? I'm not saying that DIY is always a better approach, of course, merely pointing out that going commercial is actually not an obviously superior route in this situation. More specifically, I'm pointing out that your proposal is based on flawed assumptions (that the finished product is better; that the DIY product will definitely be less satisfactory; that you gain nothing for the extra effort spent; I could go on, but then the Semicolon Police would arrest me), and that there are reasons beyond curiosity (reasons beyond wanting to learn, even!) for wanting to make a treble boost instead of buying an amplifier with that feature built in. I do agree with the last part, though. Equalizers are something of a guilty pleasure for me, and I wish they'd get more mention. I'm really happy to see a thread like this, I just wish there were more...

OK, I'm not saying that it is a better solution, but who knows if it could be a better solution?.....But at the end, it is true, I don't care, they are not mine, and I have no affiliation with the aforementioned amp or company (just for the records OK?) So please do as you wish and spend your time, efford, and money, the way you feel is right for you....
Sorry if I bother anybody with my suggestions...

 

[setmenu]

It does not seem to be an excessive amount of trouble to create a little 'satellite' test board for the Pimeta to try out a tone control circuit.

What's with all this fuss about buying a commercial amp ?

It seems all zxc wants is to do a little educational experimentation.


Setmenu

 

[zxc]

Amb, I am glad I asked about the potentiometer; even without knowing what the actual problem was

One last question before building it: Do you have any recommendations on the potentiometer? I searched digikey and mouser; and here's the only thing that I could come up with:
http://www.mouser.com/index.cfm?&han...*&N=0&crc=true
I have no idea how this will perform as a tone control potentiometer and I doubt that it has a detent in the center position. Which was the one you used; or any recommendations/ideas on something that will work, or is likely to work...

And yes; I wanted a tone-control circuitry, (which is exactly what you've provided) that can be implemented on most of the wonderful designs at head-fi. Now in future I can even use a PPA as my preamp and have descent tone controls on my home stereo

But first let's see how it will work on my Pimeta...

SDC, you are absolutely right; I allmost feel ashamed to say that I like tone controls. But I like them; treble boost puts the soul back into the music for me, and bass-boost is a must at low volumes (again, for me). And it seems that there are a lot of people in my situation. I understand that it might color the sound etc; but... I sold my Creek 5350SE just because it didn't have tone controls; and switched to an Arcam A75. By the way; the 20 year old Sansui AU-G99X was dead quite when tone controls were defeated, but had an ugly hiss when they were activated. But the Arcam is dead quiet no matter what. So I hope this is going to be something similar.

It seems that all I need is an advice on the potentiometer. I will then go ahead and order the parts and build it; and let you know about the results. Thanks, especially to amb for his help; and hopefully, the rest of us who are incapable of designing their own tone-controls can enjoy the music more... If anyone has any more ideas or suggestions; please post here.

{By the way, the picture you see on the left is an ATM playing a song on Windows Media Player. A new installed ATM (National City) crashed and rebooted at CMU campus

Isn't that fun? I can't believe they use Windows XP!!!}