[panomaniac]

Gary, you clever devil!  I spent all morning following traces on that tiny board to come up with the same schematic.  Nice work.  I posted my version over on DIY AUDIO, didn't get a chance to post it here yet.

But you mananged to find the values of L1/L2 C1-C4 which I did not find.  Good work.

I does go to show that the input is really not made for a standard preamps or CD players, but for headphone jacks.  Still wonder why they put in the LC low pass.  To keep RF out?  44.1 kHz out?  

Your observasations about the PCB are spot on.  I've been thinking about rerouting things a bit, too.  Need to get rid of the stock axial inductors, they sing at high power.

I'll post photo of the board when I get home in an hour or two.

[panomaniac]

As promised here are the photos of the PCB, front and back.

[Gary P]

I suspect that the LC filter at the input is to try to keep out of the input stage some of the switching noise the amp generates. With a SMT ferite bead inductor and 100pf the filter should have no effect on the audio portion of the signal. The inductance of the ferite bead type of inductors is usually quite small and lossy. Good for blocking out the RF of the output stage switching.

Just because the inductors sing at full power doesn't mean they are bad. Almost any inductor or transformer in an amplifier will make noise at full power.

I thought of another board mod on the way home from work today. The input  signal ground is just lumped into the ground plane at the input jack. To do things properly there should be a seperate ground connection from the input jack to the ground area at the input section of the amplifier. Would be easy to do if replacing the input jack with RCAs and connecting them up with coax. Would be harder to do if you wanted to keep the stock input plug as you would have to cut the ground plane around the input jack then run a ground wire up to the front of the board.

Gary

[Gary P]

Well, I've spent too much time this evening measuring and thinking. Looks like I've made some decisions for the general mods and what power supply caps to stuff into the little box.

With some carefull work cutting down the threaded portion of some binding posts from the scrap box it looks like they can be fit over the rectangular hole the the spring clips reside in. Also, there is just room to put a pair of RCA jacks above the board on the rear panel. Were talking a couple of milimeters to spare here.

On the board the stock capacitor will be replaced with a Panasonic FM series 1200uf cap. If the inductors are pushed sideways just a bit a 10mm x 25mm cap should fit. Their is enough lead length left on the inductors to raise them slightly then push them sideways just enough to clear the cap.

The RCA's will be directly connected to the input of the amplifier board. The volume pot and wiring harnes wil be scrapped. The knob will be glued to the front of the box to keep it looking good.

With the volume pot gone there is now a large space to add capacitors for the power supply. Four 12.5mm x 35mm Panasonic FM series 3300 uf caps will fit into the space vacated by the volume pot. I still plan on adding a pair of capacitors in the space between the battery compartments and top cover on each side of the amp. 16mm x 32mm Panasonic FC series 4700uf  caps will fit there.

This brings the total capacitance of the onboard supply up to 23,800uf of very low impedance capacitors compared to the cheap generic 330uf cap that comes with the amp. Now the AA batteries will only have to deal with the average current draw and the caps will handle the peak loads.

Looks like there is enough space where the input jack used to be to put the power switch.

If all this works out the amp will have real binding posts, RCA inputs and a substantial power supply all fit in the stock box. It will even look stock from the front view. A sleeper Sonic Impact!

I'll post some pictures as the stages of the project come together.

Gary

[panomaniac]

If all this works out the amp will have real binding posts, RCA inputs and a substantial power supply all fit in the stock box. It will even look stock from the front view. A sleeper Sonic Impact!

See Gary? I told you you were a clever devil.

Are you putting in your Black Gates as input caps?  I'll be using some nice (hope)  Panasonic caps from digikey. On board power cap will be a Panasoic FM series, too.

When you say coax, your just talkng 'bout shielded cable, yeah?  You ain't puttin' RG59 or RG6 in there, I hope!

As for the inductors, yeah, they got pushed pretty hard.  But I think it will be nice to wind my own and see if they make any difference.

Please post pix when you have them.

[JeffB]

Well, I have now received a 12 SLA battery from BatteryMart.  I hooked it up to my SI and the unit now sounds much better.  The music has more detail and a little more punch.  So I pulled out the test tone CD again.  With the added detail things sounded differently.  When playing low frequencies, I now hear clipping at much lower volume levels.  It manifests itself as higher frequency noise than the test tone.  It is kind of like a clicking or like static.  The clipping starts out small and subtle.  As the volume is turned up the static noise grows.  Eventually, the static reaches a point where it transitions rather dramatically from bad to really bad.  It is only this last transition that I was really aware of before.  I was missing that it was actually clipping at a much lower volume.  I don't know how sensitive my speakers are.  Perhaps with significantly more sensitive speakers this clipping would only occur at really high volume levels.  You might never get to the really nasty clipping level.  If as panomaniac's web site indicates that 1/8 of a watt is all that is available before clipping then I guess you can't expect very loud levels without clipping.  Since the bass frequencies are rolled off, in normal music listening, one might not have the volume up loud enough to notice the clipping.

[panomaniac]

You should get about 4.5 watts peak before clipping. The 1/8 watt referred to on my site is RMS average musical power.

Yes, the extreme lows are normally not very present in recorded music.  60~100 Hz and 500~1000 Hz are the hot zones on most music. (The thump-thump you hear from that annoying car is about 100 Hz.)

[JeffB]

panomaniac,

I am curious about your thoughts on power.  Does this rating apply to the 2024 chip itself or is it more a factor of the total circuit?  Would performing some mods provide a little more power.

If I were to guess and say my speakers are 86 db efficient.  Single 4" driver cheap driver and cabinet.
1/8 watt RMS would provide about 77 db at 1 meter.
4.5 watts peak would provide about 90 db peaks.

Of course sitting back 10 feet away volume drops even further.  This is not sufficient for me.   And thus I am always driving the little guy into clipping.  My thoughts would be to buy some speakers that are about 96 db efficient.  This brings the range to between 87 and 100, which is almost there, but I think I would want just a little more power.  So, if circuit mods can get it there that would be good to know.

[panomaniac]

Jeff,
 I don't know yet if modification will wring more power out of this chip, but I doubt it.  When all my parts have arrived modifications will be made and new measurements taken.  Stock, the SI flattens out at 10V, or 2V under supply voltage.  But there is nasty ringing before that, around 8V.  Will better parts raise the clipping threshold?  We shall see.

Like you, my home speakers are low efficeincy (84dB/watt). The Sonic will never do for these speakers, it will always clip.  Like you, I need to build some better, more efficient home speaks.  Will probably go with the EMINENCE BETA-12LTA 12" fullrange and a super tweeter.  Should give about 97dB/watt,  more than enough for the Sonic.  You might like to try the PIONEER B20FU20-51FW 8" full range (with or without super tweeter). Parts Express #290-045

FWIW: At work I listen to a pair of DIY 2 ways, Scan Speak 1.5" tweeter and Dayton 12".  They give about 94 dB/watt.  Last night I measured my average listening level.  Not as hot as I thought. Only 2.25V = 1.25 watts/4 Ohms.  At that level the music needs to be truned down to speak to anyone who drops by - it's loud.   But figuring 18dB headroom, 80 watts peak is needed for good dynamic range.  The Sonic won't do, even though the average level is within its power range.

Hope that helps. Let me know if anything needs clearing up.

[_scotty_]

panomaniac, It sounds like you have the chops to build your own amp with
higher power.  Why not buy a Tripath eval board rated for 100 or 200watts and roll your own.  With minor mods to the board and a proper power supply
you could have your cake and eat it too.  Just my 2cents,  Scotty

[tianguis]

Folks:
       You might want to check out this site. I've corresponded with Jan and his new Amp3 should be available shortly. Check Amp1 and Amp2 for lots of power, but without the convenience and purity of battery power:
http://41hz.com/

Regards,
Larry Welsh

[panomaniac]

panomaniac, It sounds like you have the chops to build your own amp with higher power.

I will Scotty, I will.    1st I wanna fool around with the Sonic.  Next I'll buy an amp or 2 from Jan over at http://41hz.com
All the power I could ever need.  Great prices, too.

[sylbarth]

Dear Gary and Panomaniac,

This is my first message on this forum, that I read with a lot of interest for more than a month. I just received my SI last week and compared it to my Audio Research VT60 tube amp. The main difference is on the bass level which is lower on the Sonic Impact but on all other aspects I think that the SI is more detailed. That's why I read this topic with a lot of interest.

I understand all the modifications that Gary explains but as I'm not a technician there's something that remains unclear for me: How do you solder a Black Gate 4.7uf cap (which is a big cap) in place of C2 and C4 which are very small ceramic caps ? I have the same question about the two resistors that you change to lower the gain ? So how do you do this or could you provide us a photo ?

Thank you again for all of your work.

Sylvain.

[BillyM]

I have heard it from a knowledgeable source that anything above the tripath-suggested 2-3uF cause no measureable increase in frequency response, only resulting an increasingly loud "POP" on power-up.  Another component to look to upgrading to remove the bass roll-off, I have been told, is the RF chokes, but have no definitive answers as of yet.

I have a new set of chokes, gain resistors, and input caps (as well as new power-caps) on their way and some 34hz-flat, 93db-1w/m speakers that show the stock SI's roll-off very well.  I will take actual Ratshack dB measurements before and after the choke replacements, AND again with the input cap replacements.

--BillyM

[Bingo]

Hi gang,
I would like to get in on this thread because I have been doing a lot of listening to my Sonic Impacts(2), which are currently set up in a horizontal bi-wire configuration, with the amp's inputs run out-of-phase(and reversed again on the speaker wire) on a pair of(don't laugh) highly modded-out Klipsch KLF-30's. The amp that powers the mid and high horns has teflon HP caps on it's inputs to hopefully take some of the low end strain off the mids and highs. I won't even tell you about my cheap little preamp... even though it is alot of fun to listen to. I'll loose all respect on that one. Nonetheless, I have a few of questions about the SI. Is this little amp, both an AD converter and digital amp, in the normal sense, and can they be used independtly of each other? Since I hear a lot of how the volume control sounds better at higher positions, is that not only reflecting on the control's sonic degridation as well as running a digital device well below it's "0" output limit? If that would be the case, would it not help if one calibrated the maxium comfortable listening level of their system  by padding down the amp's outputs and having the amp's input levels calibrated to a 0db test tone? That is, if you have a highly efficient speaker system. The main question that I'm struggling with is, is it percievable to think that you could ultimately have an all digital path, with the SI's, and have a volume control just before the raw drivers? I would love to get rid of all those passive crossover components, but how? I'll now go lay down. Get ready for my next crazy question.

[j_luke_12]

Can't resist to take a post. I'm visitng this forum daily specially this thread. I'll be having my T-amp sooner and I'm sure I'm going to do all the mod that you tried and this thread is one of my reference, so how it is?
Hope this story has an ending.

[panomaniac]

 AD converter and digital amp, in the normal sense, and can they be used independtly of each other?

Not that I know of, there is no output from the AD convertor, the connections are made in chip. Since the AD coverstion is made in a unique format "class-T" made to drive the output switches, the digital signal would do you no good, nor could you supply one of your own.

The larger Tripath chips use exteranl switching transisotrs, so the low level digital signal is present there, but again, it is made to run the switching circuits.  Tripath have said tha they plan to make a digital input chip but have not quoted a release date that I know of. They are probabaly all still caught up in the "Godzilla" law suite.

If that would be the case, would it not help if one calibrated the maxium comfortable listening level of their system by padding down the amp's outputs and having the amp's input levels calibrated to a 0db test tone? That is, if you have a highly efficient speaker system.

That is pretty much what I have done.  I run the CD player straight into the SI and use its volume control.  I made a test tone CD with tones at 100% digital level. Playing back these tones it was easy to find the clipping point with an oscilloscope, the clipping was also very obvious to the ear.  As I know that my CD player can never produce a level louder than this, I marked the volume control to indicate "Maximum before Clipping".  I can now run the SI amp at this level or lower without fear of clipping. Alas with my inefficent speakers (84dB/watt) the level is a little low for my tastes. With my set-up the max level is found at 11 o'clock on the SI volume knob.

is it percievable to think that you could ultimately have an all digital path, with the SI's, and have a volume control just before the raw drivers?

No, the Tripath chip does not work that way, there is no digital input. Perhaps when the new all digital chips come out, this would be possible.  But you have to want a volume control somewhere, in some form. Is a digital volume control better than an analog control? We'll leave that for  another thread.  Contoling the volume after the amp would be tricky, you could use L-pads, but I doubt it would sound better.  Bi-amping is a good solution, we use it all the time in pro sound, and there you can have the volume control built into the filters, analog or digital, your choice.

[Bingo]

Thanks for the input, panomaniac.
You seem to know these little amps very well. I have my system set up with my preamp volume control set wide open and the amps at about 11.00 for a nice average, realistic spl.  I am going to try to pad the preamp's output, or reduce the amp's input gains, so I may run the amp's volume controls wide open and still have a clean and comfortable listeng level. I just want to see if the amp's volume contols will sound better that way.  I was just thinking that, in all digital system, if we should put the volume controling device(if any) at the transducer end of the system, for better digital resolution.  Now I need to ask wether or not the SI's are bridged like a regularly bridged amp. If so, can these be used as balanced input ampifiers and how would I then use the output taps.  What kind of output power would be produced? Can these amps have the frequency response digitally altered, within the actual chips, in order to create bandwith limited responses to drive transducers directly, with no outboard crossover? Now I'm losing myself.  Please say, "Yes". By the way, my cat and my dog often listen to music with me, and they didn't like the SI's. Thier ears went down and back. I then added some .1mfd, oil filled-3kv caps across the LF amp's outputs and some .05mfd, oill filled-2kv caps across the HF amp's outputs. Thier ears went back up.

[panomaniac]

I have my system set up with my preamp volume control set wide open and the amps at about 11.00 for a nice average, realistic spl.

Try it the other way around. Open the SI all the way, or better yet bypass the input pot, then use your preamp to change volume. That will tell you if the SI's volume is making things worse or not.

I was just thinking that, in all digital system, if we should put the volume controling device(if any) at the transducer end of the system, for better digital resolution.

It's understandable to want to run your digital signal with as many bits as possible, at least until bit depth goes up to 24 or more.  Just remember that the average level of music is down ~18dB from peak, so the average is only using a small portion of the entire digital word. Resolution can only get worse as the level is digitaly lowered.  That's life...  And that's why in the world of digital image editing we are going to 16 bits per channel, 8 bits just don't cut it. But that's a subject for another thread.

If so, can these be used as balanced input ampifiers and how would I then use the output taps.

Not sure what you mean here.  Do you mean balanced outputs?  If so, then yes, the outputs are balanced, in a way of thinking, because neither side is tied to ground.  In fact you need to be carefull because both the speaker terminals are at +5V above ground.

[qoute]Can these amps have the frequency response digitally altered, within the actual chips, in order to create bandwith limited responses to drive transducers directly, with no outboard crossover?[/qoute]

Perhaps Tripath could do this, but not the average DIYer.  You could build a hi pass or low pass filter around the amp itself, but it might not sound right. I may try it just for fun.  Could run into all sots of phase problems, tho.

 

my cat and my dog often listen to music with me, and they didn't like the SI's. Thier ears went down and back.

My cat doesn't seem to mind, and his hearing is amazing!  
If the cat and dog are really hearing the utrasonic hash, they must be talented indeed.  The hash I see on the o'scope is at 1mHz and above. Pretty good hearing!  But there may be all sorts of other stuff in there that I can't see on the o'scope but the dog and cat can hear. Wish I had a spectrum analyler that could measure between 10kHz and 3mHz.  Would be nice to see what is really in there.

I then added some .1mfd, oil filled-3kv caps across the LF amp's outputs and some .05mfd, oill filled-2kv caps across the HF amp's outputs.

That should tame the ultrasonic hash quite a bit.  Just don't want to roll off too soon, yeah?  FWIW, i have found that a Panasonic FM series electrolytic cap on the PCB power rail cuts the hash by about 6dB - a big improvement.  Other caps, including Solen foil caps gave the same, but no better results.

[superdow]

Anyone heard anything about the upgraded version of the SI T amp to be sold by sonic impact? Wonder what the final upgrades will be, cost, and when available....

http://audioroundtable.com/SolidState/messages/138.html
Posted by Robert Cotton [ 67.113.118.114 ] on February 17, 2005 at 18:30:55:

In Reply to: Re: Doping posted by Ed Schilling on November 25, 2004 at 08:14:46:

We listened and we were impressed. Sonic Impact is reviewing two new products this month that will incorporate all of the comments we received from the field. WE are juicing up the TA2024 with a premium cabinet (wood product of course for low conduction) and tricking it out with heavy dials, 24kt binding posts, inputs for RCA or banana clips and easy access for independent power inputs.

To make things worse, we will be testing a 50 watt per channel version!

Bob Cotton