PC to MAC
If you could be a bit more specific on what area you nedd assistance tranfering from the PC, I'm wiiling to help. I use mainly Macs and also have a couple PCs that run Gigastudio, so I have pretty good experience tranfering tons of data from both kind of machines.
Tell more.
Cheers
Ric
If you could be a bit more specific on what area you nedd assistance tranfering from the PC, I'm wiiling to help. I use mainly Macs and also have a couple PCs that run Gigastudio, so I have pretty good experience tranfering tons of data from both kind of machines.
Tell more.
Cheers
Ric
Eric,
I've only built up one on test bench. I'm putting the chassis together over the next couple of days. I'm building them as monoblocks with switches to allow comparison of one module per chassis per channel vs. bridged monoblocks. I'm going to use one 500 VA transformer per channel in the PS using 35VAC secondaries. Thus, I won't have any auditory data for a few days; but I'll post it ASAP.
Vivek,
You need an oscilloscope; otherwise you'll only be guessing and wondering before it self-destructs or wipes out some tweeters.
Ricen,
The files are for ExpressPCB. It's not an image file. I'll try to attach it below (its a circuit for the STK4048XI--it dropped the file during the preview, oh well...). If this doesn't work (which it didn't), then I'll transfer the files to my Mac and upload them to my web page and let others download them from there. I just don't have the programs to upload (or the know-how) from this PC. I using a dial up right now because my DSL doesn't seem to be working...)
Regards, Robert
I've only built up one on test bench. I'm putting the chassis together over the next couple of days. I'm building them as monoblocks with switches to allow comparison of one module per chassis per channel vs. bridged monoblocks. I'm going to use one 500 VA transformer per channel in the PS using 35VAC secondaries. Thus, I won't have any auditory data for a few days; but I'll post it ASAP.
Vivek,
You need an oscilloscope; otherwise you'll only be guessing and wondering before it self-destructs or wipes out some tweeters.
Ricen,
The files are for ExpressPCB. It's not an image file. I'll try to attach it below (its a circuit for the STK4048XI--it dropped the file during the preview, oh well...). If this doesn't work (which it didn't), then I'll transfer the files to my Mac and upload them to my web page and let others download them from there. I just don't have the programs to upload (or the know-how) from this PC. I using a dial up right now because my DSL doesn't seem to be working...)
Regards, Robert
Vivek,
A basic set up would be the following:
Send in a 1kHz sine wave signal around 30 mV. Have an 8 ohm dummy load connected to the amp, along with an oscilloscope connected to this same load (in parallel). Turn on the amp and look at the signal. If all is OK, you'll see a nice clean sine wave. If the amp is oscillating, you'll see a sine wave that is not thin but very thick. It is 'thicker' due to superimposed oscillation at a much greater frequency, like 1 MHz. If you spread out the sine wave you can see at what frequency these smaller waves are buried within the 1kHz signal.
A better system would generate the sine wave from a distortion analyzer. This is what I use. Now you can also look on the oscilloscope at the distortion products. These will also show oscillatory components if present.
A safer system would incorporate some current limiting with the above test set-up. What I use is a 40 W light bulb in series with the AC supply of the amp being tested. If the light bulb immediately starts glowing with only a small input signal, you might have a short circuit or some other major problem. Oscillation will also cause the bulb to shine. If all is OK, the bulb will briefly shine then dim once the amp has stablized. As you increase the input signal, however, the bulb will eventually brightly shine and the output of the amp will clip. This occurs at the wattage of the bulb as the bulb is limiting the current. With this set-up you often don't need an expensive variac. It can be made from an extension cord with a light bulb socket inserted in one leg of the AC line.
******
My parts arrived today, so I should be able to finish off the STK amps this weekend and listen to them. I've uploaded the STK ExpressPCB file onto one of my web sites. If this works, you can download the STK module board at: http://207.158.252.106/PCBs/STK4048d.pcb. I'll post some other boards in a separate thread once I've sorted out which board is which.
I offer no support. These boards work as is, and you're free to modify them, but then you're really on your own. If you should use these boards, or derivative thereof, in any commercial product, then give me some credit; otherwise they're 'freeware'. To purchase the boards, and more importantly to be able to view them, download free software from: http://www.expresspcb.com/. Please note that I make no profit from the boards, nor have any association with ExpressPCB except for the fact that I'm one of their customers.
On the pcb, I've indicated the values of each component. While you won't get a silkscreen image, you will see the text of component values written in plated copper (a poor man's silkscreen). Most of my boards are 'miniboards'. If you order the basic miniboards they are 3 for about $60, and are 2.5x3.75 inches.
Once I get organized, I'll post more boards and images of what they look like stuffed. (I'll probably need to post some sort of stuffing guide for the active X/O as it is a very complicated stereo pcb with SMT components on both sides along with rectifier bridge, transformer and in line primary fuse--all on one miniboard.)
Regards, Robert
A basic set up would be the following:
Send in a 1kHz sine wave signal around 30 mV. Have an 8 ohm dummy load connected to the amp, along with an oscilloscope connected to this same load (in parallel). Turn on the amp and look at the signal. If all is OK, you'll see a nice clean sine wave. If the amp is oscillating, you'll see a sine wave that is not thin but very thick. It is 'thicker' due to superimposed oscillation at a much greater frequency, like 1 MHz. If you spread out the sine wave you can see at what frequency these smaller waves are buried within the 1kHz signal.
A better system would generate the sine wave from a distortion analyzer. This is what I use. Now you can also look on the oscilloscope at the distortion products. These will also show oscillatory components if present.
A safer system would incorporate some current limiting with the above test set-up. What I use is a 40 W light bulb in series with the AC supply of the amp being tested. If the light bulb immediately starts glowing with only a small input signal, you might have a short circuit or some other major problem. Oscillation will also cause the bulb to shine. If all is OK, the bulb will briefly shine then dim once the amp has stablized. As you increase the input signal, however, the bulb will eventually brightly shine and the output of the amp will clip. This occurs at the wattage of the bulb as the bulb is limiting the current. With this set-up you often don't need an expensive variac. It can be made from an extension cord with a light bulb socket inserted in one leg of the AC line.
******
My parts arrived today, so I should be able to finish off the STK amps this weekend and listen to them. I've uploaded the STK ExpressPCB file onto one of my web sites. If this works, you can download the STK module board at: http://207.158.252.106/PCBs/STK4048d.pcb. I'll post some other boards in a separate thread once I've sorted out which board is which.
I offer no support. These boards work as is, and you're free to modify them, but then you're really on your own. If you should use these boards, or derivative thereof, in any commercial product, then give me some credit; otherwise they're 'freeware'. To purchase the boards, and more importantly to be able to view them, download free software from: http://www.expresspcb.com/. Please note that I make no profit from the boards, nor have any association with ExpressPCB except for the fact that I'm one of their customers.
On the pcb, I've indicated the values of each component. While you won't get a silkscreen image, you will see the text of component values written in plated copper (a poor man's silkscreen). Most of my boards are 'miniboards'. If you order the basic miniboards they are 3 for about $60, and are 2.5x3.75 inches.
Once I get organized, I'll post more boards and images of what they look like stuffed. (I'll probably need to post some sort of stuffing guide for the active X/O as it is a very complicated stereo pcb with SMT components on both sides along with rectifier bridge, transformer and in line primary fuse--all on one miniboard.)
Regards, Robert
Bridged STK4048XI
Eric,
I completed the bridged STK4048XI monoblocks this weekend, using a 500VA power transformer with 30,000 microfarads per rail per monoblock (so 120,000 for the stereo amp). The rails are running at +/-50VDC with load. Power output is about 350 W/8ohms (53V RMS). I tested it up to 350 W into 4 ohm load with no problem. I did not test with a 2 ohm load, but the amp doesn't even warm up after playing all day on the Quad 988's which dip to almost 2 ohms around 10 kHz (as I seem to recall). I used two 2U, 250 mm depth powerbox chassis (multibox instrument case with integral heat sinks; ph for US distributor 303-439-7220).
The amps are running fully balanced with each STK module acting as a non-inverting type of op amp if you will, one receiving the + input, the other, the - input. The load is floating between their outputs. Each amp is as described in the app notes except for the following mods (referencing the Sanyo app notes): C6, C7, C9 are 220 pF ceramic COG types; R1, R4=619ohms; R2, R5=20kOhm; C3=2,200 microfarads x 2, creating a non-polar cap; C10, C13=1,000 microfarad; C11, C12=150 microfarads; all electrolytics are bypassed with 0.1 microfarad film (SMT on bottom of pcb previously discussed); there is no input DC cap; output resistors are thick-film types in 20W/TO-220 packages.
As I previously mentioned, I don't have a balanced test set-up so none were run, although each part of the bridge when run as a single ended amp, showed the same low distortion as previously discussed in this thread, producing 112W/8ohm with +/-50VDC rails.
As for listening tests, using the Quad 988 full range (with LPs, SACD, CDs), the improvement over the stock STK4048XI was incredibly obvious to all who listened. The bass was absolutely the best I've heard from the Quads running solo with details in the lower registers that I'd previously missed with other amps (this includes the Tripath 104 which is in the same power league as these bridged amps). Dynamics were wonderful (remember the slew rate doubles when bridged, so it should be on the order of 40 microvolts/sec). The soundstage was larger, highs seemed somehow crisper, but not strident nor harsh. Depth was the same as the s.e. stereo STK version, but details were better delineated. (The s.e. STDK version is DC coupled; I think this bridged version is better and certainly safer with respect to DC offset.)
Regards, Robert
Eric,
I completed the bridged STK4048XI monoblocks this weekend, using a 500VA power transformer with 30,000 microfarads per rail per monoblock (so 120,000 for the stereo amp). The rails are running at +/-50VDC with load. Power output is about 350 W/8ohms (53V RMS). I tested it up to 350 W into 4 ohm load with no problem. I did not test with a 2 ohm load, but the amp doesn't even warm up after playing all day on the Quad 988's which dip to almost 2 ohms around 10 kHz (as I seem to recall). I used two 2U, 250 mm depth powerbox chassis (multibox instrument case with integral heat sinks; ph for US distributor 303-439-7220).
The amps are running fully balanced with each STK module acting as a non-inverting type of op amp if you will, one receiving the + input, the other, the - input. The load is floating between their outputs. Each amp is as described in the app notes except for the following mods (referencing the Sanyo app notes): C6, C7, C9 are 220 pF ceramic COG types; R1, R4=619ohms; R2, R5=20kOhm; C3=2,200 microfarads x 2, creating a non-polar cap; C10, C13=1,000 microfarad; C11, C12=150 microfarads; all electrolytics are bypassed with 0.1 microfarad film (SMT on bottom of pcb previously discussed); there is no input DC cap; output resistors are thick-film types in 20W/TO-220 packages.
As I previously mentioned, I don't have a balanced test set-up so none were run, although each part of the bridge when run as a single ended amp, showed the same low distortion as previously discussed in this thread, producing 112W/8ohm with +/-50VDC rails.
As for listening tests, using the Quad 988 full range (with LPs, SACD, CDs), the improvement over the stock STK4048XI was incredibly obvious to all who listened. The bass was absolutely the best I've heard from the Quads running solo with details in the lower registers that I'd previously missed with other amps (this includes the Tripath 104 which is in the same power league as these bridged amps). Dynamics were wonderful (remember the slew rate doubles when bridged, so it should be on the order of 40 microvolts/sec). The soundstage was larger, highs seemed somehow crisper, but not strident nor harsh. Depth was the same as the s.e. stereo STK version, but details were better delineated. (The s.e. STDK version is DC coupled; I think this bridged version is better and certainly safer with respect to DC offset.)
Regards, Robert
Resistors
Eric,
I get almost all of my parts from Digikey (http://www.digikey.com/). The resistors are coded TAH20PR220J-ND. These are 0.22 ohm/20W each; unfortunately, they're $4.38 each for quantities of 1-49. I used 4 per board x 4 boards + a 3.9 ohm per board on the output (in series with the inductor). These are found on page 594 in their latest catalog; or search on-line for the above part.
Ric,
I mentioned in my last post that I cannot measure distortion as I don't have a balanced set-up. The even order distortion should be reduced by 6 dB or so as the amp is running in truly balanced bridged mode. This is not to be confused by the typical bridged amp that is run from a singled ended source and has one-half of the amp running more as a slave to the other half. In the set-up I'm using, each STK module receives half of the signal and controls the speaker load in a truly push-pull fashion. I'm sure this is why the bass and all detail is so much better.
I'm next going to try and tackle the TDA7293V, running it in parallel-bridged mode, but again not the pseudo-bridged mode that ST describes in their app note. (BTW, the ST app note on the TDA7293V has a typo on page 10/13: pins 2,3 are shown going to V-. They are not to go to V-, but to ground. (Pin 4 does go to V- as shown.) Once I do this over the next few weeks, I'll post in a separate thread. I've already made the pcb and have the parts, so it's just a matter of time...
Regards, Robert
Eric,
I get almost all of my parts from Digikey (http://www.digikey.com/). The resistors are coded TAH20PR220J-ND. These are 0.22 ohm/20W each; unfortunately, they're $4.38 each for quantities of 1-49. I used 4 per board x 4 boards + a 3.9 ohm per board on the output (in series with the inductor). These are found on page 594 in their latest catalog; or search on-line for the above part.
Ric,
I mentioned in my last post that I cannot measure distortion as I don't have a balanced set-up. The even order distortion should be reduced by 6 dB or so as the amp is running in truly balanced bridged mode. This is not to be confused by the typical bridged amp that is run from a singled ended source and has one-half of the amp running more as a slave to the other half. In the set-up I'm using, each STK module receives half of the signal and controls the speaker load in a truly push-pull fashion. I'm sure this is why the bass and all detail is so much better.
I'm next going to try and tackle the TDA7293V, running it in parallel-bridged mode, but again not the pseudo-bridged mode that ST describes in their app note. (BTW, the ST app note on the TDA7293V has a typo on page 10/13: pins 2,3 are shown going to V-. They are not to go to V-, but to ground. (Pin 4 does go to V- as shown.) Once I do this over the next few weeks, I'll post in a separate thread. I've already made the pcb and have the parts, so it's just a matter of time...
Regards, Robert
gaincard clone?
Hi Robert.
just curious: did you read about the gaincard and the "miths and legends" related?
I build a couple of clones and they sound very good. I wonder how they compare to the STKs. (I ordered 5 of them to follow your steps). Previously I've considered the 7294, but I couldn''t find a comercial good sounding amp using them. I heard them in the Tannoy active mopnitor 800 (biampled) and the Event monitors (biamped too), And always heard some kind of distorsion that is not present in other designs.
So for now I'm considering a biamped sistem with an STK for the woofer, an the LM 3875 for mid/high. (five of them) and then a sub. Target specs are : lowest distorsion and dinamics.
I'll wait anxiouxly for your veredict on the 7293.
Cheers
Ric
Hi Robert.
just curious: did you read about the gaincard and the "miths and legends" related?
I build a couple of clones and they sound very good. I wonder how they compare to the STKs. (I ordered 5 of them to follow your steps). Previously I've considered the 7294, but I couldn''t find a comercial good sounding amp using them. I heard them in the Tannoy active mopnitor 800 (biampled) and the Event monitors (biamped too), And always heard some kind of distorsion that is not present in other designs.
So for now I'm considering a biamped sistem with an STK for the woofer, an the LM 3875 for mid/high. (five of them) and then a sub. Target specs are : lowest distorsion and dinamics.
I'll wait anxiouxly for your veredict on the 7293.
Cheers
Ric
Yes, I did read about the gaincard; very interesting. As I understand the various threads, it seems to use the LM3875, which has the same topology as the LM3886 (in the Rowland, for example)--except the 3875 does not have the mute feature, which is may be a plus.
In any event, I'd suggest you try the STK on the highs and not just the LM3875. My logic behind this statement is based on what I've just discovered and discussed in this thread. Namely that the single ended STK set up sounds remarkably similar to the Rowland which uses the LM3886 style IC. The 3875 probably sounds very much like the 3886. The model 10 uses bridged LM3886s, yet sounds like the single ended STK. The bridged STK sounds vastly superior to these two. Therefore, I'd suspect the bridged STK will sound superior to the LM3875 gaincard style amp.
Now as for the TDA7293V, I'm not sure. I have compared a single ended TDA7294V to the Tripath '104, and the latter was superior. I believe the bridged STK is better than the Tripath (it is certainly more reliable: my 104 is sitting waiting for me to replace a pair of blown output mosfets). However, when bridged the STK improved tremendously, which leads me to be uncertain as to how a bridged TDA7293V will perform. The TDA may be better; I need to test it out.
To clarify what we heard with the fully balanced and bridged STK, let me say that the air on the bridged STK amp is extraordinarily good. So besides markedly better bass, the upper registers were also improved. As an example, my wife and I were listening to a flute piece that was part of a demo CD used at a recent CES. My wife happens to play the flute, and when we were listening to this track, she said this about the best flute sound that she'd ever heard. Furthermore, she said that what we were hearing was what it sounds like to her when she is actually playing the flute. To put it another way, she says that sometimes we go back and forth trying to hear any differences between various pieces of equipment. With this amp, the differences are so easily heard as to be ridiculous. This is why I'm now much more convinced that a fully balanced, bridged amp is superior.
And I'm not referring to the pseudo-bridged garbage that is so typically used. In these cases, the output of one amp is fed to a second amp via it's feedback loop, with the second one having it's input grounded. Another method is where the second amp has as it's input the attenuated output of the first amp. In either of these situations, the second amp is a slave, not an equal partner. This is why most bridged amps sound horrible. It can be a fairly inexpensive way of upping the power rating (inexpensive that is, if the impedance capabilities are ignored). Another variation, which is not truly balanced, and certainly not bridged, is were the positive portion of a balanced source is fed to the non-inverting input, and the negative portion to the inverting input. This is not fully balanced since the inverting input also is contending with the feedback loop. (This is featured on many amps to offer an XLR input.)
Therefore, a properly balanced, bridged amp simply uses two standard amps, each running non-inverted, in true push-pull configuration. Each half of the input signal is treated identically, the whole amp is more linear, and this can lead to better control of the load since the whole amp is push-pull. This, of course, requires a balanced line source, or at the very least, a phase splitter on the input to the amp if only single ended sources are available.
Regards, Robert
In any event, I'd suggest you try the STK on the highs and not just the LM3875. My logic behind this statement is based on what I've just discovered and discussed in this thread. Namely that the single ended STK set up sounds remarkably similar to the Rowland which uses the LM3886 style IC. The 3875 probably sounds very much like the 3886. The model 10 uses bridged LM3886s, yet sounds like the single ended STK. The bridged STK sounds vastly superior to these two. Therefore, I'd suspect the bridged STK will sound superior to the LM3875 gaincard style amp.
Now as for the TDA7293V, I'm not sure. I have compared a single ended TDA7294V to the Tripath '104, and the latter was superior. I believe the bridged STK is better than the Tripath (it is certainly more reliable: my 104 is sitting waiting for me to replace a pair of blown output mosfets). However, when bridged the STK improved tremendously, which leads me to be uncertain as to how a bridged TDA7293V will perform. The TDA may be better; I need to test it out.
To clarify what we heard with the fully balanced and bridged STK, let me say that the air on the bridged STK amp is extraordinarily good. So besides markedly better bass, the upper registers were also improved. As an example, my wife and I were listening to a flute piece that was part of a demo CD used at a recent CES. My wife happens to play the flute, and when we were listening to this track, she said this about the best flute sound that she'd ever heard. Furthermore, she said that what we were hearing was what it sounds like to her when she is actually playing the flute. To put it another way, she says that sometimes we go back and forth trying to hear any differences between various pieces of equipment. With this amp, the differences are so easily heard as to be ridiculous. This is why I'm now much more convinced that a fully balanced, bridged amp is superior.
And I'm not referring to the pseudo-bridged garbage that is so typically used. In these cases, the output of one amp is fed to a second amp via it's feedback loop, with the second one having it's input grounded. Another method is where the second amp has as it's input the attenuated output of the first amp. In either of these situations, the second amp is a slave, not an equal partner. This is why most bridged amps sound horrible. It can be a fairly inexpensive way of upping the power rating (inexpensive that is, if the impedance capabilities are ignored). Another variation, which is not truly balanced, and certainly not bridged, is were the positive portion of a balanced source is fed to the non-inverting input, and the negative portion to the inverting input. This is not fully balanced since the inverting input also is contending with the feedback loop. (This is featured on many amps to offer an XLR input.)
Therefore, a properly balanced, bridged amp simply uses two standard amps, each running non-inverted, in true push-pull configuration. Each half of the input signal is treated identically, the whole amp is more linear, and this can lead to better control of the load since the whole amp is push-pull. This, of course, requires a balanced line source, or at the very least, a phase splitter on the input to the amp if only single ended sources are available.
Regards, Robert
Simple Test Kit
Hi Robert,
pity about the price of those resistors - seems like worth trying though.
An interesting experiment is to plug a 'Y' lead into the L&R inputs of a stereo amp, connect a loudspeaker between the two output active terminals, give a mono signal and juggle the L&R volume pots.
This arrangement will provide flipable polarity and variable level, with an active virtual ground.
This is true balanced input throughput and output and IME this is better than SE connection.
With this setup, you can dictate both the operating level of the amplifier stages and the SPL independently.
Also by balancing the levels to achieve a speaker SPL null, the matching of the two amp stages can be simply gauged.
Try it and you'll like it.
Regards, Eric.
Hi Robert,
pity about the price of those resistors - seems like worth trying though.
An interesting experiment is to plug a 'Y' lead into the L&R inputs of a stereo amp, connect a loudspeaker between the two output active terminals, give a mono signal and juggle the L&R volume pots.
This arrangement will provide flipable polarity and variable level, with an active virtual ground.
This is true balanced input throughput and output and IME this is better than SE connection.
With this setup, you can dictate both the operating level of the amplifier stages and the SPL independently.
Also by balancing the levels to achieve a speaker SPL null, the matching of the two amp stages can be simply gauged.
Try it and you'll like it.
Regards, Eric.
I've used them both single ended and balanced bridged with my Quad 988s and with a friend's Martin-Logans (small ones, Aerius?) with no problems. They are very stable if built as I've described, but please read carefully through the thread as there were changes while building and testing.
regards, Robert
regards, Robert
couple random questions
robert,
- have you tried removing C3 (the DC blocking cap in the feedback shunt) altogether? i know it is there to reduce DC gain but does the amp still work ok w/o it? specifically, is DC stability a problem? i've used caps here before (Black Gate NP) but some people seem to think this is one of the worst places to have a cap in this type of circuit.
- have you tried the amp in an inverting configuration? i think most opamps perform, or at least sound, better when fed thru inverting input. i wonder if this chip would be stable in that setup.
cheers,
dorkus
robert,
- have you tried removing C3 (the DC blocking cap in the feedback shunt) altogether? i know it is there to reduce DC gain but does the amp still work ok w/o it? specifically, is DC stability a problem? i've used caps here before (Black Gate NP) but some people seem to think this is one of the worst places to have a cap in this type of circuit.
- have you tried the amp in an inverting configuration? i think most opamps perform, or at least sound, better when fed thru inverting input. i wonder if this chip would be stable in that setup.
cheers,
dorkus