Yes, the fast mute circuitry around the power switch, the Schottky diode and the enable pin is effective...but only when the chip is powered, when the rails fall below a threshold, chip internal mute is not effective anymore and you hear small noise.
Interresting, that may indicate that the noise is also related to the opa1642.
I have an AKG K240 MkII, 55R.
During AmpCasq design, I used an XL file (found on DIYA) to confirm that +/-5 supply was enough for it.
Not an issue, it works fine from 8.5V, let says 9V.
Using 'big' SMPS (yours is 4A, near 70W) is not the best choice, because they will be mainly unloaded thus operating in discontinuous mode. In this mode the supply is switched on and off at low frequency which may be audible. No rule, just think about it and make your own tests.
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Good info... I will procure a smaller power supply and test. I guess I could try pure DC from a 9volt battery and see if there is any audible difference.
I just got thru drilling out all the holes in the case, took me a few hours but it fits nicely and all I need to do is to spray paint the panels.
I also mounted a heatsink I had in my toolbox on the 7805...just for insurance!
I listened last night for an hour not comparing with my other amps, but it sounds great so far.
The Beyer T90s really like this amp..these are really "crisp" headphones...when you play nice stuff they sound "nice" ...play carp and its really "bad"...great for analytical listening and comparing amps..brutally honest.
I will post some pix when I get the panels painted....just going to listen for now and see how well it plays all boxed up in the enclosure..
Alex
I just got thru drilling out all the holes in the case, took me a few hours but it fits nicely and all I need to do is to spray paint the panels.
I also mounted a heatsink I had in my toolbox on the 7805...just for insurance!
I listened last night for an hour not comparing with my other amps, but it sounds great so far.
The Beyer T90s really like this amp..these are really "crisp" headphones...when you play nice stuff they sound "nice" ...play carp and its really "bad"...great for analytical listening and comparing amps..brutally honest.
I will post some pix when I get the panels painted....just going to listen for now and see how well it plays all boxed up in the enclosure..
Alex
Power Supply
Just think that the ON/OFF cycle of the smps may goes through the amp, but make your own opinion with some listening session before buying anything else, there's so much regulation and Power Supply Rejection Ratio with the two OPA chips on the board that changing power source may not affect SQ.
Typical requirements for power source are 12VDC / 300mA.
Sorry for english, or lets' say globish...
Chris
Just think that the ON/OFF cycle of the smps may goes through the amp, but make your own opinion with some listening session before buying anything else, there's so much regulation and Power Supply Rejection Ratio with the two OPA chips on the board that changing power source may not affect SQ.
Typical requirements for power source are 12VDC / 300mA.
Sorry for english, or lets' say globish...
Chris
I ordered a Jameco regulated linear dc adapter....12 vdc 1 amp. even though I dont think it will make any real world difference it will be nice to know for sure.....I like testing stuff, then I can say for real and comment on the affects good or bad.
I also ordered a few knobs to try for the volume pot.
I have compared to one of the O2 amps I have and so far they sound pretty much the same to me...both good. I will setup a blind AB test in a few days. My objectivity is as bad as most!! LOL....after spending time building there is a part of my brain that wants the new toy to sound really good!!
Chris have you done any power calculations for power available (output) at 300 ohms?
Alex
I also ordered a few knobs to try for the volume pot.
I have compared to one of the O2 amps I have and so far they sound pretty much the same to me...both good. I will setup a blind AB test in a few days. My objectivity is as bad as most!! LOL....after spending time building there is a part of my brain that wants the new toy to sound really good!!
Chris have you done any power calculations for power available (output) at 300 ohms?
Alex
Hi Alex,
Using the headphone power calculator of Bob Robinette give the following results with the cans you mentioned :
• DT1350 (80R, 109dB/mW), OPA1622 with +/-5V supply should be ok, it even can reach the max SPL of the can : 129dB
• T1 (600R, 102dB/mW), max SPL with OPA1622 with +/-5V (clipping at 4.1V) is 113dB. Certainly too short, it should be better with +/- 10 V supply, allowing 120dB SPL max.
• T90 (250R, 102dB/mW), OPA1622 with +/-5V supply should be ok, max reachable SPL : 117dB
The max SPL section of the spreadsheet (‘How Loud Will an Amp Drive Your Headphones’) is based on the max output voltage of the OPA1622 which is appx Rail-0.9V with most of loads.
But those are only figures…listening session will confirm if AmpCasq fit the various cans
Chris
Thanks again for this information. I will wait until I get the 12vdc regulated supply before I do any critical listening and post.
I did make a observation with the x-feed that on the lower impedance DT 1350's I think I can hear the affects of the x-feed circuit? Do you think that this is plausible that the lower impedance headphones are more sensitive to the affects of the x-feed circuitry?
How if possible would you change the circuit to allow for a +/- 10 v supply. I suspect a change in parts, heatsinks, Vreg?
Alex
I did make a observation with the x-feed that on the lower impedance DT 1350's I think I can hear the affects of the x-feed circuit? Do you think that this is plausible that the lower impedance headphones are more sensitive to the affects of the x-feed circuitry?
How if possible would you change the circuit to allow for a +/- 10 v supply. I suspect a change in parts, heatsinks, Vreg?
Alex
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To hear the Xfeed effect it’s mandatory to have a source which has been mixed with lot of stereo effect. Effect is obvious on some records and inexistent with others (ie. a mono record), but this is not related to the headamp. Based on my listening sessions, low xfeed position is efficient, it take back to the center sounds which where only in left or right position and it doesn’t alter the sound. IMO, the high xfeed position has a too strong bass boost.
You can do a kind of basic test : provide sound on only one input, leave other open then the play with Xfeed switch, result should be obvious, if not there may be something wrong with the headamp.
About the supply, there’s no way to go to +/-10V; 5V is part of the design choice in order to use the LM27761. Better to do some tests with the 600R can in order to confirm the need of higher rails.
Chris
You can do a kind of basic test : provide sound on only one input, leave other open then the play with Xfeed switch, result should be obvious, if not there may be something wrong with the headamp.
About the supply, there’s no way to go to +/-10V; 5V is part of the design choice in order to use the LM27761. Better to do some tests with the 600R can in order to confirm the need of higher rails.
Chris
I did as you suggested and removed one channel and tired switching to low and high x-feed and with only one channel the difference is very apparent. I also checked to make sure I had the correct resistors in the correct positions etc...all ok.
So its working , but again is it good or bad etc...I still have a hard time hearing this difference on a variety of recordings with both channels hooked up.
Alex
So its working , but again is it good or bad etc...I still have a hard time hearing this difference on a variety of recordings with both channels hooked up.
Alex
I spent a few hours this morning listening subjectively to Chris's amp I just completed and several other amps I have build and bought. I listened to AGDR's Desktop version of the O2 amp, the AGDR ODA, the O2 with Booster Board (another AGDR mod), Bottlehead Crack with Speedball mod, and a Schitt Vahalla 2 all tube amp.
Using several of my demo recordings from friends in the industry I listened over and over etc to the same recordings all with my Beyer T1 2nd gen headphones. 600 ohm. But these cans impedance vary all over the place.
Many state that a higher voltage amp is needed to drive the T1's best.
With the T1's in Chris's amp I cant listen to the T1's over about half way on the volume control. The amp will play these louder but it gets painful and its definitely in hearing damage area IMO. So to me this little amp plays the T1's rather nicely...and I compared with an amp that has many times more power at 600 ohms.
All the amps used sound really good, a statement of the present state of design, good components and good engineering and technology. Some of the amps dont play well with lower impedance cans.
To me a personal preference is that lower impedance cans seem to sound better to me that the T1's with this amp. I have no idea why, its probably my subjective bias, knowing this amp is a lower voltage amp than some others?
That said the T1's with this amp do very well....this is a dead silent amp and I am using a 16vdc IBM laptop power adapter at present and dont really know if this supply and is introducing any audible issues. Compared to the other amps I would think not at this time. I will try some good old DC batteries and have a regulated DC supply on its way as well.
The x-feed circuitry to me is not really doing anything great that I can hear with most of the recordings I listen to. I tried a wide varierty of recordings and thought I would wear out that switch!! But...never could really hear any really audible difference to my ears. With one channel only there is a drastic noticeable difference as things do indeed "move" in space. Its just with two channels hooked up its harder to tell the difference...IMO. I found some older tunes, ie Blood Sweat and Tears, that have songs starting out mostly in one channel for several seconds and if I flip the X-feed Switch down, you can hear the shift of things for sure so its working.
The sound is squeaky clean and no audible distortion of any kind is heard. In its present state it holds its own with these other amps. The only comment on a real difference between all these amps is that the soundstage is the one thing that seems to change somewhat. Powering down sometime seem to produce a small thumping or discharge type of sound, but turning the volume down makes this go away? But there are times when shutting down there is not sound.
The Bottlehead amp is like your back in row 10 listening at the symphony. while the Schitt V2 is like front row center, Chris's amp seems like its very much like the Schitt V2, right there up front IMO. This is much influenced by the quality of the recording as well.
All in all this good example where TI and its new chips have brought us...they allow for a very small package to be built that has very good specs etc..
I wish we could get this amp on an analyzer to see the plots etc...maybe my friend AGDR might be able to do this in the future?? (lol).
As soon as I get the regulated supply I will test again and with batteries.
Thanks Chris for a great little amp!!
Alex
Using several of my demo recordings from friends in the industry I listened over and over etc to the same recordings all with my Beyer T1 2nd gen headphones. 600 ohm. But these cans impedance vary all over the place.
Many state that a higher voltage amp is needed to drive the T1's best.
With the T1's in Chris's amp I cant listen to the T1's over about half way on the volume control. The amp will play these louder but it gets painful and its definitely in hearing damage area IMO. So to me this little amp plays the T1's rather nicely...and I compared with an amp that has many times more power at 600 ohms.
All the amps used sound really good, a statement of the present state of design, good components and good engineering and technology. Some of the amps dont play well with lower impedance cans.
To me a personal preference is that lower impedance cans seem to sound better to me that the T1's with this amp. I have no idea why, its probably my subjective bias, knowing this amp is a lower voltage amp than some others?
That said the T1's with this amp do very well....this is a dead silent amp and I am using a 16vdc IBM laptop power adapter at present and dont really know if this supply and is introducing any audible issues. Compared to the other amps I would think not at this time. I will try some good old DC batteries and have a regulated DC supply on its way as well.
The x-feed circuitry to me is not really doing anything great that I can hear with most of the recordings I listen to. I tried a wide varierty of recordings and thought I would wear out that switch!! But...never could really hear any really audible difference to my ears. With one channel only there is a drastic noticeable difference as things do indeed "move" in space. Its just with two channels hooked up its harder to tell the difference...IMO. I found some older tunes, ie Blood Sweat and Tears, that have songs starting out mostly in one channel for several seconds and if I flip the X-feed Switch down, you can hear the shift of things for sure so its working.
The sound is squeaky clean and no audible distortion of any kind is heard. In its present state it holds its own with these other amps. The only comment on a real difference between all these amps is that the soundstage is the one thing that seems to change somewhat. Powering down sometime seem to produce a small thumping or discharge type of sound, but turning the volume down makes this go away? But there are times when shutting down there is not sound.
The Bottlehead amp is like your back in row 10 listening at the symphony. while the Schitt V2 is like front row center, Chris's amp seems like its very much like the Schitt V2, right there up front IMO. This is much influenced by the quality of the recording as well.
All in all this good example where TI and its new chips have brought us...they allow for a very small package to be built that has very good specs etc..
I wish we could get this amp on an analyzer to see the plots etc...maybe my friend AGDR might be able to do this in the future?? (lol).
As soon as I get the regulated supply I will test again and with batteries.
Thanks Chris for a great little amp!!
Alex
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Hi Alex,
Thanks for giving us the results of your tests. I’m happy to see AmpCasq holds its own with your others amps and that you seem to like it !. Good news too is ability to drive 600R ones, or at least the Beyer T1.
Is the comparison still positive with your low impedance can (DT1350) ?
I’m also interested to have it on a analyser, is there anyone reading this thread able to do some measurements in the area of ‘La Défense’ or ‘Fontainebleau’ ?.
Chris
Thanks for giving us the results of your tests. I’m happy to see AmpCasq holds its own with your others amps and that you seem to like it !. Good news too is ability to drive 600R ones, or at least the Beyer T1.
Is the comparison still positive with your low impedance can (DT1350) ?
I’m also interested to have it on a analyser, is there anyone reading this thread able to do some measurements in the area of ‘La Défense’ or ‘Fontainebleau’ ?.
Chris
I happen to work near La Défense, and have some equipment to do measurements, see example here: http://www.diyaudio.com/forums/head...eadphone-amp-linear-audio-14.html#post3587077
If precision is good enough for you, let me know, I could give it a go.
I listened to three lower impedance heaphones listed above and the experience is still positive with some small issues:
The volume control with the 35 and 38 headphones and their sensitivity do not need hardly any movement to get to very high listening levels...so the power and gain etc are more than enough for these lower impedance headphones....some folks dont like this due to the tracking at low levels due to the mechanical vol pot mechanics can be off at low levels?
I need less than 1.4 turn of the pot from its totally "lowest" level postion to make these cans play very loud ...and very well I might add.
The 250 and 600 ohm cans need to be about the 12'oclock position, approx half way to obtain the same listening levels.
Also with the music at pause and vol cranked up to max position there is no hiss or hum, ie dead silent.
The ATH-MSR7's output SPL (sensitivity) is rated at 100 dB/mW, and its impedance is 35 ohms.
DT1350's have a nominal impedance of 80 ohms and 109 db-SPL @ 1mW (often written 109dB, or 109 db/mW)
Alex
Update: I played a test tone and started at zero volume and slowly cranked the knob up until I heard the tone, left and right to see if one channel would be heard before the other. A brute force method
to check audible tracking. The good news is with the pot I installed from Farnell is excellent and both channels seem to track well at low levels.
I also notice with the lower impedance cans that with the volume turned all the way down, I can still hear a very low level of music still playing.
The volume control with the 35 and 38 headphones and their sensitivity do not need hardly any movement to get to very high listening levels...so the power and gain etc are more than enough for these lower impedance headphones....some folks dont like this due to the tracking at low levels due to the mechanical vol pot mechanics can be off at low levels?
I need less than 1.4 turn of the pot from its totally "lowest" level postion to make these cans play very loud ...and very well I might add.
The 250 and 600 ohm cans need to be about the 12'oclock position, approx half way to obtain the same listening levels.
Also with the music at pause and vol cranked up to max position there is no hiss or hum, ie dead silent.
The ATH-MSR7's output SPL (sensitivity) is rated at 100 dB/mW, and its impedance is 35 ohms.
DT1350's have a nominal impedance of 80 ohms and 109 db-SPL @ 1mW (often written 109dB, or 109 db/mW)
Alex
Update: I played a test tone and started at zero volume and slowly cranked the knob up until I heard the tone, left and right to see if one channel would be heard before the other. A brute force method
to check audible tracking. The good news is with the pot I installed from Farnell is excellent and both channels seem to track well at low levels.
I also notice with the lower impedance cans that with the volume turned all the way down, I can still hear a very low level of music still playing.
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