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Post by bjarne on Apr 16, 2011 22:15:59 GMT
Thank you very, very much!!! To my own surprise I understood everything!  Too bad you don't recommend the negative feedback behind the output resistor!  But doesn't have it enough power for some 10-20dB feedback? This is the part where I'm stuck, not able to calculate with dB. Have you heard of load-line cancellation? Read some interesting stuff from a guy over at diyaudio: www.passdiy.com/pdf/distortion_feedback.pdfand www.firstwatt.com/pdf/art_sweet_spot.pdfMaybe you know it already! I'm really enjoying these electronic classes!!! |
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Post by Deleted on Apr 16, 2011 22:22:29 GMT
Put very simply, negative feedback can't be utilised unless you have heaps of gain to spare. This amplifier, like many simple valve amplifiers, does not.
As Frans has said , you would need an extra amplification stage to be able to do that.
SandyK
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Post by Deleted on Apr 16, 2011 22:23:45 GMT
Yup ! At least I did try with Ian's amp as he wanted less amplification. You won't know it untill you really tried hard is my motto.  Very little effect (due to the low openloop amplification) and more negatives then positives came out of it so I abandonned it. a close to 0 Ohm HA output resistance is not recommended (by me anyway) for driving most headphones.  Better put a low mu tube in it to obtain lower amplification. You might have to revise the CCS circuit in that case. |
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Post by bjarne on Apr 16, 2011 22:49:07 GMT
You won't know it untill you really tried hard is my motto. a close to 0 Ohm HA output resistance is not recommended (by me anyway) for driving most headphones. Better put a low mu tube in it to obtain lower amplification. You might have to revise the CCS circuit in that case. Damned! I like your motto quite well! I try to persue that myself. Hmm...but even Sennheiser recommends it and many Amps have it. I wouldn't push so hard if my Sony wouldn't sound like shit on the G2.  And the effect seems to be similar to experiences others made with low impedance cans on low-medium impedance amps. Ok, now you're challenging me, right? mu tube? CCS circuit? |
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Post by Deleted on Apr 16, 2011 22:52:07 GMT
From DIYAudio:
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Post by PinkFloyd on Apr 16, 2011 23:11:27 GMT
I can't believe that such a piss ant has become such a monster.......
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Post by PinkFloyd on Apr 16, 2011 23:17:00 GMT
I can't believe that such a piss ant has become such a monster....... BTW.... what idiot started this thread? |
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Post by bjarne on Apr 16, 2011 23:34:34 GMT
I can't believe that such a piss ant has become such a monster....... ? ? ? |
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Post by PinkFloyd on Apr 16, 2011 23:38:18 GMT
I can't believe that such a piss ant has become such a monster....... ? ? ? |
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Post by Deleted on Apr 17, 2011 6:59:19 GMT
The 1996 IEC 61938 standard recommends an output resistance of 120 Ohms. Most HP's comply to these standars including Sennheiser which only points to this standard and never (as far as I know) tells people to use low Ohmic output resistances specifically. Most low Ohmic cans (those for portable use) are designed to be driven with low Ohmic amps so they will sound better (in most cases ?) on low voltage, low impedant amps. Most amp manufacturers don't even mention output resistance, only which HP's can be 'used' yet it is sound defining. Try driving K701 and HD800 and a lot of other cans with a low Ohmic output and through 120 Ohm see what sounds better and use your own ears instead of comments by various people. Some cans like low Ohmic, some higher Ohm or inbetween values. This is EXCATLY why some HP's combine so well with certain amps and sound remarkably less on others. If you want to know if your Sony sounds better with low Ohmic (DT990 surely does) simply solder a wire across the output resistors of the G2 (on the bottom of the PCB) and see what it does. just don't short the output. I am currently working on an amp that will have user selectable low, medium or high ohmic outputs, can be shorted indefenitely without problems and cannot destroy low ohmic headphones and drive high Ohmic ones pretty well too (not K340 K1000 and some planars) You can also configure the gain and bandwidth and has a very HQ power supply. Opamps can be swapped if sockets are used. No tubes I am afraid but if you want a tuby sound consider the LDR volpot in front of it. So 1 amp... many faces There will be a PCB for it. It's still in infant stage and not 'marketable' yet. Will NOT be selling finished amps or kits. |
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Post by bjarne on Apr 17, 2011 14:07:10 GMT
Try driving K701 and HD800 and a lot of other cans with a low Ohmic output and through 120 Ohm see what sounds better and use your own ears instead of comments by various people. If you want to know if your Sony sounds better with low Ohmic (DT990 surely does) simply solder a wire across the output resistors of the G2 (on the bottom of the PCB) and see what it does. just don't short the output. I am currently working on an amp that will have user selectable low, medium or high ohmic outputs, can be shorted indefenitely without problems and cannot destroy low ohmic headphones and drive high Ohmic ones pretty well too (not K340 K1000 and some planars) You can also configure the gain and bandwidth and has a very HQ power supply. Opamps can be swapped if sockets are used. No tubes I am afraid but if you want a tuby sound consider the LDR volpot in front of it. So 1 amp... many faces There will be a PCB for it. It's still in infant stage and not 'marketable' yet. Will NOT be selling finished amps or kits. Oh boy, to solder a wire across the output resistors was what I meant in the first place!  My Electronic-English is obviously not the best and I mixed it up with 'to short'! I'm sorry!!! What would have been the correct terminus? To bridge? Does this harm the amp? Will there be single sided clipping? I'm willing to compare as many HP as I can get a hold of, but for now my budget is way too small for those cans. But next week my HD580 will arrive and then I can test and compare a little bit more. Your Amp sounds very good! Can I get a reservation on one of those PCBs?  My next amp will be a Opamp or solid state (the same?) anyway, so it's no bugger it has no tubes. |
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Post by Deleted on Apr 17, 2011 16:01:35 GMT
Yep I know... I just don't recommend doing that for the reasons mentioned before. Only if you want to find out if the Sony sounds better on the G2 then just short that resistor. Wouldn't leave the short in that way though, the amp simply is not designed to have 0 Ohm output impedance. I plan to finish the boards in 1 or 2 months time. Still tinkering with the design. By the time I have built, tested and used it for a while it will be available. Only a few boards will probably be made. |
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Post by bjarne on Apr 17, 2011 18:41:06 GMT
Sounds very interesting! I would love to build my next amp myself. Do you produce the boards yourself? Fine, I will test it today or tomorrow and will solder it out immediately after testing. Curious to see if I can adjust the Volume precisely with even lower impedance. About the HF-interferences which I can hear very prominent with my Sony: would it help to switch the distancer-rods for some plastic-types? And does these little things which you attach to cables help at all? I'm suspicious that the cable from my soundcard is picking up some of the HF noise. |
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Post by Deleted on Apr 17, 2011 19:01:31 GMT
The metal distancer rods are actually connected to ground so replacing them will do nothing as they do not act as antenna's.
The ferrites MIGHT do something depending on the frequency of the interfering source.
For optimal usage wind the wire 3 times though the hole (instead of 1 time one normally sees) and mount them as close as possible near the amp.
Input and power cable should be done.
more then 3 times will give no extra attenuation.
2 times or as is normally seen only 1 passage will attenuate less.
Reason it is only done 1 time in most cases is the device it is mounted on then passes EMC quality tests.
For maximum attenuation3 times is recommended and have measured/confirmed this several times in EMC labs myself.
Increasing the distance from the monitor would be my choice or encasing it in a metalic case that is grounded (connected to the common of the amp) you have to allow free airflow so a box with lots of small holes would be preferable.
I design the boards myself (Layo-1) but the bare PCB's themselves are made in a factory (in Belgium or England).
It will be professional 4 layer boards (FR4 1.55 mm thick, green).
I expect the price of the boards alone to be near 20 - 30 Euros !
Only in large quantities they would be much cheaper (say around 10 Euros each)
The initial costs are rather high due to the production proces.
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Post by bjarne on Apr 18, 2011 15:50:08 GMT
I design the boards myself (Layo-1) but the bare PCB's themselves are made in a factory (in Belgium or England). It will be professional 4 layer boards (FR4 1.55 mm thick, green). I expect the price of the boards alone to be near 20 - 30 Euros ! Only in large quantities they would be much cheaper (say around 10 Euros each) The initial costs are rather high due to the production proces. IF you were to couple the signal back from before the output resistor and make the total gain of the amp less you would effectively be correcting errors in the amp and output capacitor. in the G2 there is an output relay which should make it possible. Sounds very nice and I expected the costs to be higher. Did you split the initial costs on the board price of 20-30€? I really think it's a good price and value. One summer I did a job which was the exposure of PCBs before they got their solder-stop-lacquer. But they were quite mighty, Din A3 or bigger and I can't remember for what purpose they were. Would it be possible to fit a TPA6120a2 on your amp? Done some reading and it seems to be a good opamp. Back to business: I did it! - And it sounds great!!! I think my Sonys and your Beyers are cousins or something. And even my AKGs develop some Soundstage on 0 Ohm, and that's not what they are renowned for. Hopefully they will both sound on 120 Ohm the same!!! (Fingers crossed) Today I will order some parts to finally do the heater-mod and I will order a selection of resistors between 1 and 15 Ohm in case 120 Ohm will blow. BTW: What power must the current-adjustment-resistors be designed for? 2W? I ordered 1W the last time. Do you think I should try the feedback before the output resistor? What parts would I need? 2 resistors? And how can I calculate it? Haven't found anything on this. |
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Post by Deleted on Apr 18, 2011 16:11:33 GMT
The G2 has too little output voltage to fit 120 Ohms.
I would say max 68 Ohm output resistance.
Experimenting with 3 values should be enough, say 10 Ohm, 30 Ohm (now in there) and 56 or 68 Ohm as output resistor.
a power rating of 0.5W is already sufficient, you can't blow it, way too low power amp.
The openloop gain of the amp is way too low by itself to create any real feedback that could lower distortion significantly.
For feedback to be applied succesfully/effectively you need a rather high openloop gain.
Ofcourse you could give it a try and thus lower the gain.
1 resistor between the centrepin of the vol pot and the grid of the tube (have to cut a trace) of around 1 kOhm and 1 feedback resistor from the output resistor to the grid (4k7 or something).
you might have to mount a small cap in parallel to the feedback resistor to prevent oscilation.
an Oscilliscope would come in handy to check for this.
feedback and thus gain will vary with the volpot setting... alas... and thus also the effect.
My design will only allow 8pin DIP dual opamps, the TPA1620 is an SMD device with more pins.
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Post by lancerck on May 27, 2011 4:13:22 GMT
You guys are great. I bought an Indeed G2 HA from eBay when I realised that none of my sources headphone output was able to power my humble HD438 to maximise its potential. I have only change the traisistor to IRF510, bias to get as close to 16v as possible ( only gets about 15v, as I currently using a 19v PSU since both my Indeed 24v PSU has conk out, awaiting for a 24v Kodak Liteon 5a PSU that I have ordered). Change the output cap to 2200uF, bypas cap to 3.3uF. The sound is already astonishing. I am using it with a Telsa E88CC golden connectors currently. Thanks to you guys, without all these mods, I don't even know what I have been missing |
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Post by markdam on May 30, 2011 1:42:40 GMT
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Post by lancerck on May 30, 2011 3:32:04 GMT
I thinkthe link that you have posted refers to the MkII version. What was discussed here is the G2 version, which is a bit different. I believe the MkII is unable to swap between the 12AX7 and the 6922 without major mod as it has a fixed filament voltage supply, whereas the G2 has a built in switch that can change the filament voltage between 6 or 12v to suit the tube family. |
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Post by Deleted on May 30, 2011 5:20:30 GMT
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Post by markdam on May 30, 2011 5:56:59 GMT
GREAT hopefully mr Indeed will cancel my transaction as ive requested thought i was getting the right one..... bummer I should have checked with you guys BEFORE i clicked the buy button AARRRRGH are the G2's no longer available? |
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Post by markdam on May 30, 2011 6:41:03 GMT
well peter cancelled my transaction now i need to decide on the real G2 or garage 1217 ill wait for a review and some pics.........
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Post by Garage1217 on May 30, 2011 23:49:14 GMT
For those looking for a parts kit with the good stuff to modify their indeed, bravo, muse, miri designs... I have such a beast for a decent price on my site as well as the new project Sunrise amp that Frans and I worked on. Just a thought! All items in the kit are listed. store.garage1217.com/bravo--muse--indeed-audiophile-upgrades.html |
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Post by texan on Jun 8, 2011 13:43:43 GMT
Guys,
I'm having trouble finding a reasonable PSU... I have a G2 on the way, and I'm guessing the G1217 uses a similar PSU as what is supplied with the G2, BUT I wonder if I need a better power supply unit. The challenge here is that I'm in the U.S....
I search for about an hour yesterday and could not find a compact 24V2A DC linear regulated PSU with a 2.5mm jack.
I'm I looking in the wrong places?
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Post by Deleted on Jun 8, 2011 14:16:08 GMT
Linear power supplies with a higher wattage (25W in this case) will be harder to find.
Wether it will be audible depends on a lot of factors.
the correct plug will have to be soldered on by yourself probably or perhaps a power supply with various universal plugs.
There are enormous amounts of variations in power plugs.
the G2 does not use a 2.5mm jack plug
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And the effect seems to be similar to experiences others made with low impedance cans on low-medium impedance amps.
My Electronic-English is obviously not the best and I mixed it up with 'to short'! I'm sorry!!! What would have been the correct terminus? To bridge?
My next amp will be a Opamp or solid state (the same?) anyway, so it's no bugger it has no tubes.
