Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 8, 2010 5:49:20 GMT
No kit.. Own idea, own design, own build. The most expensive parts are the casing, the heatsinks, the vol pot and power supply. The transformers are only about GBP10.- and the other parts are also inexpensive. After it has been evaluated by subjective means and people are interested in a PCB I will design a nice dual layer PCB for it and maybe even sell the PCB's. For now it is one of a kind, the only one on this planet....(unless someone was really fast and built it within 2 days) Built one this morning Frans and it sounds incredible! I hope to have kits up and running by Wednesday Mike, You, Ian, Mick and Perhaps some others might want to hear it. If it were only for the fun of it's unusual design. Won't beat the Panda but it does sound good, better then you would expect from a little transformer. Shipping is costly though as it is very heavy. (above 2 kg) Steel casing and weighty heatsinks.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 8, 2010 12:45:37 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 8, 2010 19:09:13 GMT
Stick with class A Frans.
I just realised that it has two headphones out. One for low impedance and one for high. Great idea.
Have you noticed much difference between the two with the same headphone?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 8, 2010 21:09:01 GMT
Some of my headphones prefer low Ohmic others high Ohmic and with another the sound differs only slightly. See reply 91 on page 7 for details on the cans I tested it with. Still the KSC35/75, BeyerSkytronics, BeyerSamson, (modded) Creative Aurvana Live ! (CAL) to go, but these are un-interesting for use with this kind of amp.
Busy with the cheap buffer at this moment....
The 'dressed down' version is not gonna come near the class A but still I like to build it. Just for fun to see how it holds up to it's class A brother.
Gonna take me a few months to build it and get it to perform near the quality I am looking for. As you can see it will have to be in a nice enclosure too. Fortunately I have a similar one left. Perhaps this one can house the power supply too.
The road is paved already though...
|
|
|
Post by oohms on Nov 8, 2010 23:30:30 GMT
Here is another transformer design i stumbled across www.susan-parker.co.uk/zeus.htmI have been thinking of making a transformer output tube amp with conventional mains transformers, but i have to work out how to find the impedance of each winding
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 9, 2010 7:38:34 GMT
This design (the Zeus project as in your reply) has input- and output-transformers which are not loaded ideally. The first transformer MUST be driven properly and the output transformer is loaded with a loudspeaker which has (greatly !) varying output impedances to cope with. Phase shifts and impedance-peaks and -dips will be all over the place (in general) which will, quite audible, affect the overall sound. This amp can be picked out in AB and blind AB tests immediatly because the frequency characteristics which will be detemined by the loudspeakers impedance for a certain part . Also it is class AB (class A to a point) and therefore has odd and even harmonics and does not make full use of the transformers most positive assets (only having the more pleasant even harmonics). Another drawback is this amplifier design needs to be driven from a low Ohmic source with a high output voltage capability for the input transformer to work correctly. That's why she uses a TPA6120 (class AB) headphone amplifier to drive the input transformer. The sensitivity (gain) of this design is low so needs a high voltage (upto a few volts) to be driven. This means you will need a 5W poweramplifier to drive this endstage to get a good low frequency respons and low distortion values in the LF. The distortion figures are also higher because of the used transformers and class AB pushpull topology. It also will have some IM distortion too, caused by the MOSFET's pushpull configuration and no feedback which is almost mandatory when using an output transformer (unless it's a real good one) It differs quite a lot from my design. The only thing they have in common is the fact that both amps use a transformer to do the voltage gain. Some conventional power transformers can be used for Audio but certainly not all of them. Most transformers are optimised for low frequencies (between 30 and 200 Hz) and have steel cores (we call it: 'pisbakkenstaal' which translates to 'urinoirsteel' which is cheaper then the better quality cores and has lots more distortion then audio transformers will and also the frequency range is simply not enough. This means: exprimenting with transformers and tone generators to see which transformers perform well in this department. My electrostatic speakers use power transformers (6 of them) for audio step-up. These were power transformers from a certain Panasonic videorecorder (NV370) and these were the only ones I could find that reached 18kHz and had low distortion. They probably had a much better core material the most mains transformers. The impedance you can only determine by feeding it with a frequency (between 100Hz and 1kHz) and measuring the open output voltage of the secondary and loaded with a resistor and calculate the output reistance of the windings from these values. The DC resistance will tell you almost nothing about the impedance. the impedance ratio is the 1/(voltage ratio x voltage ratio). Hope this info helps with regard to the transformer choice.
|
|
|
Post by pcourtney1 on Jul 17, 2011 0:05:03 GMT
I like the amps to have a large voltage swing so need a high voltage on the parts. Also I like it to be class-A and needs to be able to deliver the needed currents for these high output voltages. To prevent (asymmetric) clipping in these cases the idle current must be higher then the maximum current that can ever be drawn. This is determined by the maximum output voltage swing and the output resistance + lowest impedance of the useable headphones (in this case 1 Watt in 32 Ohm) Therefore a high current is also needed. High voltages x high currents means high power demands (Watts) that are drawn constantly tis a real shame that your Class A amp is a one off Frans, I believe not enough emphasis is placed on "high voltage swings" in headphone amp design, sad but true !
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 17, 2011 0:50:16 GMT
I like the amps to have a large voltage swing so need a high voltage on the parts. Also I like it to be class-A and needs to be able to deliver the needed currents for these high output voltages. To prevent (asymmetric) clipping in these cases the idle current must be higher then the maximum current that can ever be drawn. This is determined by the maximum output voltage swing and the output resistance + lowest impedance of the useable headphones (in this case 1 Watt in 32 Ohm) Therefore a high current is also needed. High voltages x high currents means high power demands (Watts) that are drawn constantly tis a real shame that your Class A amp is a one off Frans, I believe not enough emphasis is placed on "high voltage swings" in headphone amp design, sad but true ! The "SC" Class A HA in the DIY area also uses +-20V supply rails, and has 100mA bias.
|
|
rowuk
Been here a while!
Pain in the ass, ex-patriot yank living in the land of sauerkraut
Posts: 1,011
|
Post by rowuk on Jul 26, 2011 5:16:09 GMT
So why don't we have an Indeed inspired amp with 70-150V anode and MOSFET behind? Operating the valves at their sweet spot does remove some of the "sugar coating".
I would have thought that this could have been an important mod for the G2 and similar.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 26, 2011 6:06:00 GMT
So why don't we have an Indeed inspired amp with 70-150V anode and MOSFET behind? Operating the valves at their sweet spot does remove some of the "sugar coating". I would have thought that this could have been an important mod for the G2 and similar. Robin I agree, but I think it's the safety aspect that Frans and Mike are more concerned about.Besides, some of the guys here need to get that kind of additional expenditure past SWMBO ! Alex
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 26, 2011 6:32:37 GMT
Now you have some idea what my plans are with the Sunrise PCB I have over here. It has been planned from the day the sunrise was conceived. Time, however, is the problematic part in this case. Alex touches a DIY point though (about the voltages) It is perhaps feasable to go to 48V and quadruple the output power. This is not possible with the current heatsinks and some parts have to be altered too. Also got an idea about a sortof high power configurable amp that can put out 1W and can vary between 1 Ohm and 200 Ohm or so. Very high voltages indeed. Will probably be class AB..... In class A (single ended ?) we would be looking at 100V and 0.3A = 30W heat dissipation per channel. so 60W in total requiring a 120W transformer running at 50% to get 1W output power max. It would be a monster. If it needs to drive lower than 32 Ohm headphones to 1W as well you can increase the disspated power by some factors.
|
|
rowuk
Been here a while!
Pain in the ass, ex-patriot yank living in the land of sauerkraut
Posts: 1,011
|
Post by rowuk on Jul 26, 2011 21:42:45 GMT
Getting 20V and 150V is no issue really. We need 25V to be able to get decent regulation for 20V and a very small 6:1 trafo (230V:2x20V) to raise 25VAC back to 150VAC. Then we have decent voltages for each side...........
Optionally, there is enough used valve equipment out there with decent anode and heater voltages that could also be used for single ended MOSFETS.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 26, 2011 22:05:33 GMT
We can build and design what ever we want with whatever voltage we like. That is not the issue.
The G2/sunrise is an open frame thingie. I do not recommend such voltages in an open frame. 150V DC can be lethal and would be easy to touch by accident.
The 'fun' part of these low voltage tube thingies IS the high amount of added distortion. Lots of people like that addition of pleasant sounding harmonics, making this distortion smaller doesn't make much sense in that case...
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 26, 2011 22:09:17 GMT
( Just add more Mosfets ! They have added warmth too in most implementations .
|
|
|
Post by PinkFloyd on Jul 26, 2011 22:17:28 GMT
Team "distortion" rocks
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 26, 2011 22:26:39 GMT
Team "distortion" rocks Mike Is there still a "distortion" in the Time continuum between Caithness and HeadFi ? Alex
|
|