kevin gilmore

success soon yep, 39 transistors including 2 dual matched npn.

so you say you should be able to measure why it sounds like it does... first 2 are 1khz into 50 ohm non-inductive load. notice that the rise time and fall time are not identical. also notice severe slew rate limiting in both directions and kink on the positive slope. 3rd picture is 10khz. kind of what you would expect from an amplifier with an open loop gain of around 120db and a group delay of 10us or more. i don't have the transformers, but i'll bet it looks even worse driving that transformer. pretty sure the a90d will perform exactly the same. edit: see pictures in next post. definitely same as a90d

So, after a few hours in my favorite combination of methylene chloride, acetone, toluene, benzene, and 2 other magic ingredients (basically miller-stephenson ms111 only way cheaper) Warning kids: don't try this at home. highly flammable, highly toxic, low flash point... Let the professional morons do this the eha5 discrete module in the process of giving up its secrets. every single part of the eha5 is a massive pile of crap. it takes a whole room full of highly competent engineers to produce something this fucked up. i did take the other module, hooked it up to a bench supply and hd800 headphones and got a good listen. wow is this bad. proof that obviously the lowest distortion possible in amir's s/n test is the one and only measurement that they think matters. the rest of the specs, not even close. for those that don't know, the external power brick is a single 15v switching supply at 3 amps. internally it makes -15 from the +15. except for the fact that the -15 supply seems limited to about 750ma, and it runs 4 amps from this. So maybe if you are lucky you get about 175ma max current per amplifier. No way this is enough to drive those crap transformers. transistors are 2L, G1 and the dual is k4r

the phase is going to mess with the feedback in a serious way. going to be very tricky to get right. and then there is the problem of disconnecting the headphones with audio playing. might turn into a high power oscillator.lots of magic smoke.

worse than expected. would like to see the lundhall transformer.

+/-24v is recommended mininum for lowest distortion

first make sure the bertan is positive voltage output!!!!. because they make both. edit, because its a 24vdc input. the chassis of the power supply needs to be wired to ac input ground. make sure the bertan ground goes the center tap of the transformers.

you definitely want to use the lundahl transformers, they are going to be better than anything else you can buy.

pic?

actually by increasing the gain on the apex part you seriously compromise the high frequency response and increase distortion. which may be intentional.

absolutely not. topping has potted modules including the bias module that are not available as spare parts. topping has a custom switching supply that may not easily be substituted. every one of these is likely to be dead in less than 5 years. where 40 year old stax amps continue to function even though all the silicon is obsolete. topping is flavor of the month throw away garbage.

2 part epoy glue should fix that.

add on external module. much better idea. don't want to void the warranty.

only 2 with dead bias supplys that i am aware of. both died in less than 1 hour.

fact is that the warwick headphones are single ended and not stax compatible. basically a beveridge speaker done by someone with no brain. this and the high end sennheiser are proprietary technology.

in other news, significant amounts of topping la90discretes are overheating and burning up. the eha5 is based in part of the la90d. so expect those to be burning up soon.

actually a krell master reference pair of monoblocks will drive any headphone electrostatic or dynamic. just need to add a bias supply. 800 volts peak to peak.

i'm sure ray would be happy to sell you one of his new amps, only $10k.

there are a few units with the tube front end that have been built. less than 5 i think. boosting the front end high voltage will increase the power in the current mirror that follows the tube. so you might have to change some of those parts.

would need a higher voltage opamp. otherwise should work.

grhv100 for the tube input stage.

pretty sure all of my boards have the holes electrically isolated.

so over at ASR, people have commented today that topping said that they used a step down transformer on the output of the step up transformer, an no capacitive load. flat out fraud this is... and completely meaningless published specs. if someone paid attention during the design process and actually used a real 120pf load, or even headphones, they would know how fucked up this is. the topping a90d may be decent. but my testing in the past indicates that stuff with huge amounts of open loop gain, and then huge amounts of feedback to get those magic distortion numbers usually sound like crap. this thing, and their power amp all use one switching power brick to make the positive voltage and then another switcher internally to make the negative voltage. so a switcher driving a switcher. not a great idea.

and yet the audio precision actually reports .0008 % thd at 1khz. so much for that being worth anything. sure looks like about 10 volts per microsecond slew rate. pretty grim at higher voltage levels. winding transformers correctly really is not that hard. too bad the lundhal transformers won't fit inside the box. hmm, there is that size thing again. (usa_love) what really gets me is the really poor soldering job, probably there is a significant failure rate of topping products in the field. And yet led lit sails that makes you think there are tubes inside. my guess is that the koss box sounds better than this, for roughly the same price. quoting from someone who knows how to actually make transformers like this.. quote In a transformer winding, inter-turn capacitance is generally negligible compared to inter-layer capacitance. We can approximate the winding self-capacitance within a small factor by considering only the capacitance between winding layers, approximating the layer to a conductor sheet. The highest capacitance arrangement is when each layer is wound in opposite directions, so left to right on the first, right to left on the next. That's because the first turn of the first layer is opposite the last turn of the next layer, so there's twice the voltage per layer between those turns. As the energy stored in the self-capacitance goes as the square of the voltage, this more than offsets the lower voltage difference at the other side of the windings. A lower capacitance can be obtained by winding each layer in the same direction, returning between layers, so left to right, then left to right again. The voltage between layers is now uniform at the per layer voltage. end quote transformers made this way have to be partially done by hand. no winding machine currently available does this. its why esl63 replacement transformers are $500 each.

ray maybe lies a little on the specs ?? left is 20khz sine wave, 15ma peak, bottom is 20khz sine wave 1800vppss right is 20khz square wave 500v/us, top is current bottom is voltage, 1800vppss would have to be more than 1000v/us to hit 200ma peak. only apex part that does that is the pa194, price for 4 is $1600. slewrate.PDF