congo5 Posted October 26, 2016 Report Share Posted October 26, 2016 (edited) 11 hours ago, FallenAngel said: Inputs are not shorted, nothing connected. No load on putout while testing +9V good, -17V bad pin6 to ground on opamp Not yet measured voltage base/emitter I don't know what the .5v refers to I know it's marked and easy to populate which is why I'm surprised I messed up somewhere. Update: I replaced the 4 SMC transistors, no change. As far as I know inputs should be shorted when setting bias, offset. or connected to something that has no DC on it- not floating. I connect a 10kR across the in + & - then can hang scope probes and signal on them Also true current source amps need a load, so when you test, add the jumper for higher current gain and use 50 ohm load. to check a BJT ... one way is to measure voltage--- base to emitter---VBE Edited October 26, 2016 by congo5 Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 26, 2016 Report Share Posted October 26, 2016 3 hours ago, Rossliew said: Will Birgir be building one or a couple of these and sell them off his site? It's highly unlikely Quote Link to comment Share on other sites More sharing options...
mwl168 Posted October 26, 2016 Report Share Posted October 26, 2016 To second congo5's point, the input should be shorted when you test and adjust DC offset. This is something I often forget to do too. Quote Link to comment Share on other sites More sharing options...
congo5 Posted October 26, 2016 Report Share Posted October 26, 2016 1 hour ago, congo5 said: I know it's marked and easy to populate It only takes one thing to send it into a bad place one part or connection can cause voltages to go crazy all over the place Do not use this for preamp duty! don't ask me how i know I do wonder if it could be used for the CAST Inputs>>>> 1 Quote Link to comment Share on other sites More sharing options...
stax fart Posted October 26, 2016 Report Share Posted October 26, 2016 (edited) Newbie/dumb question here: How much would cost to build a balanced version of this amp? (or at least one with balanced inputs and a 4 pin xlr output for the headphones) Edited October 26, 2016 by stax fart Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 26, 2016 Author Report Share Posted October 26, 2016 unless you use a balanced to unbalanced converter to drive this, there is no way a transconductance amp can be balanced (bridged) Quote Link to comment Share on other sites More sharing options...
stax fart Posted October 26, 2016 Report Share Posted October 26, 2016 40 minutes ago, kevin gilmore said: unless you use a balanced to unbalanced converter to drive this, there is no way a transconductance amp can be balanced (bridged) Thanks Kevin! And, more or less, how much costs to build one? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 26, 2016 Author Report Share Posted October 26, 2016 you are asking the wrong guy. I never EVER pay any attention to the cost of this stuff. which is how I ended up with $10k in excess semiconductors I will use the tubes as an annuity later Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 26, 2016 Report Share Posted October 26, 2016 My nestegg is my stash of 2SK216's and 2SJ79's... Quote Link to comment Share on other sites More sharing options...
FallenAngel Posted October 30, 2016 Report Share Posted October 30, 2016 On 26/10/2016 at 3:01 PM, mwl168 said: To second congo5's point, the input should be shorted when you test and adjust DC offset. This is something I often forget to do too. I've read that part a couple of times and it confuses me completely. What do you mean "adjust DC offset"? There are no trimpots on this amp. Where does adjustment come in? Quote Link to comment Share on other sites More sharing options...
mwl168 Posted October 30, 2016 Report Share Posted October 30, 2016 Just making a general comment on measuring and setting DC offset on the output on amps, not specific to the transconductance amp. Quote Link to comment Share on other sites More sharing options...
NoFeedback Posted December 28, 2016 Report Share Posted December 28, 2016 Hello, first post, long time reader, please don't be harsh with me, I read the forum rules a couple of times. I have Stax SR-2170 system for two years, very happy with it. However, I received an Audeze LCD-2 as christmas present (god bless christmas!), but...I don't have a proper amp for them. I thought this is a great opportunity to start my first DIY project (this transconductance amplifier). But, I have a few (probably dumb) doubts about the design. Kevin said there's no way to make a balanced/bridged transconductance amp, but looking at some commercially available products, I've found this: Bakoon AMP-51R speaker amp: ("Maximum power output: 100 watts in stereo, 250 watts in mono") http://www.bakoon.com/product/amp-51r/ Audio GD NFB-1 headphone amp (fully balanced, class A, with 4 pin xlr headphone output) http://audio-gd.com/Pro/Headphoneamp/NFB1AMP/NFB1AMPEN.htm I mean, is something wrong with those transconductance amplifiers or a design of this headphone amp with a 4 pin XLR output for the headphones can be done? Thanks for your attention, and please forgive my ignorance. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 28, 2016 Author Report Share Posted December 28, 2016 for sure the audio-gd is NOT a transconductance amp. I have one. diamond buffer output. and If the bakoon is bridgeable for double the power then it cannot be a transconductance amp. 1 Quote Link to comment Share on other sites More sharing options...
NoFeedback Posted December 28, 2016 Report Share Posted December 28, 2016 5 hours ago, kevin gilmore said: for sure the audio-gd is NOT a transconductance amp. I have one. diamond buffer output. and If the bakoon is bridgeable for double the power then it cannot be a transconductance amp. Thanks Kevin!!! Mentioned the Audio GD stuff because I read this some days ago: http://www.audio-gd.com/audio/ACSS.htm Kingwa mentions he uses the Current Conveyor Technology on his designs, like Krell and also Bakoon ("SATRI" circuit mentioned), my doubts were generated because of that. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted December 28, 2016 Author Report Share Posted December 28, 2016 current mirrors used as voltage gain stages is very different from high power versions used as output stage. as far as I know bakoon is one of the very few that make transconductance headphone amps. It really works well only with very flat impedance headphones like ortho's. 1 Quote Link to comment Share on other sites More sharing options...
NoFeedback Posted December 28, 2016 Report Share Posted December 28, 2016 3 minutes ago, kevin gilmore said: current mirrors used as voltage gain stages is very different from high power versions used as output stage. as far as I know bakoon is one of the very few that make transconductance headphone amps. It really works well only with very flat impedance headphones like ortho's. (Read with Narco's character voice): Gracias Patrón! 1 Quote Link to comment Share on other sites More sharing options...
mdr30 Posted March 3, 2019 Report Share Posted March 3, 2019 Squeezed this amp into a small Modushop case. Tight fit for the caps, but it works. Doesn't get particularly warm. An interesting alternative for planars. 10 Quote Link to comment Share on other sites More sharing options...
jose Posted March 3, 2019 Report Share Posted March 3, 2019 I did not remember this amplifier ... I don´t think I have it in my collection. Quote Link to comment Share on other sites More sharing options...
Rossliew Posted March 4, 2019 Report Share Posted March 4, 2019 Is it good for high impedance headphones as well? Quote Link to comment Share on other sites More sharing options...
MLA Posted March 4, 2019 Report Share Posted March 4, 2019 (edited) Not its forte. Really shines with planars though. Edited March 4, 2019 by MLA Quote Link to comment Share on other sites More sharing options...
jose Posted March 4, 2019 Report Share Posted March 4, 2019 Yes, it is what I had understood. Interesting. It looks like it's the size of a SquareWave. Pcb´s should not be very expensive. Quote Link to comment Share on other sites More sharing options...
MLA Posted March 4, 2019 Report Share Posted March 4, 2019 Yes, just slightly bigger than the squarewave. I logged in to check prices and PCBWAY would send me a pack of 10 for about 20 USD if I repeat my order. Good times for DIYers :) Quote Link to comment Share on other sites More sharing options...
UFN Posted March 4, 2019 Report Share Posted March 4, 2019 Seeed should do the same as well (or thereabouts) Quote Link to comment Share on other sites More sharing options...
jose Posted March 4, 2019 Report Share Posted March 4, 2019 Maybe a GB? Quote Link to comment Share on other sites More sharing options...
sorenb Posted March 6, 2019 Report Share Posted March 6, 2019 Have some from PCBNet, 1.6mm and 3oz. Anyone who wants to build the Transconductance amp and post a few pics here, can have a set or two. Promise to show a few pics of the build here, and I'll cover the shipping as well ? 2 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.