transconductance amp

[congo5]

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

[spritzer]

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

[mwl168]

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. 

[congo5]

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>>>>

[stax fart]

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

[kevin gilmore]

unless you use a balanced to unbalanced converter to drive this, there is no way a transconductance amp can be balanced (bridged)

[stax fart]

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?

[kevin gilmore]

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

 

[spritzer]

My nestegg is my stash of 2SK216's and 2SJ79's... 

[FallenAngel]

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?

[mwl168]

Just making a general comment on measuring and setting DC offset on the output on amps, not specific to the transconductance amp. 

[NoFeedback]

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.

[kevin gilmore]

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.

[NoFeedback]

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.

 

 

[kevin gilmore]

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.

[NoFeedback]

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!

[mdr30]

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.

 

 

[jose]

I did not remember this amplifier ... I don´t think I have it in my collection.

[Rossliew]

Is it good for high impedance headphones as well?

[MLA]

Not its forte. Really shines with planars though.

Edited March 4, 2019 by MLA

[jose]

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.

[MLA]

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 :) 

[UFN]

Seeed should do the same as well (or thereabouts)

[jose]

Maybe a GB?

[sorenb]

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 ?