The Singing Bush Tips 'n' Tricks

[noelectrix]

I owe you an e-mail

guess I'll rather owe you a coffee :*) ~D

 

[TungstenAudio]

Making slow progress on my Singing Bush. Decided to re-position the boards a little and add some local bypass caps.

 

[Jeffreyjuice]

Looks great!

 

[Zen Mod]

🙂

 

[Ben Mah]

The temperature has dropped a bit lately so I have the amps back in service. Yesterday I made a change to the operating point after I tried it out in LTspice. I know LTspice is not the real thing but it did give me some ideas to play with. I listened to it for a day and I think it was an improvement over the previous setup. In fact I think this iteration is a keeper.

So today I made some measurements. My previous setup was Vds=36.5V, Iq=2.3A, speaker out at 0.3R-speaker-0.3R (Speaker D). Distortion measurements were posted here:The Singing Bush Tips 'n' Tricks

My latest is Vds=38.0V, Iq=2.3A, speaker out at 0.3R-speaker-0.3R (Speaker D). This setup has lower THD than my previous setup.

Comparing it to the ZM derived Vds=36.5V Iq=2.3A 0.4R-speaker-0.2R (Speaker C), it has slightly higher THD at low power output and lower THD at higher power output. H3 is lower at all power output levels.

My power supply V+=62.5V.

So if you are building this amp, there is more than one operating point that sounds good. Of course, the THF-51S has lots of variability between samples so your results may not match mine.

I have also switched back to positive phase H2. In my system in my room, I prefer the sound to project out in front of the speakers. In the end it is a matter of personal preference and system compatibility.

Here are the distortion measurements side by side with the distortion measurements for ZM's operating point for comparision (left channel):

 

[Ben Mah]

Right channel:

 

[Ben Mah]

Also latest at approx. 5% THD, left and right:

 

[Zen Mod]

great work, as usual , Ben

of course - worth noting specifically ( you wrote that, and I'm underlining it) - both "mine" and "your" operating point specifics are more guidelines than something carved in stone

due to differences (specimen to specimen) in transfer characteristics of SITs in case and also fact of non-existing NFB to equalize things further - we can say that each amp made - is sorta specific and unique

guide-line points are more than OK to start with, but possible final tweak must be conducted in exact same way you did, using THD spectra measuring setup, and even then owner's cognitive apparatus must judge what's preferable - smidge down or smidge up

 

[plasnu]

Making slow progress on my Singing Bush. Decided to re-position the boards a little and add some local bypass caps.

I like this LED heatsink. Very nice and clean build. 🙂

 

[Ben Mah]

Thanks, ZM.

I am quite happy with this latest iteration. Previously I had mentioned a narrower soundstage. I think that is no longer the case. And the sound is smoother. Of course I am relying on my memory since I have had the amps out of the system for a while. But the bottom line is that it seems right to my ears and brain. 🙂

 

[yoshida]

Nice work, Ben-san

I'm only halfway there. can't wait listen sound.

 

[Ben Mah]

Thanks, Yoshida-san.

I am very happy with the sound of this latest operating point. It's a keeper. My experimenting is done.

Which version are you building? THF-51S? Are you going to try different operating points?

 

[jwjarch]

Boards arrived today! Thank you ZM! This one’s next after Babel J2. Still stuffing 1 million ZM resistors on that one.

 

[Zen Mod]

El Reino said that his Bush is Singing, too

🙂

 

[El Reino]

Hello all, my Singing bush sounds Beautiful. Node 30,1V and 2,2A. Left channel Thd 1 watt 0,20% 4Ohm and right channel thd 0,25% 4Ohm. Definitely keeper.

 

[soldersober]

Mine is like 1.4% THD, 2H at 1.2%, at 1W.
This is a quite assertive amp to me, I like it (a lot) at medium to loud levels, but not at all for late night whispering
I will play with stepping some components and values, will see how it unfolds

 

[El Reino]

soldersober@ what is your operation point?

 

[Zen Mod]

Mine is like 1.4% THD, 2H at 1.2%, at 1W.
This is a quite assertive amp to me, I like it (a lot) at medium to loud levels, but not at all for late night whispering
I will play with stepping some components and values, will see how it unfolds

just in case , #97, The Singing Bush

 

[soldersober]

soldersober@ what is your operation point?

62V rail, 31V at output node, Iq 2.3A, Vgs 4V
SIT is 2SK182 ES

Resistor string as per Zen Mod guide

 

[Ben Mah]

Zen Mod had 37V at output node. The distortion will decrease if you increase your voltage from 31V to 37V at the output node.

I run mine even higher.