The Singing Bush Tips 'n' Tricks

[flocchini]

I am running 36V and 2.2A on each channel
Distortion .55 and .52%
Happy listening all

 

[yoshida]

Hello

I made test bench(SIT ver. with THF51S) and it starts singing!
I use small cheap speaker at now, so I cannot judge sound quality.
But, It seems no problem. Thank you Zen Mod.

Let me ask one question.
I use 4-2SK170BL(IDSS~9) as input JFET.
Your procedure mentioned buffer Iq should be set to 20mA at first.
But, mine reaches only 19mA at full turn of pot P1(100R).
Is it OK? I think 19mA is acceptable, but I feel uncomfortable for full turn of pot.

Hi, Ben
Sorry for late reply. Yes, I want to find good operating point.
But, it will be long. I need some test environment.

 

[Zen Mod]

set yours to 10 to 14mA, so 10 to 14mV across 1R

 

[TungstenAudio]

Here is a possible new chassis from Modushop for those beastly Singing Bush builds:
Ultimate 4U 500mm Chassis - Who is interested?

 

[rhthatcher]

Over the weekend I was looking at 5U/500 for this beast build. My thought process is:


My friend's F5 Turbo Monoblocks are in 5U/400's, and they run warm, but you can hold your hand to them no problem. So not too hot. .64A per Mosfet x 45.5 V x 4 Mosfets = 116.5W per side of the chassis. That is at the "90%" bias point, it can take more heat. Hope I got that calculation right...



Using THF51 or 2SK182 in the Singing Bush: 60V x 2.3A = 138W per side. ~20W additional heat in a bigger chassis. 5U/500 should take that I imagine.



Can 4U/500 handle it? Any idea of price 4U/500 vs 5U/500? I'm already planning to have to tap the heatsinks, so a little more drill and tap is no big deal.

 

[Zen Mod]

4U/500 should be a smidge bellow the verge

in other words - yeah, with Babysitter

 

[Itsmee]

...Any idea of price 4U/500 vs 5U/500?...

2 picoDumbs is getting a price for the 4U 500mm

5U 500mm 286.00
Inner base plate 12.41
Round handles 7.70
Milled Handles 18.45
+ vat and shipping
(price in euros)

I forgot to order the feet

 

[yoshida]

set yours to 10 to 14mA, so 10 to 14mV across 1R

Thank you for answer.

 

[vitalica]

I found that I have the following problem
When I did the test, I used a used 2sk182, with a Vgs -1.78 and I could adjust the voltage of 32-35 V on its Drain .(On Gate -2.54V)
When I replaced with new 2sk182, bought from Pras170, with a Vgs -3.6V, I can no longer adjust these voltages. Max can adjust up to 24 V on its Draun. (On Gate -3.86V)
Is there any way to fix this problem? Thank you very much for your help !

 

[Zen Mod]

there is easy fix

ref. to sch in post #2 - remove R10 (10K)

if that is not enough, decrease R12 (9K1) to , say, 8K2 or 7K5

easy peasy

 

[vitalica]

That's why I like ZenMod's projects, they are exceptional and he is always with a quick and very helpful advice! Thank you very much:cult:

 

[Zen Mod]

there is always a choice/dilemma : making adjustment span broad as possible, to cover all possible cases......... or making it narrower and finer, with possible need to alter few part values

I'm always leaning to later one; call me a Chicken

 

[vitalica]

I removed R10 and now 2sk182 works perfectly:
Vds 32V, the Gate - 4.1V
Vds 34.5 V, the Gate - 4.22V
Vds 36V, the Gater -4, 45V
Thank you very much once again!
I can't wait to do an audio test

 

[Zen Mod]

as usual:

-keep us informed;
-no porn, no glory

 

[rhthatcher]

Finally my Singing Bush is assembled! It is using 2SK182ES, CLC dual mono PSU. 5U/500 Chassis. I am glad I have handles on front and back!

wires are messy with inline fuse, no wires dressed... Better porn when all the tests are done...

Test 1 (no SIT drain wire connected)

Left Channel.
set 20mV. done.
IRF source 7.5ish? It was in 7 range...
SIT Gate max negative = -3.997V

Right Channel.
set 20mV. done. IRF source also 7.5ish? Move on.
SIT Gate max negative = -3.796V

Test 2 - Connect Drain Wire

Left Channel
Set Iq. Measure 460mV. Check.
SIT Drain - best I get is 28.5V, then P2 is clicking.... I lowered iQ and played with P2 thinking this was like the F5 or SissySIT game of pingpong adjustments. It doesn’t seem to work that way…

Right Channel, similar story. 460mV and 23.68V max.

PSU Voltage under load = 67.7V Hope this is OK... I'm using Antek AN-5450 500VA 50V Donut per channel.

Should I remove R10 and try again?

 

[Zen Mod]

SIT drain , you can get 28V5 and lower, but not higher?

if that's the case, you need more negative bias for SIT than you have now

try first with removing R10

if that doesn't help, increase R11 or decrease R12

all that referring gain pcb schematic in post #2

that's exactly same case Vitalica had, post #89

 

[rhthatcher]

R10 - snip snip. Biases up easily now. It’s playing some music and cooking up to temperature.

Another general question. I’m running 4A fuse / 120vac mains. I have 2 cl-60’s to each donut. I’m blowing fuses 50% of time on power up. Should I consider changing cl-60 to a different size NTC? Bump up fuse size? Both? Other?

 

[tubesguy]

5U/500 Chassis. I am glad I have handles on front and back!

Very nice! Is that a modushop chassis, or did you source it elsewhere?

 

[rhthatcher]

Very nice! Is that a modushop chassis, or did you source it elsewhere?

Yes, it is the big 5U/500 Modushop chassis. With all the weight in this chassis I am very happy I bought the handles.

 

[Zen Mod]

R10 - snip snip. Biases up easily now. It’s playing some music and cooking up to temperature.

Another general question. I’m running 4A fuse / 120vac mains. I have 2 cl-60’s to each donut. I’m blowing fuses 50% of time on power up. Should I consider changing cl-60 to a different size NTC? Bump up fuse size? Both? Other?

you Dodo

said everything, 'xcept what VA Donuts you have in

and, I hope, you have separate fuse for each Donut

more porn, please

btw. easy remedy for blowing fuses during power up - do not power it Off, when fuse survives