Lazy Singing Bush

[JKiriakis]

A salute to ZM, beautifully organized kit complete with non-trivial requisite customs documentation, and

Seasonal Easter egg postage stamps!

I am compelled to ask:

What is the origin of the name "Lazy Singing Bush"?

 

[Zen Mod]

for Singing Bush name origin, see in appropriate thread

"Lazy" because this one is gainless, doing pretty much trivial work, comparing to origin

 

[Zen Mod]

next amp should be named "Visible Swordsman"

 

[JKiriakis]

@Zen Mod that was highly informative. I think the "for he's a jolly good fellow" emanating from said bush is meant for you. Invisible Swordsman would be a really cool name for an amp.

Question: Which specific thermistor x 4 do you recommend for your Handy Addendum PCB's?

 

[Zen Mod]

CL60 is fine

"Visible Swordsman"

 

[MEPER]

I like to have all the voltage gain in pre-amp as PSU is often finer in the pre and more rough in a power amp. I think this overall gives better SNR. E.g. IronPre driving Lazy Bush in my case.

 

[JKiriakis]

And we start again. I made a careful component inventory referencing the kit list, parts bags and schematics. Completely accurate thank you.

@Zen Mod question for you re Mu resistors:

Should 3W MOX in R4 R6 R8 R10 R12 = 1R?

And 3W MOX in R5 R7 R9 R11 R13 = 1R5?

Schematic in post #1 here indicates 10x 1R, I've read the subsequent posts on adjusting the values.

I'll be running the THF51S.

Thanks in advance!

 

[Zen Mod]

(late) edit on Jan 25. 2024. - change of Mu resistors values, as per Ben Mah's suggestion - post #17, https://www.diyaudio.com/community/threads/lazy-singing-bush.388164/post-7069779

 

[Zen Mod]

@Zen Mod that was highly informative. I think the "for he's a jolly good fellow" emanating from said bush is meant for you. Invisible Swordsman would be a really cool name for an amp.

Question: Which specific thermistor x 4 do you recommend for your Handy Addendum PCB's?

CL60

if you have single primary, use one

if you have dual primary (connected in parallel), use one per primary, so two

 

[JKiriakis]

Thanks ZM and Ben! Mu resistor popsicle

 

[Zen Mod]

clever

and yummy

 

[birdbox]

Thanks ZM and Ben! Mu resistor popsicle

Well that's just genius. I had to give it a try and sure enough the toung depressor size works as well.

What a great solution to something I know I struggle with. Worked great and slid right out after soldering legs!

Thank you @JKiriakis !!!

 

[JKiriakis]

@birdbox glad that worked out. I have used carboard or toothpicks in the past which don't work as well as popsicle sticks. Yours are even better.

@Zen Mod two quick questions please:

1) how do I orient OK1 which is the 4N35 on the Mu PCB? (EDIT - found the pinout diagram, I see now the dot on the device is adjacent Pin 1anode which connects to Pin 5 collector on to the positive side of C2)

2) is it advised to pre-set trimpots P1 (5k on the SIT board) and 10K on the Mu board)?

Thanks in advance!

 

[JKiriakis]

Awaiting backordered C8 capacitor from Mouser. Kemet 80V 15000 hours, expecting these monoblocks to persist.

https://www.mouser.com/ProductDetai...TVkIWiilMyg==&countryCode=US&currencyCode=USD

 

[Zen Mod]

2) is it advised to pre-set trimpots P1 (5k on the SIT board) and 10K on the Mu board)?

naah

they usually arrive from factory somewhere in mid position

perfect for startup

 

[JKiriakis]

Next question: I am awaiting two Pass DIY tribute chassis from Gianluca at Modushop. Monoblocks planned for the Lazy Singing Bush THF51S + IXTN40P50P

I see they are 4u/400 deluxe configuration, so two piece heatsinks.

Reading elsewhere in the forum, I believe it will be necessary to add aluminum flat bars to provide good dissipation from each device on each side of each monoblock.

1) Do you think 3/8" x 4" by 12" flat aluminum flat bar stock mounted to the sinks will work for me? That's 9.525mm x 101.6mm x 304.8mm

I can go thicker and wider for a bit more money.

2) Wise or necessary to add thermal paste between the flat bar stock and heatsinks?

 

[Zen Mod]

Good thinking - with just one OS part per side, you need spreader

1. 9,525mm is ok; if you cab choose - say that 150x200 mm is better than 101x300

2. better with than without; take care to have it in thin layer and enough screws; min M4 screws, and no need for fatter than M4

 

[JKiriakis]

Next question please:

What is the value of the flying resistor directly attached to the gate of your THF51S?

Any need to remove R16, R17, or change their values when using the THF51S?

I did order the aforementioned spreader plates, now 150x200mm. How many M4 fasteners per plate would you advise?

Thanks ZM!

 

[Zen Mod]

ref to schm in post #1

R17 used only for Schade osfe, so not fitted for THF51 or any other SIT

flying resistor, ditto to gate pin of SIT, heatshrinked properly, value 47R

if that, no need for R16 on pcb, solder wire (leading to flying gate resistor) to "G" wirepad on pcb

150*200 spreader plate ......... 8pcs of M4 screws/bolts