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So Good... I built it twice!

S-Man

Kinkless Tetrode Admirer
My favourite power amp:

IMG-3983.jpg


I have built many tens of power amps, but this is the first one I've built a second pair of.
(Actually I have had NCC200s twice, but at separate times, trying to figure out what all the fuss was about).

https://www.diyaudio.com/community/threads/the-most-popular-russian-amplifier-only-music-2-7.374372/

Now that I have the 2nd pair up and running I will be able to experiment with different configurations to try to further optimise the sound. However, my 1st set, built as a simple stereo amp beat all my other builds with separate/regulated/choke-fed/dual-mono etc. so I think it's fairly power supply agnostic.

The eagle eyed might spot a couple of caps missing - that's deliberate, part of my experiments.

As well as sounding very good it's rock solid in terms of bias stability and phase margin etc. and it has SOA protection. It doesn't use any exotic parts, although the 2SB/SDs are getting harder to find.
PCBs, BOM and documentation are all available. IIRC I got 10 for about £12 from PCBWay. The layout is technically excellent but just a bit cramped for component stuffing.

Recommended!
 
I like the look of that schematic - nice stiff/well-filtered current sources, a cascode or two, sensible time constants, Locanthi T output stage...
 
If only I didn't already have a handful of different amps in various stages of completion! Always enjoy a good pun, though.
 
And a very unSelfish way to do the frequency compensation.
Quite - appears to use lag compensation; J L Hood was a fan of this for various of his amplifiers. It makes an appearance in old DPA /Deltec amplifiers, too (which use lead+lag as a classic control system, two-pole approach)
 
Thanks for the pointer on this S-Man and the pair of boards you sent me a few weeks ago :)

I've got them built up now and biased (they bias up very stably compared to previous boards I've used) and just waiting for a couple of mechanical mods on my chassis heat sinks to get some music playing through them.

I've already worked out that it will be fairly straightforward to make the output transistors dual-parallel with the way I've made my L brackets.

Ah-yes the so-called "speed up" capacitors - I was thinking of omitting those too but have them at the moment. I can't remember who it was (Leach?) but somewhere I read said it was a fallacy that they were needed.

Looks like you have an "exotic" input cap ? :)
 
Thanks for the pointer on this S-Man and the pair of boards you sent me a few weeks ago :)

I've got them built up now and biased (they bias up very stably compared to previous boards I've used) and just waiting for a couple of mechanical mods on my chassis heat sinks to get some music playing through them.

I've already worked out that it will be fairly straightforward to make the output transistors dual-parallel with the way I've made my L brackets.

Ah-yes the so-called "speed up" capacitors - I was thinking of omitting those too but have them at the moment. I can't remember who it was (Leach?) but somewhere I read said it was a fallacy that they were needed.

Looks like you have an "exotic" input cap ? :)


Good to hear you are progressing with them.

In the past I've found that the speedup cap(s) smooth the HF a bit. Whether fitted or not-fitted sounds best is a matter of taste.

The input cap is a stacked film naked polyester. Not expensive so not sure if it qualifies as exotic :).
Actually, I built this pair from bits I had lying around.
My L-brackets go full length under the boards - nice for mounting to a chassis or heatsink but not nice for adding components.
 
The speed-up cap value should surely be based, on the amount of charge you might need to 'pull' from the base of following output-stage BJT..

..which under near saturation, in a simple EF, the base input capacitance might approach 1-10 nF - so to change that potential fast enough, at HF might well require 1-10uf+ in the 'speed-up' position
Yet with the Locanthi T is it needed..? can the cross-conduction risk be avoided without one, to other benefit..?



(that's my musing on where S-man might be going with the two parts he elided in the the pcb pic in post 1.
Looking forward to where things go from here.)
 
@S-Man; for context, what other amps have you had / built?

Do you have any boards spare?

Sorry, I would like to hang on to the last 4 boards I have.
Somewhere in the DIYA thread there are links to the gerbers. SInce the boards are less than 100 X 100mm they are very cheap.

What other amps have I built?:
Aleph 5/30
Hawk A-18
GB150
AKSA 55 and 100N
ESP P3A
NAP 200 clone
NCC200
NCC300
Maplin Mosfet
JLH 80W Mosfet
JLH 1980 Mosfet**
Alecto clone
JLH class A
Juma Class A mosfet
Ion Obelisk-alike
Leach LowTIM**
Mooly mosfet**
TGM8
Akitika GT101**
DX Blame
MyRef Fremen Edition

I'm sure there are more :eek:.

The ones marked ** are currently working/available for use.
 
Good to hear you are progressing with them.

In the past I've found that the speedup cap(s) smooth the HF a bit. Whether fitted or not-fitted sounds best is a matter of taste.

The input cap is a stacked film naked polyester. Not expensive so not sure if it qualifies as exotic :).
Actually, I built this pair from bits I had lying around.
My L-brackets go full length under the boards - nice for mounting to a chassis or heatsink but not nice for adding components.

Will be interesting to hear what you find from your experiments.

Here's my efforts so far.

https://ibb.co/DkPhzxL

I went for 63V caps where necessary as I plan to run off 50V rails, and hence go dual parallel shortly. My brackets only pick up on the mounting holes near the outputs, so I should be able to mount a 2nd pair of the transistors on the underside.
 
An observation:

None of the cascode devices (VT3, VT7, VT9) have base stoppers, so there is a risk of RF oscillation. If that were a problem, putting say 100Ohm resistors in series with the bases would avoid trouble.
 
How does this compare to the Contaminated Class A amp?

A year ago that one was looking very promising
 
Looks interesting, I've ordered a few boards to try this out. I'll have some spares if anyone's interested but I don't expect to get them for a week or two.
 
Looks interesting, I've ordered a few boards to try this out. I'll have some spares if anyone's interested but I don't expect to get them for a week or two.
I'd be interested in a pair of you have some spare.
 
I'd be interested in a pair of you have some spare.
I’ve ordered 10 boards, I’ll use 4 and 2 are spoken for so you’re welcome to a pair. That leaves 2 more if anyone else wants to give this a go.

I’ve found an article about the design and build in Russian that I’ve run through google translate. I’ll post a link if anyone is interested.
 
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Thanks S-man for the recommendation. I was deliberating which amp to build next and you made my mind up for me

I just ordered a batch of 10 boards from JLCPCB for $5 plus shipping (at the moment - CNY).
 


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