advertisement


Avondale NCC300 amp project ..

Mike Hanson said:
In my Voyagers (VBE+QUDOS), I'm pretty sure my VBE input voltage was higher than the QUDOS' output voltage. (The VBE regulates it down to match the output voltage, which is what the QUDOS requiremay be mistaken, but I thought the NCC300 was sort of a VBE+QUDOS combo. Therefore, I was surprised when I noticed your front-end voltage (±45VDC) was lower than your power-amp voltage (±57VDC). What am I missing here?!? :confused:

I'm quite keen to understand your amp, as I'm hoping to build a dual-mono 300 similar to that. I have two ±40VAC Plitron transformers waiting in the wings, which are going to be used for the two output stages. They don't have additional secondaries, though, so I have to by a third transformer for the input side. Given your message, I'm rather confused about the required output voltage.

Also, I'm wondering whether I can use a single transformer and CAP6 to power the input stages of both NCC300 boards (given their lower power requirements), or whether I need separate supplies.

And I'm concerned that I'm running out of space!!! I've got a Modushop Dissipante case, which has an internal space 120mm high, 360mm wide, and 400mm deep. I have lots of stuff to fit inside:
  • 2 x 500VA Plitron transformers
  • 1 smaller transformer for front-end (possibly with dual-secondaries)
  • 2 x Hacker-Caps for the output stages
  • Either a single CAP6 for the input stages of both boards, or two separate Hacker-Caps
  • Speaker protection module, and yet another 12VAC transformer
  • Avondale SSM2
I suspect that case won't be big enough, so I may have to go for two mono amps. I've got two spare Pesante cases, that I could use for that, although I would have to change the bottom panels to 4mm aluminum for heat dissipation. (I screwed myself once with that, so I definitely won't make that mistake again.) I would also have to get more SSM2 modules, etc. One nice thing, though: it would mean they would fit in my Mana racks. That 3U case would have to sit somewhere else. :rolleyes:

Thanks for any insight that you can provide.
Click to expand...

Your missing nothing Mike, I have run my 300's with up to 55v suppling the front end but not sure if there's any applicable gain. Rather I cant hear any and I like to have the regs 'regulating' with 5-7v headroom. I might wind them up again (50v-55v) and see. Yes you can run one PSU for both front ends if you like with a separate transformer
 
Pete MB&D said:
I think the height of you case is the answer to your problems, stack your CAP6's Hacker-caps and input transformers.
Click to expand...
Thanks. Each of my transformers is 60mm tall, so stacking them in a 120mm space is going to get a bit cramped. The CAP6's are each at least 75mm, so that's a no go for sure.

I'm starting to think I'll be reusing the Pesante cases with new aluminum bottom panels, in two mono boxes. I've got two other projects to finish before this one, though, so I've got some time to mull it over.
 
laverda said:
Yes you can run one PSU for both front ends if you like with a separate transformer
Click to expand...
Good to see this - most builds end up with separate traffo/PSU for front ends, but this is only because most builds on this scale are mono blocks.

If you manage to cram the "big" PSUs and amp boards into a single case, a shared PSU for the low-current front ends seems "obvious", since the front ends don't draw enough to "drive" the PSU and (hence) cross talk with each other. (*)

BugBear

(*) "obvious" can be wrong, of course...
 
For space saving the Canterbury windings HN5 was a good option and was designed for the Hackernap stereo power amplifier , everything you need in one transformer, job done.
http://www.canterburywindings.co.uk/standard_range.html

If I remember right though I asked Terry for 2 x 42-0-42V for the front end supply on my hackernap, I also stacked the cap 6 boards bunk bed fashion to save space.


Type: HN5
Continuous power rating: 812VA
Primary: 0-240V @ 50Hz
Electrostatic screen
Secondary 1: 35-0-35V @ 5A rms
Secondary 2: 35-0-35V @ 5A rms
Secondary 3: 40-0-40V @ 0.7A rms
Secondary 4: 40-0-40V @ 0.7A rms
GOSS band
Dimensions: approx 160x80mm
Mounting: M8x30mm bush
In a potted centre
Heavy gauge leadouts
Black acetate finish
Below is a Hackernap amp but you could do the same with the Kudos and there is enough height in a 3U case to stack Kudos and HCR200 on either heat sink

IMG_2217 by Alan Towell, on Flickr

Alan
 
Whooops Just realized this is a NCC300 tread so you will need the 400mm deep enclosure for a stereo NCC300 amp.
Using a similar HN5 transformer and pushing the NCC-300 boards towards the back case I recon you can fit everything in there, even fit in speaker protection board under the NCC300
Similar to Graham layout in fact shows it can be done :cool:
Im going to give this a try as I have a spare case and HN5 transformer :cool::D

IMG_3312 by Alan Towell, on Flickr

Alan
 
My box is 400 X 300 X100. I am planning on getting 2 large EI transformers, NCC300 X 2, Minicap6 X 2 (with 2 caps per rail for the output stage and 1 cap per rail for the front ends) in there.
Outputs will run on +/-40V
Front end +/-56V into regs and +/-40V out
The ZTXs run warm enough without over egging the VAS supply voltage.

It will need a fan!
 
S-Man said:
My box is 400 X 300 X100. I am planning on getting 2 large EI transformers, NCC300 X 2, Minicap6 X 2 (with 2 caps per rail for the output stage and 1 cap per rail for the front ends) in there.
Outputs will run on +/-40V
Front end +/-56V into regs and +/-40V out
The ZTXs run warm enough without over egging the VAS supply voltage.

It will need a fan!
Click to expand...

Outputs on 40v rails ? You’ll be missing out on the potential of the 300. It’ll run very well but so much better at + 50v rails. The ZTXs (at 55-60v rails) run at 35deg C well within their 70C spec. IIRC
 
ZTX753 is rated at 100V VCEO. Older transistors often have plenty of guardband, but if Diodes Inc have redesigned it (usual cost reduction/chip shrink) this may no longer be true. Anyway, without testing the breakdown voltage of each device it's best to stick to the spec, so +/-50V rails.

Thermal resistance is somewhere between 116 and 175 C/W. Let's assume 150 on the NCC300 pcb.
60V rails at 10mA = 0.6W
0.6 X 150 = 90C
It it gets to 40C in the box then the ZTXs will run at 130C. Max is 200C, so they should live for yonks. Don't touch the little blighters though!
 
It’s a strange thing, when you touch them with a finger tip they feel red hot, almost ‘ouch’ but the temp gun says just 34C. Ah yes 200C I remember now.
 
The temp gun is not measuring properly!
Also, remember my calcs are for the junction temp. Plastic is quite a good insulator, so they won't feel that hot.

Acually the junction to case is 70C/W, so even if you could attach an infinite heatsink, at 0.6W the case would be 42C above ambient = 70 or 80C.
 
Hi Alan - any idea approx how much a HN5 transformer costs?
(I keep asking Terry for quotes and not buying anything :-()
 
laverda said:
It’s a strange thing, when you touch them with a finger tip they feel red hot, almost ‘ouch’ but the temp gun says just 34C. Ah yes 200C I remember now.
Click to expand...

When we started using IR cameras at work we were told about the emissivity of different surfaces and told that a useful guideline was to attach a piece of black insulating tape to anything shiny and to take a reading from the black surface of the tape, worth trying?
 
S-Man said:
Hi Alan - any idea approx how much a HN5 transformer costs?
(I keep asking Terry for quotes and not buying anything :-()
Click to expand...
Don't know now David I bought 2 off him in 2014 so things will have changed no doubt since then
He always says send him an email for a price quote so best to do that.
Incidentally he also does the HN6 for 60hz but can do it for 50hz as well if you request (42-0-42)

Alan
 
So what's the best way to test my boards? I'm thinking of putting the 220R resistors and diodes in and the links and then powering the whole board up ( minus the output devices ) from just a single transformer/Cap6 board. Then it's set the front end rail voltages and finally check the bias swing and set as required?
 
You must log in or register to reply here.


advertisement


Back
Top