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Old 7th March 2009, 06:37 PM   #21
infinia is offline infinia  United States
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Default Re: god i hate nad amps

Quote:
Originally posted by sakis
anybody willing to try it is very welcome and i also have gerber export for it ....

please notice that this isa demo and it is possible that i ve made mistakes that i couldnt find with double checking !!!!!

there you go

Borrowed a couple of NAD monoblocks in the late 80's (not sure of the model) for listening tests. After a couple of days, boxed em back up. Definately much too noisey. Test over, man. Never did look at NAD again after that experience.

PCB checking. Don't you check the netlist after importing to the layout tool? Doublechecking works for me too.
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Old 8th March 2009, 12:14 AM   #22
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the 2SD753's and their complements are discontinued. you might want to look at using MJ15024/5 outputs, as they are 250V devices. for your input stage, you would be better off with a +/-15V rail derived from a separate low voltage winding and use 3 terminal regulators. Fender uses a similar zener/resistor combination in some of their amps, and they use 10 watt resistors, and it's still a reliability nightmare. the zeners run hot and are prone to shorting, and burning up the 10 watt resistors when they do. that tends to leave a lot of scorched real estate on a board. with Fender's design, that also tends to latch the amp output to one of the rails, and has a tendency to take out output devices and voice coils simultaneously. like the schematic shown, protection circuits are nonexistent.
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Old 8th March 2009, 11:56 AM   #23
Bonsai is offline Bonsai  Taiwan
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Sakis,

I would pass this amplifier by.

A 200W amp capable of driucing a real world load needs mor e output devices.

Seems to me a lot of shortcuts have been taken here.
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Old 8th March 2009, 12:38 PM   #24
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I agree with Bonsai, in the least redesign the input ltp, add another pair of output transistors and no need to use that high a voltage.

BTW the topology behind the amp is not bad, that vas will be pretty good, I am wondering who was first using that push pull type ltp, tom holman or whoever designed this amp. Ive built tom holman type amp, and find it to have monsterous good clean bass, overall a good amp.

Sakis if youre interested and not too much in a hurry, we could put heads together and redesign some parts of this amp and turn it into a interesting project.
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Old 8th March 2009, 12:41 PM   #25
AndrewT is offline AndrewT  Scotland
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I got 170W into 8r0 from +-58Vdc using a 40Vac transformer.
Your 200W target will be easily met using a 45vac transformer.
There is absolutely no need to go to +-90Vdc for a 200W amplifier.

The economic part of that 40Vac decision is, it allows one to use 63Vdc capacitors, saving a lot of space and money.
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Old 8th March 2009, 12:49 PM   #26
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Default guys thanks !!!!

Quote:
Originally posted by Bonsai
Sakis,

I would pass this amplifier by.

A 200W amp capable of driucing a real world load needs mor e output devices.

Seems to me a lot of shortcuts have been taken here.

Quote:
Originally posted by homemodder
I agree with Bonsai, in the least redesign the input ltp, add another pair of output transistors and no need to use that high a voltage.

BTW the topology behind the amp is not bad, that vas will be pretty good, I am wondering who was first using that push pull type ltp, tom holman or whoever designed this amp. Ive built tom holman type amp, and find it to have monsterous good clean bass, overall a good amp.

Sakis if youre interested and not too much in a hurry, we could put heads together and redesign some parts of this amp and turn it into a interesting project.

thanks for all but i was actually making a relaxation exrecise yesterday so thats why i made this pcb .... its exact copy of the original schematic ( unless i made some mistake ) but designed for plastic transistors and has 4 more transistors per board ( so transitor wise it will be almost enough to operate wit 90+90 rails )

i mostly did it for fun ...but personaly i would never built an amp supposed to be for PA use ( this is what are we looking at here ) without VI limmiters on board .....

also i agree that from 90 volts to 15 is a long way to go ....so also there should be some improovement

but on the other hand if this was a working circuit comercially made and the only think i did is to add a few more transistors then with a very sophisticated protection circuit it might as well work like hell .....

far more simple circuits with by far more minimalistic topology work like hell and prooved to be perfect tools to make money and sound in small Pa applications ( i refer to the modified HILL chameleon clones iv been runing for more than a year now absolutelly problem free )

thanks though
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Old 8th March 2009, 12:52 PM   #27
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Andrew you are right, 90 volts is crazy, I know some audiophile friends that have first hand experience of of 70s 80s amps and they told me this was at the time a very good sounding piece of equipment, out of curiosity at what this amp may be able to achieve Im gonna run it in simulation but redesign the front ltp and use modern devices.
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Old 8th March 2009, 12:56 PM   #28
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Default xmm

disipation wise and generaly you are both very correct ....

but then again may be you have to read the aythor's presentation about the amplifier ..... i dont know if right but the way he says things sound very attractive
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Old 8th March 2009, 01:02 PM   #29
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Sakis this is not a PA amp, but its pretty easy to incorporate VI limiters here, 2 extra trannies four resistors 2 diodes, extra pair of outputs. I will slap on a improved output stage, cfp ef which I prefer for PA and car amplifier use.

Nowadys there is not much diffrence between consumer grade hifi and pa amps, there are PA amps which are very well designed and will fit in perfectly in a home setting with comparable good sound.
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Old 8th March 2009, 01:03 PM   #30
AndrewT is offline AndrewT  Scotland
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Hi,
were the 700 series amps Armstrong's first foray into SS output stages without an output transformer?
Or did that tribute belong to the 600 series amplifiers?

The Armstrong was a fairly good value, cheap British amplifier that just got into the HiFi category, when HiFi used to mean striving for High Fidelity.

I have no idea how reliable the Armstrongs were nor how long it took them to develop transformerless output stages. This could be a risky project.
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