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tvrgeek 27th July 2012 10:42 PM

I figure I want to round out my Nakamichi ST-7 & CA-5 with an amp designed by our friend Mr. Pass. I have other amps designed by most of the names that are recognized. (Jim, John, Erno etc) The PA-5 comes to mind. I thought about a smaller Adcom, but sorry to say, I really don't like the larger ones so I was not going to jump. The Thresholds are pretty tough on the budget, considering anything that old needs at least caps, it adds up quick. Or do I jump on one of these "hot" DIY jobs?

I am using a modified DH-120 right now. No one has convinced me I need a kazillion Watts, but my 6P1 tube amp won't cut it either. Smooth is the word of the day as some of my big-band and a lot of older CD's can make some amps a tad edgy. Source is a NAD 565 CD, with or without a BurrBrown external DAC. Speakers will be my own. I call them SR-72 as they are very similar to the Zaph SR-71, just a few steps beyond. I have so many speaker and other projects going, I don't want to go as far as etching boards. I would just never get to it.

So what's the word over here in Pass-land; used, modded, or scratch? I'm partly fishing for word on how good the PA-5 was. The Hafler is several steps above it's original design, and I could always use one of my many slightly cleaned up Rotel 951's as they are beguine, if not very detailed. I want more.

tsiros 27th July 2012 10:45 PM

well, the site is

cochleus 28th July 2012 12:57 AM

I say build your own Papa Amp from scratch. There is a lot of variety of models to choose from. There is an extensive library of articles.:D There are finished circuit boards around, and plenty of very experienced builders to help out if you get stuck. And, to quote Papa himself; "Put on some sun screen, and come on in. The water's fine.":D

Melon Head 28th July 2012 05:12 AM

Check out the diyaudio store. There are few options for you to consider regarding Nelson Pass designs

tsiros 28th July 2012 01:51 PM

soft start and speaker protection boards, both for $20! sweet! :D

KatieandDad 28th July 2012 02:05 PM


Originally Posted by tsiros (
soft start and speaker protection boards, both for $20! sweet! :D

Some love the protection boards, purists hate them. Soft start boards aren't realy necessary with transformers up to 500VA per channel.

The original Pass amps don't have the protection boards but do have soft start circuitry.

A correctly built Pass amp wont need protection but may need soft start.

My Aleph 4 has neither and has 2 x 500VA transformers - Dual Mono configuration.

AudioSan 28th July 2012 02:40 PM

500VA pr chassis. not pr ch:) (230V 16A) and it realy depends on cap bank.
i tryed 1000VA 40.000uF. the fuse hold 1 of 10 times:)

KatieandDad 28th July 2012 02:43 PM

1 Attachment(s)
I've got a single chassis with 2 x 500VA connected in parallel across 240V. The 10A fuse has held for over 5 years.

The cap bank is 4 x 3 x 33000uF, i.e 100 000uF x 4 (for four rails)

If you read the original post, the originator is unlikely to be building of of Nelsons' leviathons so he probably wont need a soft start. If he has problems with fuses then he can consider adding soft start later.

AudioSan 28th July 2012 02:46 PM

without any NTC or nothing?

KatieandDad 28th July 2012 02:53 PM


Originally Posted by AudioSan (
without any NTC or nothing?

Absolutely nothing. Well it does have an RFI mains input socket, then the 15A switch then the 10A fuse then to both transformers.

There is a 90 Degree Thermal Trip in the circuit but that is doing nothing to supress the mains turn on current.

It is possible that the 2.2mH chokes are acting to limit the turn on current, as they are air cored they do have slight resistance. The bolts in the photo have been replaced by M10 nylon studding.

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