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 Post subject: Re: 845 amp project
PostPosted: 20 Jan 2016, 15:48 
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Joined: 15 Nov 2013, 10:16
Posts: 244
Location: MB, Canada
Geek wrote:
thehoj wrote:
So this amp has undergone a major overhaul.. Why? Well, I don't really know.. Maybe because I can never leave well enough alone.


You have been truly initiated :D



Haha.. I guess so.

The heatsinks (it's two next to eachother) on the top plate of the chassis are kind of ratty, rough, scratched up in appearance.. So I'd like to try and find a nice finished looking black anodized heatsink.. But this is proving to be really difficult to find! It's starting to get annoying.
I'd love to find something like this http://www.parts-express.com/sure-electronics-dc-hs11118-aluminum-heat-sink-kit-1093-x-585-x-18mm--320-3280 but much larger.

I need something that is very close to 150mm in width, between 250 and 300mm in length, and no more than 40mm in height. But I want something that looks nice :)

So far this is the only thing I can find that fits the bill pretty closely http://www.ebay.com/itm/1PC-Aluminum-E-Heatsink-For-Amplifier-300mm-145mm-50mm-/281908899925?hash=item41a3147055:g:GdYAAOSwJkJWl067 But it seems a bit pricey..

I've emailed a few heatsink places to see what they can do.. Though I have a feeling they'll be even more expensive :(

I was kind of excited when I found heatsinkUSA, because they have the right sizes (though I don't think they're anodized), but the shipping cost is ridiculous to ship to Canada..





One other note on the mosfet source follower.. Originally I was a bit concerned about the high input capacitance (Ciss) of the mosfet (1000pF), but quoting from tubelab.com:

Quote:
Mosfets in general have a lot of input capacitance. The gate to source capacitance is often large, but in a source follower the source is at nearly the same AC potential as the gate, so this capacitance is "bootstrapped". The parameter of concern is the gate to drain capacitance (Crss) or "reverse transfor capacitance". Some modern mosfets have this as low as 2 to 5 pf. Look for a reverse transfer capacitance that remains constant over the voltage range you are using.


With the Mosfet I'm using the Crss doesn't appear to go over 4pF (looking at the datasheet).. So I don't think I should run into any issues with HF rolloff. Though I'll have to do some testing with that as well.


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 Post subject: Re: 845 amp project
PostPosted: 04 Mar 2016, 09:31 
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Joined: 15 Nov 2013, 10:16
Posts: 244
Location: MB, Canada
Just thought I'd post another update.. I switched to Toshiba 2SK3564 mosfets for the source followers. Most importantly though I got a BIG heatsink (4 pounds) on top of the chassis now to primarily assist with dissipating heat from the mosfets which are mounted to the underside of the top plate. The heatsink will also assist with dissipating heat in general with any of the other parts attached to the chassis which create heat (filament regulators).

The heatsink was from HeatsinkUSA, and I had a contact of mine put some threaded holes in the base of the heatsink, as well as anodize it black for me. It's attached to the top and I love it. I suppose maybe it looks a bit utilitarian, but I like it.. And the heatsink covers up a bunch of holes that were in that top plate from when this amp had some other parts mounted to it.

The guts aren't exactly pretty, but it's very solidly wired up. I have no concerns about any part of the internals.
Not sure if I ever mentioned it, but the capacitors in the HV B+ supply are all polypropylene film rated for 1400V. The electrolytics that I used in the power supplies for the mosfets are all Nichicon 10,000 hr @ 105C rated caps.
The amp as it stands (having the driver as well as the raw DC supply which feeds the filament regulators in separate chassis') weighs in at 96 pounds!.. I will NOT be moving this thing around very much. Each output transformer weighs 20 pounds, and the power transformer weighs 26 pounds..

As biased, I'm measure 35W output power over a resistive load just before clipping. This is with a 1Khz sine wave input signal.
The amp is easy to adjust bias, with locking PEC pots accessible on the top. I put a little switch on top of the amp as well which allows me to switch the bias range to an appropriate range for either 845's or 211's. As pictured the amp is using 211's.

I also picked up a pair of Klipsch Forte speakers made in 1986. They're a pretty efficient speaker, in the 96 - 98 db 1w/1m range I believe. They're an excellent match for this amp though. Sound surprisingly nice at very low volumes, and good God can they make some incredible volume if I'm so inclined.
I'm FINALLY just able to sit back and enjoy listening to this amp. It's been so so so much work for me to build this thing :). Though I've loved doing it.


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 Post subject: Re: 845 amp project
PostPosted: 04 Mar 2016, 18:08 
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Joined: 06 Jun 2008, 18:23
Posts: 5144
Location: Australia
Golly.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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 Post subject: Re: 845 amp project
PostPosted: 21 Apr 2016, 20:18 
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Joined: 15 Nov 2013, 10:16
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Location: MB, Canada
Got the new driver built in its matching chassis.. Thought I'd share some pics of it all set up, driver and power stage together at last!


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 Post subject: Re: 845 amp project
PostPosted: 22 Apr 2016, 03:49 
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Posts: 5144
Location: Australia
Golly

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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 Post subject: Re: 845 amp project
PostPosted: 15 Oct 2019, 15:58 
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Joined: 15 Nov 2013, 10:16
Posts: 244
Location: MB, Canada
Here for a 3 year check in..
A lot happened with this amp over the last 3+ years.. Just thought I'd post an update for anyone who's interested.

First things first, about 2 years ago one of the secondaries in the power transformer for the power amp shorted, and the transformer was basically toast.. I contacted Heyboer who had wound it for me, and they said they would do a new one for me at no charge. Very good service I have to say.

Anyways, I made a few adjustments to what I had them wind in the new PT, and I also took a few windings out of that main PT and used individual transformers for a few things.
I also drew up in eagle CAD and had built for me at allpcb.com PCB's for my bias supplies, as well as the positive and negative power supplies that I use in the mosfet source follower circuitry. It just makes for a cleaner build, and less chance of me screwing something up with using perfboard.

Anyways, I just kind of lost interest in working on this amp for a little while. A few months ago though I decided to dive back in. I spent quite a bit of time wiring everything up, taking some additional measures to deal with dissipating heat sources inside the chassis, and overall I think this iteration of the amp is much more robust, though it's basically the same amp technically speaking as before.

I also sold my Klipsch Forte speakers and picked up some Zu Omen MkII dirty weekends (which I absolutely love).
I sold my Rega Planar 3, and picked up a Clearaudio Concept turntable and a Nagaoka MP-200 cartridge, which I also really love.
I also have a second turntable currently set up for playing records that aren't in the greatest shape.. Just something I could throw anything on. It's a Sansui FR-D3 with an Audio Technica AT95E cartridge. Great sounding turntable as well.
I have a little switcher beneath the turntables that lets me switch between either turntable as a source.

As for other equipment that you can see pictured in the pics below, I am using a Schiit Mani phono stage for the turntables.
I'm using a Schiit Modi 3 DAC, and I actually have a Schiit Loki 4 band EQ in the mix now. It's in the signal chain for both my turntables, and my digital source.
Say what you want about EQ, or this EQ in particular, but I love what it can do for me.

As for digital source I'm using a Raspberry Pi 3B with a Digione SPDIF transport, connecting via coax to the Schiit DAC.
I'm running Volumio on the Raspberry Pi, which I also really enjoy using.

One other little tidbit that I just added, which you may notice as the little black box between the driver and the power amp is an Arduino controlled stepper motor with an IR receiver. I have pulleys rigged up on the volume control of the driver stage and the stepper motor with a belt connecting them, and I can adjust the volume up and down with an IR remote now. Kind of a brute force type approach to adjusting volume remotely, but I enjoy the aesthetic, and it works really well.

Anyways, here are some pics. Everything looks a little rough around the edges, but I've been enjoying a lot of music over the past few months and I don't want to change a thing. It sounds great quiet, and it sounds great loud.


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 Post subject: Re: 845 amp project
PostPosted: 15 Oct 2019, 15:59 
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Joined: 15 Nov 2013, 10:16
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Location: MB, Canada
Here are a couple more pics.
The turntables, and then off to the side my tiny record collection, and record cleaning stuff.


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 Post subject: Re: 845 amp project
PostPosted: 15 Oct 2019, 17:16 
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Joined: 06 Jun 2008, 18:23
Posts: 5144
Location: Australia
I’ve read a number of varying reports about Zu speakers. Some appear to hate them others love them. I guess you are in the second camp. I was tempted to get a pair but now very happy with my DIY Altec 511B horns with top of the range Italian Faital Pro compression drivers and 12” woofer.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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 Post subject: Re: 845 amp project
PostPosted: 15 Oct 2019, 20:08 
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Joined: 15 Nov 2013, 10:16
Posts: 244
Location: MB, Canada
mwhouston wrote:
I’ve read a number of varying reports about Zu speakers. Some appear to hate them others love them. I guess you are in the second camp. I was tempted to get a pair but now very happy with my DIY Altec 511B horns with top of the range Italian Faital Pro compression drivers and 12” woofer.


Yeah I've heard varying reports as well. They're a fairly efficient speaker with nice specs though, and from what I read about them they seem to be a good all around speaker.
They've also got a really nice finish on them, nice hardware, high quality control in the construction process, and built in the USA.
Anyways, they just really do it for me. I listen to a pretty broad spectrum of music, and they sound pretty great across the board to my ears.


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 Post subject: Re: 845 amp project
PostPosted: 05 Nov 2019, 19:39 
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Joined: 05 Nov 2019, 19:16
Posts: 3
Location: New Orleans, LA
Hello Gents,
Superb build and so exciting to see it can be done DIY.
I'm brand-new here, and am about to dive into my own DIY journey. I'm looking to start with Speakers that I will drive with a system very similar, if not identical to what you've built here, "thehoj". Your painstaking efforts have yielded what appears to be a system sonically rivaling a "Cary Audio" build.
I have hopes of building a system that sounds as close to this as I can get, but for a fraction of the $50K plus price tag. I was an Electronics Technician in the Coast Guard for 30 years and am quite comfortable with solder, a solder gun, flux and alcohol LOL. The voltage issue does not frighten me,, as I worked on many systems, including a 1,000,000 Watt Loran Transmitter during my career. I hope not to offend, is it possible to build a system similar to yours for under $5,000-$10,000?
My desire is to fill my 20'X 15' vaulted ceiling living room with ample, gorgeous sound from many genre's.

Reading your posts was a delight. You clearly put a tremendous amount of time and effort into creating a masterpiece.
Look forward to your input.
Kev56


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