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Old 19th January 2013, 06:07 PM   #1521
carsten.witt is offline carsten.witt  Germany
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Join Date: Jan 2006
Location: Berlin

sorry not finished, but see ........

Click the image to open in full size.
Actual playing: Mac mini - WaveIO- Pass D1 Clone - P1.7 Clone - Aleph mini - Spendor BC1 on my working space.
Out of Photo:
- On the left side the Pass Ono Clone (Dragan), glue to dry
- On the right side the AJ like in this case
Click the image to open in full size.

Other comes .........
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Old 20th January 2013, 06:31 AM   #1522
TC Goh is offline TC Goh  Hong Kong
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Default My F5T Build


A few months ago, I began looking for an upgrade to my tube power amp. Although it sounded very smooth, it didn’t have the bass punch and control of my previous SS Aragon 4004.

A fellow enthusiast sent me Nelson Pass’s F5T article. I was intrigued by the minimalist and simple design and most of the opinions of diyers who have built the F4 and F5/T were positive. Also, there is a community of very experienced builders on the forum who will be able to help me trouble shoot any problems.

I know there are very good PCBs on diyaudio which many diyer’s have used with very good results. However being a novice, I was looking for a ‘turnkey’ solution. I ended up getting the F5T kit from FetAudio. As usual, Spencer was very helpful.

Frankly, soldering the PCBs together was the easiest bit.

Interestingly, the case proved to be the most challenging (and expensive, to my surprise!!). This almost stopped the build on its tracks! Anyway, after a few false starts, I finally managed to find a Chinese seller who was prepared to drill and tap all the holes to mount the PCB (plus Mosfets and MUR diodes) and also all holes on the back and front plate. The process was complicated as the seller made some mistakes and I made some changes after placing the order. It was a mess. This ‘ding dong’ went on for 2 whole weeks with over 100 emails. At that time, I couldn’t abandon the build as I had paid for the cases and bought all the other stuff!

Anyway, I think the cases came out alright and do look nice, don’t they? If I had to do it all over again, I would get the cases sorted before anything else!

As for filtering, I used Rifas PEH series (now Kemet) 63V caps. These are superb as they are low ESR and inductance. TX are two 2*25V 500VA toroidals. I couldn’t get 24V ones at the VA I wanted easily. Bridge diodes are Vishay, as suggested by Nelson. I use two for each rail as the TX secondaries are just too thick/stiff. As for smoothing, I went for CLC instead of CRC.

The rectified DC output at the caps are about 32.2V (loaded), and are within 0.1VDC across all four rails. I had to include an AC power delay board to prevent the house circuit breaker from tripping!

Biasing the amps was most interesting. Although I had familiarized myself with the biasing procedure earlier using my PS, I still had two close calls, both with electrifying results! The first was when the MM probes accidently touched a nearby cap and the second was when I was removing a grabber clip. In both instances, there was a huge spark. The tip of the grabber clip was vaporized and the MM probe was left with a huge burnt mark!!! These amps can sure deliver a huge amount of power. I was fortunate as the amps appear unaffected. The lesson here …. ‘turn-off amps, remove AC power connector, discharge caps then attach/remove probes’. I have now put in some bleeder resistors, just to be safer.

The amps are biased to 1.4A per channel. The heat sinks are warm to the touch after an hour so I guess it passes the ‘Pass’ heat test. Maybe I should be a Pass FAB – Fearless Amplifier Builder. Increase bias to 2A!!!!

I did plan to have speaker protection using the NEC upc1237 chip initially but after reading up, I think the conclusion was that this offers limited protection as relays don’t react fast enough to cut power off. I hope this is right. So I started listening using my daughter’s home stereo speakers, just in case. Hey, these are Sony’s ….. Ha ha…

All this build work was fun but what about the sound? In one word … ‘awesome’. I have the bass punch and control I wanted/missed. Furthermore, the bass is extended and goes really low. Mids and highs are very natural and transparent. Overall, the sound is really smooth and relaxed. Perhaps I finally now have an amp that has enough power to drive my 4 ohm Thiel CS2.4s.

The mids and highs are where the most significant improvement over my previous amp are. The clarity and smoothness is just amazing. The tube push-pull power amp now sounds lethargic, by comparison.

I hope this was the sound Nelson heard with his F5T.

I am not sure what to do with P3 though. Just left it untouched, for now. Ideas?

At the start, the amps sounded terrible. Mids and highs were harsh. However, after a day of burn-in, they began to perform, delivering sweet sweet music. I guess this is normal? Everything is new and the caps probably need time to form before doing their thing.

Of course, I tried bridging the two amps, initially using my daughter’s stereo speakers again. As it turns out, I am not a FAB after all. Ha ha…

With the Thiels, the musicality and bass punch/extension improves further. Unfortunately, I can’t really say for sure as there is a problem with my pre amp. The darn thing hums!!! In bridge mode, the F5T is so powerful that the hum is clearly audible. Really annoying! Hence, I am now looking for a new pre amp… what a bummer! Er…. on the other hand ….. do I see a new build on the horizon? You bet!!! Yippie !!!!

Anyway, I would like to thank Nelson Pass for releasing this wonderful design to the diy community. I guess I was fortunate to be able to jump in at this stage, benefitting from the tremendous amount of improvements from preceding versions. I must admit I am fast becoming a Pass’ian!!!

Thanks Mr. Nelson Pass. You’re the Man!

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Old 20th January 2013, 08:05 AM   #1523
MASantos is offline MASantos  Portugal
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Awesome build!!! Do you mind sharing the supplier and cost of those cases?
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Old 20th January 2013, 03:47 PM   #1524
ijscobar is offline ijscobar  Netherlands
Join Date: Sep 2012
Originally Posted by TC Goh View Post

Interestingly, the case proved to be the most challenging (and expensive, to my surprise!!).

Nice cases! Do you mind sharing where you got them?
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Old 20th January 2013, 10:43 PM   #1525
TC Goh is offline TC Goh  Hong Kong
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Location: Hong Kong
Default Cases


Thanks. I bought the cases off a seller in China but he appears to be on vacation. However, I have written to him. If there is enough interest, maybe I can get him to reduce his prices and I can get another two!!! ha ha... Don't ask me why I need another two case as in Hifi land, logic doesn't always prevail!!!

So, can you PM me?

Oh, here is the setup for my biasing practice run.

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Last edited by TC Goh; 20th January 2013 at 10:55 PM.
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Old 20th January 2013, 11:06 PM   #1526
boywonder is offline boywonder  United States
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Default Let's talk inductors.....

TC Goh:

Did you wind the CLC chokes yourself or buy them?

Last edited by boywonder; 20th January 2013 at 11:10 PM.
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Old 20th January 2013, 11:27 PM   #1527
TC Goh is offline TC Goh  Hong Kong
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They are Solens 1mH. I couldn't find insulated AWG14 wires here. So, in the end, it was just quicker to just buy.


Last edited by TC Goh; 20th January 2013 at 11:31 PM.
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Old 21st January 2013, 01:42 PM   #1528
bcmbob is offline bcmbob  United States
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Default The Ugly Duckling

I finally got through the "discrete" door. I've been building chip based amps for about three years and always had that "Pass" whisper floating around the room. Completed a pair of Nelson's Amp Camp design a month or so ago, but still wanted to try something bigger.

This is a kit ........ link removed by moderation .....---that probably can't be called a pure Pass amp but is a similar approach. It has speaker protection on-board that was an adventure to get to work but is functioning as designed now. There are two pair of power transistors missing from each board as I learned the hard way about the need for double checking the tightness of the heat sink attachment bolts.

The amps sound great and I understand all those comments about the smoothness of this approach. Just bench speakers so far but I'm sure I'll be thrilled with the sound when I move them to the Sunflowers. I have read a lot about discrete amps not being well suited to low efficiency speakers, but from what I'm hearing (even without all the power transistors) I'll never need anything stronger - big surprise. Although, there might be a diyAudio Store F5 build in the not to distant future.

Hopefully the "ugly duckling" will soon become a lovely swan with some reconfiguration and a nice chassis. I couldn't be happier with the active support I received from the vendor of this kit. There are many differences between this and the MyRefs I'm used to, and all my questions and mistakes were resolved promptly.
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Bob M.
"Arrange Whatever Pieces Come Your Way."
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Old 21st January 2013, 08:40 PM   #1529
norb is offline norb  Germany
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Default Preamp project

Dear TC Goh, maybe something like this:

An integrated B1 / PearlPhono Preamp. Add a switch, some power supplies, turn-on delay and you get a perfect preamp in no time .... or thereabouts.

The Pearl Phono are original PCBs, the B1 and power supply PCBs are self-designed to be able to use existing parts, most of all capacitors.

I added a „quick charge“ circuit (R7, R18, D2) to the B1 bias voltage supply, which charges C2 to within 1,5 volts of its final voltage within 18s and output muting relays, which enable audio signals after 20s, so you don´t have to wait that long after a cold start of the Preamp.

Inputs are switched by an ELMA Type 04 2x6 gold plated rotary switch.

The power supply PCB has 3 small toroids for catering the B1 and the Pearls individually. The small perfboard on top is the turn-on delay circuit.

The case is made from 2mm laser cut steel plates and milled steel bars with M4 threads to bolt it all together, knobs lathed from 50mm round steel bar. All steel parts are brushed and finished with a transparent glossy varnish.

The steel case provides excellent shielding, there is no noise pick-up by the Pearls or the B1 from the transformers or other electromagnetic interference. Of course the metal case is well grounded.

Soundwise the B1 is like a short piece of wire with high Z at one end and low Z at the other.
The Pearls to me - having always preferred CDs - were kind of a revelation, they made me get a serious turntable instantly.

Thanks very much, Mr. Pass and Mr. Colburn.

..... and yes, the case was the hardest part.
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Old 21st January 2013, 08:42 PM   #1530
R-K Rønningstad is offline R-K Rønningstad  Norway
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Originally Posted by TC Goh View Post

A few months ago, I began looking for an upgrade to my tube power amp. Although it sounded very smooth, it didn’t have the bass punch and control of my previous SS Aragon 4004.

It is nice to see the power switch located on the front panel for a change!
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