DIY Pass F5 amp

To those who may have heard, it is none other than the designer himself of Passlabs who has shared this circuit and patience to 'splain the working with pictures and documentation. To get started, here is my casing.



and the commercial product, available at not less than USD 3000.






some specs
SPECIFICATIONS
Gain 20 dB balanced, 20 or 26 dB balanced
Freq. Response - 0.5 dB at 2 Hz, -2 dB at 100 KHz
Power Output 60 watts/ch 8 ohms
90 watts/ch 4 ohms
Maximum Output 30 volts, 8 amps
Distortion (1KHz) 1 % @ 60 watts, 8 ohms
3% @ 90 watts, 4 ohms
Input Impedance 10 Kohm unbalanced
25 Kohm balanced differential
Damping factor 50 nominal
Output Noise 600 uV unweighted
DC offset < 100 mv
Power Consumption 300 watts
Temperature 25 degrees C. above ambient
Dimensions 12 " W x 12" D x 10.5" H
Shipping Weight 60 lb.

and the documents here

http://www.firstwatt.com/downloads/F5%20Power%20Amplifier%20for%20PassDIY.pdf

Hi Chua

Looks like a fabulous project! Thanks for sharing it with us. Look forward to seeing more shots as the work progresses. The current and voltage ratings make it an ideal amp for my Quad ESL's.

What speakers will you be using it with?

Regards

Hi Chua

I had a read of the document you linked to. I loved this bit by Mr. Pass...

Audiophiles are often concerned about the effects of capacitors in audio circuits, but a quick examination of the schematic will put your concerns to rest.

Simply Awesome. And a brilliant technical writer. Too bad our fellow Malaysians generally don't like to learn how to build things and mod things Chua as my Learning to Mod Interest Check thread showed us. It would have made a truly fabulous DIY group build project. Not too hard... and a member here has a solution for the hardest bit which I think you have purchased one... the enclosure...

Regards

See Nelson Pass philosophy of continuing using brute PSU with normal industrial rectifier. He doesn't believe in fast recovery types for power amps.

Say, can u point me to links to the PCB & case ? Thanks man.

Regards,
Joe Ling

Nelson is also known as PAPA in diyaudio. He is prolific and very unselfish in sharing, even for the trivial petty things.

The other other guy in the thread is John Curl. If you want some good preamp, check his thread.

You should look at CViller (first choice) if not Peter Daniel.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=134554

As for the case, check hifi4sale thread. look for PCH1 or PCH2.

Hi Chua

When you mention Mr. Curl, are you talking about his blow torch preamp, or something else he offers DIYers?

Do you have a link to the Daniels preamp? Thanks!

Regards

Yeah. that's the blowtorch preamp.

Here is the work in progress on F5.

Hmm, another PassDiy fans. Glad to meet you.

Well, I hv completed one of passdiy many yrs ago. I hv made the Son of Zen during my school days. I'm not with any electronic background and all the efforts were from my friends. I only did the assemble parts and itching. My friends help me did the soldering.

The quality I used most were audio grades especially capacitors. Although the power amp. is just only around 10 watts being achieved but the quality of the sound is very good.

Hi Chua - How is your f5 project progressing? I have just started on acquiring the parts for the pass f5/B1. Perhaps we can compare notes when I have my parts in-place and assembled.

this is a interesting project to do. good for beginners too.

@chua55

Very impressive... hats off to you.

If u feel the horniness to build another clone amp of some famous brand, i got the schematics for a clone Krell KSA-50 amp.

Pls PM me if u want the DIAGRAMS and are keen to build one.

mthoi wrote:Hi Chua - How is your f5 project progressing? I have just started on acquiring the parts for the pass f5/B1. Perhaps we can compare notes when I have my parts in-place and assembled.

You have your ps board using 8 caps (with 35mm max dia)? I am looking for one. if not I will just solder point to point. I am using Nichicon, could have used RIFA white sausage if not $$$. Most of the resistors I use PRP, Holco. heard Welwyn is good.

the F5 slows as I was building the tda1541a, adding shunt reg to the dac and receiver chips so that I have dual stage regulation. also modding the output stage to pass D1 discrete single ended. will try the charge transfer power supply (works like battery supply, dark background).

Krell KSA50 is a common diy project, and there is a little Krill too. Among the diy amp, passion burns for Pass amp.

Hi Chua, I got the PSU's PCB board from e-bay (Jims_audio). There are 2 stores (probably more) selling Pass f5 parts - Tubeshunter and Jims_audio (do a store search for "pass" of "f5" in e-bay). Tubeshunter has a full kit for the PSU but a bit pricy.

I got the f5 and B1 kit from Jims_audio in e-bay. The f5 comes with all the parts but the B1 is a bare PCB - some effort in sourcing for the parts. Got mine mostly from Parts Connexion. I have not decide on the signal parh capacitors for the B1 - probabally use Mundorf ZN (octave) or Obbligato (diy-hi-fi supply).

I find it cheaper to source for a PSU kit (@RM 70) in e-bay and use the kit's caps (4 units of Rubycon 10,000uf, 50v) for the f5 PSU. That works out to an average of RM17.50 per capacitor - I think it is selling about RM 37 per piece in other e-bay shops.

I am still looking for a enclosure, a 300VA toroidal x'former (25V-0-25V) and 2 heatsinks - prefereably from a local supplier - do you know of any electronic shop that carry these items? Tx

It depends on whether you want to go for dual mono or single. I got my EI 400VA 18-0 18-0 Tx from Multicare transformer from JP and there is another one in Kepong who can do it too.

As for the casing, try PCH 1 or PCH2 from the hifi4sale thread under generic hi-fi chasis. F5 needs a really big heatsink.

I will post some photo shoot of some of the completed F5 by others.

Alas, the transformer for the job should be 2x18V ac on the secondary output. check the correct BOM here.

http://www.diyaudio.com/forums/showpost.php?p=1823039&postcount=103

Chua - 2 secondaries of 18-0, 18-0 is ok. If you need the PSU schematics, PM me.

here are more photo. [sometimes I just cant resist looking at it for the second glance]

Hi Chua - how is the progress of your F5? I have just assembled the PSU unit and is stable at +/- 25.11V without load. I think it is acceptable from all the comments in diyaudio forum.

I would connect the F5 boards tomorrow - will update with pics when done.

look aside, hows the sound ?

Welcome to the neutral and transparent sound. That is the general comments after power up the unit as reported by most of the guys who built it.

I'm doing the same project too

Powered-up the boards yesterday nite. Made some mistakes and overloaded (turned the bias too high) one channel - probably damaged the jfets since it is immediately hot on power-up. Moral of story - curb enthusiasm and dont work when tired! Ordered new replacement jfets.

The other channel seems to be OK - got the bias going. Will continue testing (with resistor load and cheap speakers) before hooking-up to speakers.

Anyone has a pair of 2sk170BL & 2sj74BL handy and for sale? Pls PM me. Tx

mthoi, I'm waiting mine from ebay.. could hv few extra if i didn't burn it

I bought some, burn a few, left a tiny no. I will check if I have enuf for that. do u want to consider buying 20 pairs and match them to get the correct Igss - Vds.

Hi Chua, Would be nice if you can sell me 2 pairs of 170/74 for temporary measure. It is Ok if it is unmatched. I just want to do some "work" over the raya break. Pls call me 012 2236517, if you have any to spare.

I have placed an order for 4 pairs matched 170/74s on e-bay. Not sure if thery would be really "matched" as claimed.

Hope you can get it up running in stereo. the works are wonder and do post some picture to poison us.

we have Kuching F5 guys on the way too.

Hi Chua - tx for the 2 pairs of 170/74. I found out that it is one of the MOSFETS that was actually faulty (IRFP240). Ordered from RS and hopefully it can be delivered after Raya. I have made some progress in tuning the bias of both F5 channels using the pair of working mosfets.

The latest development is that I have hooked up the single channel to a pre-amp/CD and a cheap RM35 Pasar Rd speaker. It produces sound - and quite "good" as well! All very exciting!

I would test a bit longer before I connect the F5 to my Harbeth 3PES. I would post some pics when I get the F5 fully up and running.

Hi MTHOI,

Good news on your F5. Looks like u got it done first, perhaps the first in Malaysia too.

do present your photo and poisons us with the neutral sound of DIY F5.

Hi Guys

For those venturing into the exciting world of solid state DIY amplification modification, a few words of warning would be in order.

It is very important, no... it's absolutely crucial for one to check after performing ANY internal work in an amplifier that there is no DC voltage present at the amplifiers output...i.e. the speaker terminals.

When an amplifier is working correctly, you should be able to measure a varying AC voltage output present at the speaker terminals. But when you measure for DC voltage at the output, there should ideally be NONE.

If there is SOME DC, then what happens is that your speakers voice coils will eventually burn out. You then need to replace your drivers. This can be extremely expensive.

I learnt this the hard way back in the early 90's when I built my first pair of Naim NAP 135 monoblocks. One simple connection error on my part resulted in some DC voltage present on the output of the amplifiers.

I never paid attention to the faint burning smell that could be detected shortly after switching them on as they appeared to be working correctly and everything was sounding great. End result, 5 minutes later I had a ruined pair of Linn Kans which I personally went to the UK to select and hand carry back. But that's how we truly learn.

DC on the output of any solid state amplifier is deadly to your speakers. And headphones too. I hope this will save someone from some misery!

On a happier note, as chua55 says, some new pictures would be most welcome indeed MTHOI !

I just completed the F5 after burning 3 mosfets! This is my learning lessons.
AS usual, I was not careful with the trimpot during adjustment. There is not much room for error.
Those building it, please start with the lowest R across the gate and source of the mosfet when you start powering it up.
I bought the chasis from one of the posting here and I wish the heat sink is about 20 % bigger. I have only adjust the bias up to 0.54V . The recommended bias id 0.6 V. After powering up in a non aircon room for 1 hour , the heatsink can only be touched for about 6 seconds.
The Sound
I am using the promitheus DAC and there is no capacitor in the DAC and the amp in the signal path.
The background sound is really quiet and very very transparent. bass is surprising deep and tight in the OB5 speaker kit from GR research.
Vocal is tactile and the illusion of musicians in the room is very real.
Sound stage is also very good.
cheers
kp93300

so it runs super hot. look like it is better to use the PCH 3 / PCH 4 series.

I notice investing amp really give a lot of return.

stupid suggestion: install a fan on it?

Although it look fugly but do help a lot.

and yea, chua, where did you get your 2sj108 and 2sk370?

How to install a fan without noise? It is so quiet and no hiss from the speaker at idle !
thank you

kp93300

Last nigth a bass player came to listern and commended positively on the bass reproduction .
He performs frequently at dinner funtions and likes the bass the vocal very much.
I am amazed that that it is only about 20 W !
kp93300

Pretty encouraging comment!

jazzy let's F5 together....

I am using 2sk170BL and 2sj74BL from HOHODIY before they close shop. I used a lot of these for the Current mirrors of the TDA1541a and did manage to burn a few of them.

many guys have actually put a fan using a 12 V computer fan. however, it is better you relook at the biasing to reduce the heat.

I got the PSU's PCB board from e-bay (Jims_audio). There are 2 stores
(probably more) selling Pass f5 parts - Tubeshunter and Jims_audio (do a
store search for "pass" of "f5" in e-bay).

Do you know if Tubeshunter has good quality PCB and/or is trustable vendor ? I would prefer to buy
the PCB from the DIYaudio Store, but Tubeshunter also has a full kit
with MATCHED pair of Fets, and this would save me a lot of time...
http://cgi.ebay.fr/DELUXE-F5-STEREO-FET-MOSFET-AUDIO-POWER-AMPLIFIER-KIT-/380241064394?pt=LH_DefaultDomain_0&hash=item58882231ca

So the second question is: do you know a place where we can get MATCHED fets for the F5 ??

Many thanks !

Just for info: I finally bought the PCB from DIYaudio store, and the transistors friom Tech-diy.
Starting the assembly...

Nounours18200 wrote:Just for info: I finally bought the PCB from DIYaudio store, and the transistors friom Tech-diy.
Starting the assembly...

Looking forward to your build. Please update us with some photos later