Pass F5 Power Amp

[Tripmaster]

I present my F5 (taa-daa!)...yet another one of Nelson's designs rolls off the virtual production line :)

http://i374.photobucket.com/albums/oo189/Tripmaster_photo/FrontLarge.jpg
http://i374.photobucket.com/albums/oo189/Tripmaster_photo/RearLarge.jpg
http://i374.photobucket.com/albums/oo189/Tripmaster_photo/InsideLarge.jpg

I finally got around connecting it to my Brines FT1600s speakers and was mightily impressed when compared to the various amps I have owned over the years. The drive, weight, bass and texture of the sound certainly put a smile on my face!

[swampy]

Looks really well made and good attention to detail. I made the F5 also but bought a ready made case from Italy. Took a little while for mine to settle down and run in.

[Techno Commander]

Very tidy work. :)

[Tripmaster]

cheers guys:)

[jonners]

Very nice work Richard! Where did you get the boards and metalwork from?

[Tripmaster]

Thanks John

I bought the boards from Cvillers group buy on DIYA and ordered the sheet metal from an ebay company (www.forwardmetals.co.uk) They roughly cut it to size and I filed and drilled to suit. They were excellent to deal with and surprising cheap.

Have you started tinkering with the LDRs?

[StanleyB]

Nice work, but a couple of very important observations from a product designer ( me :eyebrows:) might not go amiss I hope ;).

1. Don't twist the Left and Right signal wires from the PHONO input sockets like that. This type of process is used in CAT5 etc to cut noise and extend upper bandwidth. It also has a filtering effect on low frequencies. On top of that, the way you did it you could get added crosstalk problems.
My suggestion is to used individually screened wires from the connectors to the Left and Right PCB. I suggest getting an old stereo pair or phono leads. Cut off the connectors, and use the lead to connect from the input sockets to the PCB. . Don't forget to solder the screen (ground) wires on the lead to the case at one end, and an earth terminal on each PCB.

2. The output signal wires to the speaker connectors also need changing. Again, don't twist them the way you did. Use individual lengths of speaker cable wires to go from PCB to speaker connector. Those connections from the PCB to the speaker sockets can carry high currents. The wires you use are telephone wires that handle far less current.

I hope I have not upset you by making some critical comments :). Feel free to ignore them of course.

[Tripmaster]

Nice work, but a couple of very important observations from a product designer ( me :eyebrows:) might not go amiss I hope ;).

I hope I have not upset you by making some critical comments :). Feel free to ignore them of course.

Hi Stanley

Not a all, I am a relative noob at this :)

I have just changed the speaker output to some silver coated 18ga cable, this will have a much higher rating. I'll have a look at the input later today.

[Ali Tait]

Great job Richard.How does it sound?

[Tripmaster]

Great job Richard.How does it sound?

Fab!

I'm currently swapping out the input/output cables and will give it another go in a bit.

The bass is amazing to honest, very low and well controlled. Its really shows a new side to the MLTLs

[Ali Tait]

Fostex Fe167e?

[Tripmaster]

Fostex Fe167e?

Yep, more details via my signature

[Ali Tait]

I have a pair too.Currently using Duncan's Tripath to drive them.Sound very good.I'd imagine the F5 sounds great.

[Ali Tait]

Ah,mine are not quite the same,but use the same drivers.

[Tripmaster]

Nice work, but a couple of very important observations from a product designer ( me :eyebrows:) might not go amiss I hope ;).

1. Don't twist the Left and Right signal wires from the PHONO input sockets like that. This type of process is used in CAT5 etc to cut noise and extend upper bandwidth. It also has a filtering effect on low frequencies. On top of that, the way you did it you could get added crosstalk problems.
My suggestion is to used individually screened wires from the connectors to the Left and Right PCB. I suggest getting an old stereo pair or phono leads. Cut off the connectors, and use the lead to connect from the input sockets to the PCB. . Don't forget to solder the screen (ground) wires on the lead to the case at one end, and an earth terminal on each PCB.

2. The output signal wires to the speaker connectors also need changing. Again, don't twist them the way you did. Use individual lengths of speaker cable wires to go from PCB to speaker connector. Those connections from the PCB to the speaker sockets can carry high currents. The wires you use are telephone wires that handle far less current.

I hope I have not upset you by making some critical comments :). Feel free to ignore them of course.

Done! anything else? ;)

http://i374.photobucket.com/albums/oo189/Tripmaster_photo/RewireInandOutLarge.jpg

[StanleyB]

Looking good :).

[MartinT]

Very nice work, Richard. Casework is particularly difficult to get right with a home project and yours looks very professional. I love Nelson Pass' designs and have owned three of his preamps (X2, X1 and now an XP-20). How does it sound now that it has settled down and has the new wiring?

[Tripmaster]

Very nice work, Richard. Casework is particularly difficult to get right with a home project and yours looks very professional. I love Nelson Pass' designs and have owned three of his preamps (X2, X1 and now an XP-20). How does it sound now that it has settled down and has the new wiring?

It really is a cracker with my speakers. Some have complained as it has low gain and isn't suited driving difficult loads. But its more than loud enough in my lounge. Its by far the best amp I have had, and I would go as far as to say it one of the best I have heard.

It was surprising simple to construct and I didn't any issues, apart from the input/output wiring:doh:. There is a slight hum coming from the speakers, and I haven't had time to workout if its a hum loop or transformer hum. I have to put my ear with in a couple inches from the drivers to hear it so its not an issue, but I would like to get rid of it.

[Dave Hewitt]

Hi Richard
Try one of the Pass b1 buffer clones from E bay as an input to your amp,this made my f3 clone and Daves f5 better in our opinion.Have an f1 and f5 clone waiting to be sorted at the moment.I found the litespeed better working into a buffer.
Regards Dave.

[Tripmaster]

Hi Richard
Try one of the Pass b1 buffer clones from E bay as an input to your amp,this made my f3 clone and Daves f5 better in our opinion.Have an f1 and f5 clone waiting to be sorted at the moment.I found the litespeed better working into a buffer.
Regards Dave.

Hi Dave

Thanks. I'm using a Lightspeed that a lashed together a while back but I'm just about to complete another. I also have the PCBs and parts to built a Salas DCB1 (Direct Coupled B1 buffer)

It's exciting to know it can only get better! :)

What do you think of the F3?

[Puffin]

:rave:

[Tripmaster]

:rave:

DJ Puffin on the wheels of steel

:gig:

[leo]

Sorry I missed this, real nice work on the F5 build Richard ;)
I've been looking at these amps as a possible next build, please keep us updated

[Tripmaster]

Sorry I missed this, real nice work on the F5 build Richard ;)
I've been looking at these amps as a possible next build, please keep us updated

Do it :) Once you have invested in the heat sinks, 18vac transformer and lots a smoothing caps there are at least five amps you can build

[Dave Hewitt]

Hi Richard,
In my opinion the f3 had the edge on the f5,sounded more like a tube amp to me probably best silicon version of single ended triode.Chris [Hornucopia] has it now ,sounded superb on his very expensive speakers.If I had to criticise the f5 it would be the rather small sound stage,all in my opinion of course.
Dave.

[Mike]

Nice work, Richard, especially on the casework! :)

That's always the bit that gives me the most problems! :steam:

[Dave Hewitt]

Hi Richard ,Meant to ask before,Where did those superb looking heatsinks come from? Dave.

[Tripmaster]

Thanks Mike :)

------------

Dave

I purchased a set for Puffin and I. They came via Chris Wujek over on DIYA but originated from Conrad in Australia. http://www.conradheatsinks.com/products/flat100_350.html#MF35

Model Number MF35-151.5

Conrad will ship direct, and its doesn't work out too expensive.

[Strosek]

Very nice work!

I've built all of the DIY Pass Amps and the F5 is my clear favourite! Huge soundstage, tons of bass and everything a high end amp should be. There are some mods to that do improve the sound quite a bit and I'd be happy to share them with you, just PM me. May I ask what you set your bias at?

In my opinion the only real downside to this amp is that it has fairly low gain and you need a good pre amp or really efficient speakers to take full advantage of it.

That being said it's a real winner Class A at it's best!

Oh, where did you get those heat sinks.... Very nice

[Marco]

Hi 'Strosek',

Welcome to AOS :)

Could you please pop into the Welcome area and introduce yourself to our community by supplying your first name, system details and music tastes, as this is the requirement for all new members joining AOS.

Cheers! :cool:

Marco.

[Tripmaster]

Hi 'Strosek',

Welcome to AOS :)

Could you please pop into the Welcome area and introduce yourself to our community by supplying your first name, system details and music tastes, as this is the requirement for all new members joining AOS.

Cheers! :cool:

Marco.

I guess I'm too late! :eyebrows:

[sondale]

Very nice work!

I've built all of the DIY Pass Amps and the F5 is my clear favourite! Huge soundstage, tons of bass and everything a high end amp should be. There are some mods to that do improve the sound quite a bit and I'd be happy to share them with you, just PM me. May I ask what you set your bias at?

In my opinion the only real downside to this amp is that it has fairly low gain and you need a good pre amp or really efficient speakers to take full advantage of it.

That being said it's a real winner Class A at it's best!

Oh, where did you get those heat sinks.... Very nice

With my F5s I did the mod mentioned in Peter Daniels (DiyAudio) F5 thread to remove the temperature compensation / protection parts - makes it a very simple build - BUT NEVER SHORT THE OUTPUT - otherwise smokin'. Mine runs quite hot (I cannot always pass the heat test - keeping your hand on the heatsink for 5 seconds) but they stablise at hot - perfect for winter.

Soundwise - everything I could wish for - especially the bass.

Have you sorted the hum yet Tripmaster?

Almost forgot - a B1 buffer (of whatever persuasion) will help between the LSA and the F5 - gotta build the new Blue Hot-Rodded DCB1.

ALan

[Strosek]

Those are the mods I was referring to;) Great sounding amp!!

The F5 should be dead quite, no pops clicks hums burps or farts. The first thing I would check is that the rectifier diodes are COMPLETLY insulated. I also had a hum and tracked it back to that. Even if you check it with a meter and they look fine double check because a hum is a sign of a problem:)


Let us know if that helps:)

[Puffin]

Those are the mods I was referring to;) The first thing I would check is that the rectifier diodes are COMPLETLY insulated. I also had a hum and tracked it back to that

Oh yes, I remember..............

and there was something else on my F2 that was so blatantly obvious. I hadn't insulated the phono sockets. Spent too much time poring over everythign else!:doh:

[Tripmaster]

Hi

I haven't had a great deal of time over the last week, so I still have hum. I've checked RCAs, rectifiers etc...

Its low level, so its only a minor annoyance. Still want to sort it though. I may buy another transformer, power supply etc...and build a pair of monoblocks. I know the hum would vanish if I could separate each channel ground.

[Strosek]

I should have looked at what rectifiers you used before asking you to check them. Sorry... Those are fine and don't require insulation. Here's what I would do...

Using the phone wire twisted together is fine (not great) for the inputs but for the outputs use larger gauge wire and don't twist it together. I would also retouch all the solder points on the inputs and outputs as they require a lot of heat to get right. Check your boards and make sure that all your solder joints look shiny and clean.

Give that a try and let me know... I Highly doubt that anything will change if you build monoblocks because the circuit should be dead silent built as it is.

Double and triple check you grounding scheme as well:)

Good luck and let us know if anything changes.

[Strosek]

I almost forgot.... Check that the output transistors are fully insulated from the heatsinks. Use your meter to make sure you have zero continuity from the metal of the output and your chassis.

[Tripmaster]

Thanks

http://theartofsound.net/forum/showpost.php?p=136997&postcount=15

The input and output wires were change later on in this thread, you may have missed it :)

[Tripmaster]

I almost forgot.... Check that the output transistors are fully insulated from the heatsinks. Use your meter to make sure you have zero continuity from the metal of the output and your chassis.

Done! ;)

[Strosek]

I'm sorry... That's what I was talking about with the wires. That looks great!

Please let use know what the problem was when you find it:) Now I'm really curious!

[sondale]

I have just manage to induce hum on my mono F5s - I added a Behringer DCX2496 and a couple of ASP250 amps to my system (running two sub-woofers) and not only was there hum there was a noise which sounded like my speakers ripping apart - this died away after about 30 minutes.

When one of my input leads to the DCX2496 (left channel only) was removed - no hum - it did not matter what I did with the right channel dcx2496 lead.

I eventually traced it all back to the earth lead on the dcx2496 mains cable - remove this and problems solved. With the earth lead still attached I had to have the mains plug sat in the nearest mains socket to the F5s - this reduced considerably the hum but did not eliminate it.

So I am going to look carefully at the left channel F5 to see why it is so intolerant - it has to be slightly different to the right channel.

Just to avoid confusion I have a TwistedPair B32 DAC from which I feed the single ended output directly to the F5s driving full-range units, the balanced outputs from the B32 go to the Behringer DCX2496 and then to the ASP250's.

Alan

[Strosek]

OK.... I just downloaded the large picture of the inside of your amp and after looking at it under the microscope I think I MAY have found your problem.

It looks to me like you have connected the power supply ground to the chassis ground and in turn connected it to your mains ground.... Is that correct?

Always ground your chassis but the power and signal ground should be separate from the mains ground. The mains ground in your home has tons of crap in it and that may be filtering back into the signal giving you a hum.

If I'm wrong please post another picture showing your grounding scheme because 9/10 that's your problem:)

Give that a try and let me know!

[Tripmaster]

OK.... I just downloaded the large picture of the inside of your amp and after looking at it under the microscope I think I MAY have found your problem.

It looks to me like you have connected the power supply ground to the chassis ground and in turn connected it to your mains ground.... Is that correct?

Always ground your chassis but the power and signal ground should be separate from the mains ground. The mains ground in your home has tons of crap in it and that may be filtering back into the signal giving you a hum.

If I'm wrong please post another picture showing your grounding scheme because 9/10 that's your problem:)

Give that a try and let me know!

Hi

I have joined the grounds from the power supply, and have place a CL60 in series, then connected this to the safety earth terminal.

http://i374.photobucket.com/albums/oo189/Tripmaster_photo/CL60.jpg

I applaud your enthusiasm ! :)

[Strosek]

Thanks;) I like a challenge!

OK, I think I see the problem... The 4pin connector with the green and yellow and the lime green and yellow are not required and may be the cause of your hum.

The chassis needs to be grounded to earth for safety. Great you've done that . BUT you also connected that same earth connection to the caps for some reason. The circuit gets it's negative polarity from the bridge rectifiers not from the earth ground.

Also why did you use so many C60's... I have a HUGE transformer and it works great with just one C60! Also why put one on the earth connections? Just curious.

Try removing what I'm saying and tell me if the hum goes away.

Thanks!

[Tripmaster]

Thanks;) I like a challenge!

OK, I think I see the problem... The 4pin connector with the green and yellow and the lime green and yellow are not required and may be the cause of your hum.

The chassis needs to be grounded to earth for safety. Great you've done that . BUT you also connected that same earth connection to the caps for some reason. The circuit gets it's negative polarity from the bridge rectifiers not from the earth ground.

Also why did you use so many C60's... I have a HUGE transformer and it works great with just one C60! Also why put one on the earth connections? Just curious.

Try removing what I'm saying and tell me if the hum goes away.

Thanks!

Hi Dan

I guess you are on 120v mains? From what I understand I needed to increase the number of CL60s from one to two for 240 volt supply. It was recommend I add a third CL60 to enable me to use a 1.25T rated fuse. 500VA transformer.

I have highlighted the ground connection with thermistor on the following schematic

http://i374.photobucket.com/albums/oo189/Tripmaster_photo/F5PSUGround.jpg

I have disconnected the connection from the PS/Thermistor/SE point before but the hum remained. :scratch:

[Strosek]

You're right I had assumed a 120 volt supply... Sorry;)

Well without having the amp in front of me I don't think we can go any farther unfortunately... I would however encourage you to keep searching for the problem. The circuit should be dead silent and this is truly a lovely amplifier you've built and it really deserves to function correctly!

Good luck:)

[Tripmaster]

Hi Dan

No worries, I will. Thanks for your help :)

Regards

[Strosek]

OK one last try......

That power LED indicator you used has a metal body is there any way it's shorting with the chassis? And last but not least did you use rubber insulation washers on both sides of your toroidal transformer?

NOW I give up! :)

[Tripmaster]

OK one last try......

That power LED indicator you used has a metal body is there any way it's shorting with the chassis? And last but not least did you use rubber insulation washers on both sides of your toroidal transformer?

NOW I give up! :)

Yes there is a rubber washer on both sides of the transformer, and there is rubber bung separating the LEDs from the case. At first I thought the hum may have been caused by the transformer location, so I removed it from the case and I remove the LEDs from their mounts at the same time. Hum remained.

[Dave Hewitt]

Hi
Looks to me you need less thermistors on uk mains instead of more.The currents are halved when the voltage increases,as per pass circuit diagram.
Dave.

[Ali Tait]

Hi Dave,
Not seen you around for a while,how's things?

[Dave Hewitt]

Hi Ali
Not been so good with the old ticker,got my name down for a pacemaker.
[ with external power supply of course].Thanks for asking Ali.

[Ali Tait]

I knew that mate,glad to hear you're getting sorted out.Hope it's a linear supply! :)

[Strosek]

I knew that mate,glad to hear you're getting sorted out.Hope it's a linear supply! :)

LOL Well said!!

[hornucopia]

Hi Richard,
In my opinion the f3 had the edge on the f5,sounded more like a tube amp to me probably best silicon version of single ended triode.Chris [Hornucopia] has it now ,sounded superb on his very expensive speakers.If I had to criticise the f5 it would be the rather small sound stage,all in my opinion of course.
Dave.
Just found this!
Dave did a great job and the F3 is still sounding great through my "very expensive speakers"! (Ocellia Calliope .21 Grandis Silver Signatures. You KNOW they're good as they have too many names?)
A really good match.
Currently running from a 'Glow One' valve amp(my bed/phones amp) as someone asked me how they sound, but back to F3 soon.
Stay well, Dave.

[hornucopia]

...in fact, thinking on it, my F3 has a hum too!
Just as likely to be some 1 mm unscreened stub somewhere I guess.
Here's the insides, you circuit fans! (courtesy Dave)

[HighFidelityGuy]

Hi Richard. Are you still having problems with your hum? That's hum, not bum. I don't want to know about your bum. :lol:
Anyway, from looking at your photos it looks as though some of your signal input/output wires are run quite close to AC power wires. It may just be an optical illution caused by the 2D nature of photos though. However if they are close to each other I'd try seperating them out as much as possible and if they have to cross each other do it at 90 degrees. If that doesn't help you could try sheilding the speaker output wires with a braided sleeve connected to ground. Something like THIS (http://www.hificollective.co.uk/catalog/-c-61_85_213.html) could work. :)

[Tripmaster]

Hi Richard. Are you still having problems with your hum? That's hum, not bum. I don't want to know about your bum. :lol:
Anyway, from looking at your photos it looks as though some of your signal input/output wires are run quite close to AC power wires. It may just be an optical illution caused by the 2D nature of photos though. However if they are close to each other I'd try seperating them out as much as possible and if they have to cross each other do it at 90 degrees. If that doesn't help you could try sheilding the speaker output wires with a braided sleeve connected to ground. Something like THIS (http://www.hificollective.co.uk/catalog/-c-61_85_213.html) could work. :)

Hi Dave

Sorry for not responding sooner...I missed your post!

I still have a slight hum. The picture is unfortunately playing tricks as the wires are quite far apart.

A while back I removed the transformer from the case, bended the wires out of the way, and powered up the amp. It hummed. If I disconnect either channel from the power supply, the powered channel would be hum free. As soon as both channels are connected the hum returns.

I plan to rewire the amp and I will try a different layout, but I'm enjoying the music at the moment and I'm loathed to start fiddling! :)

[roob]

Can you buy these amps as a complete kit with everything needed to build ?

[Ali Tait]

http://cgi.ebay.co.uk/pure-class-F5-F-5-power-amplifier-Kit-w-power-supply-/160502239999?pt=LH_DefaultDomain_0&hash=item255eadd2ff

[Reid Malenfant]

So find some very large heatsinks, a rather large transformer, case etc etc...;)

[Puffin]

Not wishing to cast aspertions on the quality of a kit I have never heard, but I built an
F2 using boards bought on Diyaudio. The boards are first class quality. I had to source all the parts. Parts alone including custom wound transformer were about £200. I would say that to get something that sounds akin to the sound of original Pass amps ($3,000 some of them) the quailty of the parts used is crucial.

The kit may sound fine, and you could always play with it by substituting better quality parts later.

http://i73.photobucket.com/albums/i239/saxonsex/F2004.jpg

[Ali Tait]

So find some very large heatsinks, a rather large transformer, case etc etc...;)

Ok smartarse,find a more complete kit then!

[Reid Malenfant]

Ok smartarse,find a more complete kit then!
No doubt i couldn't Ali ;) Frankly i only thought that PCBs would be available on a certain DIY forum with a certain Mr Pass who has a HAL9000 computer avatar :eyebrows:

But what i was attempting to get accross is that there is no one fix solution, anyone interested will still need to bone up on lots of different things & frankly it's a shame :( Not everyone out there understands it all & duff information could lead to a certain inevitable result :rolleyes:


2982

[Dave Hewitt]

Hi,In my experience with f5 boards the e bay ones are as well made as, if not better than the diy audio group buy ones.
Dave.

[Tripmaster]

Here is a link to the 'Cviller (http://www.diyaudio.com/store/pcb-bank/f5-pcbs.html)' F5 amp PCBs. You will still need to make a decent power supply, but this can be easily constructed using the point to point method or by using proto board. I think Cviller (http://www.diyaudio.com/forums/members/cviller.html) still has a few power supply PCBs. It might be worth contacting him.

All of the other parts can be easily obtained within the UK. If you decide to build an F5 let me know and I will be happy to help you out with some of the part numbers.

If you buy the PCBs through the official DIY-Audio shop, some of the profit is used to fund the website. :)

[fdlsys]

...If I disconnect either channel from the power supply, the powered channel would be hum free. As soon as both channels are connected the hum returns...

My apologies for resurrecting this thread, but since I'm having a similar problem, I was hoping that Richard might have found the solution for this?

With both channels running, speakers connected, but only one input channel connected, hum is minimal - almost inaudible.
As soon as the shield of the other RCA plug touches the socket of the input connector while inserting it, the hum starts.
The same happens on both input channels.

My F5 is built exactly to the spec, including the PSU recommendations.
Filter cap across (220V) AC.
Each AC entry line via separate thermistor.
120000 uF.
Everything star grounded to 0V and 0V via thermistor to the external ground.
Input as well as speakers get 0V reference via the PCB, not directly from the physical star-ground point (0V).
Wires within a pair (input/speakers) are the same length and tightly twisted, and at a fair distance (about 15cm at the closest point; the PCBs themselves) from the transformer, and about 13cm distance between input and output wire pairs.

As you can imagine, I'm a bit stumped with this...

Thanks in advance, Mike

[Stratmangler]

Post 36 on this thread over on DIY Audio might help http://www.diyaudio.com/forums/pass-labs/186655-unable-fix-hum-my-f5.html

[fdlsys]

Chris, thank for that.
I did come across that thread, but the circuit (4-device per channel), symptoms and the final solution (doubling up the power caps) do not seem right for my configuration which is a normal F5.

One thing from that thread that went a bit sideways - I'll try it, even though it doesn't make sense to me - is grounding one channel via the other channel, instead of having both directly on the 0V "star" reference.

Cheers, Mike

[jostber]

Zen Mod over at the DIY audio forum is the main guru at the Pass Labs gear. More on him:

http://i.diyaudio.com/display.php?M=385522&C=b8381b8e1780263477f33ead831053b4&S=92&L=17&N=54

[fdlsys]

Thanks mate, I'll give it a try.

[HighFidelityGuy]

It sounds to me like a ground loop problem, possibly caused by the phono lead shields (signal 0V) on both channels being joined together at more than one point along the signal path and then possibly being joined back together again through another route like a chassis ground. If that makes sense? I would try and check each piece of equipment and see if the signal 0V from the left and right channel are joined together and also if they're joined to chassis ground. Try to make sure that they only join together in one place, preferably your amp and also that they either don't connect to chassis ground or only connect to it once. Or something along those lines. :scratch: I'm not an expert on this type of stuff but I've had similar issues in the past and that's the advice I was given. I had to resort to using a ground isolation transformer between my preamp and subs.

Good luck. :)

[fdlsys]

Makes sense, thanks!
Grrr... I hate de-soldering...