A little Audio project I have virtually completed

[spuddevans]

For the last few weeks I have been working on building a HiFi amplifier, and I thought I'd share a few pics for your visual enjoyment.

This is the front panel view,



Some close up's of the knobs (what I made myself)








And the Inside view (I havent finished the lid yet)



And some close-ups of the insides with some identifier labels.











A few details on this project.

The valve pre-amp circuit is taken from the one in this link . I made one very slight change to the HT psu circuit. Because the 100uF smoothing caps I had were packaged as 100+100 caps, I added an extra RC stage.

The main amplifier modules are based on the LM4780 chipamp ic, they have their own bridge rectifier and smoothing caps so only need 28-0-28 VAC supply. Each module is a stereo amplifier, but by having 2 of these modules it means that I can Bi-Amp my speakers. (use one amplifier for each speaker cone, not just one amp for left and one for right) I dont know if this will make a big difference or not, but I thought it would be fun to see

I also got a remote control circuit that also has a bunch of relays on it to select the input.

I turned the volumn, power and input selector knobs out of some brass, and then engraved the designs on my mill.

When turned on, power is only applied to the valve heaters and the remote control circuit, then to switch on the rest of the power you just press the silver power button below the volumn knob, and then that turns on a latching relay that powers up the main transformer that feeds the amp modules and also feeds a step-up transformer that gives the HT supply for the valves.

I used my newly aquired bending brake to make some brass "U" channels to run the ac wiring, you might be able to see one running the width of the amp under the amp modules, and there is another one that runs along the bottom edge just behind the front panel.


I still have the lid to finish off, I have to drill some cooling vent holes above where the big heatsinks are. And I also have to modify the pre-amp circuit to increase the gain (the plans give the option for 7 or 11 times gain, I choose 7 but I think I need the extra gain)


I cant tell you how it sounds as I have only hooked up just a little speaker to check if it has hum or problems, and I am very happy to report that it is as quiet as a dead mouse, even turned up full. But when doing this test I noticed that the gain is not as much as I need, so I will modify it and then test it on my main speakers.

Tim

[Bernd]

Tim,

Very professional looking. I really like the knobs. Nice job. 

Bernd

[saw]

Oh yes, this is realy somthing. Great work. 

[Brass_Machine]

Very nice. Inspiration right there. I have been dying to build a tube (sorry, valve) amp for a long time. I have a few tubes (valves!) in my shop for some headphone/practice amps to do up one of these days.

Going to look at the link you provided.

Whats the silver button for under your volume control? Motorized control? So the knob moves when you use the remote?

Very nice!

Eric

[andyf]

A really professional job, Tim. I'm sure it will sound as good as it looks.

Love the smiley power knob:

Andy

[spuddevans]

Thanks for all the comments guys.

Whats the silver button for under your volume control?

That button switches on a latching relay (well, an ordinary relay wired to be latching), the relay switches the power on to the main transformer and the Valve ( tube ) HT psu. The reason for this is to let the heaters on the valves warm up before applying the HT voltage to them ( I believe that not letting the valves warm up before applying the HT does shorten their life )

The button also has a groovy blue led in it.

Motorized control? So the knob moves when you use the remote?

Yup, looks pretty groovy when it does, plus the remote can select the input as well ( I only have 2 inputs, but the controller can have up to 5 )



Thanks for looking,

Tim

[bigmini]

For the last few weeks I have been working on building a HiFi amplifier, and I thought I'd share a few pics for your visual enjoyment.

<SNIPPED PHOTOS>
I still have the lid to finish off, I have to drill some cooling vent holes above where the big heatsinks are. And I also have to modify the pre-amp circuit to increase the gain (the plans give the option for 7 or 11 times gain, I choose 7 but I think I need the extra gain)


I cant tell you how it sounds as I have only hooked up just a little speaker to check if it has hum or problems, and I am very happy to report that it is as quiet as a dead mouse, even turned up full. But when doing this test I noticed that the gain is not as much as I need, so I will modify it and then test it on my main speakers.

Tim

Very nice knobs Spuddevans. If you don't mind me asking though, how did you make the splines? or did you use imperial pots with a flat and setscrew? I've been meaning to make some custom knobs myself, but the splines have me stumped. The only way I can figure to make them is by using an old pot shaft and pressing the knob on.

[Bluechip]

Just get some splined knobs and machine them down to make an insert for the knobs you make?

Cheapo items. As an eg.

http://www.rapidonline.com/Tools-Fasteners-Production-Equipment/Fasteners-Fixings/Knobs/15mm-Three-colour-mixer-knobs/64709/kw/Knobs

BTW, the flatted shafts are not always imperial sized. I got some BCD rotary switches a few weeks ago that are 6mm. flatted. Which is annoying, as the knobs I wanted to use are 1/4" fitting .... always a snag ain't there ...

Dave BC

[spuddevans]

Very nice knobs Spuddevans. If you don't mind me asking though, how did you make the splines? or did you use imperial pots with a flat and setscrew? I've been meaning to make some custom knobs myself, but the splines have me stumped. The only way I can figure to make them is by using an old pot shaft and pressing the knob on.

Hi Bigmini Thanks for your comments. Re the knobs, I didnt make the splines, I think only the vol pot had splines, but I just measured the OD and then bored a corresponding hole, then I bored a hole in from the bottom for a grub screw. To avoid damage on the pot I turned a little slug of brass that goes into the hole before the steel grubscrew goes in. (I remember Bogs showing that method of avoiding marring shafts with grubscrews, Thanks Bogs ) Because these knobs are fairly large in diameter, I was able to make the brass slug long enough that it does not fall out of the hole for the pot shaft.

BTW, the flatted shafts are not always imperial sized. I got some BCD rotary switches a few weeks ago that are 6mm. flatted. Which is annoying, as the knobs I wanted to use are 1/4" fitting .... always a snag ain't there ...

Dave BC

Aint that the truth. On this project the vol pot and the input selector switch were both 6mm, but the power switch was 1/4", but when you're making the knobs, you can just make the hole to suit the size needed.

And for the question not asked / answered....   How does it sound?

Well, truth is, I have not hooked it up to my main speakers yet as I want to adjust the gain of the preamp. I hope to make the adjustment today, and then I will bring a pair of small bookshelf speakers out to the workshop and give it a test. So sorry, the question will have to remain unanswered for a littl longer

Is there an over arching plan for air-flow through the assembly?  Also are there specific measures in place to reduce interferance in the cabling and selection of grounding points, etc...?

The airflow plan is as follows; as it came, the 19" rackmount case came with a series of 4mm x 2" slots (hows that for mixing standards ) on the bottom panel that span from one side to the other towards the rear of the case. As it came, the lid has no holes or slots in it except for the holes for the fixing screws.

My plan is to drill a pattern of holes directly above the 2 main heatsinks to allow the hottest air to be exhausted. My hope is that this will be enough without having to resort to forced convection, ie a fan.

If my plan fails miserably, plan B is to put in a 12v fan, but just run it on 6-8v, much quieter.


Regarding reducing interferance, I have tried to follow good audio earthing practice. I'll trace the signal from the start. The inputs have their shields connected together, and then that is connected to the batch of relays that switch the inputs via just one of the shielded cables (the others have the shield connected at one end). Then after the relay board, the signals (L+R) are wired through shielded wires (again the signal ground is connected at both ends in only one cable) to the Vol pot. Then from the pot the signals are fed into the valve preamps, but at this point the signal ground is connected to the star ground.

The signals are then wired through screened cables (screen connected only at one end) to the amp modules.

The ground from the AC power supply is also connected to the star ground, along with the ground from the valve HT psu. The grounds from the speakers are all connected to the star ground.

The star ground is the bottom plate of the case. I also routed some of the AC cables through brass channels to screen them from sensitive circuitry.

Nice looking presentation...

Thankyou, glad you like it.


Tim

[spuddevans]

And for the question not asked / answered....   How does it sound?

And now the question is answered..............



It sounds pretty darn good   (well to my ears anyway)


I modified the preamp circuit, hooked up the little speakers to test, and it all went well. So I brought the amp into my office where my big speakers are (Homebuilt from plans from HiFi World - KLs9 Click here for some specs ), hooked them up with some silver plated speaker cable, connected my ipod to it, switched on and then turned it up.


I cant fully describe the sound as I am recovering from a heavy cold, and also I had to replace a tweeter in one speaker, so it needs a few hours to "bed-in" before a true judgement is made. I will say that the Bass is very well controlled and tight, but nice and deep too. The amp can be pushed all the way to the max on the vol pot without any audible distortion.

I do plan on running some audio tests with my measuring mic and some software on the pc, just to see the measured response.


Tim

[Brass_Machine]

Stunning looking amp Tim.  Glad it sounds good too.  I need to get off my arse and build one. 

Eric

[spuddevans]

Thanks Eric The big grin on my face was just as big as when I 1st got either of my engines running for the 1st time.

I gotta do a little mod to my mill in order to drill the pattern of cooling holes in the lid. So once I get that done then it'll be full steam ahead on the lid and then onto the next project 



Tim

[spuddevans]

Just had an extended listening session this afternoon, the sound continues to improve little by little as the new tweeter beds in and also as my new amp gets run in.

Something I have noticed is that the 2 LM4780 amp modules are running hotter than I am happy with, so I am going to add some extra heatsinking to what's there. So I'll be taking it back out to the 'shop to add the heatsink.



Tim

[spuddevans]

So after deciding that the original heatsinks were too puny, I have since replaced them with 2 somewhat more beefy ones.



As far as I remember when I got this heatsink (I cut it in half to make 2 smaller heatsinks for this amp) it was rated at 1.2CW (I dunno if cutting it in half results in 2 2.4CW heatsinks or if there is any other factors involved), hopefully this will run a little cooler. It was a beast to mount though, very hard to get a little screwdriver in to tighten the mounting screws.

I also have been working on the lid, here's my progress;



and a backlit version




As you can see some of the holes have not gone all the way through, but a little work with a file on the underneath will sort that out. ( the problem is that the metal deformed slightly and the drill didnt punch all the way through, just left a dimple on the underneath. a few swipes with a file should clear that away and reveal the holes )

The holes are 1.7mm diameter, and there are about 1700 of them   


Tim

[Imagineering]

The holes are 1.7mm diameter, and there are about 1700 of them   

Tim

Good that the CNC Conversion worked then, isn't it.

Murray.

[spuddevans]

Good that the CNC Conversion worked then, isn't it.

Murray.

You better believe it!!! I wouldn't have even dreamt about doing this without cnc.


As it was it took about 3.5 hours to drill it (split up into 5 little sessions) after I modded my mill slightly to get the ability to drill into the center of the lid.


I'm toying with the thought of putting in a few LED's to backlight the holes, might look cool?


Tim

[spuddevans]

Well, one step forward, and a whole leap back.

I just finished the lid off and carefully reassembled the amp, then took it to my listening room along with my cd player and a couple of my fave cd's, plugged in the speakers and cd player, turned the power on and then after waiting a couple of mins to let the valve heaters warm up, hit the power switch to apply the power to the 4780's and the HT supply, and there was a sickening "CRACK!!"

I immediately turned the power off, and smelt the familiar scent of exploded silicon.    

I took the lid off and couldnt see exactly where the problem was, so I turned the power back on very briefly to identify the exact whereabouts of the problem, I immediately saw that the RH amp module emitted a flash and another crack from the 4780 chip.

A little further testing revealed that there is a 16ohm short from the faulty chip's heatsink and ground (the heatsink should be at -VE as it wasnt electrically isolated from the chip, but I had kept the heatsink clear of touching any ground's (or at least I thought I had!! ) ) This short is steady at 16ohms to ground, even when applying pressure in all directions to the heatsink.


So I have to order a spare 4780, I guess I'll order a couple to be sure, and then I'll take it to bits and replace the faulty chip and make sure that everything else is ok. I'm also going to get a couple of isolating washers for both amp modules.



So, I'm sorry to report that the audio test will have to wait for a week or so for me to get the replacement and then fit them.


Tim

[Chazz]

Beautiful work!  What is the Wattage rating of your amp?

Cheers,
Chazz

[spuddevans]

Beautiful work!   What is the Wattage rating of your amp?

Cheers,
Chazz

Thanks mate

The wattage is 2x 30watts per side, it is configured as biamp so there is one 60 watt stereo amp for each speaker.

So I guess the total max wattage would be 120watts, I say the max wattage as I am not running it at full gain, I have modified the amp circuit to reduce the gain somewhat so I would guess that I have it running at 60watts rms max, my speakers are around the 89dB sensitivity mark so that is plenty loud enough for me.


Although at the moment one amp chip has had the blue smoke let out of it, so the amp is currently rated at 0 watts rms


Tim

[Jonny]

Missed this one, nice work there Spuddy love the case and knobs but not keen in brass.

Next step to alter the sound 6N copper purity, silver plated wire throughout.
Separate ground outside, dont use the supplied earth, will be able to tell if its raining!
Junk them cheap 1/2p resistors, go for Holco or Vishay on input stages, got mine from Croft amps down the road- wow.
Another biggy is the change of the cheap diodes to something like Schotky, work tremendous with rectifiers.
For about £150 you may well have a better performer than a multi £k amp and pre amp setup!

To alter the actual sound play around with cabling if load tolerant, i used anything and everything i could get hold of in a tri wired setup, even tv coax steel core for Dynaudio base drivers. Interconnects same thing, most are not neutral except the dry Roksan and liquid Audionote tonearm silver stuff.
Caps will change the sound too, forget what i ended up with.

[spuddevans]

Just to update this, I have replaced the faulty chip, but in my haste to get it all back together again, I soldered a couple of signal grounds to the other amp module pcb instead of to this one (as they had been originally) and now, while the amp is working ok, I have a constant low hum.

I will have to re-solder the wires back to their original places, but I also have worked out that I need to lower the heatsinks where they mount to the chipamps because it is very easy for the lid to be deformed and short the heatsinks to ground So I will re-wire it when I do that.

As it stands, the hum does not get any louder when the amp is turned up, so at least I can drown the hum out

I have also hooked up my Sony DVP-S7700 player to the amp and I am just blown away by the combo. The Sony puts out a much higher level of a signal than the ipod nano, and so drives the amp much louder!!!

The bass is rock solid and soooo deep!! and the clarity of the highs and midrange are crystal clear, and never harsh even at high volume. I think that when I get the hum sorted out, this little amp will do me very well.

Missed this one, nice work there Spuddy love the case and knobs but not keen in brass.

Thanks Jonny.

If I was to make the knobs again I would be tempted to make them out of Ali' and then powder coat them, that'd take care of any tarnishing.

Next step to alter the sound 6N copper purity, silver plated wire throughout.

I have used silver plated OFC screened wire for all the signal paths

Separate ground outside, dont use the supplied earth, will be able to tell if its raining!

I've sorta already got that, I have installed an earth spike outside, but it is not seperate, it is connected to the rest of the house's earth system.

Junk them cheap 1/2p resistors, go for Holco or Vishay on input stages, got mine from Croft amps down the road- wow.

I do realise that they are not the greatest for super-fi audio, but they were all I had at the time. Maybe later on when I get a few hours listening on it, if I feel that I am not happy with the sound I will look at replacing them, maybe do just one side so that a comparison would be made easy.

Another biggy is the change of the cheap diodes to something like Schotky, work tremendous with rectifiers.

Already beat you to it bro!! I spent the extra when ordering componants and got high speed recovery Schotky's, well overratted for V and A.

For about £150 you may well have a better performer than a multi £k amp and pre amp setup!

That was the plan, instead of spending 2-300 on a commercial amp, I spent about 250 on components and got the enjoyment of constructing it myself.




Tim