I’m in sonic heaven with my new amp now!

Wait!

I don’t know about you but I’m certainly not like this. I know most folks would be satisfied with their tube amp after the first build but not me. I’m not like the 95% here. I’m an Alpha Diyer, I’m the top dog 5%.

But first of all, forgive me for I’m an uncouth fella. No, I don’t spout Byron, I don’t drink red wine or whatever the fancies that elitism hobbyists like audiophiles like to engage in. Instead, let me confess. I’m a pot bellied, hair receding, foul mouthed dude. Led Zep is my type of music and I love my brew of common man stout. In this regard, I’m the 95% Sir. Why heck, I even pick my nose in public. [*facepalm*]

An Alpha Diyer is always exploring ways to improve on his system. So much so that in the back of his mind, a trip to a hardware store, departmental store, IKEA etc is always an audio excursion.

And so, I’ll illustrate what an Alpha Diyer will do once he built his amp. And it’s certainly no lounging around.

But first of all, let me introduce you to the Expletive Factor. You know the reaction when the sound improved by so much that you JUMP (standing up doesn’t count) up from your seat and start spouting swear words, expletives… so bad that I can’t even write them here? (I still want this site to be family friendly, okay?)

What we are looking for is BIG XXXXing improvement in sonics. Not subtle changes that you have to A-B like hell, until your face looks like you are constipating to hear the difference. Imagine an improvement so great that you leap out off your listening chair and spew the most colourful language known to mankind!

Better still, if you swear words that aren’t in your daily vocabulary. That can only mean the sonic improvement is HUGE!

Okay, here’s what an Alpha Diyer will start off with.

Build the best power supply you have heard — Very High Expletive Factor
I mean it. The best power supply you have built, heard and optimized. Not because some dude (like me) said so. We all value different things in audio so it’s best to go back to your experience.

For me, I like choke input, lots of chokes, not too high capacitance and 100 Hz hum reduction via tuned choke.

I arrived at this supply after years of building tube amps. The 47uF caps are Solen metalized polypropylenes but the 20uFs are oil capacitors. Oh yes, the supply is HUGE, HEAVY and screams ALPHA all around. Notice there’s no electrolytics anywhere.

Move beyond simple self bias stage — Very High Expletive Factor
Initially I had a simple self bias stage at the cathode. However, you can’t move earth if you stop here. You got to experiment.

On another amp I built years ago, I used LED at the cathode and didn’t quite like the sound. The bass got too boomy. Looking back, it could be the speakers’ issue rather than the amp.

Anyway, for this mod, I’m using Cree Schottky diodes here, as illustrated by Maxamillion on Audio Asylum. 3 diodes gave me the cathode bias I need.

Optimize parafeed — High Expletive Factor
In my first build, I was using a 5k:8 parallel feed output transformer from Magnequest. The 4.7uF parafeed cap was optimized for bass response. A huge improvement over the initial 3.3uF.

As I was using 16 ohm speakers and I need a bit more gain from the tube, so I went for 3k:16 ohm trans also from Magnequest. Now the 4.7uF cap just doesn’t give me enough impact.

I don’t have any 6.8uF or larger caps. The next larger I have is a GE 17.5uF oiler so this went in and the bass impact came back after some running in.

Less Gain Stages — High Expletive Factor
Every gain stage somehow changes the signal. So if you could get by with less, do it! The 6E5P could actually put out 1-2W of power but as my DAC only outputs ~2V, the output power delivered to the speakers is now only ~0.3W.

By right, I should put in another gain stage to squeeze out more power from the 6E5P but since my speakers don’t need much power, I could get away with this. So what’s wrong with 0.3W?

Optimize signal/return path — High Expletive Factor
This makes hell lotta difference! If you ever worked on PCB layouts on high speed digital designs, the phrases “short signal path”, “return path”, “ground plane” etc all carry significant meaning to you. I’m not smart so I suffered and learned the hard way before I learned all this and I’m still learning.

Okay, that’s all I have done so far. In the spirit of this article, I’m not done yet! To be tried in the near future…

WE coupling

Try other spud tubes
Top of my head, 417, 5842, 6C45pi, 7788… Actually I have all these tubes in hand…

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Oscilloscopes are great stuffs. However, not every diyer owns one, nor can afford a quality scope.

You may be surprised but it’s only recently that I got hold of a scope. Yeah, all this while, all the designing, all the debugging were all done without one.

{mosgoogle}

I’m going to show you how it’s done. In Bob Pease’s “Troubleshooting Analog Circuit Techniques”, if you could only learn one lesson from his book, let it be this : “when it comes to troubleshooting, most of the time, rely on your wits!”.

And a basic understanding of the workings of your circuit. To best illustrate this, let’s look at this sample circuit.

Yup, circuit taken from a 1958 GE Tube Manual. The manual actually shows 35C5 as output tubes but for simulation purpose, 6L6 was used. Also, tube stuffs are easier to understand. Now let’s look at what happens when we pump in a small signal at the input.

First thing first, let’s explain the subsequent pics. The circuit is shown on the right and the “steady state” (or running) signal is shown on the left. This wonderful software is called Micro-Cap circuit simulation software. I downloaded the evaluation version. You could use Linear Tech’s Switchercard too.

Now let’s apply 10mv at the input. On the circuit, that’s the furthest left end, labeled “Tr”. We apply a little input to see what does the amp do with it.

That was the input. At output of first 12AX7, we could see a much magnified signal just in front of C3. The 12AX7 plate sits at 47.2VDC. Hey, we fed in 10mVAC and now we have 700mVAC riding on 47.2VDC. Makes sense? So this 12AX7 gain stage has amplified the signal by 70x, which is plausible as 12AX7 has an amplification factor of 100x, so theoretically it could amplify up to 100x.

Now what happens at plate of second 12AX7? Or output of second stage? Just in front of C4?

A 600mVAC signal riding on 82.5VDC. So since we feed this stage 700mVAC, the signal has been attenuated? Well, this stage isn’t a gain stage you see, it’s actually phase splitting the signals so that the 2 output tubes each receive signals of opposite phase. This form of phase splitting is known as “a concertina phase splitter”.

It’s clearer if we look at signal at grid of both 6L6 tubes.

Note that there’s no more DC voltage there. That’s what the cap does! Note also the grid voltages are at opposite phase, meaning they are inverse of each other.

Okay, up to here, what’s the point of all this? It’s just to illustrate the workings of the amp. Now that you understand how the amp works and how the signal changes along the signal path, debugging will be easy.

Just get a test CD with a 1kHz test tone, or download a 1kHz test tone and burn it to your disc. Then repeat this track in your CD player.

This 1kHz tone will be like the function generator outputting the 10mVAC in the example above. Why 1kHz? Well, because any El Cheapo multimeter could measure it! Besides, 1kHz is the de facto standard test frequency for audio gears.

Then with your multimeter set to VAC, you could now measure the voltages at each stage of your circuit.

So if input is 100mV (magnitude controlled by your volume control or preamp), after first stage, what would you be expecting to measure? See if you don’t understand your circuit, you can’t debug it. Even with a scope.

And so on. Yeah a scope is nice, but since tube circuits are so simple, if you hear distortion, either the tubes are at fault or the design is suspect. Or just a component failure. Easy to change and check.

With a scope, you could certainly do more, like if there is a phase splitter, the outputs you could see whether it’s in phase or not, but what if you only have a multimeter and want to check whether there’s phase splitting going on?

Red probe on one of the 6L6 grid, black probe on the other 6L6 grid. It should measure TWICE voltage on one grid. Look at the above waveforms again. The multimeter measure the difference between its 2 probes.

Bob Pease is right. Rely on your wits!

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DIY Extraordinaire

It’s not very often that I meet a
DIY extraordinaire like Mr. Chang here. His work puts many commercial amps to
shame…

This is a tube preamp based on a
Sansui circuit. It has phono functions in addition to tone controls, loudness
switch etc. Beautiful eh? If you click on the picture, you’ll be rewarded with a
better view. Check out the silkscreen… 

Aha! A Dynaco ST70 clone! A switch
in front allows the user to select between different driver tubes, as used in
different generations of ST70. The voltage and current gauge is used to monitor
the bias of the EL34s. The switch on the right selects which output tube you
want to monitor! Currently using JJ E34L tubes. 

I actually promised Mr. Chang I
will build this circuit before passing over to him but too much work got to me
and before I knew it, Mr. Chang got it built! Circuit can be viewed on Projects
page. Circuit is 5842 driving 2A3, SE of course. The tiny output transformers at
the rear are Hammond 125ESEs. They might be a little tiny for a 2A3 but
listening is believing! Give me this amp any day over commercial amps! As you
can see, Mr. Chang took extra steps to enclose the power trans, Hammond 10H
choke and the 125ESEs. 

The attention to detail is
unbelievable! 

Great craftsmanship!

Way to go! 

Great job! 

Well done! 

You certainly inspire me!

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Matching the current is critical to sonics here. If you could find matched tubes, great. But over time, even matched tubes will age and most probably, they won’t be matched anymore. Therefore it’s critical to have some adjustment on the tube currents.

There you have it! By varying the pot, we could adjust until both tubes are conducting the same current. Well, as close as you can get. Without too much effort, I managed to get one channel within 1mA while the other channel was within 5mA. If you have trouble getting the tubes to “behave”, sub the 15 ohm with 20 ohm.

After all the improvement, complicating a simple amp, I brought it over to YH’s place. YH uses Harbeth 82dB, 6 ohm speakers. Room size is 16′ x 24′. To say the Simple EL84 faces a daunting task… is an understatement. Well, what can I say? This 10W little bugger drives the Harbeths very well! Except for some complex passages and musical passages where it clipped, the Simple EL84 is a winner. We played a Consonance (Opera Audio) M99 integrated in this same system a week ago. Let me tell you this: the Simple EL84 CREAMED the M99! There’s simply more life in this little bugger. Bass control is simply excellent… for a tube amp.

The EL84 naturally has a sweet sound so the usage of neutral ECC99 and Auricaps help it excel. Sweet front end tubes and caps might give you diabetes! But if you like it, then what do I know? Experiment and tell me what you like!

Hey, if you are longing for a tube amp, but can’t afford one. Here’s your ticket.
If the Simple EL84 can drive the 82dB Harbeths with aplomb, it should be able to drive most commercial made speakers. 88dB? No problem! Unless your listening room is many many times bigger than YH’s.

After the Simple EL84 survived the Harbeth test, brought it to test with other speakers as well. Tried it with 85dB Musical Technology speakers, and 91dB Monitor Audio bookshelves. Again, the Simple EL84 proved itself equal (and even surpassing) some of the much more expensive gears over there. I luv this baby!

Let’s face it, comparing to single ended amps, reveals a not so easy-going midrange and treble but if you favour better bass control and dynamics, you know which I prefer. : ) Single ended amps need very efficient speakers, which are mostly HUGE and COFFIN-LIKE in appearance. Here’s another alternative for you, courtesy of DIY Paradise.

Options? Lots of! You could build all NOS line-up. 5687 driving 8BQ5s. You could build all new tubes line-up. JJ ECC99 driving JJ EL84. Or you could mix and match. There’s certainly more but this will have to do for now.

Before I wrap up, here’s what you need to build the Simple EL84.
Output trans, 8kohm primary impedance. 10W is fine. (New Hammond stock will have this little critter.)
Power trans. 240-0-240V @400mA, 4-0-4V @6A (for 8BQ5), 3.15-0-3.15V @3A (for 5687 or ECC99).
The 23kohm plate load resistor consumes ~2W. Use 5W or higher.
The cathode 390ohm, you could use a 1/2W.
Ditto with 220kohm grid leak. 1/8W is fine as well.
500ohm pot can be 1/2W or more. Ditto with 1.2ohm current sense and 15ohm current adjust.
The LM317 on YHLMCCS (highly recommended) is best fitted with TO-220 heatsink. Run it at 70mA if you think 80mA is too hot. (It is, to a certain extent.)

Lastly, TOOBS! NOS 8BQ5 @RM20 each for a limited time. JJ EL84 matched quad @RM140. JJ ECC99 @RM45. NOS 5687 @RM40. See price list.

Continuing the journey… Variation of the Same Theme

diyparadise.com

The post Updating the Simple EL84 appeared first on diyparadise.

Okay, sonics wise leaves a lot to be desired, but this is where the actual fun begins.

Began by soldering cathode bypass caps for the ECC99. 470uF/10V should be good enough but as usual, play with this value. I haven’t spent time optimizing it yet. Now gain is higher and you don’t have to crank up the pot like before. But I thought without the cap it sounded clearer. Anyway, let it run in first.

Next, wired in 1.2ohm resistors to every cathode of EL84 to check their current. Need to know how “matched” these tubes are. Well, what did I see?

My goodness! Matching is way way way off! One guy conducts 30mA, the other 50mA so cumulatively they measure 80mA but this is not right. We want each guy to be conducting 40mA, within a few mAs.

So, swapped around a few tubes until they match pretty well. If you are lazy and don’t want to buy so many tubes, you should insist on matched tubes. This will make your life much easier. Alternatively, hang on first. A network to adjust current should be out soon. After I got my mix pretty well, fired it up and…

Sonics is sooooooo much better this time. Even had non-audiophile housemate jump at the improvement! Clarity is improved. Veil is thinner (is there such a description?) but there’s still room for improvement.

YH’s Lazy Man Constant Current Source
YH has suggested to me many times to swap the cathode resistor for a constant current source. But with me being LAZY, I abhor the process of finding suitable transistors (to conduct 80mA in this case) and all the works. Anyway, YH then showed me a pretty easy scheme! So easy you should knock yourself on your head if you don’t try it!

After implementing the YHLMCCS, and verifying the current and voltages are okay (it works like a charm!), fired it up and… Non-audiophile housemate jumped higher this time! Veil is gone. Clarity is good. More amazingly, the BASS. Wham bang boom! Superb bass definition! Many DIYers have commented on how constant current source change their sound and better bass definition is certainly one of them. But hearing it myself is enlightening!

Sonics wise, this is something I could live with. But got to make it easier for DIYers to construct this amp. Proceed to the Update.

diyparadise.com

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Okay, actually building this integrated amp is a piece of cake. But I took so longggggg…

Chassis
I was determined to make a nice amp as my previous attempts all have a “frankensteinian flair”. So I took extra trouble to get the chassis done up really nice. Got hold of a nice piece of 1mm aluminium chassis. 1mm sounds too thin right? But it’s holding up almost 20kg of iron pretty well right now. Anyway, took me 1 day to drill all the holes I need. 1 day to paint and… an eternity for it to dry!

I used hammertone paint here. Was told that “they’ll dry within an hour”. Really? Okay. Applied first coat (diluted with thinner of course) and left it under the sun to dry. An hour later, was happily applying second coat when I noticed the previous coat was “moving”! Dang! Needless to say, third coat was many hours later. Still not fully dried. Got fed up. Became desperate. Left chassis under the sun. Left it in the car parked under the sun… I thought this should be okay right? But as I grabbed the chassis, I left my fingerprints everywhere! Grrrrr!

Wiring
Seriously, watching paint dry has never been this interesting. Okay, enough talk about the chassis. Made me mad! Wiring is straight forward. Was determined to do it nicely this time as well, but my attention span only lasted a few solder joints. After that was sloppy, sloppy, sloppy job again… Now you know me. But when I rebuilt the power supply circuitry (to kill hum) I rebuilt the signal circuitry as well, using tagboards. Everything looks neater now, but this is relative.

Testing
Testing is easy. Just make sure all voltages are pretty close to that on schematics and you are fine. Sometimes you get a big difference and it could be either your incoming VAC or your heater voltage being out of whack. So check your incoming VAC and heater voltages as well.
Does the power supply circuitry look different? Does the 1.1uF cap bother you? Without the 1.1uF, the ripple on the power supply is about 40mV. With this cap, it went down to single digits. You can read more about it here.

First build
My first build gave me bleeding highs. My ears bled when I hear the highs. Even violins are horrible. What’s wrong? Guru YH suggested the phase splitting isn’t up to mark. Basic electronics tell you that you can improve the phase splitter performance quite easily… but that is another article…

Anyway, as I attempted to kill whatever hum that I was still having, I rebuilt the power supply AND rebuilt the signal circuitry. The layout looks cleaner now. Fired it up and… the highs are okay! Whatever I did wrong previously, I must have done it right this time.

Listening
Critical listening revealed several flaws. The sound is veiled, muddied. The highs are okay but the bass is quite rolled off. Also, you need to crank your volume pot quite high… Hmm…

Complicating the Simple EL84.

diyparadise.com

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and his DIY journey…

Another macho man comes forward!
Rest of you weaklings, go ahead and oogle!

2A3 power amp sitting nicely on
pair of evil looking “Afterburner 12”. See the preamp on the right? It’s waiting for
it’s turn…

Great woodworking, Gab! Were you a carpenter in
your past life?

Another view, but I still can’t get
enough of it… Yeah, I know, I’m sick…

Whoa! And now is the preamp’s turn!
Lots of glass!

With the tubes on, it looks like a
battleship… 

The attention to detail is
marvelous! The wooden transformer cover is a winner!

The bastard in me have to
nitpick… how come they don’t match the nice flooring? (what an idiot!) :
) 

Great job, Gab! You sure inspired me
to go ‘woody’!

Gabriel can be contacted at gabvoon at
pd dot jaring dot my

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How to Make a Transmitter Class Amp
Nicholas Chua

Yo dude! Nicholas — cool dude — here, presents you this “little” amp for your building/listening pleasure…

Transmitters have always been the talk of the town with Wavacís 833a to Kondo San infamous 211 Ongaku. Many diyers have often long for amps like this. After my stint with an 845 amp, I decided to make myself a transmitter amp. It was the looks and the powerful sound of the transmitter that got me going. However the sound was thin and lifeless for me so I decide to make an amp that could beat a commercial offering hence the quest for my FIRST Transmitter Amp. Should I call it Simple Transmitter Amp perhaps?

There are countless types of transmitters available for low power region. There is the infamous 211, the 845, 811A and a relatively unknown GM70. The GM70 being a Russian offering had superior quality build over most Chinese transmitters. Unless you have yourself a GE or Amperex than the cheap Chinese stuff can really ruin it for you. In terms of specs the GM70 has a mu of 6.9 and Rp of 1800 and best part can be run at below 1KV. Why diyers should not cross the 1KV region, parts are expensive and most important there is this thing called the corona discharge. To avoid going into theory lets say it is dangerous this corona discharge thingy. I had to pot my output Trans with a special wax when I started playing with 1KV and above voltages. But below that everything else is fine

So enough of theory, I went and bought myself a quad of GM70 in lieu of building a PP for it. Of course with any transmitter amp you need yourself a relatively meaty driver. After some searching on the net I found a lovely pentode called 12GN7A. It has a Transconductance of 36mV. When triode strapped it has a mu of 40 and an Rp of 2K. Of course no curves are available for the tube; I had to test the tube to get the mu and the Rp of the tube. But why go for 12GN7A when 6c45 and 5842 are so easily available from Yeo? I find personally 6c45 is thin and solid state like when used as a driver while this 12GN7A has the Sonics of the 5687 neutral with a tinge of warmness in it. The tube also has a very weighty sound due to the low Rp of the tube and a high mu for use a 2 stage amp. What I like best is that the tube is can withstand 400V on the plate and has a12Watt dissipation. The tube is one hell of a driver looks like an el84 but with black plates. The driver was chosen as it can take a lot of voltage on the plate making it ideal for swing a decent amount of voltage. It has the capability to swing close to 80 Vrms when properly loaded that into a 10K load. With a 2K load, swing drops to 40Vrms. talk about meaty. Of course you could use it as a pentode and larger swings are appreciable. I know many people use this tube as a pentode and the love it. But I am a triode fan and choose to build it as a triode connected as I am to lazy to regulate the screen voltage. Other types of pentode that I have investigated are the 6688 but if possible another good driver to look into is the infamous D3A. However be expect to pay lots of many for this. Only made by Siemens and Halske or their derivative departments.

Let me talk a bit more on the Gm70. It has a blardee large heater requirements of 60watts 20V at 3A. By turning on the heater only, the whole tubes glows and it is already hot this way. Imagine the heater is requirements is already hotter than the standard tiga ratus B. The mu of gm70 is 6.9 thus making it easy to drive unlike the 845 which requires a lot of swing hence the reason to choose the GM70. Easy to drive, more power and better looking. Best part of the Gm70 is that the Max plate Dissapation is 125Watt unlike the other smaller brothers 211 75 watts and 845 around 100W ( not advisable with Chinese unless the new 845BM is bought from China, not out yet). The plate of the GM70 looks much bigger than the 845 from Shuguang. However no such thing as free lunch, the tube is much cheaper than any other transmitters but requires a special base. The base can be bought from Dehavillean for only 150USD per pair or Teflon socket around 15 pounds per pair or just connect it with wires and use a capacitor clamp to hold it, another way is to modify a 6c33 base it would work too. When properly build with suitable drivers the GM70 has a power output of 48Watts Single Ended. This way diyers can break free from Single drivers and drive EStats perhaps and other conventional speakers that we all started on. However I use the beast to drive my Fostex 206 and really make it into a party animal now. So Coral owners get ready to build an amp that transforms your speakers into a wild animal.

So on with the amp design

Attached above is the schematic for the first iteration of the GM70. Of course before we can run we must crawl first. The first iteration has a power of only 12-14 Watts only, thru a 9K transformer. Of course as time pass by I will release future upgrades to turn this amp into a truly might beast. But for now just stick with 14 Watts first. For those who would like to try this amp with a lower voltage reduce the B+ from 730V to around 450V. The power would be reduce to 8 Watts then but then it would give you a test of transmitter magic at a lower voltage. This amp deals with HT if you feel uncomfortable with it then build the 450V version. With the 450V used fixed bias instead with a voltage of -70 applied to the grid. This can be used with the 730Volts version too, by doing this reduce the B+ to 650Votls and use fixed bias. Fixed bias gives a more dynamic sound too.

Here the 12GN7a requires the maximum gain hence the use of Choke loading for purpose of loading. This way the Mu of 40 is achievable and a low Rp of 2K is achieve. The low Rp is needed to drive the Gm70 properly. Of course plate chokes are hard to come but let me know if you need some as I have some. I am a big fan of Iron and Oil caps hence I when ahead and used Paper in Oil caps for C2. But any other brand is useable; I hear Mundofts are excellent for this.

The output Trans was a 9K Trans that I design and got it wound. It has 8 layers of primary and 7 layers of secondary interleave for maximum coupling. The Trans that you should get should have this much layers at least because this would help to reduce the corona discharge in the trans. The Trans is wound using Z11 for best signal coupling. Of course it would be advisable to get a high power rating Trans so that it can be used when we convert the amp into a 48Watt Se. The Plate Choke was another of my own design using 6 layers to minimize leakage inductance and wound again with Z11.

The rest of the parts in the Amp are pretty straight forward where the rating for C1 is 10Volts and C3 should be at least 200V. I used Siemens PolyProp here. C2 however should be at least 630Volts and above. I personally used 1KV here. This is because the voltage at turn on will be high around 730V and will drop to 250V later. Hence the cap has to be rated for that much hence the recommendation of the Mundofts here with their higher ratings.

The power supply

With any transmitter amp, the Power Trans design is the most critical, failures here would cause catastrophic damage. The secondary is a 540-0-540 here for the B+ of 730-750. Also I did not draw is the switch to ground at the CT of the 540 supply. This is turn on once the heaters of the tubes have been on for 1 minute. This way cathode stripping is prevented, nobody likes to crank 7000 rpm when the engine is still cold so treat the valves with care and they will outlive you this way.

With a voltage of 20V there is not way AC heating can be used as the hum would be insanely loud. The heater of the GM70 is a DC heating with CLC to reduce the ripple in the heater supply. Of course this helps to act like a current source. Heaters like to see a Norton source (constant current) and not a Theiven source (constant voltage). They sound better with a current source heater supply. DC heating often gets a bad name when Theiven source is used with 317 regulating the voltage. The results are often dry sounding but not with a choke it sounds very AC like milky and sweet like chocolate au lait. A choke acts like a passive current source. Of course one could use an active CCS like 317 and co but remember at 3A, there a lot of heat dissipation to handle there and the chips would not less long this way. So I went ahead and use a choke instead. I recommend that the inductance be increase but this is what I have you instead. Values around 50mH would be better. However remember to reduce power loss the resistance should not be too big and should be rated for at least for 4Amps. Resistance of less than 0.5 R must be used. But the value of 15mH works fine too. Preferably the choke should be interleave and section to increase its capability to filter the HF hash emitting from the charging of the large filter cap that is needed to be used.

The Sonics of the amp I would not lie to you, it is great with lots of potential. Feels like a very powerfully 300B and 2A3 amp. It has the nice midrange of the 300B but with the balance tonal of the 2A3. Bass control is excellent here and the amount of bass that can be pump out is insane for a SE amp; there is more high frequency extension with this amp then my 300b amp. What I like in particular is that at low volume and high volume the sonic character is the same. This trait shows the control and power sufficiency of the amp to control the speaker when both posh listening and the wild rocking head banging volume levels is played.

The amp plays both rock and other music well. Ziggy Stardust by David Bowie plays now with me rocking in the middle. Because of good bass control, double bass plays with great authority. The expansion of the double bass is now very apparent like the how it should sound when you stand/sit 2meters away. Normally in most amps, the double bass is the often miss played instrument where the sound is muffled, not there at all, worst the box is heard but not the string being plucked. With this amp Charles Mingus is king and plays on. For the classis people, Moonlight Sonata LP never sounded better with the sound piano being like it was played in the moonlight where the pianist plays for you only. The decay of the piano sounds real like it supposes to be. Piano another great instrument for judging oneís amp has it as everything you need to judge an amp speed, dynamics, body, decay and etc. New World Symphony Largo LP Brass sections did not lack the speed and timbre associated with SE amps but it is noted that it is still slower than it should be. Because of the non-feedback the speed is not compromise where feedback tends to muddle with the speed as some of the signal is feedback to input thus slowing the sound. But with all SE amps there is more swing in orchestra pieces. Separation of the instruments seems to be good too and there clear audible distinct between instruments being played not just a sound wall.

Endnote build the amp feel the music then get the itch to make it better with the next segment adding in the proper driver stage to drive the GM70. Till then rock on and smell the solder fumes remember no pain no gain unless you die trying.

I attached the rat nest, electric chair amp of mine with the 2A3 as driver. Pic taken as monoblock, there is another block. Expected weight for this is around 70 pounds per block

Enquiries about Nicholas’ baby/monster (depending on how you look at it) can be sent to nickcrap@hotmail.com

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Chokes in C Major

How to make your chokes sing in tune…

I like power supply with lots of chokes and very little capacitance. But sometimes this isn’t practical as this results in VERY heavy, VERY bulky behemoths. Your better half surely would prefer something cute and tiny. But such things are a dent to our manhood no?

To compromise, the alternative is no chokes at all BUT you are not a REAL MAN.
Or less chokes and more capacitance. But there is a limit on how much capacitance you can go. Too much and your tube rectifier gets strangled to death. Too little and you’ll have nice hummmmmmmm…. Besides, music gets dull and lifeless with too much caps. Seems like the colouration (and quality) of the cap becomes a lot more prominent.

Which brings us to tuned chokes, aka “making your chokes sing”, aka “tuning your chokes to the music” blah blah blah…

See this supply? Without the 1.1uF cap, the ripple is about 40mV. It’s LOUD and IRRITATING. With the 1.1uF, the ripple is less than 10mV! Herein lies the beauty of tuned chokes. Just one little measly cap and you are done! You can save money as you don’t need those big swanky expensive high capacitance caps. That’s why I sell only the 50uF and 100uF (the JJ 500uF is another story). I’m a dictator. I sell only parts I like to use. : ) The network between the transformer and the diodes are optional. Circuit courtesy of the late John Camille from Botthelead.com.

It works like this. Chokes and capacitors work differently. One guy’s impedance rises with frequency while the other falls with frequency. At some point, they will meet each other and cancel each other’s effects right?

First of all, what’s the purpose of power supply filtering? To filter out hash above DC. Anything above 0.0000001Hz, we don’t need. This is where RC and LC filters come in. They are LOW PASS FILTERS. You can calculate their effective working frequency using the equation f = 1/[2*pi*R*C]. In our power supply, what is the main component of this hash that we want to filter out? The 100Hz ripple! If you use full wave rectification, then it’s the 100Hz ripple. If you use half wave, then it’s 50Hz. If the incoming supply at your area is 60Hz then it’s 120Hz and 60Hz respectively.

Now tuned choke works by targetting at this main component of hash, which is the 100Hz ripple (in our case here). Thus we want the cap and choke to resonate at 100Hz. The equation for resonance is f = 1/[2*pi*sqrt(L*C)]. So if we know L and f, then we could calculate the C needed for this supply, which would be C = 1/[sqr(2*pi*L)*f].

Look at the above circuit. L is 2.6H. f = 100Hz, so C is… about 0.97uF. Please try it yourself, you lazy tweet!

Aha! so easy heh? Just by paralleling the 2.6H choke above with this 0.97uF cap I get an additional tens of dB reduction in 100Hz hash?

Unfortunately, life is not so simple. The 2.6H rating is meant to be AT A CERTAIN CURRENT. If you are running less current, the inductance should be higher. If you are running more current, it should be lower. Furthermore, there’s a tolerance in the ratings. Hammond rates their chokes at 15% tolerance so the above choke could be anywhere between 2.21H and 2.99H. I once used chokes from some big time manufacturer. Rating says 5H but I found that it’s more like 3H…

It would be swell if we could measure it’s inductance but such equipment is beyond our budget. There are ways to guess the inductance but we don’t need all that complexity. Just try this.

From calculation, we know it’s somewhere around 0.97uF. So let’s try with 2 pcs of paralleled 0.47uF. This is 0.94uF as for paralleled caps, you add the capacitance. Parallel it with the choke and measure the hum level. You could measure this at speaker output. Then swap this cap with 1uF. Repeat with 1.1uF, 1.2uF… Chances are, you will find one or a range of values with pretty low AC hum. The capacitance that resulted in the lowest measured hum is the one you will want to use. Don’t have a multimeter? Use your ears! Hook it up to some speakers. Best is high sensitivity speakers. Listen to the hum. Try other caps. The one with lowest hum to your ears is the one to use.

As you can see, all this takes a lot of work. But you only have to do this once. Once you got it, it’s a done deal. I have a supply that I have varied the current between 50mA and 100mA. The tuned choke just works perfectly! Err, what about voltage rating of caps? If you can splurge, get high voltage ones. Otherwise you can calculate. In the circuitry above, my supply needs to pump out approximately 180mA. 180mA thru 26ohms gives a voltage drop of 4.68V. This is DC. We need to account for AC as well, so 2x should be enough. This means you could get by with a 10V cap. But quality is not critical here (this is what I think. If your experiments contradict this, let me know.), so just get some cheap mylar 630V caps. They are really cheap.

Err, any drawbacks? Other than the various trial and errors? Actually there is. With the addition of the paralleled cap, the frequency response of your power supply not only has a dip at the resonant frequency, 100Hz, but it has a peak as well. If you are not careful, this peak will creep into the audible region. Maybe you can use it to boost your bass a little! But maybe it could add some unneccesary boom to your bass. The best bet is to try to simulate it with Linear Tech’s excellent SwitcherCad. If you are lazy, just drop me a mail…

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How to Convert your PP amp to Triode mode

Ever wonder why idiots like me rave about Pentode Push Pull amps in Triode mode? Don’t you hate idiots like me as your amp is only wired for Ultra Linear (or *gasp* Pentode mode) and Triode mode now becomes the sweet tasty Forbidden Fruit everyone raves about but you can’t taste?

Oscar Wilde said the only way to get rid of temptation is to yield to it. And if you know which end to hold the soldering iron, read on.

Shown here is a Jadis Orchestra amp.

Close up for you near-sighted folks.

OK. See the yellow and orange wires? The yellow ones are wired to pins 3 of EL34 while the orange ones are wired to pins 4.

Pin 3 is the anode while pin 4 is grid2.

The yellow wires go to the ends of the output trans so the orange wires is most likely (and it is in this case) the Ultra Linear taps.
Thus our amp here is wired in Ultra Linear mode.

 

To convert to triode mode is a piece of cake. Just wire a resistor between anode and grid2 pins, meaning between pins 3 and 4. Leave out the ultra linear tap on the output trans. See below.

 

 

That’s all it takes! Easy huh? Most common values of this resistor is 47ohm or 100ohm. Either one will work fine. Leak/Mullard claims one is better than the other, but you can’t go wrong with either. Although 1/2W is usable, go for 1W or higher.

A DIYer did the above to his Jadis and these are his exact words.

Hi yeo, fire up the jadis yesterday and wow yes there is a major difference. On the penthode the sound was a bit forward and fatter but on the triode the forwardness is pulled back and the mid/hi is more sparkle and more open leaving more space between the different instruments. Bass was not as heavy as penthode but more in control. Overall 1st listening is good but not to say that in ultralinear is bad just difference in characteristic. In triode mode it is more refine but in penthode you get the sunday live jazz lounge ambience with big chesty vocal( can be a bit fat) with a lot of air in the vocal range but the instrucments is a bit gluey.

Personally I find that triode mode has more realism but please bear in mind one very important point. Going from UL to Triode mode, you lose about half the power. If you have 40W in UL, now you have 20W in Triode. Not a problem for my 97dB sensitive speakers but if your speakers aren’t efficient enough and need all that juice, then for sure your experience with Triode mode won’t be positive.

That’s all for now!

 

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