#tweaking electronics

All audio equipment has flaws. Some are flaws in concept but usually execution. If you prefer the word weaknesses or foibles that is fine. The internoise is full of stories where some guy has rebuilt a classic unit with new or premium components. An example of that from a factory is the rebirth of the Citation one and two made in China but with top quality parts that did not exist in the 1950s. Still using a 70 year old circuit mind you.

Good technicians simply may want to fiddle. Poor technicians with basic skills like I am will fiddle too. A little bit of this and a bit of that and old becomes new.

I have not done wholesale replacements of premium resistors or fancy Russian oil and paper capacitors. I have replaced or bridged signal path capacitors with film types. I have split power supplies for separate left and right stereo channels in amplifiers. I have not changed anything in my ARC preamps except for vacuum tubes. Oh and spritzing them with contact cleaner. I did that.

I had an old preamp that used OPamps and came from designers that had left SAE years ago. In that one I dropped in a much larger capacitor in the power supply. That made a very significant difference in the Bass. Arguably it came from the factory with sufficient PS filtering. That simple change made a big difference. In some designer's minds a power supply capacitor is to filter out hum from the wall current. Once the hum is so many db down its fine. In others it is a reservoir of energy for the output.

But all manufacturers need to invest wisely in parts and components. If they think a given part is good enough then a better one is a waste of money. Some of the better products are just basic solid designs built well with all the tweaks done from the factory. Several good power amplifiers will split the power supply and otherwise be pretty plain. Rectifiers are not expensive but doubling the number of PS capacitors can be.

Then there are the conceptual flaws. Zero-feedback versus lots for example. Usually it is simple faith that fill-in-the-blank is the best. Experts in one method will cheerfully point out the problems with any other method. Well reasoned and backed up with plots and data and proof. Like that recent post I did about the ZOTL Amp where they proved that any tube amp using an output transformer is hopelessly compromised.

Finally there is the practice of voicing electronics. Adjust some part or other of the circuit to make it sound "right." When Bob Carver won his bet about making his cheap amp sound exactly like a premium amp it was a exercise in voicing. That you can do that means something other that accuracy and precision is driving preferences of reviewers.

This is one of the first super amps. Back then a super amp was anything over 100 Watts / side. This was 200 / side. Another was the Phase Linear 400, then 700 (the flame linear). And of course the Dynaco Stereo 400. At roughly the same time (late 70s) there was the Ampzilla which was also 200 / side.

The Phase Linears were designed by Bob Carver.

The Dynaco, SAE and the Ampzilla were designed by James Bongiorno. The Dynaco 400 was done by JB, before he went to SAE. The Ampzilla was after. In any event JB was a prolific audio system engineer. And good at his job.

The 2400 was one of the early SAE products and it was the very first super amp I heard. It may be a refined version of the Dynaco circuit, parts look really similar. A friend working in a stereo shop borrowed one and brought it to our Dorm in college one evening. We hooked it up to my speakers as they were the most resilient ones. That SAE was big and silver and had two huge meters on the front. We could not feed it audiophile quality stuff, but we were still impressed.

As stupid kids we just wanted it loud and it did that effortlessly. It was also what prompted me to buy a Dynaco as it was far more affordable.

The 2400L was a later version with LEDs instead of analog meters but the same amplifier circuit. I almost wish I knew electronics better, but I always dig up circuit diagrams if I can. The circuit design and topology are where the genius lies. Designers have a style. They try this and that. New parts are invented and they will see what can be done. The 2400s had fully complementary circuits. The positive side and negative side wiring and transistors were exactly mirror imaged. On one side NPN and the other PNP. What that means is they flow opposite polarity current. It looks elegant.

Certainly it was well regarded in the day and there are many fans still in Solid State Audiophiles.

James B left SAE to found GAS who made and sold the Ampzilla it was a further refinement of the fully complimentary circuit. It was originally a diagram and list of parts in Popular Electronics magazine. Then GAS made kits and full factory amps eventually. The Ampzilla is a bit strangely packaged, but was very respected by audiophiles.

There may be stages of refinement and improvement through these amplifiers, but all the Bongiorno designs are very similar.

There is a 2400L for sale near me. It is a reasonable price at $650.00. It was checked out and well here I am writing about it so yes it is tempting. Probably better in stock form than my Dynaco in stock form, but the black beast is not stock.

To duplicate the Dynaco tweaks to the 2400 what would I have to do? Well I would need to split the power supply in two. Four new capacitors, two bridge rectifiers, and small bridging caps. That is easy, and as new caps are smaller room could be found. I would also have to change at least 4 and as many as 8 signal path capacitors from polar electrolytic to film in each channel. That may be risky as they may be used as diodes in circuit. I suppose diodes could be added in line. Or I could just use better electrolytics.

The box with the unicorn is supposed to arrive Friday. One of the first things I must do is figure out if the phono input had been modified. During that era the "high end" manufacturers were expecting that people with money would use MC phono cartridges. Those use higher capacitive loading. The ACR SP14 cost about $7k brand new in todays money.

The ARC SP14 came from the factory with 600 pf loading on the phono input. Add in the connecting wires and you get 700-800 pf. That is a lot! Audio Technica MMs like my AT440 and AT7 will scream in pain with that load. The Grado Opus has really low inductance so it is less sensitive to that, but I like those other cartridges too. The resistance value is also adjustable with solder. The old Stereophile review had the unit modified to relatively low resistance to suit the MC cartridge he was using.

You can see how these values affect the response of cartridges when they are exactly wrong at this site. https://www.hagtech.com/loading.html The ideal load for MMs is 47k ohms and as little pfs as you can manage.

I expect that many really good phono pickups have got a bad rep from this very issue.

So I gotta flip the SP14 over and see what has been added in or not. If there are extra resistors I have to remove them. I also plan on pulling out or at least disconnecting the factory 560pf capacitors if they are still there. Without that the impedance is 50 pf just like the SP12.

So my head has been into opening boxes and fiddling so I also start to think about my Amplifier. It is old and the usual thing is the signal path capacitors need "attention". I have a complete set of parts for the driver boards including new PC boards I bought "just in case". So I could pull them out and replace the whole thing. That is a lot of work and risky. But there are a couple of capacitors in the signal path. I have ordered a replacement set for those. Nice audio grade film caps to replace electrolytics.

But first I have to get the new preamp running.

I know enough about electronics to be dangerous.  I also know how to be effective.  I have built stuff from scratch, but to be completely honest I have never actually designed a complex audio circuit.  But I have tweaked the living wee out of them.

I mucked deeply into my tube equipment as parts from 40 or 50 years ago simply were not that good. That was just swapping out for new and better.

I am much more reserved in transistor stuff. My favorite tweak is to the power supply.  If you are in the high end cult you may buy plugs to go from the wall to your precious equipment that cost silly money.  If you do you are silly.  Golden ears will swear they hear an effect, and they actually may, but better or not is not a given.

Power to your machines comes from the wall socket.  The wires in the wall are plain single conductor and unshielded unless you built your house to order. The power to your home comes through high voltage cables and line transformers and is not really very clean.  Perfectly clean power would be a 60hz pure sine wave. (50hz in many places on the globe)

Even with fancy plugs the power coming into your devices is not perfect.  You may buy surge protectors and filters for your computers and TV that is all about noise and poor quality power.

My thing is dealing with this inside the box.  All audio equipment resolves alternating current into direct current.  It takes the noisy sine wave and makes it clean and steady plus + and minus - volts.  The quality of that is how steady.  Tiny variations can be heard.

Electrical power has a wonderful analog, water. Imagine you had a device that runs on water pressure (analog to volts) and is available in large volumes (analog to amps).  Now think of that water coming from a fast moving stream that surges and jumps (analog to the house current).  You want it calm and placid.  You dig a pond or build a dam to hold the water and calm it down.  The calmer the pond the more steady the supply.  If you want it really calm you make as big a pond as you can so the effects of the stream are dissipated.

It is exactly the same in amplifier power supplies.  The pond is a thing called a capacitor.  It charges up and acts as a reservoir of power.  The bigger the capacitors the bigger the pond the calmer the power for the machine.

The first thing you can do is plug the biggest capacitors in that will fit.  The downside is you can overwhelm the rectifier device that separates the plus and minus as a big capacitor that is not charged draws huge currents at start up.  For small devices that is not much of an issue for big ones it is.

Also there is the fact that big capacitors are like batteries using chemicals.  They are very fast high current batteries, but they only respond well to low frequencies.  Noise on the line will get through to your precious circuits. Noise being anything that is not exactly 60 hz pure sine wave.  The fix to that is to ground the capacitors with a smaller film type that respond to high frequencies.

The final big picture thing is each channel needs it’s own power.  If you have stereo you need two power supplies.  see below.

                 A tale of three amplifiers

I have three stereo amplifiers.  Each is considered good for its time and is collectable. They are very different.

Carver Magnetic field  M -200 T.  Roughly mid to late 1980′s vintage. This is a cool device.  The magic part is the power supply.  A standard power supply converts wall current to DC at 60 hz in North America.  That means the capacitors get charged in pulses 60 times per second.  You can hear 60 hz it is that background hum that is so annoying.  As I understand it Mr Carver did the simple and brilliant thing of artificially increasing the AC frequency so the power supply is charged far more often therefore requiring smaller capacitors to filter the current. They can therefore respond much faster.  It sounds very nice and is also one of the beasts tweaked to sound like a cost no object high end amplifier in a blind test.

Harman Kardon Citation 12.  This is a classic design from the early 70′s and is  half the rated power of the Carver.  Its magic is the power supply.  Inside the box it is two completely separate amplifiers.  This means Two power transformers, two full wave rectifiers, 4 power supply capacitors. It is otherwise dead conventional.

The difference between these two is far more than just the power supply, but the Carver shares the power between two channels so a big sound in one channel will draw power from the other.  It is subtle but this hobby is all about subtle.  The Citation sounds better even though it has poorer test scores.  The way it sounds better is the stereo image drawn between the speakers is clearer and more steady.

Even though both are “old” they both have been repaired and tuned up in the last two years so they are fresh.  I credit the superiority of the Citation to the separated power supplies.  One channel is free from the other.

Dynaco 410 / 416.  The beast. Design dated to the 1970′s. I built this thing from mostly prefabricated circuits while adding extra output transistors.  The Amplifier circuit is identical to the Dynaco 416 but in a black box.  I built it with two separate full wave rectifiers into two completely separate capacitor banks each the same size as “stock”.  That avoids the problem with excessive current at turn on.  So it is dual mono just like the Citation, but for sharing the HUGE transformer which is ok cuz its HUGE.

The capacitor banks are bridged with film capacitors to kill the noise from the wall.  All by itself this thing sounds amazing.  It is clear and clean and has huge bass and solid stereo imaging.  I fear no amplifier that may come against it.

Comparing all three the Dynaco is the king.  There is no contest on the clarity and the performance.  Recall that the Carver is reputed to be indistinguishable from very expensive high end amps of the day.

The final bit is my tweak to the tweak.  Just before Dynaco Inc. bit the dust they made an accessory to their top 416 model that was an enormous additional capacitor bank to plug into the 416.  It has a pretty complicated circuit to control the charge at turn on.  If it did not, it could fry the house wires.  I built one with a stupid simple charge circuit.  I found a bunch of big capacitors and built a set of 4 banks with 1 Farad of total capacitance.  That is 50 times the size of the stock design.

My trick here was that the capacitors charge through big resistors to limit current going in.  Those are them back fed through really fat diodes to let the current out very fast.  The effect of plugging it in is profound.  An already quite amp goes silent.  The image of a well recorded orchestra is solid where you can place every instrument and feel the metallic sound of the brass and the woody sound of the woodwinds.  In Rock the bass is solid and deep.  Vocals are just amazing.

Now the car stereo geeks will go meh.  “We use one farad caps all the time.”  Not the same kids.  The power in a capacitor is proportional to the square of the voltage.  A car uses 12 to 14 volts.  My beast uses 74 volts. That is about 30 times more power.  You could weld with it.

The Carver and the Citation have at best factory tweaks to “normal” circuits.  The designers were very good to brilliant.  The Dynaco was designed by a team that included people working on state of the art (1970′s) and included great and brilliant names too.  It was very good, but they were accused of hobbling it to hit a price point.  The 416 was apparently an attempt to un-hobble it.

I have vintage equipment.  I respect the Carver and the Citation and do no more than keep them maintained. The Dynaco is another matter.