This I have been experimenting - call it a hunch - on the effects of bypassing electrolytic capcitors (Nichicon FW and KW) with 0.1 uF TDK ceramics (Mouser 810-FK28X7S2A104K) with the diamond buffer circuit used in both my B-board preamp and Sapphire headphone amplifier.

This being a mod, I had to solder the caps to the underside of the boards, attached to the leads of the Nichicon 100uF electrolyic capacitors.

I used four ceramics per channel, one per active device in the diamond buffer if you like.

I did several other changes on the B-board at the same time, so it wasn't obvious until I modded the Sapphire in the same way what was the result of the bypassing. Anyway, with both the improvement was immediate and dramatic: any sense of "transistor-like" treble glare is completely quenched. The whole top end takes a step backwards, not in extension, but in prominence.

Less audiophile detail, more swinging mojo.

Nor the remake, the original. Good film. Story shakes out something like "Twelve Angry Men in the desert": Put together a small, random group of people and pressure them to complete a task. In the case of "The Flight of the Pheonix" this is to make an airworthy plane (this one) from the crashed remains of another (this one).

So. We start with my old red Gainclone case, and a pair of these buffer boards , and a Takman resistor, 24 position stepped attenuator from eBay, unassembled, and start working to transform something old into something new.

Here's my LM3875 gainclone. Served me well, but it is time to bid adieu! (at least to the guts):


Opened up, we see the circuit board, such that it is, and my home-built 11 position attenuator:
...

I tell people: "Buy a nice, heavy power transformer. It will sound better."

They are skeptical, because the circuit only draws a couple of watts, and less than 100 mA current.

The image below shows how the power transformer, and rectifier diodes, actually work much harder than you would estimate from looking at the output power.

It shows a zener regulated supply with a load drawing 100 mA at 20 V. That's 2 W.

As a result of the capacitor input filter directly after the diodes, however, the diodes and transformer do not conduct current all the time, but instead for just a couple of milliseconds twice every cycle of the AC wave. They have to supply all the output current in just that short space of time. As you can see in the simulation, the diodes are pushing peak currents well in excess of 1A or 10x the output current. This is a typical "normal" power supply with a initial ripple ratio of a modest 1/40, things...

A real, honest-to-goodness voltage regulator has three parts: a fixed voltage reference, an error amplifier, and a pass element.

Most people only put eyeballs on the final, all-wrapped-up-in-a-tidy-IC-package version, typified by the LM7812, or with a couple of extra gain-set resistors, the LM317. These chips have a working bandwidth about about 2 kHz, as they are designed to 1) reduce 120 Hz ripple and 2) be rock stable no matter what abuse they are subjected to. As a result at audio frequencies and above they are pretty much noise generators...

Knowing this, many people have set out to build better regulators for audio work.

The most obvious route is to build a high performance LM7812 from discrete components. (Most excellent review here.) AD797 for the error amplifier, high stability, low noise voltage reference, etc. The trick though, is stability. The LM7812 is low bandwidth not because it's too cheap to manage anything better, but because...

Finally got around to some more comparison listening with the Sapphire headphone amplifier. To recap: the circuit has an open loop diamond buffer output, so the op amp is just providing voltage gain. It configured for a non-inverting gain of 21 dB to match my 300 ohm HD600 headphones. Pretty much textbook operating conditions.

The op amp inputs are impedance balanced at about 1 kohm. This is about the crossover point where you start thinking about using FET input stages, but BJTs should still be fine.

I'm interested to see if there is a definite signature to a FET-input opamp. The original build called for an OPA134, which is a JFET input circuit. I tried the OPA27, which is a low-noise, high-input-current BJT design, and last night I tried the NE5534A, a classic general purpose audio opamp with bipolar inputs.

I've long been in agreement with Douglas Self on the NE5532/NE5534 : anyone who reports these op amps sound bad is either not using...

I was asked to suggest a voltage regulator for the First Watt (Pass DIY) B1 buffer. One thing led to another and the next thing I'd sketched up a circuit board for the buffer as well as the regulator.

It's like a B-board, but with the JFET buffer instead of the diamond buffer, and with a single supply and, hence, the coupling caps front and back. Since it's using JFETs for the buffer I used a JFET for the pass device in the regulator, too.

Full credit to Nelson Pass for his design.

Eagle files do not show 2SK170 because the package is not in Eagle. All transistors 2SK170 or equivalent. Zener is 18-22V DO35 or DO41 i.e. Vishay BZX85. V++ is 5-15 V above whatever you select the Zener reference to be.

This is a followup of sorts to the X-reg, though there is nothing original about the circuit this time around.

It's just a Zener voltage regulator with a series pass transistor. I lifted this particular configuration from the Pionner C-21 preamplifier and re-tuned it for op amp applications. My main interest here is trying to make a small and convenient board layout.

I've used this circuit block already in the Sapphire amp and come away impressed.

The output is about 1 V less than the Zener voltage, and the input voltage should be about 3-6 V above the Zener reference voltage. I'm working here with 17 V unregulated supply and 12 V Zeners, but the values can be reconfigured easily enough for any output from 4-24 V

This is a low current circuit. If you are just powering a few op amps, no heatsinks are needed. Above 25 mA small heatsinks are a good idea. The circuit is not designed for output currents above 100 mA.

Found this today: DC Coupled Amplifiers for Audio from an 11 year old web page by one Knut Harald Nygaard.

I've taken some minor liberties with the circuit, shown in the second, color image below. Replaced the current sources with resistors and moved the output buffer out of the feedback loop.

Note the resultant double symmetry of the dual-diamond buffer topology, highlighted in blue.

Douglas Self on op amps for audio, which I read before in slightly different form, on another web site somewhere, many years ago... today was a refresher course.

Excerpts from op amps in small signal audio design, by D. Self [Part 1, part 2, part 3, part 4].

I suppose I should get with the times and start using the LM4562 seeing as it is available in DIP8 now. (I had this memory that it was only SOIC, go figure...) Pity it's dual only. On the other hand, that leads to some neat ideas, like a compact version of the Sapphire amp for example, or the X-reg.

I am struck by how few choices we really have when it comes to practical op amps for audio in single DIP8 packages. There is the NE5534, TL071 and TL051, the OPA134, the OPA604, and OPA27, OPA627. Maybe the AD797 but I have yet to see the point. Given that the TL1071 and derivatives are outdated and replaced essentially by the OPA134, and given the excessive cost (and questionable sonic benefit)...