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Why do I need a preamp?

Posted 14th May 2015 at 07:22 AM by cspirou

One of the things that confused me a bit when I started this hobby was the distinction between a preamp and an amp. Looking up info on a preamp usually was met with a definition that a preamp controls volume and switches inputs, which never made sense to me because my amp always had volume control and multiple inputs.

Well it turns out that what I (and most people) considered an amp was actually an integrated amp. It never really made that much sense to me to separate the functions in a separate chassis and I would roll my eyes seeing preamps worth at least as much as the price of a good amp. Discussions about the different sound of a preamp are a bit weird for me too. While I don't doubt that different preamps sound different, it seems like people are just separating components to do some mix and matching.

However after being in this hobby for a bit of time I have discovered some solid reasons to have a separate preamp(besides wanting to separate everything)...
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Old

Success!

Posted 12th May 2015 at 04:08 AM by Mike94531
Updated 12th May 2015 at 04:12 AM by Mike94531

Finally finished these up....I attempted to paint them with a hammer finish spray paint..boy did they turn out bad!

So I found a roll of carpet at Lowes and bought a couple cans of spray adhesive.

The speakers sound pretty good..we'll see how they sound when I get around to building my Pass F5 amplifier...so far I only have the boards I bought from the store...expect a few months for sure at the rate I get things done!

Yes, that is real carpet...$20 for the roll..I know I won't win any beauty contests with them but for garage speakers I think they are pretty nice, I also saved some money by using left over wooden hanger rods for the center section supports!

Not sure what kind of grills I am going to put on them for protection out here in the garage, I might have to print something out when I get my 3D printer in a few weeks.

I also included a snapshot of the tool path my CNC Bridgeport used to cut the holes in the front...
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Old

Standard Resistor Values for RJM Audio Projects

Posted 11th May 2015 at 09:15 AM by rjm (RJM Audio Blog)
Updated 14th May 2015 at 10:40 PM by rjm

From now on every effort will be made to consolidate to the following values, 1/4W metal film:

1, 4.75, 10, 47.5, 100, 150, 221, 475, 1000, 1500, 2210, 4750, 10000, 22100, 47500, and 100000.

Also, the 1/4W 47 ohm and 68k carbon comp. resistor is widely used as damping and bleeder functions, respectively.

Exceptions will be made for the RIAA eq. of the Phonoclone and VSPS circuits, and the business end of the X-reg, where specific, non-standard resistance values are required.

*****

On resistor selection-

I honestly don't know if one resistor sounds better than another. I do know, however, that one resistor can be more expensive than another. At Mouser your basic 1/4W metal film resistor can run between 5 cents and 2 dollars in 100 unit quantities. Setting aside sound quality, it's not at all clear that you are getting any kind of material benefit at all by getting the expensive parts. Instead, it really...
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Old

Commentary on the TDK Life on Record A33 Wireless Weatherproof Speaker

Posted 10th May 2015 at 03:23 AM by rjm (RJM Audio Blog)
Updated 11th May 2015 at 04:58 AM by rjm

There is something freakish about a brick-sized block that sits there and plays room-filling music ... with no wires attached whatsoever and no obvious moving parts. It gave me the same "I'm living in the future!" sense of wonder I got buying my first 1 TB hard drive.

It doesn't take too much searching the internet to discover that among wireless portable (bluetooth) speakers, the TDK A33 is highly recommended for its exceptionally good sound quality. That comes with a massive caveat, however: Most of the people writing these reviews only have Bose, Beats, and the internal speaker of their iPhone as references for comparison.

So does the A33 sound good in a hifi context?

Read on to find out...

No, okay don't bother. The answer is "no".

But it doesn't sound bad. I'm listening to it now as I type this, hooked up via the AUX input to my Onkyo PCI-200SE sound card, with the A33 tucked under the...
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Old

A headphone amplifier gain calculator

Posted 2nd May 2015 at 05:30 AM by rjm (RJM Audio Blog)
Updated 2nd May 2015 at 05:33 AM by rjm

You input the headphone sensitivity and impedance, and it spits out what I think is the ideal amplifier gain.

Even if you disagree (personal preference, difference input levels, etc.), the difference will be consistent regardless of headphone as long as the specified parameters are correct.

The gain value setting is tailored to normal line level input and listening fairly loud with the volume control at 9~10 o'clock. The output series resistance is assumed to be zero ohms.

Adjust as desired, and note that 3~6 dB either way will still be a usable. If your amp has a large output series resistance the gain Av should be scaled up as,

(Routput + headphone Z)/(headphone Z)
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Old

Building a vacuum tube amp vs a solid state amp

Posted 22nd April 2015 at 11:35 AM by cspirou

This is my article about comparing vacuum tube amps vs SS amps. There are more than enough places that compare there two types from the aspect of sound. I will avoid that and only concentrate on the differences from a DIY aspect.

Solid state amp pros

*Transistors are cheaper than vacuum tubes
*PCBs are available for many amps
*Transistors are usually more reliable and last longer
*power supplies use lower voltages than tube supplies and therefore are much safer. also no need for a separate heater supply
*usually don't need output transformers
*chassis work is typically limited to front and rear panel

Solid state amp cons

*Often necessary to buy a large heatsink
*If no PCB is available, designing and making your own PCB can be cumbersome
*If you don't use a PCB, point-to-point wiring is very difficult
*Need to be careful with electrostatic discharge. Easy to fry a transistor if you aren't...
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Old

Exploring laptop sound

Posted 16th April 2015 at 11:38 PM by fas42
Updated 27th April 2015 at 05:08 AM by fas42

As mentioned elsewhere, now have a laptop with reasonable internal sound, a HP Compaq 6830S (not a Pavillion, sorry!) of quite some vintage. My mainstay Dell over many years prior lost its sound many years ago, a USB port got cooked, and took down the sound circuitry at the same time; and what I was using as an interim, another Dell of nominally very good quality, had downright faulty sound, buzzed and rattled - was plain sick ...

OK, so the exercise here will be to see how good I can get the newly "installed" HP unit's sound to be, by my measures, using minimal or zero internal hardware tweaking - essentially working out what factors impact the sound, and whether the negatives can be circumvented. This gives an idea of how I go about things, what I use to "measure" with, what I'm listening for.

Trying a couple of CDs that I use often the signs were good - obviously no bass, and the volume is very restricted, but otherwise the sound was 'correct'...
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Old

What's the PSRR of an emitter follower?

Posted 16th April 2015 at 01:28 AM by abraxalito

I asked this question of Yahoo and didn't find anything much - a few people mentioning the PSRR of their C-multipliers but no simulation results and no algebra. So I fired up LTspice for myself to take a look. The transistor models are the usual Gummel-Poon ones LTspice provides (one up from hybrid-pi) which look to be decent enough for this purpose.

I went for two EFs (sometimes called EF2) as that's probably a more practical arrangement in an audio amp. Some designers even prefer EF3 to get much lighter loading on the VAS/TIS. The EF load I made independent of the bias current so I could learn more about biassing. I used AC simulation to have a look at how the PSRR varied over the audio band.

Turns out the PSRR depends on at least three circuit details and one inherent characteristic of the EF transistor used. In no particular order the circuit aspects which matter are the source impedance seen by the base of the EF, secondly the load impedance seen and finally...
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Old

Are PSRR plots all they're cracked up to be?

Posted 15th April 2015 at 04:19 AM by abraxalito

My experiments last autumn with putting a transformer between a chipamp and a drive unit left me with one nagging question. Why was the sound so much clearer with the trafo than without, given that the trafo's voltage ratio was relatively low (1.5:1)? Even Frank was surprised at so much change and suggested some other effect was in play (amp instability). I've not ruled out amp instability but I have made some progress on understanding chipamp PSRR.

The first trafo experiment was done with the TDA7265 - I've since tried trafos on two other chipamps - TDA8947 and LM4766 with similar subjective results - a much clearer sound, more depth to the soundstage and so many tiny details on recordings becoming clearer that the experience has become akin to headphone listening. The trafo ratio has increased - 2.5:1 for the TDA8947 (21V rails, bridged) and 5:1 in the case of the LM4766 (again bridged), running on 62V total supply.

My current listening system is LM4766 with...
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Old

Cost optimized active crossover

Posted 7th April 2015 at 07:03 AM by abraxalito

I've driven the BOM cost of this board down quite hard by choosing some 'disrespected' opamps to build it around - TL084s. They go for 0.5RMB on Taobao (about $0.08, same as a recycled TDA1387). Listening so far is positive but I've got no audiophile opamp reference to check it against. In terms of bang for the buck though, its going to be very hard to beat. All filter caps are NP0 ceramics, resistors are bog-standard thick film 0805s.

What's different about this build for me is its fully balanced and classA operation in order to cancel power supply noise. To get classA operation from TL084s means the feedback/filter networks must be very high impedance so as to draw under 100uA peak currents. Opamps aren't used as output buffers, rather I've gone for emitter followers loaded by two-transistor CCSs.

The picture is my second prototype, using the best (aka lowest ESR) caps I could get hold of - Nichicon HZ and Nippon Chemi KZE. All the copper wires sticking up around...
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