"How to Design and Build Audio Amplifiers"
TAB, 1980, 350 pp.
Middleton, Robert G.
"Hi-Fi Stereo Servicing Guide"
"Stereo Troubleshooting and Repair Manual"
Speakers (DIY etc.)
Digital Format Definitions:
"One of the early forms of surround sound in home theater came from the company Dolby Laboratories. It was called Dolby Surround. Dolby Surround was a 3-channel surround sound that contained information for the left speaker, right speaker, and mono rear channel surround sound. While the surround sound played out of two rear speakers, the same information was reproduced out of both. It was a mono signal played by two speakers. The mono surround tracks were also frequency limited (100 Hz to 7kHz). Because the surround sound was limited in frequency response and was mono, the surround sound provided little more than subtle ambiance to the sound."
Dolby Pro Logic
"Dolby Pro Logic is an improvement over standard Dolby Surround. It is a 4-channel surround sound that has information for the left, right, mono surround sound (frequency limited) and adds a new center channel. The center channel, among other things, "anchors" the dialog to the image. The four channels (left, right, center, surround) are encoded onto two audio tracks. Dolby Pro Logic decoders uses a technique called matrixing to derive the center channel and surround sound channel information from the encoded 2-channel signal. DVD discs marked as "Dolby Surround" are really 4-channel Dolby Pro Logic."
Dolby Digital 5.1 or AC-3
"As stated earlier, Dolby Digital is the standard audio format on DVD. Dolby Digital (formerly called AC-3) is a significant upgrade to Dolby Pro Logic. Dolby Digital has up to six discrete channels of information. Five of the channels are full frequency (20 Hz 20kHz) and one channel is dedicated to reproducing low-frequency effects (LFE). Six-channel Dolby Digital is often designated as 5.1, symbolizing the five full-frequency and one LFE channels. Dolby Digital uses discrete surround sound, where the left rear surround and right rear surround channels are independent and are not frequency limited. The ability to play independent sound in the surround sound channels, creates a more realistic soundstage during DVD playback."
Dolby Digital Surround EX
"Dolby Digital Surround Ex represents the next step in surround sound processing. It improves upon standard Dolby Digital by keeping the two discrete rear surround sound channels (left and right) and adding a new center rear surround sound channel. This way, sound can be steered directly behind the viewer. This is very effective for scenes that have "fly-overs" or need to place sound directly behind the viewer. Dolby Digital Surround Ex debuted with the theatrical release of Star Wars: Episode I-The Phantom Menace. Dolby Digital Surround Ex is currently not available on DVD."
"Digital Theater Systems (DTS), introduced in 1993 on the film Jurassic Park, is another six channel surround sound technology that is now making its way onto DVD. DTS uses less compression than Dolby Digital (3.5 to 1 vs. Dolbys 12 to 1), has a higher data rate (1.5Mbits/sec vs. Dolbys 384 kbits/sec) and is said to sound better than Dolby Digital. Dolby counters this claim by stating compression can be optimized using a technology called "perceptual encoding," where the compression algorithm uses the knowledge of how humans process sound, to optimize their compression. DTS encoded DVDs require a special DTS decoder that is separate from a Dolby Digital decoder. Most newer DVD players offer a DTS output and many new home theater processors offer both Dolby Digital and DTS decoding."
Longer Explanations and Interesting Papers:
A Brief History of DTS Audio on DVD
Cables ( RCA to DB25 / DB25 to RCA / rca to db25 / db25 to rca ):
Forum on 6 Channel Switches
Audio/Video Wiring Page
Audio Cables: General Information
Connectors, Connections and Wiring
DB25 (THX) Pin-Out Assignment
DB25 Female to Female Cable
DB25 4-Way Switch Box - $11
Db25 to 8/rca/m snake - 9.9' (B&H)
OneCall (Monster Cable)
Quadraphonic Quad discussion
Re: db25 to rca cable
Using Audio Stage Snakes
Building an Audio Snake
Hosa Dual RCA to 1/4 Phone Plug Cable
Equipment Owned by the Author:
Rotel RSP-980 Preamp (THX, Dolby Pro-Logic)
JVC XV-FA95GD DVD/DVD-Audio/CD Player
"The A-27 Integrated Amplifier was the most expensive component in the Series 20 line, with a list price of $1250.00. Pioneer clearly intended to incorporate much of the circuit design from the M-type amplifiers, but have a greater degree of control than the C-21 pre-amp. It used the "Magni-Wide" DC power amplifier section, but also used a total of three other all-DC-configured amplifier stages: a DC phono equalizer amp, a DC flat amp and DC "head amp" for Moving Coil (MC) type phono cartridges. Like the M-25, the A-27 used RETs in the output stage. It also used automatic Class AB switching, operating in Class A mode until the sudden audio peaks automatically switched to Class B.
The front panel was a very clean design. A 32-step attentuator was used for the large volume control knob. The function selector was all the way to the right for Phono 1, Phono 2, Tuner and Aux. The tone control section could be bypassed completely if desired via one of the toggle switches. All the other control knobs were mounted behind a clear smoked plastic panel. All in all, the A-27 was superb industrial design, as well as "musical"--as audiophiles like to say.
The phono equalizer section incorporated dual Field Effect Transistors (FETs) to guarantee a wide dynamic range and a signal-to-noise ratio of 90 dB in the phono section. Selectable load resistance and load capacitance allowed audiophiles to be able to select various different phono cartridges of their choice.
The A-27 used two large power supply transformers, one for each channel, positioned on the left of the chassis, and four electrolytic capacitors. The circuitry employed 206 semi-conductors: four FETs, 122 transistors and 80 diodes.
The A-27 was rated at 120 watts per channel into 8 ohms, from 5 hz to 30 kHz with no more than 0.012% total harmonic distortion. Between 20 Hz and 20 kHz, toal harmonic distortion was a mere 0.008%--virtually non-existant distortion! Intermodulation distortion was only 0.006%. The A-27 entire frequency response ranged from 5 Hz to 200 kHz.
It measured 17.88 inches wide, 6.63 inches high and 18.44 inches deep. It weighed 56 pounds, 7 ounces. The M.S.R.P. of the A-27 was $1250.00."
"I just wanted to share my latest Kenwood audio adventure. This is my first post to this group.
I've got a pair of Kenwood L-07M amps that I purchased in 1978 that I recently modified. I had a Kenwood L-07C pre-amp until about 1985 when it started giving me grief (flaky MOSFET, relatively low S/N). For context, I now use a Nakamichi CA-5 preamp (vintage 1986, original owner), and for source material I use a variety of CD players all running through a Musical Fidelity A324 DAC (get's rid of all the digital grundge and phase distortion). I still have my 1975 Kenwood turntable (nothing special), that I use regularly, and a Kenwood KT-6500 Tuner. BTW, if you ever wanted high-end sound from a CD juke box, the A324 is the way to go. Finally, the amps currently drive a very revealing pair of Revel F30s (more about that later).
The L-07M adventure began when the DC protection circuit started to degrade in 1997. Fellow L-07M owners may have experienced this - you know, when the amp takes 10-20 seconds for the protection relays to turn on instead of 1-2 seconds, and then over time (years) it continues to degrade until it takes nearly an hour for the relays to turn on. Well, it took about 5 years for my DC protection circuit to reach the one-hour mark. Fortunately, since these amps only burn 35 watts on idle, I just left them on 24/7.
I finally found a very talented audio engineer - the designer of the high-end Wavestream Kinetics V8 tube amplifier - to work on my L-07M amps. I knew I was in good hands when I found that he still listened to a Kenwood KA-9100 bolted to Mirage speakers.
Back in 1985 when the L-07C preamp started failing, I purchased the original service and owner's manuals for the L-07M - just in case I might have problems with those. Who knew that I'd need them 18 years later!
I'll digress for moment - the only reason I still have the L-07M amps is because every 2 years or so, I drag the amps down to the local audio shops to run the amps side-by-side with other high-end amps (including Krell and Levinson). I always go in thinking I'm going to lay down $4-5k on new amps, and I always come back surprised that the L-07M amps sound better than most amps in that price range. OK - the Krell and Levinson monoblock amps are definitely smoother and more dynamic, but it's pretty subtle. I wasn't thinking "I got have those amps". Frankly, even the Levinson/Krell dual-mono amps do not match the L-07M amps for imaging, only the Levinson/Krell monoblocks beat them (to my ear). If you can't tell, I'm a big believer in monoblocks.
Further digression - I added the Revel F30 speakers in 2001. If you want a revealing speaker, these are for you. But the high frequency harshness on the L-07M became hard to ignore with this revealing a speaker, even with basic mods like wiring, interconnects and cables. FYI, the Revel F30 has a mid-range to die for if you like piano and vocals.
Back to the L-07M mods.
Besides fixing the DC protection circuit, which turned out to be a hard to find leaky transistor and diode, we reviewed the topology of the amp and replaced or by-passed about 13 electolytic capacitors with high quality film caps. The film caps shunt the high frequencies much better than the electrolytics, smoothing out the somewhat tizzy/grainy high-end, and sweetening the mid-range just a tad.
Other very simple DIY mods done to these amps over the years that smoothed out the highs while increasing the resolution and dynamics:
Kimber cable for internal power
Cardas wiring for internal signal
replaced the AC power plug with an IEC connector and 14ga cable
replaced the binding posts with Cardas posts
You'd be amazed what a difference some signal/output wire and a power cable can make. I was a cable skeptic back in the 1980s until I started using Kimber on my speakers and Cardas for interconnects.
Wow! I was shocked at just how smooth these amps are now with the capacitor upgrade. The audio engineer - the designer and builder of $20-40k tube amps - was equally surprised. The mod'd L-07M amps have a silky smooth top end and a sweet mid-range (comparable to tubes), complementing the Revel F30 speakers very nicely. I used to think that the L-07M amps were ultimately bass amps and too harsh on the top end. No more, I love these amps. The audio engineer was so impressed with the sound that he wants to find a pair of L-07M amps for himself.
The other thing that amazes people about the L-07M, myself included, is the fact that these amps stay so cool. The rule of thumb is that hotter = better. Not so with the L-07M. I'm still breaking in the amps, and they are just getting smoother and smoother. I used to be a break-in skeptic, but I've heard it enough times to believe something changes - I just don't know what.
If anyone wants to part with their L-07M amps, call me. I'd like to mod them and drive my 5.1 system with them (Revel M20 rear speakers and C30 center).
If anyone wants to mod their L-07M amps, I have the original schematics and parts lists. And, if you want a professional to do the work for you (it might take 6-8 weeks for him to order the parts and put them in), I can provide contact information."
"I have 4 of these as well now. I'll be doing some fun stuff in the future, like trying new Motorola low distortion perforated emitter bipolar outputs, and replacing caps, etc. I would love to simply put black gate caps in all positions (except the 2 main supply caps).
I can tell you the input on these is DC coupled, so there is not one cap in the audio stage signal path from input to output. Other nice to know design highlights include a jfet cascode front end, and fully regulated front end/driver supply."
NAD 2400 Monitor Series Amplifier
NAD AV-117 Surround Sound Preamplifier
Panasonic AG-LD30 Laser Disc Player
Akai GXC-740D Cassette Player
Yamaha CDX-1100U CD Player