Why are there no "how to guides" or posts/ threads on Amplifier Mods and component upgrades etc???

In fact, most audio devices, even the most expensive ones, are not designed for audio. This has to do not only with circuitry but also with construction, components and more.

The simplest and most effective modifications that anyone can make are, for example, to bridge all contacts, e.g. any solder sockets or connectors. These things sound like scrap metal. Even on loudspeakers.
If you want to learn how to solder, you should completely re-solder your devices: remove the solder and re-solder with minimal solder;-)
If you dare, you should try putting power supply units together. The myth is channel-separated power supply units. Simply connect them and listen;-)
If you know a bit about circuits, you could simply bridge unnecessary amplifying stages. Many stages only make noise and prevent music. They were only developed to amplify visible lines without much visible change - not to listen music;-)
 
I dont want to re invent the wheel or redesign the amps circuits. All i want to know is what parts have people swapped/uprated etc. What if any weak points or common faults exist. In the case of recapping what cap value and make did you change to .
For the once popular dynaco ST120, there are four simple hacks. Increase size & fins of the woefully inadequate heatsinks. Replace the PC14 driver boards that cause cold crossover distortion with apex AX6. Change the slow 200 khz ft output transistors into something at least 1976 epitaxial with 3 mhz ft. Install the "TIP" mod from the service bulletin that eliminated tendency to oscillate. Or dive into IC amps with the updatemydynaco service.
Popular models sold since 1966, the designers did not make such howlingly stupid mistakes. Other obvious limitations, the popular receivers 1975-1990 had wimpy power transformers, tiny heat sinks, and cheap controls. Not easy to stuff a massively bigger transformer or more aluminum sinks in that tiny jammed case.
You hit on re-e-capping. Nearly every 20 year old high hours use product needs that. Low power, (polite sound, no dynamics). too few highs or lows, hum, fuzzed low sensitivity FM section, or other obvious problems. While there are fans of pricey "audio" caps, and others that like to double and quadruple the stock value, I find industrial grade "long life" caps of same value from 5 vendors, panasonic, nichison, rubicon, vishay, kemet, bring the unit back to "like new" performance. Buy caps from major distributors in your country, not counterfeits from ebay amazon gumtree or aliexp. I've put >400 ecaps since quitting work 2008 in various amps, preamps, radios, mixers, and electric organs, with great success. Some potentiometers, connectors, and fans were occassionally required.
 
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Here are more tricks. A $50 beat to death road warrior PA amp of 100-1000 watts/channel will always outperform any consumer receiver of 50 watts. Use the FM phono sections & source selector of the reciever, bypass the power section and go to directly to $50 road warrior that you refurbished. I picked up one unit for $40+freight that had been in a dumpster, the connectors and knobs were broken off. Filthy, and worthy of some serious work. The PC boards, case, heat sinks, were fine. The e-caps & fan were worn out.
Another trick from multiway speaker section. A pair of speakers built from a popular plan on that forum nearly always outperforms the garbage speakers sold in big box stores these days. Performance equivalent to $$$$$ boutique units can be achieved for $500 to $1000 each. Some testing equipment (mikes, stands, PC, cables, free software), a test room, ( I use the yard at 3 AM) and some carpentry skills are required if you don't buy a kit. Which kits are worth buying are also discussed.
 
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In the same spirit...


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Only in the UK. 😢 That’s OK, I just bought a used 100W Sony receiver to mess with. There is a lot of digital stuff in it though, could be challenging for me. It really cranks out the tunes (a real 100W) and seems pretty clean so far, and the best thing is it was only $35. It will replace a Chinese crap digital amp that was supposed to be 50W but I doubt it was even 10.