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Old 5th December 2008, 10:11 PM   #171
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I have two (maybe 3) Fisher PA 301 chips up in the attic. My 1985 receipt lists them as Sanyo chips.
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Old 6th December 2008, 12:20 AM   #172
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Quote:
Originally posted by Speedskater
I have two (maybe 3) Fisher PA 301 chips up in the attic. My 1985 receipt lists them as Sanyo chips.
Cool Speedskater!

You could see if they have the "loudness" button done with resistor padding and a cap per channel, and if there's the weird Japanese style balance control arrangement. Those two things are the worst distortions from the amplifiers of that era. I think it works to "patch in" at the output of the volume control, which, typically, leaves the bass-n-treble controls and the pre all functional.
If a source plays nicely that way (check first for DC), you can possibly patch from lineout to a brand new volume control. That will knock out the balance control and loudness button on most older Japanese transistor/chip receivers.
Check the service manual. Maybe a slight mod will have those up to nearly hi-fi.
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Old 10th December 2008, 04:29 PM   #173
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Default Re: STK Kits

Quote:
Originally posted by jazzy939
Greetings fellow STK fans!

I bought an amplifier kit that uses the STK401-040 last saturday.
Took 1 hour to assemble it on a sunday afternoon! Its a 25W+25W RMS amplifier.

I was amazed to the sound I heard coming out from my speakers, TDL Electronic's RTL3. The bass is deep and thick. The control is excellent, the staging is wide and big. I also have a TA2024 amp. I'd say it is as good but better (louder!). Whatever the T-Amp can do, so did the STK.

I also found that my local electronic stores still have a number of STK modules for sale! Initially I was planning to build a GainClone (LM3886), but now that I have the STK, goodbye GainClone!
Need to stock up a few before they run out...

I am now a confirmed STK fan!

Have fun guys, I know I am..

I agree STK chips sound great!!!!
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Old 12th December 2008, 07:31 AM   #174
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Default Re: STK Kits

Quote:
Originally posted by jazzy939
Greetings fellow STK fans!

I bought an amplifier kit that uses the STK401-040 last saturday.
Took 1 hour to assemble it on a sunday afternoon! Its a 25W+25W RMS amplifier.

I was amazed to the sound I heard coming out from my speakers, TDL Electronic's RTL3. The bass is deep and thick. The control is excellent, the staging is wide and big. I also have a TA2024 amp. I'd say it is as good but better (louder!). Whatever the T-Amp can do, so did the STK.

I also found that my local electronic stores still have a number of STK modules for sale! Initially I was planning to build a GainClone (LM3886), but now that I have the STK, goodbye GainClone!
Need to stock up a few before they run out...

I am now a confirmed STK fan!

Have fun guys, I know I am..
Very interesting service manual for STK 465, showing things done right. Its amazing. How to ac couple the nfb a bit more cleanly (drive first the cap), and how to get along without a bootstrap cap like ST uses for TDA7294 (use a resistor instead).

There's a lot of STK 457, 459, 460, 461, 463, 465 showing up on E-bay. Some state Generic, some don't say, and some say Authentic Sanyo.

The current model 465, substitutes for 461, 463 too, as there is no internal difference in the 3 higher power models. The 465 does 30w per channel at 0.08% distortion, yet the 1% figure is higher than the mechanical limits of most 8" and 10" drivers.

Interesting for DIY, using a $28, 4 amper, Hammond EI core 36vct (18+18vac) transformer with 465 will downrate it to a 463, resulting in 25 clean watts per channel on 8 ohms; however, a peak rating would be 200w combined output if given 4 ohm speakers (as modern amplifiers are advertised). http://www.mcmelectronics.com/product/STK465
Kind of spendy, but you get some authentic tunes this way.

But, if you need more. . .

There's also this: http://www.mcmelectronics.com/product/STK4231V closely related chip with 100 watts per each of 2 channels, while THD = 0.08%. In other words its 100w per channel, effortlessly. The peak rating is beyond the mechanical limits of most speaker drivers. As with most amplifiers, for 4 ohm speaker support, decrease the voltage, and double the heatsink, whenever the possibility of 4 ohm speakers are expected.

Also, check out NE5534 at Decibel Dungeon.

STK + good power supply + a bit of fine tuning + a good buffer/pre = JAW DROP
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Old 12th December 2008, 04:53 PM   #175
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Hi daniel,
Some questions here, related to your posting..

What is meant by a 'good power supply' really?

Currently I am driving my STK amp via a simple JFet pre/buffer, which make the sound really excellent!

I am blur on the 'fine tuning' part.. any clues?

Thanking you in advance..
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Old 12th December 2008, 11:26 PM   #176
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Default Fine tuning, start with power

Quote:
Originally posted by jazzy939
Hi daniel,
Some questions here, related to your posting..

What is meant by a 'good power supply' really?

Currently I am driving my STK amp via a simple JFet pre/buffer, which make the sound really excellent!

I am blur on the 'fine tuning' part.. any clues?

Thanking you in advance..
That's one heck of a question.


The fine tuning is about the same for any amplifier in that you start in the same place.
Its not the input circuit.
Its not the NFB.
Its not the pre.

Actually, you do need those functional; but, at first, you just "rough them in" with "known good" components or whatever you favor / have on hand.

The main effort for fine tuning is at the power circuit:
Here is where you can get your low bass notes.
Here is where you can either cause or prevent ringing midbass.
Here is where you can get your audio upper midband both slightly euphonic and also clear.
And, some of your power circuit decisions can affect the heat output of the amplifier.

I like to view the power circuit as three seperate boards:
Rectifier board
Power supply board
Amplifier board

I like to see these connected so that there are "poles" between, and we can use either a resistor or an interconnect cable to establish a pole.

Assumptions:
The amplifier isn't bridged
The power supply is linear unregulated
Not everyone owns very huge speakers and those that do might like to hear them do their thing.
Many chip-amps of all sorts, are slightly bass shy from 20hz to 50hz
The STK chip that we're using is a model that pre-dates "modernized" (fictional) power output advertisements.

Rectifier board:
Common choices for transformer are 4a, 6a, 8a.
Most of our STK application notes will call for the 4a, but may I encourage you to go "1 step up" and get a "generous" amperage transformer, if budget allows? In the linear, unregulated power supply that's one sure-fire way to get some good bass and avoid the typical midbass issues. As for midbass, its so much easier to cause it than remove it. Like a bell, the larger size transformer rings a lower pitch. Like a loudspeaker's crossover, the power supply is a filter for the transformer.
Sure, you do have the option of using a purposefully overlarge dual-secondaries toroid transformer and eight of MUR860, but, I'm not promoting that, as it doesn't match the classic applications.

However, the classic applications of these STK used EI core, and most of them were center tap:
From the service manuals of the original amplifiers, we can see large ceramic caps at the rectifier. While 3-pin ceramic caps are rare, we can do the same job with regular ceramic caps. They'll need to be physically large, such as almost 1cm across the disc (although smaller physical sizes can work). This is incompatible with soft switch diodes, so use regular diodes or a 1 piece bridge block, like the currently popular KBPC2504.

Before giving the sizing chart, I'd like to reference the CarlosFM power supplies:
One way to get enhanced bass from the amplifier is to locate a pair 4700uF caps at DC side of the rectifier board. If you get too much bass, just size down a bit to 3300uF. One or two pair of Cornell-Dublier's Mallory SEK 50v 2200uF is also an option. The rectifier board is where you put the "bassy" caps. This disturbance is a signal and so, it belongs close to the rectifier, if anywhere at all. Later, our power supply board will be able to smooth it out to cleaner DC.

Here's the chart for paralleling small caps to your diodes at the rectifier board (click on picture):
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Old 12th December 2008, 11:38 PM   #177
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In the original service manuals, there's about 8" of cable from the rectifier board (above post) to a pair of 10,000uF caps.

Refer to the carlosFM power supply thread to see this in action.
You can use the interconnect cable or resistors, and the usage of resistors is documented on the carlosfm power supply threads.

Bleeder resistors go on the power board, not the rectifier board.

Also, see chipamp.com's power supply. Recently, I used a board like this, but omitted its onboard rectifier. Of course, I did use a rectifier on its own seperate board. Its described in the above (previous post). I connected it as described in original STK service manuals, via the 8" of cable.
Rectifier - 8" cable (or resistor) - power board - cable - amplifier board.
Another way to see it is:
AC2DC board - 8" cable (or resistor) - DC board - cable - amplifier board.
EDIT: See also the CarlosFM power supplies here on diyaudio.com.

This layout is (mostly) in order from lowest pitch to highest pitch.

This structure, as described, supports the STK application guide's 100uF capacitors, which are at the amplifier board.

Optional, and as documented on the CarlosFM 2005 PSU, you can add a 2uF to 6uF poly cap from V+ to V- at the power terminals of the amplifier board. This can reduce the efforts of capacitor selection for the power circuit of the amplifier board.

EDIT: 1 pair of 10uF acts "almost" like a single 4.7uF. The single isn't seen in original STK applications, but it is an option.

Last up, you can choose some smaller caps. Often seen are 33uF, 10uF (mentioned above), and/or 100nF. The 100nF can be polypro, mylar, or ceramic disc or ceramic multilayer. These do affect the treble.

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Old 12th December 2008, 11:52 PM   #178
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So, we have nice, clear, strong support from the power circuit, and have used it to eliminate midbass abberations, while thoroughly supporting bass response from the speakers.

Next up. . .

The NFB cap and the Input filter cap both do pass audio signal.

My selection method is to simply grab 5 of the most likely to work, interview them, and use the winner. Your NFB cap can be a 2x larger than documented, and it can become important to do so if your Input filter cap is sized overlarge.

A poly cap will often be as effective as a 5x larger electrolytic, although this is not true of Nichicon's ES or Elna's Cerafine and other specialty models.

My service manual says 100uF for the NFB cap. In this example, if I have used a poly input cap, or an audio specialty electrolytic, then I would need to size the NFB cap up to 220uF, else the bass may be a bit strange.

The bypass cap practice may also be used for NFB caps and for Input filter caps. High quality ceramic disc caps will help you determine the correct size to use. Its usually between range 150nF to 3nF in size.

Well, we've chased the signal from the plug, all the way to the power amp's input jack, while mostly keeping spec with original manuals for authentic sounds. Amplifier: Power + Input = Output.

The main point is avoiding using the input circuit to correct blunders at the power circuit. There's no input filter cap "perfect" enough to do that. So, get good power first.

I'll let somebody more knowledgeable than I go through the buffer/preamp stage. This page at Decibel Dungeon http://myweb.tiscali.co.uk/nuukspot/...ainclone2.html does illustrate adding a buffer to your power amp.
EDIT: Although the pre may be inside the amplifier enclosure, it is a separate unit.

Cheers!

P.S. Smaller size questions are good too.
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Old 13th December 2008, 12:21 AM   #179
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Simpler alternative, photo is here.
Not shown: Bleeder resistors go under the 2nd pair of 2200uF caps.
EDIT: Not shown: The first pair of 2200uF caps (those closest to the rectifier) may be, instead 4700uF caps, if you'd like more bass. Those closest to the rectifier need to be rated for 2x rail voltage (like for 25v rails, use 50v caps).
For the rest: Click photo.
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Old 13th December 2008, 01:05 AM   #180
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Sample:
This has 1 pair 4,700uF and 2 pair 10,000uF
Not shown: Notice the striped cable from the transfo is the 0v line, which also runs down the center of the power supply via a thick cable.
Not shown: Bleeder resistors under the first pair of 10,000uF
Not shown: Resistors shown are wrong--use Non-Inductive resistors or a length of interconnect cable instead.
Perhaps the prettiest power supply that I've made, and it took only 8 minutes.
EDIT: This is related to the carlosfm power supplies. See those threads here at DIYaudio.com for more information.
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