I present something to you that is not so pretty but works and sounds damn good for what it is.
Built around the TDA7384 which is a 24wpc (4ohm) x4 class AB chip from a broken pioneer car head unit.
Headphones are on their own independent amp built around the TA8217P which gives ample volume and sounds really good!
Was designed for PC speakers but drives headphones perfectly.
Best of all this chip requires no coupling capacitors and can be wired direct to the audio in (coming from the internal preamp).
Swept the chip on my scope from 5hz all the way up to 70kHz and reproduces a clean flat sine wave out to the cans. Square wave looks equally impressive on both amp chips which I will post pics of at a later time.
Preamp was built using 6 discrete transistors and I used Elna audio grade electrolytic capacitors wired in series with negatives back to back to make them sound better for AC coupling between stages and completely remove any volume wiper causing voltage swings on the outputs of the preamp.
The passive tone board came from a junked Sony A/V receiver and was real simple to reverse engineer.
Inputs go directly to the selector switch, then out to the Tape Out and the Volume pot input, then from volume -> preamp -> tone board -> chipamps.
Sound is incredible!
I had to use a lot of stiffening capacitance in the power supply, 4x6800 and a few smaller caps near the chip itself, even more capacitance in the power supply board which was swiped from an old radio shack 13.8v bench supply. Lots of RF bypassing on the VCC lines .1 and .01uF caps put in because I use a lot of radio equipment.
I am running the chip at 14.8v regulated which gives the full 12 watts w/o clipping into all 4 speakers at 8ohms. I have not tested it with 4ohm speakers but I am sure it could reach the full 24wpc at that impedance.
With loud consistent bassy stuff like trance techno the power supply can get REAL hot at full volume yet the heat sink for the chipamp hardly even gets warm!
I am use to this power supply getting hot in operation though even when it was a bench top power supply so doubt it will burn itself out.
Not a real powerful amp, but it is exactly what I called it.. a studio amp. Going to use this to power two Jamo cornet 40III and two KLH Pro-11 for my little recording/party/mancave studio.
Click here for on site schematic
This is literally what I started with and it was a mess, even slightly dangerous because the pins were all bare and fragile. I eventually took all the grounds from that chip and star grounded them right to the heat sink, glued the wires so they could not get knocked around and put some protection between the chip pins so nothing will ever short out. Even if so, I have everything fused.
While putting the case together and making holes, built out of an old dead RANE DJ mixer box, cut the metal top myself and front/back faceplate using some heavy duty Fiskars scissors carefully, then drilled and painted. They fit over the original metal which let me hide some screws behind the front faceplate. Drilling the holes for the controls through two pieces of metal at the same time and making it just right was no easy task! The RCA jack holes were no easier since they were blocks of 4 jacks in one plastic unit...
This amp is dead quiet when turned on, no thumps, no nothing. Not even the faintest hiss through the preamp circuits at full volume with no input.
I can drive the PA chip to clipping if turning it fully up so the preamp does give it plenty of head room for the line inputs.
Thanks and this is my first thread here. Been lurking
Built around the TDA7384 which is a 24wpc (4ohm) x4 class AB chip from a broken pioneer car head unit.
Headphones are on their own independent amp built around the TA8217P which gives ample volume and sounds really good!
Was designed for PC speakers but drives headphones perfectly.
Best of all this chip requires no coupling capacitors and can be wired direct to the audio in (coming from the internal preamp).
Swept the chip on my scope from 5hz all the way up to 70kHz and reproduces a clean flat sine wave out to the cans. Square wave looks equally impressive on both amp chips which I will post pics of at a later time.
Preamp was built using 6 discrete transistors and I used Elna audio grade electrolytic capacitors wired in series with negatives back to back to make them sound better for AC coupling between stages and completely remove any volume wiper causing voltage swings on the outputs of the preamp.
The passive tone board came from a junked Sony A/V receiver and was real simple to reverse engineer.
Inputs go directly to the selector switch, then out to the Tape Out and the Volume pot input, then from volume -> preamp -> tone board -> chipamps.
Sound is incredible!
I had to use a lot of stiffening capacitance in the power supply, 4x6800 and a few smaller caps near the chip itself, even more capacitance in the power supply board which was swiped from an old radio shack 13.8v bench supply. Lots of RF bypassing on the VCC lines .1 and .01uF caps put in because I use a lot of radio equipment.
I am running the chip at 14.8v regulated which gives the full 12 watts w/o clipping into all 4 speakers at 8ohms. I have not tested it with 4ohm speakers but I am sure it could reach the full 24wpc at that impedance.
With loud consistent bassy stuff like trance techno the power supply can get REAL hot at full volume yet the heat sink for the chipamp hardly even gets warm!
I am use to this power supply getting hot in operation though even when it was a bench top power supply so doubt it will burn itself out.
Not a real powerful amp, but it is exactly what I called it.. a studio amp. Going to use this to power two Jamo cornet 40III and two KLH Pro-11 for my little recording/party/mancave studio.
Click here for on site schematic
This is literally what I started with and it was a mess, even slightly dangerous because the pins were all bare and fragile. I eventually took all the grounds from that chip and star grounded them right to the heat sink, glued the wires so they could not get knocked around and put some protection between the chip pins so nothing will ever short out. Even if so, I have everything fused.
While putting the case together and making holes, built out of an old dead RANE DJ mixer box, cut the metal top myself and front/back faceplate using some heavy duty Fiskars scissors carefully, then drilled and painted. They fit over the original metal which let me hide some screws behind the front faceplate. Drilling the holes for the controls through two pieces of metal at the same time and making it just right was no easy task! The RCA jack holes were no easier since they were blocks of 4 jacks in one plastic unit...
This amp is dead quiet when turned on, no thumps, no nothing. Not even the faintest hiss through the preamp circuits at full volume with no input.
I can drive the PA chip to clipping if turning it fully up so the preamp does give it plenty of head room for the line inputs.
Thanks and this is my first thread here. Been lurking
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No replies yet? Is it that ugly? 
If anyone is interested here is the schematic showing the preamp...
Pretty basic really, first transistor is a phase inverter and buffer, then the main preamp transistor (around 20db gain), then the output buffer to feed a low impedance to the input of the balance/tone circuit.
This is more than enough buildup gain for the loss in the passive treble/bass controls before it hits the chipamp.
If anyone is interested here is the schematic showing the preamp...
Pretty basic really, first transistor is a phase inverter and buffer, then the main preamp transistor (around 20db gain), then the output buffer to feed a low impedance to the input of the balance/tone circuit.
This is more than enough buildup gain for the loss in the passive treble/bass controls before it hits the chipamp.
What? The images are showing up just fine for me and for others?
Here are the direct links..
http://i.imgur.com/GbgWkoJ.jpg
http://i.imgur.com/OzEckju.jpg
http://i.imgur.com/sxHuKwJ.jpg
http://i.imgur.com/a9a9osU.jpg
Yeah I thought about that but oddly this chip barely gets warm to the touch at full volume and long play. The original heatsink for the car stereo was really tiny and even that only got mildly warm so I think I am in the clear
Let me know if the images do not show up for others here please. I am using imgur to host them which always works fine for others I know. Maybe you are using adblock and it is blocking them from showing in the posts?
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Well hopefully that worked. I uploaded them to the diyaudio photo gallery and inserted the image link tags where my off-site link tags were.
Kind of odd any software would block imgur or photobucket though when so many sites use it. Even some peoples pictures in the Chip Amp Photo Gallery are linked to imgur or photobucket so I would imagine you can't see theirs either.
Huh I never knew the tape outs were buffered.
I wondered about that while designing this but checked my Marantz 1200 and a modern Motorola A/V receiver and both just were direct connections from the input selector to the tape out so I figured that is the usual way it's done.
Good thing is I never had trouble with those other amps so my homemade one should be fine for my setup.
How common is it to buffer that in modern equipment now?
Very uncommon.
A good way of avoiding the buffers and giving a no distortion output is, separate selectors for listen and record.
Switch the record selector to a different source than listen and the distortion is on the channel you are NOT Listening to.
Revision to the preamp schematic. I found the last 10uF x2 off the 4.7k resistor on the emitter of the final preamp transistor is not needed. A simple polarized cap of between 10 to 22uf with the positive going to the emitter is fine.
Polarization is not necessary there since the collector of the transistor is tied to the positive rail anyways with no further upswing.
Not that it makes any difference, but one less part.
The previous caps are necessary however since the previous stages are biased class A with both negative and positive swing.
At least I think I got that right.
Who cares is sounds good.
Polarization is not necessary there since the collector of the transistor is tied to the positive rail anyways with no further upswing.
Not that it makes any difference, but one less part.
The previous caps are necessary however since the previous stages are biased class A with both negative and positive swing.
At least I think I got that right.
Who cares is sounds good.
.
<< I just noticed that in the schematic, you have an un-buffered Tape/Mix output. Many of us old-timers remember the distortion problem that turning the tape recorder off, would cause. >>
Including Douglas Self. He uses a buffer to solve (rather, prevent) this problem in his "Precision Preamp," described in "Self on Audio."
.
<< I just noticed that in the schematic, you have an un-buffered Tape/Mix output. Many of us old-timers remember the distortion problem that turning the tape recorder off, would cause. >>
Including Douglas Self. He uses a buffer to solve (rather, prevent) this problem in his "Precision Preamp," described in "Self on Audio."
.
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