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Transistor Preamp
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Old 7th January 2019, 04:19 PM   #351
xrk971 is offline xrk971  United States
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All simple single rail SE Class A preamps need clean power. But that’s easy. A 12v Class 2 wallwart, feed a DC-DC step up or down, followed by cap Mx, the CRCRC. This gets me battery like low noise hum-free performance.

Sometimes just a Class 2 wall wart and cap Mx are enough for -100dB 50/60Hz hum level. Which sounds fine as below audible.

Here is another Hugh Dean Preamp is headphone amp with JFET driving a BD140. This one sounds excellent.

MOSFET Source Follower Headamp

Click the image to open in full size.

A little hand etched prototype with on board cap Mx:
Click the image to open in full size.
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Last edited by xrk971; 7th January 2019 at 04:23 PM.
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Old 7th January 2019, 04:42 PM   #352
Mark Johnson is offline Mark Johnson  United States
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Hilarious use of a "base stopper" resistor on a common emitter BJT amplifier! Not a MOSFET, not an emitter follower, a BJT operated in common emitter.

Quite a howler.
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Old 7th January 2019, 05:54 PM   #353
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Mark Johnson View Post
Hilarious ...
Much of the thread has been kinda sorta hilarious, but not in a good way when I think about the underlying causes.

To heavily paraphrase Winston Churchill, "Never have so many used so much silicon to such little effect."


-Gnobuddy
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Old 7th January 2019, 08:42 PM   #354
gigigirl is offline gigigirl
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Default Any good small, easy,

"Any good small, easy, high fidelity transistorised preamplifier circuit that i can build"

I agree, the title of the original thread is shown above.

Why not buy a simple kit from E/Bay as per shown below for $8

Musical Fidelit A1 Stereo Preamp Preamplifier Tone Board DIY Kits Dual Channel | eBay

Food for thought.

cheers
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Old 8th January 2019, 11:00 PM   #355
sgrossklass is offline sgrossklass  Germany
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Here's one I came up with several years ago. I make no claims regarding originality or elegance. Simulation says this one should do 10 Vrms at <0.01% THD10k (dominant 2nd by far). Do read the notes on design objectives and caveats.
Regular version:
Transistor Preamp-3trans-preamp-png
Simple bootstrapped cascode input version with 4 whopping transistors:
Transistor Preamp-3trans-preamp-casc-new2-png
I tweaked this one a little after noticing a bit of a slew rate problem in the original design, it's closer to 0.002% now and stability appears unaffected, with current noise remaining uncritical. Maximum output is slightly higher, too (15 Vrms). As mentioned in the notes, PSRR for the cascode version tends to be a hint lower but still sims at >100 dB (70 Hz - 25 kHz) like this, with further tweakability up top when throwing a minimum of additional RC filtering at the 48V rail (e.g. 10R + 47 || 100n). Your mileage (LEDs) may vary.

If someone would like to do a layout for this and try it out, be warned - this one's a little hottie and may be somewhat unforgiving in terms of ground and power routing. I never was entirely satisfied with power-on pop either.
Attached Images
File Type: png 3trans-preamp-new.png (39.5 KB, 305 views)
File Type: png 3trans-preamp-casc-new2.png (27.3 KB, 177 views)
Attached Files
File Type: zip 3trans-revisited.zip (3.2 KB, 8 views)

Last edited by sgrossklass; 8th January 2019 at 11:18 PM.
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Old 10th January 2019, 02:03 PM   #356
keilau is offline keilau  United States
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Quote:
Originally Posted by gigigirl View Post
"Any good small, easy, high fidelity transistorised preamplifier circuit that i can build"

I agree, the title of the original thread is shown above.

Why not buy a simple kit from E/Bay as per shown below for $8

Musical Fidelit A1 Stereo Preamp Preamplifier Tone Board DIY Kits Dual Channel | eBay

Food for thought.

cheers
Do you know what is the quad Opamp IC used in this kit?

I decided on a JC-2 clone. The schematic is pretty faithful to John Curl's original. It may be an older design, but the topology is still very good sonically. The simplicity of the circuit allow builder easy matching of components. The PCB provides a neat looking finished product.

The volume control and input selection are relay based linear step ladder volume with remote also from e/bay. Waiting for delivery. Will report how good or how bad it sounds in a few months.

Last edited by keilau; 10th January 2019 at 02:27 PM.
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Old 10th January 2019, 03:04 PM   #357
prasi is offline prasi  India
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Quote:
Originally Posted by keilau View Post
Do you know what is the quad Opamp IC used in this kit?
TL084CN from the ebay kit image.
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Last edited by prasi; 10th January 2019 at 03:11 PM.
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Old 10th January 2019, 06:43 PM   #358
keilau is offline keilau  United States
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Quote:
Originally Posted by prasi View Post
TL084CN from the ebay kit image.
Thank you for the sharp eyes.

There are many good opamp preamp board on e-bay. My favorite is this one.
NE5532 Preamp HiFi Pre-amplifier Assembled Board (With servo power supply) 978078957192 | eBay A board using dual opamp is easier to upgrade. I also like the servo controlled power supply onboard which assures low noise in the audio band.

The TL-084CN is perfectly fine for many application. The PSRR of the TL-074/-84 series is not very good. A good rectifier/regulator board is highly recommended for the Musical Fidelity A1 clone board which can make it sound very good.

Last edited by keilau; 10th January 2019 at 07:05 PM.
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