tangent
Top Mall-Fi poster. The T in META42.
Formerly with Tangentsoft Parts Store
- Joined
- Sep 27, 2001
- Posts
- 5,969
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- 58
In another thread, Kelly said:
Quote:
I decided that I could do worse than the Creek OBH-11 without going to such extremes. Witness the destruction:
Op-amp: TL082 running from 12V. (This is sufficient for the task, according to the datasheet. Real life is a different story....)
Power supply: Build your own from a transformer, a bridge rectifier, and a 100uF capacitor. Given a 20mA load, this will ensure 480mV of ripple on the rails. This is sufficient to avoid frying 2001G, and yet enough that the META42's C2 will still allow plenty of ripple through to the amp stage.
Resistors: No need to go with cheap carbon. Just configure them so that you get a hundred millivolts or so of DC offset on the output of the amp. Not enough to fry the headphones, but enough to cause a loud pop when you turn the amp on, and to make the headphones "swing" improperly.
Power caps: A lone pair of 100 uF Radio Shack 'lytics. If possible get the ones on the back of the peg still in the "Archer" packaging, so you can be sure they'll fail early. Leave out C3, C4 and C5.
C1: X7R Ceramic. 'Nuff said. Make it 100pF, so that, combined with the 10MOhm R2 you need to meet the next requirement, you get a -3dB bass rolloff point of about 160 Hz.
Volume control: Linear taper Radio Shack pot; use a 1Mohm model, if available, and certainly no lower than 250Kohm. Use two mono pots, not a single stereo one. Call it a "feature": integrated balance control. Be sure to get the type with a metal shaft, and then use a metal knob and leave the cases ungrounded so that you get hum in one channel when you touch the knob.
I/O jacks: Cheap 1/8" jacks. Get the kind that don't grip properly, so that you have to keep a constant upward pressure on the output jack to avoid ground hum, scratchiness and channel loss.
Current Source: 220 ohm resistor only. This will bias the op-amp into class A to the tune of about 27mA on average -- within the chip's specs, and way more than necessary. This should serve to completely rob the chip of any dynamic qualities it possesses.
Can one do worse? Hell yes. I'm just getting started.
I invite comments. This thread should be educational -- I've always believed in the instructive value of a bad example.
Quote:
I challenge any DIYer to build a META42 properly (ie, you have to follow the design and the solder points have to be made properly) using the crappiest component choices you can possibly choose--the cheaper the better. My hypothesis is that this amplifier will still be much better than the Creek. |
I decided that I could do worse than the Creek OBH-11 without going to such extremes. Witness the destruction:
Op-amp: TL082 running from 12V. (This is sufficient for the task, according to the datasheet. Real life is a different story....)
Power supply: Build your own from a transformer, a bridge rectifier, and a 100uF capacitor. Given a 20mA load, this will ensure 480mV of ripple on the rails. This is sufficient to avoid frying 2001G, and yet enough that the META42's C2 will still allow plenty of ripple through to the amp stage.
Resistors: No need to go with cheap carbon. Just configure them so that you get a hundred millivolts or so of DC offset on the output of the amp. Not enough to fry the headphones, but enough to cause a loud pop when you turn the amp on, and to make the headphones "swing" improperly.
Power caps: A lone pair of 100 uF Radio Shack 'lytics. If possible get the ones on the back of the peg still in the "Archer" packaging, so you can be sure they'll fail early. Leave out C3, C4 and C5.
C1: X7R Ceramic. 'Nuff said. Make it 100pF, so that, combined with the 10MOhm R2 you need to meet the next requirement, you get a -3dB bass rolloff point of about 160 Hz.
Volume control: Linear taper Radio Shack pot; use a 1Mohm model, if available, and certainly no lower than 250Kohm. Use two mono pots, not a single stereo one. Call it a "feature": integrated balance control. Be sure to get the type with a metal shaft, and then use a metal knob and leave the cases ungrounded so that you get hum in one channel when you touch the knob.
I/O jacks: Cheap 1/8" jacks. Get the kind that don't grip properly, so that you have to keep a constant upward pressure on the output jack to avoid ground hum, scratchiness and channel loss.
Current Source: 220 ohm resistor only. This will bias the op-amp into class A to the tune of about 27mA on average -- within the chip's specs, and way more than necessary. This should serve to completely rob the chip of any dynamic qualities it possesses.
Can one do worse? Hell yes. I'm just getting started.
I invite comments. This thread should be educational -- I've always believed in the instructive value of a bad example.