| Jonathan Z |
I've seen so many posts on this topic here and elseware that I'm fairly consufed at this point.
I need a simple volume/balance control pre amp between a CD and active crossover setup. Thats my first op amp need.
Second, I will be building the active crossovers and presume that the op amps for it, if I want good sound, will have to be as good as those you would expect in a good pre amp. Is this a valid assumption, if so, which op amps?
Below is a list of ones that Ive seen referenced. Of the bunch, the AD825 and OPA627 seem favored. However, building two 3 way crossovers with the OPA627 would be quite expensive and I'm wordering if its worthwhile. I've also recently seen the AD Buf-04 which looks like it might be good for this.
Thanks in advance for your advice and suggestions!
AD744
AD746
AD811
AD825
AD827
AD844
AD846
BUF634
LM6172
LM6181
LM6182
LT1360
LT1363
LT1364
OPA275
OPA2134
OPA2604
OPA627
THS6012
TLE2072 |
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| JasonL |
I'd use a LF356 if you need the schematic that i have and used for my active x-overs please let me know ill post it..
jason |
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| Peter Daniel |
| The best way is to built your own discrete op amp. This is what I have been using in my crossovers. Although that circuit is from 1988 it is very similar to the active stage used in the current Pass Labs crossover (must have been designed by the same person;) . Beside the schematic I show the actual modules I've built. Very simple and compact. There is also additional info about D.I.Y. Op Amps at: http://passdiy.com/legacy.htm |
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| HarryHaller |
Replace 2N5566 with 2SK389 and BJT transistors with 2SC2240 and 2SA972s and you will have a very good circuit. I would put 100 ohm gate resistors on the jfet. I have done this jfet swap for the 2N5566 with great improvement in sonics many times.
H.H. |
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| Peter Daniel |
Good info Harry. By replacing 2N5566 we will also be OK with the New Law since 2N5566 is in metal case.;)
Any further improvements? Maybe we could backengineer Pass Labs crossover instead of waiting for upcoming project. |
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| P.Lacombe |
I agree with H. Haller and H. Potter, discrete op amps provide very superior quality of sound, and are not expensive. But good filtering an decoupling of power supplies are essential.
Regards, P.Lacombe. |
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| HarryHaller |
This true with Op Amps and discrete designs. Especially with circuits with poor PSRR.
H.H. |
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| mlloyd1 |
The posted circuit with HarryHaller's suggestions sounds like a good bet. If you're looking for easy but good, the AD744+AD811 makes a good gain block, too.
mlloyd1 |
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| Apogee |
Looking at the schematic vs the modules, I see four bjt devices on the modules yet the schematic only lists three...
Am I missing something?
Would the elders please enlighten....
Thanks,
Steve |
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| rljones |
| I've built an active 4th order x/o using AD8610 using all SMT devices and with a very highly filtered power supply. I agree with a very clear power supply; the x/o uses a C-L-C-R-C configuration using double bridge recitifiers. The total capacitance is 132,000 microfarads (22k per cap; L = 10 mH; R = 1.2 ohms). This +/-22VDC supply (which is as quiet as a battery on my scope) is then locally regulated using precision zener shunts for a +/-13V supply for each channel. I am very happy with the sound. |
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| audionut |
"I need a simple volume/balance control pre amp between a CD and active crossover setup. Thats my first op amp need."
Why not incorporate the volume control and such into the active crossover and eliminate all of the circuitry associated with a preamp in front of the x-over... |
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| Peter Daniel |
Apogee,
Actually you should see 3 transistors and 2 current regulator diodes in black plastic cases plus one transistor in metal case.
I removed one diode from ea. module for a different project. Sorry for confusion.
:)
That's what I would do. I'd put volume pot in front of crossover. The hi/mid section would have direct output to the amp and the subwoofer section would have another pot at the output for bass adjustment. |
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| HarryHaller |
Zetex ZVP3306, Toshiba 2SK389, and jfet current sources as above (two in paralell for 8 mA) Circuit is shown as unity gain but can be configured for gain feedback resitors. 1.6K resistor can be pot for offset adjustment. Based on Nelson Pass discrete op amp article. I like all fet circuits better than bipolar. Current sources can also be made with Jfet( ie. 2SK170BL) with Ids greater than 5mA with pot for adjusting current.
H.H. |
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| Jonathan Z |
About power supplies filtering/decoupling....Can any of you point to web pages that cover this topic or provide a quick overview?
On discrete vs. IC op amps...Is discrete really better. I look at some IC op amp specs which seem very impressive. Further, I'm uncertain about the time/effort involved w/ discrete vs. IC actually paying off in sound quality. Your thoughts please....
Thanks!
P.S. Not looking to start a relegious debate here on discrete vs. IC! |
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| jam |
Nice circuit Harry.
Would some degeneration on X2 help any, in place of R8?
Jam |
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| Peter Daniel |
I believe that discrete circuits sound better because of their simplicity. Don't look at specs of op amps because when it comes to sound they don't mean nothing.
On the other hand there are some very respectful and good sounding designs using op amps (Madrigal and Jeff Rowland preamps) that you cannot disregard op amps completely. The choice belongs to you and depends on your personal preferences and how complicated you want your project to be.
Here is a good link to combined lineamp and crossover with an artwork: http://www.borbelyaudio.com/xover.pdf |
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| tiroth |
| quote: | Originally posted by Jonathan Z
P.S. Not looking to start a relegious debate here on discrete vs. IC! |
too late... |
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