Erm it's 27 years old ! Seems a bit like restoring a Chrysler K Kar.
Fine if the contraption has some strong sentimental attraction.. otherwise.. Why?
Fine if the contraption has some strong sentimental attraction.. otherwise.. Why?
I was using Ti documentation of 65deg/W. I see the DS of OPA2604 on page 3 is 108deg/W from die to ambient for SOIC8 and 47deg/W for DIP.
For power dissipation of 0.33W, SOIC8 the differential temp is 0.33X108=36deg. So if ambient is 40deg, the die is only 40+36=76deg.
For DIP, differential temp is 0.33X47=16deg difference. So if ambient is 40deg, die is only 56deg.
BTW, I use more than worst case of 10nA bias current at 75deg. If you read Fig.5 on page 6, the bias current is 3nA. even say worst case doubling, it's only 6nA. Noise from bias current is not the dominant factor.
I don't think noise is not that important. If noise is an issue, I would worry more about the 10nV/rtHz voltage noise and a few hundred Hz 1/f noise corner frequency.
I would use DIP8 package. OP ask about +/-15V.
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The Lords of Commerce want us to buy the same thing over and over again and again, sending the 4 year old audio trash to the landfill. Look at all the threads pleading for help in repairing Behringer and Mackie trash.
I rebel. They win on televisions, the government turned the analog stations off. Audio, I can repair it, you can repair it, he can learn to repair it.
Anything this old will have parts with leads that can be replaced with a $50 soldering iron, not a $700 heat blow workstation. No microscopes required even for 66 year olds.
I'm building new driver boards for a 1971 stereo amp using about $2 in parts to reuse the 1990 output transistors I put in it. Screw *****, let them poison all their school children with industrial waste without my money. Lots of the parts on my board were salvage from PCAT power supplies the Lords of Commerce rammed down my throat over & over again, 5 PS in one PC in 7 years. At least PCAT power supplies are only $30. I don't buy a new cell phone every year either like the Lords of Commerce have dictated.
A 80's amp, the transformer heat sink and case can be reused even if the design is too weird to be repaired. I use NEMA CE laminate & no PC boards at all.
It's Indepencence Day here. During the fireworks my neighbors were letting off, imported from you know where, I took a 1998 speaker out the front door, powered it with a 1961 tube amp, played five Sousa marches at 35 W from a 1979 turntable. It sounded commanding bouncing off the brick factory wall 250' feet away. Next July 4 , a repaired 1300W amp on the same speaker.
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I've been reading over all the repsonse and it's a lot to take in. I like the idea of FET inputs because I'm a big fan of MOSFET amps. There "sound" is what I like.
Now that I have the pre running its time to tackle the op amps. Is their a common voltage for op amps or a voltage rating that that allows more choices? IC 201 and IC202 are PDIP-8 which allows for easy switching so I would like to be able to play with a few different op amps to see if I can honestly tell a difference.
IC101 and IC102 are also PDIP-8, I am assuming for the phono section along with IC301 for headphone.
IC101 and IC102 are also PDIP-8, I am assuming for the phono section along with IC301 for headphone.
if you consider an Adcom to be congruent to a K car then what to you consider a worthy vintage design?
i'm still partial to old H/H V800 mosfet amps myself so i understand rebuilding what was once considered (and to some is still) a good amp.
Did you measure with no sound the DC voltage on +input, - input, and output? If all the same and somewhere within a coupla volts of analog ground, no problem in the op amp IC's. The DC offset if due to IC input offset, and usually with capacitor coupled input not a problem in audio. Op amps start clipping with input within a couple of volts of the supply voltages, and with 2 v input signals and >10v rails, DC offset is usually not a problem.
Use a Pamona dip clip and a pamona grabber to measure IC pins with power on, if you short the wrong two pins, it will blow the IC up. When there is another component connected to the IC pin, is us usually safer to measure voltage on that lead.
Redesigning for +-22 v capable IC's is a stretch for a newbie. If they work I'd leave them alone. If they are amp modules with a heat sink surface, the modern replacement is a LM675, a LM386, a LM1875, a LM3886, or similar TO220 power amp IC. You'd need a daughter board to convert the pin layouts from old board to new part.
Use a Pamona dip clip and a pamona grabber to measure IC pins with power on, if you short the wrong two pins, it will blow the IC up. When there is another component connected to the IC pin, is us usually safer to measure voltage on that lead.
Redesigning for +-22 v capable IC's is a stretch for a newbie. If they work I'd leave them alone. If they are amp modules with a heat sink surface, the modern replacement is a LM675, a LM386, a LM1875, a LM3886, or similar TO220 power amp IC. You'd need a daughter board to convert the pin layouts from old board to new part.
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My wife is going to run me the pre and a few supplies to play with while I am at work.
To be completely honest the op amps work but I am wanting to play and learn. Eventually the pre will probably be sold because I've got a nice Adcom GFP 750 and GFP 710. BUT I have an opportunity to learn and play on this pre so I thought what the heck. Some may see this as a waste of money but I see it as an educational tool. 🙂 Thanks to Mooly I was able to track down the issues I was having and get it back up and running and the recap.
I would like to some how rework the circuit to allow me to swap op amps.
If you are talking about fitting different opamp on a dual opamp DIP package, try this:Audio Upgrade Adapters | Cimarron Technology, Inc.. Ainami introduced me and I ordered a bunch of SO8 to DIP and two single opamp SO8 to DIP. They work and I am using one right now in my system.
You been on this thread?:http://www.diyaudio.com/forums/solid-state/293756-suggestion-opamps.html. You might find it interesting. I am making test jig and ordered quite a few opamp to test.
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You need to alter the rails to a slightly lower value which would then allow different opamps to be tried.
There are two ways of doing this:
1/ Altering the value of zener diode D903 from a 12 volt device to something lower. Something in the region of a 10 volt or 9.1 volt zener should be suitable and would bring the rails to around -/+18 volts.
2/ Keep the original zener and alter R909 (very blurry on the diagram, the 121k that goes to the base of Q904) making it somewhere in the region of 270k.
And for the 15 volt supply:
Trial and error... R917 and R918 (both 15k) may need simply removing. Measure the 15 volts and see what it is. That result determines whether we add a different value of resistor. If the voltage is over 15v we do. If its lower than 15 volts then we reduce the of R915 and R916. Impossible to predict what the voltage will be because it depends on the gain of the two transistors.
I was afraid of that. I am a big fan of tubes and the warmth of mosfet amps. My experience with bipolar amps have always sounded sterile to my ears.
My wife was not able to bring my the pre to me Saturday and I am currently at a energy conference all this week. Sadly this project is on hold until I return Friday of this week.
Warmth IMHO is what a recording engineer does to a voice by boosting 5000-8000 hz. If you want that buy a graphic equalizer.
I've got a tube amp, I've got bipolar transistor amps. The PAS2 preamp was highly accurate until the paper caps went geriatric on me. Now with mylar caps 10% over value (.022 instead of .02) it is bright and sizzly. My RA88a modified op amp disco mixer is more accurate, but hums slightly.
My dynakit ST70 tube amp was great for 1961, but even with new plate caps, metal film resistors, new electrollytic caps and new output and rectifier tubes, is a bit fuzzy compared to the Peavey CS800s straight through op amp-BJT transistor amp. The ST70 has 1% harmonic distortion, the CS800s .02%. The dynakit ST120 BJT transistor amp needed an upgrade to have decent idle OT bias current, but with that sounds very similar to the CS800s, even though it has capacitor input and capacitor output.
If define "accurate" as making a Steinway grand piano on record, sound like the Steinway console piano located between my speakers. Less the commanding grand piano bass of course. Acoustic piano is the toughest sound to reproduce IMHO, with bells and percussion right behind in difficulty. I still have 14000 hz ears, rare in motorcycle chain saw and firework addicted USA. Until I found the SP2-XT speakers, no speakers were accurate enough for piano reproduction, only headphones. I've had 3 generations of less fuzzy speakers since my Mother bought an RCA stereo with 2" speakers with Top Value stamps. I've had the PAS2/ST70 since 1970.
MOSFET output transistors, I read, have so much dead area at crossover due to the high turn on voltage, ~4v, that they require nearly 100 ma idle current to sound good. I haven't bought or built any, nearly all were imports after the US hifi industry died. Jfet input op amps are useful mainly for not loading down moving coil cartridges IMHO. I have a moving magnet cartridge and the ST33078 BJT op amps sound fine, although the 4558's the disco mixer came with, hissed much too much.
Building a LM49811-mosfet output board for your chassis and power supply might be fun. there are various discrete op amp board for sale in Europe. Then compare a mosfet board to a LM3886 all BJT board using same chassis. In my opinion design details are more important in amps than the actual technology. For example, classic valve has a tube driver board (12AX7) for my ST70 that is supposed to be much more accurate than the 7199 board it came with.
Enjoy your quest for the sound you seek.
I've got a tube amp, I've got bipolar transistor amps. The PAS2 preamp was highly accurate until the paper caps went geriatric on me. Now with mylar caps 10% over value (.022 instead of .02) it is bright and sizzly. My RA88a modified op amp disco mixer is more accurate, but hums slightly.
My dynakit ST70 tube amp was great for 1961, but even with new plate caps, metal film resistors, new electrollytic caps and new output and rectifier tubes, is a bit fuzzy compared to the Peavey CS800s straight through op amp-BJT transistor amp. The ST70 has 1% harmonic distortion, the CS800s .02%. The dynakit ST120 BJT transistor amp needed an upgrade to have decent idle OT bias current, but with that sounds very similar to the CS800s, even though it has capacitor input and capacitor output.
If define "accurate" as making a Steinway grand piano on record, sound like the Steinway console piano located between my speakers. Less the commanding grand piano bass of course. Acoustic piano is the toughest sound to reproduce IMHO, with bells and percussion right behind in difficulty. I still have 14000 hz ears, rare in motorcycle chain saw and firework addicted USA. Until I found the SP2-XT speakers, no speakers were accurate enough for piano reproduction, only headphones. I've had 3 generations of less fuzzy speakers since my Mother bought an RCA stereo with 2" speakers with Top Value stamps. I've had the PAS2/ST70 since 1970.
MOSFET output transistors, I read, have so much dead area at crossover due to the high turn on voltage, ~4v, that they require nearly 100 ma idle current to sound good. I haven't bought or built any, nearly all were imports after the US hifi industry died. Jfet input op amps are useful mainly for not loading down moving coil cartridges IMHO. I have a moving magnet cartridge and the ST33078 BJT op amps sound fine, although the 4558's the disco mixer came with, hissed much too much.
Building a LM49811-mosfet output board for your chassis and power supply might be fun. there are various discrete op amp board for sale in Europe. Then compare a mosfet board to a LM3886 all BJT board using same chassis. In my opinion design details are more important in amps than the actual technology. For example, classic valve has a tube driver board (12AX7) for my ST70 that is supposed to be much more accurate than the 7199 board it came with.
Enjoy your quest for the sound you seek.
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Warmth is between 5KHz to 8KHz? Not 500 to 800Hz or lower? I just designed and test my preamp board to increase warmth by attenuate 1dB from 800Hz up. That gave me a little more warmth and bottom.
I'm Just going by what Shure does to their "vocal" microphones. I think I've seen reviewers on recordinghacks.com call it "presence".
If mister bored184 has been playing guitar amps, yes, some are tuned for "warmth". Each brand has its own sound, which is more brand specific than technology specific. Not hifi at all.
I'm trying to encourage testing of amps & speakers with piano source, which reveals inaccuracy. All these adjectives, aren't very instructive. Demonstration tracks in stores don't help anything. Heavy bass rock, thumping hip hop, light jazz with a horn drum & bass, (klipschhorn demo I heard) vocal solo, who knows what that should sound like? I heard an award winning Armericana music star in person talking from 3 feet away; she doesn't sound anything like herself on stage in performance. Producer magic.
If mister bored184 has been playing guitar amps, yes, some are tuned for "warmth". Each brand has its own sound, which is more brand specific than technology specific. Not hifi at all.
I'm trying to encourage testing of amps & speakers with piano source, which reveals inaccuracy. All these adjectives, aren't very instructive. Demonstration tracks in stores don't help anything. Heavy bass rock, thumping hip hop, light jazz with a horn drum & bass, (klipschhorn demo I heard) vocal solo, who knows what that should sound like? I heard an award winning Armericana music star in person talking from 3 feet away; she doesn't sound anything like herself on stage in performance. Producer magic.
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There you see the folly of using meaningless subjective terms to describe an effect: Nobody else knows what you are talking about!