You didn't say what brand and model your mixer is that hisses with all the gains turned down. I've been looking at a Peavey band mixer schematic today to see if there are compromises made. The low hanging fruit on hiss is the feedback resistors. The input op amps I looked at had 10 k input resistance, and 470 k feedback resistors bypassed by 10 pf. That 470k could be quite hissy if carbon comp or carbon film type. Metal film resistors are reputed to be much quieter and cost about $.18. I changed the carbon comps 100k and over in my dynakit preamp and power amp to vishay and multicomp metal film resistors, and gained a lot on quiescent hiss.
The second thing is hiss is the op amp. The 4560 used in some Peavey mixers is only 1.2 microv noise which is hardly less than the 1.4 microv 4558's I found objectionable at 50x gain in my RA88a mixer. Mixers need a certain amount of drive current to drive cables and inductors in the tone controls, the 4560 is only 2k ohm large voltage swing characterized, but it does have that 5 v/microsec slew rate showing some drive current available. The ST33078 op amps I got for $.38 each for my RA88a were much lower hiss than the 4558's, and will drive 600 ohm large voltage swing, showing more current. I used 33 pf to keep them from oscillating, so the 10 pf feedback resistor bypass cap Peavey was using for the 4560 may be a little light.
Other bargain choice would be the JRC4580, which has the 5.5 slew rate, a better 0.8 microv noise spec than the 4560, but still large voltage swing characterized at 2 kohm.
AT over $2 apiece the LM4562 has 600 ohm large voltage swing for long cables, slew rate 15, and a noise spec that is not comparable to the others but is reputed to be very good. I might try one of those on the master and monitor outs of the mixer to drive the long cables to the speakers and monitors. Not inside the mixer. The NJM4562 is not the same part, it has a nice 0.6 microvolt noise spec but large voltage swing is again specified at 2 kohm and there is no slew rate spec.
I put my RA88a mixer op amps in phosphor bronze sockets so I could swap around conveniently. After I got the ST33078's in, though, I stopped. The only thing objectionable at this point is the hum, which is above the PAS2 tube preamp it replaced, but not too bad. I think board layout has something to do with the hum, and I don't etch or layout PC boards yet.
Hope you have some youth with a long attention span that can replace all your mixer parts some evening - those caps would be tedious if you do them yourself. The Peavey mixer I looked at had the same input caps, 22 uf on the 1/4 phone inputs and 47 uf on the 4 pin inputs.
As far as "audio" caps, I've been buying "industrial" caps with long service hours rating, and made my geriatric equipment sound better than it was when I bought it. I'm not even sure what an "audio" electrolytic cap is. I suppose it is important to have ripple specified at 60 hz, since many caps now are made for switcher supplies with the ripple spec measured at 100 khz or something. I've been happy with long life caps I got from Nichicon, Panasonic, Rubicon, and found no fault with United chemicon and multicomp except the country of origin and the short lives specified. Vishay Sprague comes only in 1000 hours life and a couple of years in my H100 organ so far has lasted fine, although I used up some Sprague Atomlytics in eight years that I installed in 1971 in the tube ST70 amp, which ran quite hot.
The second thing is hiss is the op amp. The 4560 used in some Peavey mixers is only 1.2 microv noise which is hardly less than the 1.4 microv 4558's I found objectionable at 50x gain in my RA88a mixer. Mixers need a certain amount of drive current to drive cables and inductors in the tone controls, the 4560 is only 2k ohm large voltage swing characterized, but it does have that 5 v/microsec slew rate showing some drive current available. The ST33078 op amps I got for $.38 each for my RA88a were much lower hiss than the 4558's, and will drive 600 ohm large voltage swing, showing more current. I used 33 pf to keep them from oscillating, so the 10 pf feedback resistor bypass cap Peavey was using for the 4560 may be a little light.
Other bargain choice would be the JRC4580, which has the 5.5 slew rate, a better 0.8 microv noise spec than the 4560, but still large voltage swing characterized at 2 kohm.
AT over $2 apiece the LM4562 has 600 ohm large voltage swing for long cables, slew rate 15, and a noise spec that is not comparable to the others but is reputed to be very good. I might try one of those on the master and monitor outs of the mixer to drive the long cables to the speakers and monitors. Not inside the mixer. The NJM4562 is not the same part, it has a nice 0.6 microvolt noise spec but large voltage swing is again specified at 2 kohm and there is no slew rate spec.
I put my RA88a mixer op amps in phosphor bronze sockets so I could swap around conveniently. After I got the ST33078's in, though, I stopped. The only thing objectionable at this point is the hum, which is above the PAS2 tube preamp it replaced, but not too bad. I think board layout has something to do with the hum, and I don't etch or layout PC boards yet.
Hope you have some youth with a long attention span that can replace all your mixer parts some evening - those caps would be tedious if you do them yourself. The Peavey mixer I looked at had the same input caps, 22 uf on the 1/4 phone inputs and 47 uf on the 4 pin inputs.
As far as "audio" caps, I've been buying "industrial" caps with long service hours rating, and made my geriatric equipment sound better than it was when I bought it. I'm not even sure what an "audio" electrolytic cap is. I suppose it is important to have ripple specified at 60 hz, since many caps now are made for switcher supplies with the ripple spec measured at 100 khz or something. I've been happy with long life caps I got from Nichicon, Panasonic, Rubicon, and found no fault with United chemicon and multicomp except the country of origin and the short lives specified. Vishay Sprague comes only in 1000 hours life and a couple of years in my H100 organ so far has lasted fine, although I used up some Sprague Atomlytics in eight years that I installed in 1971 in the tube ST70 amp, which ran quite hot.
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I said in my first post, a Mackie SR•32 VLZ. The resistors are all surface mount and the op amps aren't the best but decent. Do you think recapping the board is worth the money?
An audio cap is specialized to work in the audio frequency range, but that's about it.
An audio cap is specialized to work in the audio frequency range, but that's about it.
Sorry, didn't go back. I think your hiss comes from something else beside the e-caps. If you had a mike input missing the bass compared to the others, I'd say the coupler cap on that input had gone dry, but SM58's don't produce a lot of bass anyway. You could buy an older mixer like mine that has leaded parts. It may need a pot or three, but those can be for sale. I don't know yet the 98 Unity 12 Peavey has leaded parts, I can't get the ends off without a rubber hammer or stronger arms than I came with. (and I lift weights now, a 5 lb one). Somebody on Peavey website forum will know what they sold that has leaded parts. The reason I talk about them, we're 500 miles from the Peavey factory and our craigslist is full of them, also behringer. Also, Peavey will give away the schematics and sell you parts (unlike Behringer, for example). I'm sure my mono Ampeg mixer has leaded parts, it has an old spring reverb, but even I want stereo vibrato these days. (leslie sim).
To get a modern mixer that doesn't hiss at high gain, you have to get into the exclusive pro stuff IMHO, which is $$$$. I like taking old generic quality stuff, adding $20 in quality parts, and making something superior out of it.
Does your headphone output hiss? Do you have a VTVM, VOM or scope to measure the hiss out the mixer mains?
I may be too pessimistic on surface mount parts. I'm too old, vision is deteriorating and I have tons of hand built things to work on, but kids with a soldering iron might be able to work on surface mount. Newark certainly sells a lot of surface mount parts. Try searching over on tools and equipment forum to see how low you can go to replace resistors and op amps surface mount.
To get a modern mixer that doesn't hiss at high gain, you have to get into the exclusive pro stuff IMHO, which is $$$$. I like taking old generic quality stuff, adding $20 in quality parts, and making something superior out of it.
Does your headphone output hiss? Do you have a VTVM, VOM or scope to measure the hiss out the mixer mains?
I may be too pessimistic on surface mount parts. I'm too old, vision is deteriorating and I have tons of hand built things to work on, but kids with a soldering iron might be able to work on surface mount. Newark certainly sells a lot of surface mount parts. Try searching over on tools and equipment forum to see how low you can go to replace resistors and op amps surface mount.
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Okay, for you Mackie mixer hiss, Newark is stocking high drive current low noise 33078 for <+-18 supplies for $.81 each in surface mount. MC33078P - TEXAS INSTRUMENTS MC33078P - IC, OP-AMP, 16MHZ, 7V/ us, DIP-8 | Newark element14 US
There are different surface mount packages, look at the picture before ordering.
If your power supplies are +-15 v or lower you can use the ST brand 33078 for $.27 each.
These will possibly require more feedback resistor bypass than you have now to not oscillate with 33078, (4560 had 10 pf) so here are some 39 pf @100v ceramic smd at $.02 each 08051A390JAT2A - AVX 08051A390JAT2A - CAPACITOR CERAMIC 39PF 100V, C0G, 5%, 0805 | Newark element14 US
You'll need additional ceramic bypass between the + and - supplies somewhat near the op amps, so here are some 0.1 uf @ $.07 with leads that you can tack onto the existing traces, or drill holes if there is room between traces. MCFYU6104Z6 - MULTICOMP MCFYU6104Z6 - CAPACITOR CERAMIC 0.1UF, 50V, Y5V, +80, -20%, RAD | Newark element14 US I bent the leads over on mine and put them between +8 and -8 tracks on my disco mixer, one near each pair of op amp packages. They were an inch away, didn't involve signal ground at all, and still killed the oscillation the 33078's were experiencing.
For high noise feedback resistors here are some SMD metal film 470k at $.01 if that is the value your mixer has: CRCW1206470KJNEA - VISHAY DALE CRCW1206470KJNEA - RESISTOR, THICK FILM, 470KOHM, 250mW, 5% | Newark element14 US
Newark doesn't sell carbon film surface mount resistors, only "thick film" so maybe your "thick film" feedback resistors are metal film already. That will require some research. on the part datasheets.
You'll need to check the dimensions of these SMD parts against those on your mixer to see if they are a physical fit.
Those circle light magnifying glass devices look useful for this.
When people talk surface mount they talk about solder paste and hot air tools. I'm no expert on that.
Good luck.
There are different surface mount packages, look at the picture before ordering.
If your power supplies are +-15 v or lower you can use the ST brand 33078 for $.27 each.
These will possibly require more feedback resistor bypass than you have now to not oscillate with 33078, (4560 had 10 pf) so here are some 39 pf @100v ceramic smd at $.02 each 08051A390JAT2A - AVX 08051A390JAT2A - CAPACITOR CERAMIC 39PF 100V, C0G, 5%, 0805 | Newark element14 US
You'll need additional ceramic bypass between the + and - supplies somewhat near the op amps, so here are some 0.1 uf @ $.07 with leads that you can tack onto the existing traces, or drill holes if there is room between traces. MCFYU6104Z6 - MULTICOMP MCFYU6104Z6 - CAPACITOR CERAMIC 0.1UF, 50V, Y5V, +80, -20%, RAD | Newark element14 US I bent the leads over on mine and put them between +8 and -8 tracks on my disco mixer, one near each pair of op amp packages. They were an inch away, didn't involve signal ground at all, and still killed the oscillation the 33078's were experiencing.
For high noise feedback resistors here are some SMD metal film 470k at $.01 if that is the value your mixer has: CRCW1206470KJNEA - VISHAY DALE CRCW1206470KJNEA - RESISTOR, THICK FILM, 470KOHM, 250mW, 5% | Newark element14 US
Newark doesn't sell carbon film surface mount resistors, only "thick film" so maybe your "thick film" feedback resistors are metal film already. That will require some research. on the part datasheets.
You'll need to check the dimensions of these SMD parts against those on your mixer to see if they are a physical fit.
Those circle light magnifying glass devices look useful for this.
When people talk surface mount they talk about solder paste and hot air tools. I'm no expert on that.
Good luck.
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