Congratulations on finding your error. Glad the amp works.
What sources do you need to boost with the preamp? If you don't need RIAA for a moving magnet or moving coil LP cartridge, then mixers can work. Preamps can be quite pricey, whereas the market is deluged with used mixers with bad pots, particularly the master volume pot. I reworked a PV-8 for $50 purchase price including freight, $2 for a pot and $5 for 2mm screws to mount it. Freight on the pot and the screws were $8 each, but I added those to other items to fill out the box.
5532 is a great op amp. OPA2134 looks by the specs to be twice as noisy. OPA2134 also has excessive slew rate (20v/usec) and will require local ceramic bypass caps on the power supply (.1 uf) and a feedback resistor bypass cap (33 pf) to avoid oscillation. I had oscillation with ST33078 which is quieter than OPA2134 and cost $3.80 per 10 but has a similar slew rate. Killed the oscillation by installing the capacitors mentioned. That is an upgrade to my Herald RA88a mixer with riaa inputs, which was a great bargain @ $15 in a flea market but probably can't be found anymore. Also sold as an Olson RA88a.
The PV8 had 4565 op amps and was quiet enough for 8 sources simultaneously on as is. No RIAA input, though. The shorting rotary selector switch of a preamp like in a PAS3 is very difficult to buy now. Most preamp builders use a relay for each source and a microprocessor to select them See line level forum.
There are 5532 mixer boards available on ebay here. They could be good enough, they are certainly cheap enough.
For more sophisticated preamps, see line level forum. I don't see the point of going below 80 db s/n, I have a natural gas pilot light in my music room and the noise of the PV8 mixer with the sources shut off is quieter than that. I also don't see the point of the holy grail vacuum tube preamp. I own a vacuum tube PAS2 preamp and the RA88a and PV-8 sound as good and use 1/10 the electricity. Also produce 1/20th the heat into the room of the PAS2 that the air conditioner has to pump out.
Happy shopping & maybe building.
What sources do you need to boost with the preamp? If you don't need RIAA for a moving magnet or moving coil LP cartridge, then mixers can work. Preamps can be quite pricey, whereas the market is deluged with used mixers with bad pots, particularly the master volume pot. I reworked a PV-8 for $50 purchase price including freight, $2 for a pot and $5 for 2mm screws to mount it. Freight on the pot and the screws were $8 each, but I added those to other items to fill out the box.
5532 is a great op amp. OPA2134 looks by the specs to be twice as noisy. OPA2134 also has excessive slew rate (20v/usec) and will require local ceramic bypass caps on the power supply (.1 uf) and a feedback resistor bypass cap (33 pf) to avoid oscillation. I had oscillation with ST33078 which is quieter than OPA2134 and cost $3.80 per 10 but has a similar slew rate. Killed the oscillation by installing the capacitors mentioned. That is an upgrade to my Herald RA88a mixer with riaa inputs, which was a great bargain @ $15 in a flea market but probably can't be found anymore. Also sold as an Olson RA88a.
The PV8 had 4565 op amps and was quiet enough for 8 sources simultaneously on as is. No RIAA input, though. The shorting rotary selector switch of a preamp like in a PAS3 is very difficult to buy now. Most preamp builders use a relay for each source and a microprocessor to select them See line level forum.
There are 5532 mixer boards available on ebay here. They could be good enough, they are certainly cheap enough.
For more sophisticated preamps, see line level forum. I don't see the point of going below 80 db s/n, I have a natural gas pilot light in my music room and the noise of the PV8 mixer with the sources shut off is quieter than that. I also don't see the point of the holy grail vacuum tube preamp. I own a vacuum tube PAS2 preamp and the RA88a and PV-8 sound as good and use 1/10 the electricity. Also produce 1/20th the heat into the room of the PAS2 that the air conditioner has to pump out.
Happy shopping & maybe building.
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Hello Indianajo! all right? I am currently using OPA2134 in a pre-phono and subsonic filter, I have no problems with noise, which surprises me a lot. I'm using the Elliott Sound Products P06 + P99 project .. they are currently the best pre-phono I've ever assembled and listened to. However, this pre-phono, my cd player, and my cell phone are very low on this amplifier, so I want to use a pre-amplifier. Currently I set up a buffer circuit with a little gain to solve this volume problem. But I wanted to make a more improved circuit, one that is linear and is matched to the input impedance of the amplifier. Do you know of a good quality linear pre-amplifier circuit?
Thank you in advance!
Inverting op amp circuits with no capacitors or inductors in the feedback circuit are inherently linear, within their bandwidth. The 33 pf feedback capacitor around the resistor I used on the 33078 circuit, it kills the gain above several megahertz. Which is not used for audio circuits.
You build a pre-amp circuit, you are going to get into selector logic or buy a very expensive rotary switch. I think dynacodoctor has the switch, it is $40 or more. You want gold plate contacts for 1 v 2 v signals. Mixers just sum all the inputs together, and with metal film resistors and quiet op amps like the ST33078 & the NJM2068 there is plenty of signal to noise ratio for home use. Mastering they need a 110 db s/n but that is not home use.
If you scan around the analog line level forum you will see many threads where the OP wanted some recommendations for preamps. I think there was a sapphire selling boards, I can't remember them all since I found I could buy good mixers with bad pots for $30 + freight. I bought a Peavey MMA-800 mixer last week for $15, the only thing was wrong was the input connectors were missing on all 8 channels. But the freight was $32, the guy was addicted to fed-ex the expensive brand. The used market prices may be different in mercosur zone.
You ought to be able to change the feedback resistor out of your existing P08 project to raise the gain a little. Rf/Ri=gain. You may also be able to change the feedback resistor on the input transistor of you AX14 boards to jack up the gain. I did that to my AX6 board, since my ST120 board on the other channel has 28 db gain.
You build a pre-amp circuit, you are going to get into selector logic or buy a very expensive rotary switch. I think dynacodoctor has the switch, it is $40 or more. You want gold plate contacts for 1 v 2 v signals. Mixers just sum all the inputs together, and with metal film resistors and quiet op amps like the ST33078 & the NJM2068 there is plenty of signal to noise ratio for home use. Mastering they need a 110 db s/n but that is not home use.
If you scan around the analog line level forum you will see many threads where the OP wanted some recommendations for preamps. I think there was a sapphire selling boards, I can't remember them all since I found I could buy good mixers with bad pots for $30 + freight. I bought a Peavey MMA-800 mixer last week for $15, the only thing was wrong was the input connectors were missing on all 8 channels. But the freight was $32, the guy was addicted to fed-ex the expensive brand. The used market prices may be different in mercosur zone.
You ought to be able to change the feedback resistor out of your existing P08 project to raise the gain a little. Rf/Ri=gain. You may also be able to change the feedback resistor on the input transistor of you AX14 boards to jack up the gain. I did that to my AX6 board, since my ST120 board on the other channel has 28 db gain.
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