Anyone here know or listened to Denny's mods suggesting that it's better than what ARC did?
I don't know if I would be up to making new boards for the pre amp and phono section. Kind of defeats the purpose of the ARC SP3xx. Someone could find a large junk pre amp and gut it to make a totally new pre-amp....Not the ARC SP3xx.
And from some folks that sent these back to ARC for upgrades, they didn't like the way the pre amps sounded when they got them back. It would be interesting to see the Schematic that ARC uses for their upgrade. My mail box is open should one find it's way to it.
Cheers,
I don't know if I would be up to making new boards for the pre amp and phono section. Kind of defeats the purpose of the ARC SP3xx. Someone could find a large junk pre amp and gut it to make a totally new pre-amp....Not the ARC SP3xx.
And from some folks that sent these back to ARC for upgrades, they didn't like the way the pre amps sounded when they got them back. It would be interesting to see the Schematic that ARC uses for their upgrade. My mail box is open should one find it's way to it.
Cheers,
The SP-8 - all tube power supply IIFRC - was supposed to be pretty sweet. I don't know the potential for serious mods to the SP-3. I keep mixing up mods I did but the SP-6 upgrades were mostly capacitor swaps. The old ARC schematics are on the internet maybe?? If not, I might have a couple. I bought that SP-6 I mentioned and lost it in a bum deal. I wish to this very day I still had it. Good luck Sync!!
Phil
Phil
5-15-18: Update
The preamp has developed a bit of a crackle-like distortion in the right channel over about a month - at first I could barely hear it, but now action is required.
I've eliminated the speakers by switching them, and the amplifier by switching the RCAs. The crackle is not just in the phono section as I have switched my phono over to the aux input and the crackle was there as well - so has to be the line stage. Trying to eliminate tubes as a culprit, I tested them all and they were all good. I then cleaned the tupe sockets and tried as best as I could to retension the pin holders, and then cleaned them again. Crackle still there.
I've replaced most all the components on both boards, so the obvious culprits the spring to mind are few - tube sockets, a coupling cap in the right channel, or the power resistors (which I did not replace). I doubt it is a coupling cap - I checked capacitance on all the caps onboard and got the correct values - and they are only a few years old. To eliminate the tube sockets, I ordered some nice new ones from Tubes and More and will order up some new power resistors as well.
I will need 2x 10W 10 Ohm, and 2x 5W 75Ohm wirewound resistors. I did test the ones there in circuit, and I got 10ohms spot on for one of the originals and 7.5 for the other - so that may be the problem. Any recommendations for these resistors?
The preamp has developed a bit of a crackle-like distortion in the right channel over about a month - at first I could barely hear it, but now action is required.
I've eliminated the speakers by switching them, and the amplifier by switching the RCAs. The crackle is not just in the phono section as I have switched my phono over to the aux input and the crackle was there as well - so has to be the line stage. Trying to eliminate tubes as a culprit, I tested them all and they were all good. I then cleaned the tupe sockets and tried as best as I could to retension the pin holders, and then cleaned them again. Crackle still there.
I've replaced most all the components on both boards, so the obvious culprits the spring to mind are few - tube sockets, a coupling cap in the right channel, or the power resistors (which I did not replace). I doubt it is a coupling cap - I checked capacitance on all the caps onboard and got the correct values - and they are only a few years old. To eliminate the tube sockets, I ordered some nice new ones from Tubes and More and will order up some new power resistors as well.
I will need 2x 10W 10 Ohm, and 2x 5W 75Ohm wirewound resistors. I did test the ones there in circuit, and I got 10ohms spot on for one of the originals and 7.5 for the other - so that may be the problem. Any recommendations for these resistors?
Well, first time scoping a circuit, but I think I learned some useful information.
I used a signal generator to generate a 200hz wave and put that into the aux input. I saw no or very little distortion in the left channel, even when cranking the volume pot up. However, that was not the case at all with the right channel. I got significant distortion on both legs of R37 and R29, and one leg on R26, R27, R31, R35, and R38. I switched tubes and did the same checks and the results were identical.
New sockets get here tomorrow. Will do some more poking around later tonight.
I used a signal generator to generate a 200hz wave and put that into the aux input. I saw no or very little distortion in the left channel, even when cranking the volume pot up. However, that was not the case at all with the right channel. I got significant distortion on both legs of R37 and R29, and one leg on R26, R27, R31, R35, and R38. I switched tubes and did the same checks and the results were identical.
New sockets get here tomorrow. Will do some more poking around later tonight.
Hope your rebuild is going well, I thought I would post a picture of the SP-3 phono simulation using the original values in the feedback, it’s not very smooth, but if you check out Joe Curcio’s SP-3 mods, the Response curve is much flatter, their isn’t a sag in the upper bass, lower midrange you see in the picture.
I’ll post a pic of the simulation of the mods, when I get a chance.
http://www.curcioaudio.com/SP-3 Mod Documentation.pdf
I’ll post a pic of the simulation of the mods, when I get a chance.
http://www.curcioaudio.com/SP-3 Mod Documentation.pdf
Attachments
The low frequencies will be somewhat more extended when unloaded, depending on the input
impedance of your amplifier. If the preamp outputs are heavily loaded, the distortion will rise
compared to unloaded.
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