I thought I would make a thread on my CA 800, a little back history first. I got this amp with the intention of fixing and restoring it only to find out the transformer died when the class A/AB switched failed (a common issue when fixing these and as I already have 1000 I wasn't too impressed with the sound I imagine the 800 would be similar. 1000 doesn't come even near my Sansui and they have both been recapped and restored. So I decided to part out the boards to someone who needs them and build an integrated amp using the Gainclone idea. Although my original thought was to go with a class A design like a JLH but I was worried about cooling. I still may go back to that in the future depending on how I like the LM3886's.
I'm using a single LM3886 per channel with the circuit being the attached schematic below. For the transformers I'm using a pair I have from some Yamaha CA 600's for a dual mono design. I might try to get the existing CA 800 preamp to work with the amp not sure how I will do that yet or I might just go with a passive tone control board and have a switch to bypass making sure input impedance and the 20 DB reduction is matched between passive and bypassed tone controls. Ignore the ugly paint job on the Bell covers, I was gonna use them in another project but opted not to and they'll be painted back to black or if I can to match the heatsinks.
I'm using a single LM3886 per channel with the circuit being the attached schematic below. For the transformers I'm using a pair I have from some Yamaha CA 600's for a dual mono design. I might try to get the existing CA 800 preamp to work with the amp not sure how I will do that yet or I might just go with a passive tone control board and have a switch to bypass making sure input impedance and the 20 DB reduction is matched between passive and bypassed tone controls. Ignore the ugly paint job on the Bell covers, I was gonna use them in another project but opted not to and they'll be painted back to black or if I can to match the heatsinks.
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So I opted to go for a board instead of point to point. It's difficult for me to not damage the chip and keep the pins separated. The board is KMTech. It's missing the output stability components I plan on adding those at the speaker selector switch. They also tied in the power ground and signal grounds together so I'm only using a power ground on the board and separately Ill run all signal ground separately to signal ground. I might add some filter for a signal ground but ill know later. Should get parts tomorrow and then I can power up. I should mention that all parts that I've sourced except the PCB boards are digikey or mouser, none of this fake/used bs.
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I'm also trying to separate my rails from my signal/preamp boards. All power supplies are up on top as you can see. I have my speaker output close to the mains in wiring which bothers me so I may end up wrapping that wire in aluminum foil with heatshink over it and of course, the foil with have a wire attached to ground. Not sure if that will work but I figure it can't hurt. I also got a bit of AC on the black layers of the transformer not sure if this is whats called eddie current?
So in principle you are recycling a Yamaha chassis + 2 Yamaha transformers and some hardware (specially heatsinks) by building 2 gainclones there?
I don´t see why that wouldn´t work and sound fine.
As you are noticing, you´ll have to be careful with grounding, I guess the slight hum you mention more probably comes from grounding than electrostatic interference.
As of using the 800 preamp to drive it, why not?
Since its transformer has died, and perhaps the power amp, but not the preamp, you may feed it from the "dual 600/gainclone" power amp supply, you will probably need to add some multipin connector to each chassis so you can send various DC voltages to preamp.
Using that Preamp will be far easier and more flexible, you´ll keep a lot of features while building a new Preamp from ground up will mean way more work.
Of course, it´s your time, but looks very doable.
I don´t see why that wouldn´t work and sound fine.
As you are noticing, you´ll have to be careful with grounding, I guess the slight hum you mention more probably comes from grounding than electrostatic interference.
As of using the 800 preamp to drive it, why not?
Since its transformer has died, and perhaps the power amp, but not the preamp, you may feed it from the "dual 600/gainclone" power amp supply, you will probably need to add some multipin connector to each chassis so you can send various DC voltages to preamp.
Using that Preamp will be far easier and more flexible, you´ll keep a lot of features while building a new Preamp from ground up will mean way more work.
Of course, it´s your time, but looks very doable.
Yah I thought about just using the 800 preamps but I wanted to go passive. Just to keep it simple and a lower noise floor. I might add a preamp later if I can't get enough volume out of it.
Played the amp for about an hour all seemed well. I got the original tone control to work passively but there was not enough adjustment to make a difference which makes sense looking at the schematic. I mounted the output stabilizing filter on the LM3886 boards. I figure the closer to the chip the better? idk. I also wound my own inductor which I'm not happy with so ill end up remaking it and I only had 1-watt resistors for the 10 ohm and 2.7 ohms. I would like to use at least a 5 watt for the 2.7 my reasoning is it's connected to ground and if that went then it could take out my L100's. Not sure I should rely on Spike to protect it.
Also, my unregulated rails are 40v. I was able to bring it down from 43v by adding diodes after my rectifier and using a 3k 1 watt bleeder resistor. I might try a thermister in there as well.
Played the amp for about an hour all seemed well. I got the original tone control to work passively but there was not enough adjustment to make a difference which makes sense looking at the schematic. I mounted the output stabilizing filter on the LM3886 boards. I figure the closer to the chip the better? idk. I also wound my own inductor which I'm not happy with so ill end up remaking it and I only had 1-watt resistors for the 10 ohm and 2.7 ohms. I would like to use at least a 5 watt for the 2.7 my reasoning is it's connected to ground and if that went then it could take out my L100's. Not sure I should rely on Spike to protect it.
Also, my unregulated rails are 40v. I was able to bring it down from 43v by adding diodes after my rectifier and using a 3k 1 watt bleeder resistor. I might try a thermister in there as well.
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