What I did is adjust it to match the right channel when a 1kz signal is applied but now I realize TVR3 needed to be adjusted instead
What are the values of TVR1 and TVR2 ?
Maybe TVR2 is coarse and TVR1 is fine. They are in series, that means the total series resistance of two pots and R139 is relevant.
So try to readjust to 3mV without signal, using TVR1. Or TVR2 very very carefully.
shows TVR1 at 202.
And TVR2 at 101
I noticed the TVR1 is VERY touchy.
TVR 2 much finer adjustment if I’m aiming for 3ma with no signal
And TVR2 at 101
I noticed the TVR1 is VERY touchy.
TVR 2 much finer adjustment if I’m aiming for 3ma with no signal
So the instructions are wrong. TVR1 = 2k, TVR2 = 100 ohms. Use TVR2 if the range is sufficiant.
Or set TVR2 in the mid position while watching the voltage, then pre-adjust with TVR1, then fine adjust with TVR2.
Or set TVR2 in the mid position while watching the voltage, then pre-adjust with TVR1, then fine adjust with TVR2.
TVR3 does adjust when I change it.
I’ve only touched TVR3 in the left channel and kept it alone in the right.
Both channels now match and the amp is cooking.
I’ve only touched TVR3 in the left channel and kept it alone in the right.
Both channels now match and the amp is cooking.
Yes. Back to 3mV. Give or take .5mv.
With signal i set the left channel to match the right at 14.6mV. Should I go ahead and just bump this up to 20mv?
The only equipment I have to play a 1khz sine wave is from my computer directly into the RCAs. I don’t know if that is sufficient enough.
With signal i set the left channel to match the right at 14.6mV. Should I go ahead and just bump this up to 20mv?
The only equipment I have to play a 1khz sine wave is from my computer directly into the RCAs. I don’t know if that is sufficient enough.
It is unclear to what amplitude of the 1k input signal the 20mV are related to.
So I would leave it alone now.
So I would leave it alone now.
Ok. I will leave for now until I know exactly how to do it. However, when doing some research I saw these Big Sky modifications shared online and was thinking about performing a few of them. At the very bottom it mentions you just bias with a signal playing through it with the top cover on.
https://www.diyaudio.com/community/threads/parasound-hca-3500-upgrade.357272/
https://www.diyaudio.com/community/threads/parasound-hca-3500-upgrade.357272/
Alignment: TVR1 (idle bias) = ~4mV (+/-1mV) DC across R51 (or any of the .22Ω emitter resistors) with top cover on. Increase idle bias to ~20mV (+/-2mV) if dynamic bias circuit disabled. TVR3 (dynamic bias) with a signal applied for ~20mV (+/-2mV) DC with top cover on.
The big white film caps are very good as long as they not fail.
Upgrading small old lytics would not hurt.
47k feedback resistor upgrade is a good idea. But then also upgrade the 1.8k shunt, that is missing in the modification.
Dynamic bias - I do not know, I personally not like it, same with dc servos.
Large quality caps I would never change, or only if it gets boiling hot inside so that they detoriate.
That amp has external heatsinks, so I would leave all nichicon great supply in place.
Upgrading small old lytics would not hurt.
47k feedback resistor upgrade is a good idea. But then also upgrade the 1.8k shunt, that is missing in the modification.
Dynamic bias - I do not know, I personally not like it, same with dc servos.
Large quality caps I would never change, or only if it gets boiling hot inside so that they detoriate.
That amp has external heatsinks, so I would leave all nichicon great supply in place.
I’ll make sure the amp is operating correctly first before considering any upgrades.
A HUGE thank you to @Bernhard for the help on this! And anyone else offering feedback.
Sorry @malibutwins, I might be keeping this one a bit longer.. got some Magnepan LRS+ and YG Acoustic Carmel 1 that need to be heard with this amp
I was looking at how easy it would be to recap it and I know how to unplug the heatsink and board completely… but there is only a 1 inch gap between the heat sink and board. Can the aluminum block where the mosfets mount be detached from the actual heat sink?
That would make it very easy to recap and make changes.
A HUGE thank you to @Bernhard for the help on this! And anyone else offering feedback.
Sorry @malibutwins, I might be keeping this one a bit longer.. got some Magnepan LRS+ and YG Acoustic Carmel 1 that need to be heard with this amp
I was looking at how easy it would be to recap it and I know how to unplug the heatsink and board completely… but there is only a 1 inch gap between the heat sink and board. Can the aluminum block where the mosfets mount be detached from the actual heat sink?
That would make it very easy to recap and make changes.
I haven’t lugged it up my stairs yet to listen in my main room. I currently have a pair of Klipsch Super Heresy hooked up in that room, so will need to move those to set up Magnepan or my YG Carmels.
I did start making a part list to replace all the electrolytic caps and a few resistors recommended by Big Sky Audio. Most of the upgrades appear to be easy part swaps; I’m just confused about a few notes but I think I’m going to start a separate thread to document the recap and ask some questions about the mods and parts I couldn’t find. A lot of capacitors are removed on the upgrade list but aren’t replaced.
C7, C8, C12, and C13 are already Rubycon Black Gate so I’ll probably leave those in.
I’ve already emailed Michael Percy about Holco resistors and Relcaps.
I did start making a part list to replace all the electrolytic caps and a few resistors recommended by Big Sky Audio. Most of the upgrades appear to be easy part swaps; I’m just confused about a few notes but I think I’m going to start a separate thread to document the recap and ask some questions about the mods and parts I couldn’t find. A lot of capacitors are removed on the upgrade list but aren’t replaced.
C7, C8, C12, and C13 are already Rubycon Black Gate so I’ll probably leave those in.
I’ve already emailed Michael Percy about Holco resistors and Relcaps.
The bias adjustment instructions are correct. TVR1 sets idle bias. Leave TVR2 alone unless you cannot get 3-4mV with TVR1. TVR2 is more of a coarse adjustment. If you have to adjust it, be very careful and only a slight amount.
TVR3 sets the auto dynamic bias. Just a low amplitude audio signal is needed to trigger it. The dynamic bias circuit reduces amplifier high bias to conserve energy and reduce heat for extended periods when no music is playing.
Keep the Black Gates and do not replace them. Upgrade sheet does state that they may already be BGs.
TVR3 sets the auto dynamic bias. Just a low amplitude audio signal is needed to trigger it. The dynamic bias circuit reduces amplifier high bias to conserve energy and reduce heat for extended periods when no music is playing.
Keep the Black Gates and do not replace them. Upgrade sheet does state that they may already be BGs.