@wengtech -
I chuckled a little reading your post. I sent a message directly to ZM asking essentially the same question two days ago. I should have posted here. I also wanted to experiment with other front ends (later) with the complementary output stage.
I was originally going to just 'mod' my BA-3 for use with a new power supply that I had built, but then I wanted to take it a little further. It broke my heart to disassemble it, but I think it will be 'better' when I get it how I want it. I still want to build the SE output stage.
For you and perhaps others, this is a selection of the notes.
As my adventures progress I'll post more here. I hope you will too. Looking forward to see what you come up with.
This is the current state of the poor thing...
I chuckled a little reading your post. I sent a message directly to ZM asking essentially the same question two days ago. I should have posted here. I also wanted to experiment with other front ends (later) with the complementary output stage.
I was originally going to just 'mod' my BA-3 for use with a new power supply that I had built, but then I wanted to take it a little further. It broke my heart to disassemble it, but I think it will be 'better' when I get it how I want it. I still want to build the SE output stage.
For you and perhaps others, this is a selection of the notes.
I wanted to clean up (the amp) and use what I’d learned since I built it to have some fun. The first goal was to use it with my new ... PSU. I did some measurements with the previous PSU, which was essentially 2x First Watt type PSUs in dual mono. {snipped} I can do better.
When I built it, I knew that the output stage was for all intents and purposes an “F-4” minus the buffer. I also know that some folks have built the “crippled” F4. So… BA-3 output stage is essentially a crippled F4.
I don’t “need” voltage gain from my source to (most of my) speakers. Even with a passive pre-amp into an F4, I can play plenty loud with some speakers. Where I get the gain (pre or power or both) is still a fun balance, but I really don’t “need” gain.
Can I … should I… Have the “BA3” front end as a separate ‘module’ from the Complimentary output stage + bias boards? The new PSU is ~32VDC loaded. So… probably on the edge for using the BA-3 input stage (don’t want to cook JFETs), but it should be fine with the complimentary output stage. I’ll just (reduce the bias).
I’m thinking I could try the new 2022 FE with the output stage etc. There seem to be all sorts of wonderful combinations. Also, now that the PSU is a separate module from the other chunks, if (example) I wanted to run the 2022 FE at a higher voltage than the output stage, I could.
Am I nuts?
Why do I ask? B/C My tube pre-amp has higher gain => higher voltage output than any SS preamp I have. Also, I’d like to hear what it sounds like. The Zout is 200R.
Any concerns?
Fun stuff ahead…
Of course his response was exactly the same As my adventures progress I'll post more here. I hope you will too. Looking forward to see what you come up with.
This is the current state of the poor thing...
thanks, i will try.
btw is it possible to have bigger output power by rising the voltage, maybe into 65v?
any bias adjustment needed? i'm aiming for 300W power output, with reasonable heat dissipating.
Not to jump in, but it might save the experts some duplicate typing....
How many output pairs?
65V Rails (unloaded) won't get you to 300W into 8R. You can get north of 200 though. You can do that math.
Check dissipation per device and how much current you'll want for your particular load. 220W (~60Vp) into 8R => 5A2
How many output pairs?
65V Rails (unloaded) won't get you to 300W into 8R. You can get north of 200 though. You can do that math.
Check dissipation per device and how much current you'll want for your particular load. 220W (~60Vp) into 8R => 5A2
@wengtech -
I chuckled a little reading your post. I sent a message directly to ZM asking essentially the same question two days ago. I should have posted here. I also wanted to experiment with other front ends (later) with the complementary output stage.
I was originally going to just 'mod' my BA-3 for use with a new power supply that I had built, but then I wanted to take it a little further. It broke my heart to disassemble it, but I think it will be 'better' when I get it how I want it. I still want to build the SE output stage.
For you and perhaps others, this is a selection of the notes.
I wanted to clean up (the amp) and use what I’d learned since I built it to have some fun. The first goal was to use it with my new ... PSU. I did some measurements with the previous PSU, which was essentially 2x First Watt type PSUs in dual mono. {snipped} I can do better.When I built it, I knew that the output stage was for all intents and purposes an “F-4” minus the buffer. I also know that some folks have built the “crippled” F4. So… BA-3 output stage is essentially a crippled F4.I don’t “need” voltage gain from my source to (most of my) speakers. Even with a passive pre-amp into an F4, I can play plenty loud with some speakers. Where I get the gain (pre or power or both) is still a fun balance, but I really don’t “need” gain.Can I … should I… Have the “BA3” front end as a separate ‘module’ from the Complimentary output stage + bias boards? The new PSU is ~32VDC loaded. So… probably on the edge for using the BA-3 input stage (don’t want to cook JFETs), but it should be fine with the complimentary output stage. I’ll just (reduce the bias).I’m thinking I could try the new 2022 FE with the output stage etc. There seem to be all sorts of wonderful combinations. Also, now that the PSU is a separate module from the other chunks, if (example) I wanted to run the 2022 FE at a higher voltage than the output stage, I could.Am I nuts?Why do I ask? B/C My tube pre-amp has higher gain => higher voltage output than any SS preamp I have. Also, I’d like to hear what it sounds like. The Zout is 200R.Any concerns?Fun stuff ahead…Of course his response was exactly the same
As my adventures progress I'll post more here. I hope you will too. Looking forward to see what you come up with.
This is the current state of the poor thing...
View attachment 1220295
btw that was a very brave decision to tear down what is already good
but that's the DIY guy, always never enough
Wait... How? My build and Wengtech's are likely different. I don't know about theirs, but if I were to increase my rail voltage to +- 65V with no other modifications, I'm pretty sure my amp wouldn't last too long and my heatsinks would be beyond Nelson's temp scale... like melting to the center of the earth...
Truly confused...
Oh... and since we have your attention, could you plonk these (and related) posts into the BA-3 amp thread if appropriate.
Truly confused...
Oh... and since we have your attention, could you plonk these (and related) posts into the BA-3 amp thread if appropriate.
Might want to check out the Class D folks for that kind of power.. 5W ~ 30W of Class A goodness is more along the lines of "reasonable" hardware around here. With proper speaks it's plenty loud and satisfying enough.i'm aiming for 300W power output, with reasonable heat dissipating.
60v peak / 1.414 = about 42V RMS ==> output power is 42^2 / 8 = 220 W RMSNot to jump in, but it might save the experts some duplicate typing....
How many output pairs?
65V Rails (unloaded) won't get you to 300W into 8R. You can get north of 200 though. You can do that math.
Check dissipation per device and how much current you'll want for your particular load. 220W (~60Vp) into 8R => 5A2
current is 42 / 8 = 5.25A RMS
dissipation for 6 deep is (5.25A / 6) x 60v = 52.5W per device x 12 devices = 630W per channel
is that correct? that is insanely HOT!!!
It seems impossible, although IRF240 Pd rating is 150W per device.
monoblock?
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I think you may have an extra sqrt(2) in there somewhere. If that's the case the dissipation per channel would be a bit lower (still quite high, in the 450W per channel range).
Perhaps just go for high bias A/B to keep the thermal more manageable, instead of full class A?
Perhaps just go for high bias A/B to keep the thermal more manageable, instead of full class A?
Mr. Pass' recommendation for building the Ba-3 as a preamplifier (or gain stage) is to use the following JFETs:
"BA3 Gain Stage: 6-8 mA (2SJ74 operated at 5 mA) / 8-11 mA (2SK170 at 10 mA)"
Does this mean that the 2SJ74 (matched) pair doesn't need to be matched with the 2SK170 (matched) pair?
And what repercussions would this have on the adjustment of P3?
As I don't have the tools to use P3 properly, would it be safer to simply use a quad of 2SJ74/2SK170 with matched IDSS?
"BA3 Gain Stage: 6-8 mA (2SJ74 operated at 5 mA) / 8-11 mA (2SK170 at 10 mA)"
Does this mean that the 2SJ74 (matched) pair doesn't need to be matched with the 2SK170 (matched) pair?
And what repercussions would this have on the adjustment of P3?
As I don't have the tools to use P3 properly, would it be safer to simply use a quad of 2SJ74/2SK170 with matched IDSS?