I am not there yet. Can only work some days in the weekend and a very few evenings during the week.
Will post pictures as the work progresses 🙂
I liked M2X very much. Then I got the VFET kit amp and I got interested in SITs. After that I built Lazy Singing Busch with the THF-51s.
I think I would still like M2X today. But Lazy Singing Bush will be hard to beat......even for a F8 🙂 .....we will see......but I like that it has some gain. Then I can go directly from DAC to F8 if DAC is put into preamp mode. In the future maybe DAC in fixed output mode and then Pumpkin-Iron set to 0 dB?
15 dB of gain is more than enough. Don't know if Pumpkin + F8 is a good thing? .....don't know either if Pumpkin is spelled correct......
Will post pictures as the work progresses 🙂
I liked M2X very much. Then I got the VFET kit amp and I got interested in SITs. After that I built Lazy Singing Busch with the THF-51s.
I think I would still like M2X today. But Lazy Singing Bush will be hard to beat......even for a F8 🙂 .....we will see......but I like that it has some gain. Then I can go directly from DAC to F8 if DAC is put into preamp mode. In the future maybe DAC in fixed output mode and then Pumpkin-Iron set to 0 dB?
15 dB of gain is more than enough. Don't know if Pumpkin + F8 is a good thing? .....don't know either if Pumpkin is spelled correct......
as long you think of right one, spell it as you want
anyhow, for any amp which is happy enough with preamp of gain adjusted by choice in range of 0db to +8db, Iron Pumpkin is right thing
Now that we talk a bit of Pumpkin pre.....
If I build Pumpkin BAL pre and use BAL out from DAC or P3 can I get 8dB of gain on SE-out from pre?
E.g. DAC has 2.1vpp on SE and 4.2vpp on BAL out. What I am after is if I can get 8 dB from 4.2vpp. Could be useful if I use a follower amp after Pumpkin.
Iron Pre has some gain limitations regarding this......but works very well in SE mode and 12 dB settings. Then 4.2vpp + 8dB will be about the same.
If I build Pumpkin BAL pre and use BAL out from DAC or P3 can I get 8dB of gain on SE-out from pre?
E.g. DAC has 2.1vpp on SE and 4.2vpp on BAL out. What I am after is if I can get 8 dB from 4.2vpp. Could be useful if I use a follower amp after Pumpkin.
Iron Pre has some gain limitations regarding this......but works very well in SE mode and 12 dB settings. Then 4.2vpp + 8dB will be about the same.
As written before - Iron Pumpkin is settable (jumpers on AVC module) as 0db, +2db, +4db, +6db, +8db of gain; applicable for both SE and Bal
speaking of Bal, inputs configurable either as SE or Bal, output Bal and SE (simply tapped from Bal, using pos. phase and GND)
so, take +6db setting as easy to calc
though , today's "standards" are sorta clear regarding SE signal (2Vrms is common) while not so regarding Bal signal; let's just take same value ..... 2Vrms, even if it's usually more; just for giggles, let's also count with 3V5rms and 4Vrms
feed 2Vrms SE signal in, you get 4Vrms at SE output and 8Vrms at Bal output
feed 2Vrms Bal signal in, you get 2Vrms at SE output and 4Vrms at Bal output
feed 3V5rms Bal signal in, you get 3V5Vrms at SE output and 7Vrms at Bal output
feed 4Vrms Bal signal in, you get 4Vrms at SE output and 8Vrms at Bal output
caveat = case for avoiding (when single, positive phase buffer doing tremendous work of driving both phases of AVC) using SE Input and BAL Out and gain set to +8db; everything fine with SE In -SE Out and Bal In - Bal Out
there is no free (sonic) lunch, but - as it is - there is already so much of same in Iron Pumpkin; it started solely as bespoke attenuator, then I got to everything else in package as whyDFno??
now, if someone is keen/desperate for more gain, Iron Pumpkin is hard to beat as selector + volume controller (set to 0db), then followed with separate HiGain stage of choice
due to nature of things, there is no even possibility to think of implementing proper HiGain stage in same case with Iron Pumpkin; proper means stage itself, necessary rail regs, Donuts ..... and all of that means space ......
speaking of Bal, inputs configurable either as SE or Bal, output Bal and SE (simply tapped from Bal, using pos. phase and GND)
so, take +6db setting as easy to calc
though , today's "standards" are sorta clear regarding SE signal (2Vrms is common) while not so regarding Bal signal; let's just take same value ..... 2Vrms, even if it's usually more; just for giggles, let's also count with 3V5rms and 4Vrms
feed 2Vrms SE signal in, you get 4Vrms at SE output and 8Vrms at Bal output
feed 2Vrms Bal signal in, you get 2Vrms at SE output and 4Vrms at Bal output
feed 3V5rms Bal signal in, you get 3V5Vrms at SE output and 7Vrms at Bal output
feed 4Vrms Bal signal in, you get 4Vrms at SE output and 8Vrms at Bal output
caveat = case for avoiding (when single, positive phase buffer doing tremendous work of driving both phases of AVC) using SE Input and BAL Out and gain set to +8db; everything fine with SE In -SE Out and Bal In - Bal Out
there is no free (sonic) lunch, but - as it is - there is already so much of same in Iron Pumpkin; it started solely as bespoke attenuator, then I got to everything else in package as whyDFno??
now, if someone is keen/desperate for more gain, Iron Pumpkin is hard to beat as selector + volume controller (set to 0db), then followed with separate HiGain stage of choice
due to nature of things, there is no even possibility to think of implementing proper HiGain stage in same case with Iron Pumpkin; proper means stage itself, necessary rail regs, Donuts ..... and all of that means space ......
A little bit of progress. M1 and M2 not soldered yet.
For speaker return I will probably use the solder terminal at the board (instead of at caps). Will probably not make much of a difference. The distances are very shot. A short trimmer for the Bourns is necessary. Will se if I can find something non-conducting that can work. But we are not there yet.
I will not cut the M1/M2 legs short as usual but have something I can clamp a wire for a DMM.
For speaker return I will probably use the solder terminal at the board (instead of at caps). Will probably not make much of a difference. The distances are very shot. A short trimmer for the Bourns is necessary. Will se if I can find something non-conducting that can work. But we are not there yet.
I will not cut the M1/M2 legs short as usual but have something I can clamp a wire for a DMM.
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Aleksandar
You said
"now, if someone is keen/desperate for more gain, Iron Pumpkin is hard to beat as selector + volume controller (set to 0db), then followed with separate HiGain stage of choice"
Any particular high gain stage in mind? 😊
You said
"now, if someone is keen/desperate for more gain, Iron Pumpkin is hard to beat as selector + volume controller (set to 0db), then followed with separate HiGain stage of choice"
Any particular high gain stage in mind? 😊
For my set-up 6dB Pumpkin with your amps is perfect - only exception is the MoFo - do have 12db Onetics unit to use but maybe an active stage would be interesting - II'll add to the list
In principle one channel is now read for first initial test. Speaker return wire and input wires will be installed if initial test passes.
I will try to make a trimmer for the Bourns pots. It needs to be a small one. After that I plan to power it up slowly using my vario-trafo.
To secure the two power transistors I added extra small shims and split washers......just to have a little more confidence.
I also tested that isolation pads works. For that I always use DMM set to highest ohm setting (e.g. 20M) and not the "bip-setting".
At 20M setting the DMM is more sensitive and it should display "Infinity".
I will try to make a trimmer for the Bourns pots. It needs to be a small one. After that I plan to power it up slowly using my vario-trafo.
To secure the two power transistors I added extra small shims and split washers......just to have a little more confidence.
I also tested that isolation pads works. For that I always use DMM set to highest ohm setting (e.g. 20M) and not the "bip-setting".
At 20M setting the DMM is more sensitive and it should display "Infinity".
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Meper,
You NEED goop between the ceramic insulator pads and OS devices and heatsink.
Without the thermal compound the device will not cool efficiently and can be damaged.
You NEED goop between the ceramic insulator pads and OS devices and heatsink.
Without the thermal compound the device will not cool efficiently and can be damaged.
Watch out with those keratherm pads, do not put too much torque on them or they can fail.
I had this problem with TO220 and keratherm, the sharp metal edges of the TO220 cut through the keratherm and made contact with the heatsink.
I much prefer the ceramic/alumina pads, better performance and reliability.
I had this problem with TO220 and keratherm, the sharp metal edges of the TO220 cut through the keratherm and made contact with the heatsink.
I much prefer the ceramic/alumina pads, better performance and reliability.
So far I have not had any problems with the Keratherm pads. I have used them for many builds. I selected them only because they were recommended in this forum and DIY Store sold them. I hope it will work for this project also. I have used limited torque. I checked for sharp edges also.
I powered up one channel and made a rough adjustment of offset and bias.
Left DMM is offset (24 mV) and the other is bias (voltage over 1R || 1R5 = 0R6). So 1.1V is a bit more than 1.8A.
Rails are approx. +-24 VDC. Should I settle for 1.1V or can I go for 1.2V if possible?
Next time I power up without vario-trafo as I did not see any smoke or bad smells of something getting very hot.
The goal for offset is just to be below 50 mV?
Probably less than 30 mV is possible. Maybe less than 10 mV.
Left DMM is offset (24 mV) and the other is bias (voltage over 1R || 1R5 = 0R6). So 1.1V is a bit more than 1.8A.
Rails are approx. +-24 VDC. Should I settle for 1.1V or can I go for 1.2V if possible?
Next time I power up without vario-trafo as I did not see any smoke or bad smells of something getting very hot.
The goal for offset is just to be below 50 mV?
Probably less than 30 mV is possible. Maybe less than 10 mV.
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1A8 is nice figure, do not insist on more, IRFP150 is a beast, but still caged in TO247, so think of dissipation; SSouth is in same case, but much sturdier, heat-wise
DC Offset - 50mV is same good as 30mV as 10mV; shoot that in temperature equilibrium
power them both (channels) and listen; and then cry, because you were Babelfish-F8-less for all these years
DC Offset - 50mV is same good as 30mV as 10mV; shoot that in temperature equilibrium
power them both (channels) and listen; and then cry, because you were Babelfish-F8-less for all these years