Yes, understand - at four transformers per channel it does add up.
I have a full 5.1 setup, but only the stereo LR channels have a stepped attenuator - all the other just a fixed 1:2 input step-up.
If your source is digital, then one doesn't need the attenuators, otherwise it looks like the only option is the SILK STA-522A Transformer Volume Attenuator, or a stepped inductor, if you use depletion mosfets they are ground referenced. I prefer transformers as I like my system to be galvanically isolated.
I am working on a stepped-attenuator design myself in the background - but nothing finalized yet; it will be expensive since it uses Amorphous cut c-cores.
As to the EI-120 x 2" transformers, the input-stage SE line-driver can be simply quad-filar 0.8mm wound to nicely fill the bobbin. The output transformer does need the dual chamber bobbin, quad-filar 1.0mm wire. Perfect winding with nice flat layers is nice, preferred, but not absolutely essential.
Hope this helps.
The source is going to be a minidsp flex, I'm going to be doing some cheating with the crossover. That is also why I need 4 channels.
Are you using a turntable as source?
Yes, it does.
Are you using a turntable as source?
Yes, it does.
There is a transformer manufacturer local to me who tells me he can make the transformers at a more palatable price. PM me if this is of interest to you.
Hi,
Yes, I have a turntable for vinyl - and just for an easy life (not!) I designed my own pickup cartridge which uses a Jico SAS MM stylus.
🙂
Choke input supplies are much quieter but almost unheard of outside niche valve use. I had / have plans to try one on the JLH 69 but life keeps getting in the way.
Hope everyone is keeping well.
I was able to spend time during the recent Christmas holidays to build a new pair of monobloc power amps.
Heatsinks are 400 x 300 x 85mm, wall-boxes are 300 x 250 x 150mm. The aluminium handles (very necessary) and feet are made from stuff I had to hand.
Chassis work is completed, still have to wire them up.
Each amp weights 20kg!
🙂
I was able to spend time during the recent Christmas holidays to build a new pair of monobloc power amps.
Heatsinks are 400 x 300 x 85mm, wall-boxes are 300 x 250 x 150mm. The aluminium handles (very necessary) and feet are made from stuff I had to hand.
Chassis work is completed, still have to wire them up.
Each amp weights 20kg!
🙂
Beautiful job Susan!
With heat sinks that large are you still running 75 watts in 2:1?
Mine weigh about 40 lbs each / 18 Kg also.
I find myself forever changing between 2:1 and 4:1 on the output transformer's configuration and then back again. The bass on my system is a tad loose at 2:1 and very tight at 4:1; but 4:1 leaving not much power / headroom to spare. I wish there were a 3:1 option for the output transformer. But a 3:1 option would require a hexa-filar wound transformer I'm guessing. I can think of no other way but the primaries wound in push-pull series as
as follows.
Taking a guess I'd say the output impedance would drop to about 0.6 Ω .
This could be a happy medium between 0.25 Ω and 1 Ω for 4:1 and 2:1 respectively.
This would be more Z than McIntosh amplifiers which are about 0.35 Ω but still amazing for what it is.
With heat sinks that large are you still running 75 watts in 2:1?
Mine weigh about 40 lbs each / 18 Kg also.
I find myself forever changing between 2:1 and 4:1 on the output transformer's configuration and then back again. The bass on my system is a tad loose at 2:1 and very tight at 4:1; but 4:1 leaving not much power / headroom to spare. I wish there were a 3:1 option for the output transformer. But a 3:1 option would require a hexa-filar wound transformer I'm guessing. I can think of no other way but the primaries wound in push-pull series as
- [MOSFET1 SOURCE POSITIVE] W1-W2-W3 [GND] W4-W5-W6 [MOSFET2 SOURCE NEGATIVE]
- with secondary wound as two groups in parallel as
- [OUTPUT POSITIVE] W7 | W8 | W9 [CONNECTION] W10 | W11 | W12 [OUTPUT NEGATIVE]
Taking a guess I'd say the output impedance would drop to about 0.6 Ω .
This could be a happy medium between 0.25 Ω and 1 Ω for 4:1 and 2:1 respectively.
This would be more Z than McIntosh amplifiers which are about 0.35 Ω but still amazing for what it is.
I wish this was adaptable for car audio use but I guess it's probably impossible 😕
Susan, you never seize to amaze.
Going from 5.1 to 7.1 or are these for outdoor use? 😉
Wishing you all the best in 2025.
Having owned similar amps (Be Yamamura, RIP) using VERY expensive bespoke transformers I know that these amps of yours will
sound exceptional....and from what I have gleaned from your posts will be very reliable. Mine were not.
Have a great year.
sound exceptional....and from what I have gleaned from your posts will be very reliable. Mine were not.
Have a great year.
20 years later and this design just looks better than ever.
Thanks 🙂
I run 4:1 for all my amps.
These are going to run at 48V DC, so the new amps will be idling at circa 100 Watts each.
The current amps with 200mm tall heatsinks run at 60W, and they get up to around +50°C (although they aren't black anodized).
To test run 3:1 one could always move one set of the quad-filar windings from the secondaries to the primaries.
Thanks 🙂
The wall-box, heatsink, and other connector parts were purchased at the beginning of 2009, so it's taken a while to get going with this project!
I am building a new stereo system, which will be able to be taken out to demo.
Although I have done so a couple of times in the past, the current system is in daily use from 9 am to 11 pm; so I don't want to take it away.
I am separately building a couple of extra channels for 7.1 with a straight line driver etc, but this has priority.
Best 2025 wishes 🙂