Zero Feedback Impedance Amplifiers

[Susan-Parker]

Hi P-A

Originally posted by peranders
Very neat. A tubeless tube amp!

Thanks.

Partly because of the design constraints like having a big heatsink and needing to protect the input transformer from external fields...

And as the heart of the amplifier is it's output transformer it seems nice to promote it visually.

The handles are very useful.

I also wanted to keep the overall size small in footprint as each monoblock is meant to live next to the speaker it is driving.

Best wishes,
Susan.

[Netlist]

My neighbor’s boy who is now 16 looked over my shoulder and asked me if I could assemble this beauty for him.
He's playing Bass guitar and thought this would really impress his friends musicians. Such a cool amp behind him on top of his father's old Kustom III Bass.
I told him it was for violins, not for bass

/Hugo

[Upupa Epops]

Dear Susan, on all yout measuring I only see results by low or middel levels, which says nothinh abot real listenig quality of amp, mainly if they are made with some " weak " music. Try it make with symphony orchestra and high level, this is real arbiter of quality. Pavel

[Susan-Parker]

Hi Hugo,

Originally posted by Netlist
My neighbor’s boy who is now 16 looked over my shoulder and asked me if I could assemble this beauty for him.
He's playing Bass guitar and thought this would really impress his friends musicians. Such a cool amp behind him on top of his father's old Kustom III Bass.
I told him it was for violins, not for bass

/Hugo

You might sling together a 2 stage toroid version and see if he likes the sound with his guitar?

For a Bass he doesn't need more than 20 kHz or so bandwidth at the top end as I doubt that the speakers go up that far.

The 15" drivers could be wired in series for 16 ohms, which should work nicely across the swinging inductor of the output toroid for low distortion (that should come from the guitar if desired, not the amp). Those drivers are probably quite sensitive.

The sound could be quite impressive

Best wishes,
Susan.

[Susan-Parker]

Hi Pavel,

Originally posted by Upupa Epops
Dear Susan, on all yout measuring I only see results by low or middel levels, which says nothinh abot real listenig quality of amp, mainly if they are made with some " weak " music. Try it make with symphony orchestra and high level, this is real arbiter of quality. Pavel

Low to middle levels i.e. 1 to 12 watts are what I listen to. I can't drive the speakers any louder as I would damage my hearing.

As Mike can attest, 12 or so watts is VERY loud (The Matrix, lobby scene) in my living room.

What one also realizes when listening to this scene is how compressd the film sound really is. I have fired a hand gun (Kimber 45 ACP) and a sub-machine gun (H&K MP5 9mm) at a club (in Dallas) and even with hearing protection they are LOUD.

Also I do my testing in the bedroom/office where I am only running (at the moment) a single amp, usually in bits on the test bench.

Finally I only have a CD source (SACD planned) and playing loud classical music where the average data rate can drop down to 12 bits resolution, isn't really a good test of the amp. ..

... although saying that what one does hear is what is missing.

Hence my preference for recordings that are less dynamic in range as they maintain a higher data resolution.

The amp will drive up to the supply rail quite happily, so max power is max usable power.

Best wishes,
Susan.

[Netlist]

Originally posted by Susan-Parker

You might sling together a 2 stage toroid version and see if he likes the sound with his guitar?

Well, this would be a good opportunity to finally tackle this amp.
If he collects the money I'll build.

/Hugo

[mikelm]

Could Susan or someone explain to me in laymans language why it is that a SMALL toroid tranny is recommended for the i/p gain stage for the initial trial version of the amp. Why not a BIG one

Because my transformer volume control has a voltage gain of 2 a 120V+120V : 25V+25V would be OK in my system.

What is it about a 25VA one that would be better than a 120VA one.

I would have thought that the bigger core would allow less windings - less capacitance - lower resistance.

Could you please explain

many thanks

mike

[Workhorse]

Originally posted by Susan-Parker
Hi Pavel,



Low to middle levels i.e. 1 to 12 watts are what I listen to. I can't drive the speakers any louder as I would damage my hearing.

As Mike can attest, 12 or so watts is VERY loud (The Matrix, lobby scene) in my living room.

What one also realizes when listening to this scene is how compressd the film sound really is. I have fired a hand gun (Kimber 45 ACP) and a sub-machine gun (H&K MP5 9mm) at a club (in Dallas) and even with hearing protection they are LOUD.

Also I do my testing in the bedroom/office where I am only running (at the moment) a single amp, usually in bits on the test bench.

Finally I only have a CD source (SACD planned) and playing loud classical music where the average data rate can drop down to 12 bits resolution, isn't really a good test of the amp. ..

... although saying that what one does hear is what is missing.

Hence my preference for recordings that are less dynamic in range as they maintain a higher data resolution.

The amp will drive up to the supply rail quite happily, so max power is max usable power.

Best wishes,
Susan.

Hi SUSAN-PARKER MIEE,

Could you imagine what will happen to us when we listen to our 1800Wrms amp, i think it wouldl damage our ears, but they are still intact.
besides this We have completed our version of your amp and will post the photos soon.

regards,
kanwar

[analog_sa]

Hence my preference for recordings that are less dynamic in range as they maintain a higher data resolution.

Wow, this really sums up cd sound very well.

[Susan-Parker]

Hi Mike,

Originally posted by mikelm
Could Susan or someone explain to me in laymans language why it is that a SMALL toroid tranny is recommended for the i/p gain stage for the initial trial version of the amp. Why not a BIG one

Because my transformer volume control has a voltage gain of 2 a 120V+120V : 25V+25V would be OK in my system.

What is it about a 25VA one that would be better than a 120VA one.

I would have thought that the bigger core would allow less windings - less capacitance - lower resistance.

Could you please explain

many thanks

mike

Well, a smaller transformer is less expensive and would of course be easier to drive... being smaller... wouldn't it???

The 15 VA toroid did run up a little higher than the 30 VA but as the later was 20 years or older and a different spec not easy to really tell as the difference was small.

A quick test using a OP275 dual opamp balanced drive, and a 120K Rterm across the 230 output (plus a scope probe):

Test was maximum frequency for a given output voltage before distortion was visibly apparent or the output had dropped by -3dB.

15VA toroid 115+115 : 2 x 12
=============================
Drive across both 12 volt windings - i.e. 24:230 step up.
111 mH across both windings, 230 pF Pri to Sec.

4 Vac (11.7 Vpp) 20 Hz to 27 kHz
7 Vac (20 Vpp) 20 Hz to 25 kHz
12 Vac (35 Vpp) 20 Hz to 10 kHz
22 Vac (60 Vpp) 20 Hz to 5 kHz


217 VA toroid 115+115 : 2 x 31 @ 3.5A
=====================================
Drive to one 31 volt winding - i.e. 31:230 step up.
98 mH per 31 V winding, 727 pF Pri to Sec.

4 Vac (11.7 Vpp) 20 Hz to 65 kHz
5 Vac (16 Vpp) 20 Hz to 50 kHz
14 Vac (40 Vpp) 20 Hz to 17 kHz
28 Vac (80 Vpp) 20 Hz to 8 kHz
56 Vac (160 Vpp) 20 Hz to 2 kHz


Um, interesting.

I am not sure how well the transformer volume control will do though.

Best wishes,
Susan.