Zero Feedback Impedance Amplifiers

[Susan-Parker]

Dear all,

Please note that at time of this posting all my personal domains have gone - for whatever reason I don't know (my accounts are paid btw).

I cannot receive any emails and my webpages are missing until this is resolved.

Woe and grief

Aagh,
Susan.

[Netlist]

Perhaps only a server downtime?

/Hugo

[Susan-Parker]

Hi Hugo,

Originally posted by Netlist
Perhaps only a server downtime?

/Hugo

... now back.

A bit of a fright

Thanks.

Best wishes,
Susan.

[darkmoebius]

Originally posted by Susan-Parker
A bit of a fright

The new additions to your website are great, especially the greater construction and parts descriptions

[Susan-Parker]

Hi darkmoebius,

I hope you are keeping well.

Originally posted by darkmoebius
The new additions to your website are great, especially the greater construction and parts descriptions

Thanks.

I don't know what happend, but all is now working again.

I will be putting up more detail construction info, pics and better schematics etc. for the amplifiers during the next 7 to 10 days.

Best wishes,
Susan.

P.S.

I now have a 16 million point FFT software update to try out (previously it was only 1 million points). Guess who is a happy person

[Dartagnan]

Hello Susan,

I'm very interested in putting together a Zeus, and I'm curious whether some pieces I have lying around could be pressed into service.

For output transformers, I'm wondering about some Tannoy THD 60 transformers I have that come from CMS8 ceiling units for stepping down 100V signals. They claim to handle 180W program, and they have input taps for 7.5W, 15W, 30W, 60W, and 120W. I imagine these are multiple taps on a single winding.

If impedance equals voltage squared over power, I believe this translates to impedances of 1333, 666, 333, 166.5, and 83.25 ohms.

Do these appear to work, and which impedance would be best? Or would it depend more on the primary inductance, (which I don't really know how to measure)? I recognize they're not quad-filar wound, but might they still pass respectable bandwidth, intended as they are for audio?

Thanks,

Dart

[EWorkshop1708]

I got some old car speakers with little impedance amps built on to the magnet assy. 2 of these speakers. One speaker was messed up, but I kept the amplifiers.

60W @ 4ohms was their rating.

The output transformers on these have no secondary, but instead the speaker is connected across the whole primary, while 2 NPN darlingtons drive the two halves of the transformer.

The peak output voltage is double the supply voltage (13.8V)

They are VERY loud. Even off of a 6V lantern battery, they played loud.

I'm going to take the two amps I have and build them on to a new PCB, and make a simple stereo amplifier.

[Susan-Parker]

Hi Dartagnan,

Thank you for your post and interest.

Originally posted by Dartagnan
Hello Susan,

I'm very interested in putting together a Zeus, and I'm curious whether some pieces I have lying around could be pressed into service.

For output transformers, I'm wondering about some Tannoy THD 60 transformers I have that come from CMS8 ceiling units for stepping down 100V signals. They claim to handle 180W program, and they have input taps for 7.5W, 15W, 30W, 60W, and 120W. I imagine these are multiple taps on a single winding.

If impedance equals voltage squared over power, I believe this translates to impedances of 1333, 666, 333, 166.5, and 83.25 ohms.

Do these appear to work, and which impedance would be best? Or would it depend more on the primary inductance, (which I don't really know how to measure)? I recognize they're not quad-filar wound, but might they still pass respectable bandwidth, intended as they are for audio?

Thanks,

Dart

If you can email me with more specs etc I will have a ponder and get back to you (may take a couple of days).

I have tried these myself originally but they generally don't have symetrical windings.

You could however try running using just the speaker side windings on a pair of transformers - effectivly bridged single ended.

Has been seen to work - can't remember the post number but if you look through this thread there is a schematic.

Can you rewind the transformers? Probably your best bet. Tedious if it's all welded together but not any more than winding a toroid.

Otherwise the mains torroid low voltage inding pair seems to be a good starting point for the output, and has adequate bandwidth, without incuring large costs.

Note the distortion figures though - compare the Zeus 2:1 and 4:1 ratios.

Hope this helps.

Best wishes,
Susan.

[Workhorse]

Hi Susan-Parker MIEE

The amp is now under serious testing condition as follows.

Input Signal 100Hz sinewave
Load 2 Ohms heater element
duration 6Hours Continous testing.

Input Stage Consists of:

Dual Differential input Line Driver Balanced with V swing at 15 Volts

regards
Workhorse Technologies

[Dartagnan]

Thanks for the replay, Susan.

Unfortunately, I can find no more specs on the THD 60 in Tannoy's literature. Yes, the laminations are welded and would require substantial grinding to seperate.

What made me think these transformers might be usable in a Zeus was that the wattage taps seemed to indicate they would lend themselves to split primaries. For example, using the common tap as the negative and the 60W tap as the positive, grounding the 120W tap would yield two 83-ohm primaries. Lower wattage taps would yield higher impedances.

But you have experimented with these transformers already? When you say they generally don't have symmetrical windings, do you mean for example that the 120W tap doesn't have exactly half the turns of the 60W tap?

Sorry about the basic questions, but I don't have means of testing (or much know-how, really. )

Thanks,

Dart