How about a Power Follower with an IPT?

[mtlin12]

I've built my DC adjustable Power Diamond Buffer Follwer announced at diyAudio about 6-month ago.



And last month I had a chance to have an A/B test wih my firend's DIY 300B & his ALTEC-604C high efficiency speaker.
His 300B is driven by 5687 and an interstage transformer.






Many of them were impressed of the Power Follower driven by an old MacIntosh C-20,
especially the very high & low Freq. vs his Full Music 300B.

But the gain is still a little bit not enough, the volume was almost at max..
My 10x s.s. pre-amp with the power followr , of course could not dirve
the 107dB speaker loud enough, because the listening seats were about 20 ft from the speakers!

One of my friend is interested of my design, and he is going to add an optional IPT (Input Tranformer)
about 10dB gain with my Power Fllower.

I think it is a good idea, what do you think about a Power Follower with an IPT ?

Power Follower's schematic PDF is at http://www.diyaudio.com/forums/attac...amp=1120105130,
but without standby circuit.

[Workhorse]

Hi MTLIN,

The Transformer should of good quality capable of reproducing the frequency of entire audio band.. and also it input/output impedance must be matched with source/Load respectively..to avoid any overloading...

K a n w a r

[Steve Eddy]

Originally posted by mtlin12
But the gain is still a little bit not enough, the volume was almost at max..

You say you didn't have enough game with the volume "almost at max..."

What if you turn it all the way up to the max?

[b]One of my friend is interested of my design, and he is going to add an optional IPT (Input Tranformer)
about 10dB gain with my Power Fllower.

I think it is a good idea, what do you think about a Power Follower with an IPT ?

I think it's a great idea.

Question. What's the output impedance of your solid state preamp?

se

[mtlin12]

Hi Workhorse,

I know nothing about how to design , make or measure an IPT,
so I have to count on my friend's sample maybe at nextweek.

Originally posted by Steve Eddy


You say you didn't have enough game with the volume "almost at max..."

What if you turn it all the way up to the max?




I think it's a great idea.

Question. What's the output impedance of your solid state preamp?

se

My step attenuator cannot set to the max. of input , its max is about -3dB.

The output impedance of my solid state preamp DB-01 is very low I think below 100 mOHM,
because it use a diamond buffer output with RE only 10 OHM and is NFB design.

[mefistofelez]

Steve Eddy wrote:

I think it's a great idea. [A follower with an input transformer]

Dear Steve,

I have two questions to you as a resident transformer expert:

1. How would one implement feedback?
2. How would one select the transformer?

Thank you,

M

[Steve Eddy]

Originally posted by mtlin12
My step attenuator cannot set to the max. of input , its max is about -3dB.

Oh. Well then, fix it.

The output impedance of my solid state preamp DB-01 is very low I think below 100 mOHM,
because it use a diamond buffer output with RE only 10 OHM and is NFB design.

Ok. That should be fine then.

I'd recommend using something like CineMag's 1:5 microphone input trnnie, the CMMI=5C.

se

[Steve Eddy]

Originally posted by mefistofelez
I have two questions to you as a resident transformer expert:

1. How would one implement feedback?

Not sure what you mean here. We're talking about an input transformer, not an output transformer. The output of the input transformer would just feed the input of the follower.

2. How would one select the transformer?

Depends on what you're wanting to achieve.

If you're just wanting to take advantage of a transformer's ground isolation and common-mode noise rejection, and don't need any voltage gain, then pick a nice 1:1 input trannie like a CineMag CMLI-15/15B.

If you need voltage gain, what I've been using have been various microphone input trannies which can be had in 1:2 to 1:10 ratios. Though keep in mind that the microphone trannies have been optimized for a 150 ohm source impedance and when loaded properly present a 1.5k ohm input impedance which can be too low for some source components.

Now, Mike LaFevre at MagneQuest has been working on producing some of the old Peerless line level designs (he owns the Peerless name and all their original engineering) and that's looking promising. SY has been doing some measurements on some prototype 15095 trannies (a 1:10 step-up) and so far they seem to work just fine directly driving drive a grid or gate and subsequently offering a much higher input impedance than 1.5k.

se

[mtlin12]

Originally posted by Steve Eddy


Oh. Well then, fix it.



Ok. That should be fine then.

I'd recommend using something like CineMag's 1:5 microphone input trnnie, the CMMI=5C.

se

The hand-made 24-step ladder type attenuator is quite difficult to be fixed,
but I'll try to short the max. level's input resistors.

Thank you for the information of microphone input trnnie, but it seems to be used in low input level,
how will its THD performance be in high voltage output ?

[Steve Eddy]

Originally posted by mtlin12
Thank you for the information of microphone input trnnie, but it seems to be used in low input level,
how will its THD performance be in high voltage output ?

Oops. Sorry. I've been talking about step-up transformers and buffers on two different threads as well as with someone in EMail and got situations mixed up.

In your situation, I'd use a 1:2 output transformer on the output of your preamp which would give you another 6dB of gain.

By the way, is there any way to get any more gain out of your preamp?

se

[SY]

Now, Mike LaFevre at MagneQuest has been working on producing some of the old Peerless line level designs (he owns the Peerless name and all their original engineering) and that's looking promising. SY has been doing some measurements on some prototype 15095 trannies (a 1:10 step-up) and so far they seem to work just fine directly driving drive a grid or gate and subsequently offering a much higher input impedance than 1.5k.

Into a typical high gain triode load of 100pF (input capacitance plus Miller), they were excellent, better than the original Peerless, and held up well even at 15V out.