All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble

[gk7]

Had a look at the files from the link you posted and could not find any simulations of IMD for the F5, only THD.
And the distortion spectra from the F5 simulation dont look like those NP measured with an AP.

[wahab]

Originally Posted by gk7

Had a look at the files from the link you posted and could not find any simulations of IMD for the F5, only THD.
And the distortion spectra from the F5 simulation dont look like those NP measured with an AP.

Amps that have high THD will have high IMD as well...

The Nelson Pass THD measurements you re talking about
are made at 1W RMS output power....

[gk7]

At least they are measurements. Estimating IMD from a THD simulation that does not match
reality makes no sense to me.

[wahab]

Originally Posted by gk7

At least they are measurements. Estimating IMD from a THD simulation that does not match
reality makes no sense to me.

What is senseless is that you dont understand that i simulated THD
at about 6W RMS while nelson pass did measurements at 1W
(for an amp that basically dissipate 100W/channel..)....

Anyway i also simulated IMD ratios for this amp and they are quite high.

Of course , i dont simulate at 1W level , as as such low levels almost
any amp will appear as good enough and Nelson Pass knows it...

[gk7]

Originally Posted by wahab

What is senseless is that you dont understand...

wahab, please refrain from telling me what I understand and what not, OK ?
I have yet to see if real world measurements match your simulations.

[gaborbela]

Originally Posted by wahab

There s a little mistake on the final schematic post 99.

R10 and R12 are marked 100K while they should be 33K each.

I re edited the schematic with the correct values.

Hello wahab

Thank you, I did corrected!
I have some question about the following capacitors.
C9 & C10 is 1 000uF?
C7 & C8 is 10 000uF? I need to know because the size of the capacitor on the layout.
Do the amplifier can be fully driven from a CD player or will need a preamp?
Please let me know
Thank you very much!

Greetings Gabor

[wahab]

Originally Posted by gk7

wahab, please refrain from telling me what I understand and what not, OK ?
I have yet to see if real world measurements match your simulations.

Although the measurements say that it has about 0.1% THD
at 1Khz /20W (not good enough for CD standard) Nelson Pass
specifies it at 1% THD/25W....

http://sportsbil.com/other/NELSON%20...WATT%20AMP.pdf

Besides , this amp has low gain as he used as much as possible
of it to increase NFB resulting in a meager 15dB voltage gain.

Reducing the gain of the amp discussed in this thread ( wich
is about 30dB) to the same value , would reduce its distorsions by 15dB ,
i let you imagine what would the difference become compared with the F5
in the graph above...

[wahab]

Originally Posted by gaborbela

I have some question about the following capacitors.
C9 & C10 is 1 000uF?

Yes , they can be mounted in a separate PCB but in this case put a pair
of 220uF on the amp PCB for wires decoupling.

Originally Posted by gaborbela

C7 & C8 is 10 000uF? I need to know because the size of the capacitor on the layout.

This is in fact the power supply minimal caps , on the amp PCB 220uF are enough.

Originally Posted by gaborbela

Do the amplifier can be fully driven from a CD player or will need a preamp?

It has a gain of 30 so it can be driven by almost any CD player ,
if necessary the gain can be increased without substancialy altering
the global perfs just by swapping the relevant resistance , R13
in the schematic below.


On another note , hope that your artwork is still in the doing
as it would be valuable to slightly mod the differential and VAS
current sources voltage references in a way that at powering on
the input stage and upper side of the VAS become functionnal
before the VAS current source start to conduct.

This way , the negative feedback will be available micro seconds
or so after the amp is powered on and any eventual pop will be
suppressed or at least reduced to a meaningless amplitude.

Also , it appeared that one of the 33pF compensation capacitor
of the VAS was simply useless , it can be suppressed.

For the remaining 33pF compensation capacitor , it must be connected
with a distance as short as possible from the base of Q6 to Q8 collector.
Also , the track joining Q6 collector to Q8 emitter must be short as well.

On the components side , the transistors used are among the most adequate
for the intended purpose but if they are either too expensive or too difficult
to find there are other models that can be used , just let me know about it
and i ll provide a list of valuable replacements.

I put the updated schematic below , sorry for the late mods, but happily
it is the last ones.

[dadod]

Originally Posted by wahab

Yes , they can be mounted in a separate PCB but in this case put a pair
of 220uF on the amp PCB for wires decoupling.



This is in fact the power supply minimal caps , on the amp PCB 220uF are enough.



It has a gain of 30 so it can be driven by almost any CD player ,
if necessary the gain can be increased without substancialy altering
the global perfs just by swapping the relevant resistance , R13
in the schematic below.


On another note , hope that your artwork is still in the doing
as it would be valuable to slightly mod the differential and VAS
current sources voltage references in a way that at powering on
the input stage and upper side of the VAS become functionnal
before the VAS current source start to conduct.

This way , the negative feedback will be available micro seconds
or so after the amp is powered on and any eventual pop will be
suppressed or at least reduced to a meaningless amplitude.

Also , it appeared that one of the 33pF compensation capacitor
of the VAS was simply useless , it can be suppressed.

For the remaining 33pF compensation capacitor , it must be connected
with a distance as short as possible from the base of Q6 to Q8 collector.
Also , the track joining Q6 collector to Q8 emitter must be short as well.

On the components side , the transistors used are among the most adequate
for the intended purpose but if they are either too expensive or too difficult
to find there are other models that can be used , just let me know about it
and i ll provide a list of valuable replacements.

I put the updated schematic below , sorry for the late mods, but happily
it is the last ones.

You can do some more improvements.
1. increment LTP tail current as jfet vorks bettter close to the Idss.
2. use floating cascode for the LTP, look at attachment.
3. Use Hawksford enhaced cascode for VAS.
4. You do not need to have the same impedance at the jfet LTP input and FB, you can use much smaller resistor for the FB and could do without capacitor.
dado

[homemodder]

This is interesting, first many claim that simulations results make THD look better than possible real world results.

GK7 youre claiming it makes a good amp look bad.

Btw Wahab is correct, High THD means high IMD. F5 doesnt have low distortion figures but tube amps have even higher and are loved by many although it doesnt mean that they reproduce sound accuratly. Many prefer music with sound effects which is what these high distortion amps do, including F5.

F5 is probably the worst amp I ever played through my BW 804s, even a secondhand 30 euro cheapie rotel sounds better especially with regards to bass. It is not everyones cup of coffee nor does it match many types of speakers.