-Drive two mono power amplifiers from a single ended signal, divided in one true mode for the first amp channel and the other inverted for the second, then they are called bridged amps.
-If you drive them with a balanced preamp output, then you have balanced bridged.
-What remains is a fully balanced power amplifier, what also differs between the three amigos is the grounding arrangement.
All three have the load between two opposite phases, while the load sees +/-40V across it the outputs of the individual power amps are at +/-20V.
On the other hand, each power amp output sees only half of the load.
Fait a compli, twice the voltage and twice the current, and the preamp still only has to deliver the peak voltage a single channel needs.
Which remains +/-20V continuous.
-If you drive them with a balanced preamp output, then you have balanced bridged.
-What remains is a fully balanced power amplifier, what also differs between the three amigos is the grounding arrangement.
All three have the load between two opposite phases, while the load sees +/-40V across it the outputs of the individual power amps are at +/-20V.
On the other hand, each power amp output sees only half of the load.
Fait a compli, twice the voltage and twice the current, and the preamp still only has to deliver the peak voltage a single channel needs.
Which remains +/-20V continuous.
I need a bit you r ideas to get rid of a hum-bug in one of my F4s...
As written before, I habe build two F4 and use them in mono-mode. One of them is humming like hell, but not out of the amplifier / loudspeaker, it is more like a mechaniscal hum from the transformer itself. It is not subtile, you can hear it in 5m distance very well.
I build the second unit in the same way, and it is quiet. So, the theory of DC in my AC-Power can't be applied here...they have the same AC.
So, I thought: Well the Transfomer is a faulty unit...I went back to one of Germany's best transfomer-producers who works as well for Burmester and other High-End-Companies and ordered a special-Audio-Version which is hum-free, potted but as well designed to be "softer" ( I beleive more inductance) produced, so optimized not to hum and not optimized on total efficiency, which is as well the trick with the Thel.de units, which normally never hum.
Ok, I just exchanged the Transformers and guess what: It hums as well.
Soooooo....I guess something is giving the transformer a very hard time. Could this be a faulty rectifier diode ? Any ideas what to test /exchange ?
As written before, I habe build two F4 and use them in mono-mode. One of them is humming like hell, but not out of the amplifier / loudspeaker, it is more like a mechaniscal hum from the transformer itself. It is not subtile, you can hear it in 5m distance very well.
I build the second unit in the same way, and it is quiet. So, the theory of DC in my AC-Power can't be applied here...they have the same AC.
So, I thought: Well the Transfomer is a faulty unit...I went back to one of Germany's best transfomer-producers who works as well for Burmester and other High-End-Companies and ordered a special-Audio-Version which is hum-free, potted but as well designed to be "softer" ( I beleive more inductance) produced, so optimized not to hum and not optimized on total efficiency, which is as well the trick with the Thel.de units, which normally never hum.
Ok, I just exchanged the Transformers and guess what: It hums as well.
Soooooo....I guess something is giving the transformer a very hard time. Could this be a faulty rectifier diode ? Any ideas what to test /exchange ?
That's a possibility. Perhaps you want to measure the
current that it's drawing and compare that with the other,
or even exchange transformers.
current that it's drawing and compare that with the other,
or even exchange transformers.
My simplistic trouble-shooting logic would be to exchange transformers as a first step.
Does the trouble follow the transformer?
Divide and conquer should be the trouble-shooters motto.
7/10
Does the trouble follow the transformer?
Divide and conquer should be the trouble-shooters motto.
7/10
as Papa said- after xformer , first suspicious things are diodes and caps ..... if amp is otherwise functional ;
next thing ( I remember few years ago thread where we go through much troubles , to realize what was culpriy for hum and xformer overheating ) is to check that you didn't make any mechanical short circuit in/on xformer ?
if you aren't careful - it's easy to make short winding through toroid , with bolting/fixing hardware .
been there ....... when I was slightly younger ...
next thing ( I remember few years ago thread where we go through much troubles , to realize what was culpriy for hum and xformer overheating ) is to check that you didn't make any mechanical short circuit in/on xformer ?
if you aren't careful - it's easy to make short winding through toroid , with bolting/fixing hardware .
been there ....... when I was slightly younger ...
Zen Mod said:as Papa said- after xformer , first suspicious things are diodes and caps ..... if amp is otherwise functional ;
next thing ( I remember few years ago thread where we go through much troubles , to realize what was culpriy for hum and xformer overheating ) is to check that you didn't make any mechanical short circuit in/on xformer ?
if you aren't careful - it's easy to make short winding through toroid , with bolting/fixing hardware .
what about mis-wiring the phase of the transformer?
Well, I exchanged the transformer as a first step - trouble stays.
There is a big difference though between the two amps:
- The one which has no hum: I have 24.5V at both rails equally. I used Schottky diodes (MBR1645) and only 0.11 ohm in the PSU-filter, so no wonder that the voltage is a little higher. voltage drop is somthing around 0.24V acrosse V+1 and V- on these reistors.
- On the humming unit, I have slightly higher voltage drop, but I have +23.7V and -22.7 V...so, something weird happens in the PSU. I am now exchanging the rectifiers and the caps together and let's see what happens...
There is a big difference though between the two amps:
- The one which has no hum: I have 24.5V at both rails equally. I used Schottky diodes (MBR1645) and only 0.11 ohm in the PSU-filter, so no wonder that the voltage is a little higher. voltage drop is somthing around 0.24V acrosse V+1 and V- on these reistors.
- On the humming unit, I have slightly higher voltage drop, but I have +23.7V and -22.7 V...so, something weird happens in the PSU. I am now exchanging the rectifiers and the caps together and let's see what happens...
luvdunhill said:
what about mis-wiring the phase of the transformer?
What do you mean by that ?
Blitz said:
check this link out:
http://www.plitron.com/standard_schematics.asp
see the "dots" on the diagram? these refer to phase of the windings. I usually put the "dot" to ground on both sides.
Ok, understand, but no, I did everything right there. In the meantime I have exchanged the rectifieres and the capacitors. Quietness !! No noise at all. So, I guess it has been either the rectifieres or the capacitors, I guess more the first ones. I mounted them as well on the heatsink and measured if they have any shorts, but there must have been a mistake still...tomorrow I will remount them on the heatsink (new ones of course and let's see what happens then...Iam really looking forward to this, if I thought the F4 sounds great, now without a foulty PSU and with Jensens 4-Poles and with new, High-End 800VA-Toroids...I am really lookings forward to get it up and running again, let's see what happens, must be great stuff.
Anyway, thanks for all the ideas and input, great community here !!
Anyway, thanks for all the ideas and input, great community here !!
Schotty rectifiers are a little different than regular silicon diodes
in that they can't be put in seriese for a higher reverse brakedown rating. During the - voltage swing the rectifiers conected to the + cap will be subjected to +25v from the cap
and the -25v swing for a total of 50v which exceeds there
45v reverse brakedown rating.
in that they can't be put in seriese for a higher reverse brakedown rating. During the - voltage swing the rectifiers conected to the + cap will be subjected to +25v from the cap
and the -25v swing for a total of 50v which exceeds there
45v reverse brakedown rating.
Are you sure ? We have one winding with 18V and one bridge rectifier which works into 0 - 24V and we have a second winding with a separate bridge rectifier which sees -24V - 0 Volt..so how can a diode see -24v and +24v ?
That 18v is AC. During one half cycle the diode charging the cap
will only have to deal with the ~.4v voltage drop across it but
during the next half cycle this diode will be reverse biased where the anode is seeing the +25v from the cap and a -25v at the cathode for 50v total. So I expect one of the diodes is failing.
Hay I hope I am wrong here I have a few 80A 45v schottys I
would like to use with a 16v transformer but am scared to use
them for this reason!
will only have to deal with the ~.4v voltage drop across it but
during the next half cycle this diode will be reverse biased where the anode is seeing the +25v from the cap and a -25v at the cathode for 50v total. So I expect one of the diodes is failing.
Hay I hope I am wrong here I have a few 80A 45v schottys I
would like to use with a 16v transformer but am scared to use
them for this reason!
Re: Re: F4 power amplifier
The only complaint I could offer is that I think 12V rails for the
Mosfets is low. I usually presume that the devices are not good
below 4 volts Vds minimum as the linearity and capacitance
go to hell at these low voltages. Usually I like something more
like 24 volts.
lineup said:
The only complaint I could offer is that I think 12V rails for the
Mosfets is low. I usually presume that the devices are not good
below 4 volts Vds minimum as the linearity and capacitance
go to hell at these low voltages. Usually I like something more
like 24 volts.
Ok, got everything up and running now with the new 800VA.transformer, a new bridge with mbr1645 and four Jensen 47000uF/25V per channel..without the CRC, simply C.
Well...this is a shocking dead-silent amplifier. You don't hear anything. Not from the amp, not from my 95db Speaker. The only think you hear is music.
With this silence as a backround, it seems to do an even better job to model all the details.
I am not yet sure how the JEnsens compare to the Panasonic TSHA in CRC. It could be that the character of the amp changed a bit onto a drier direction, before it had somemore body, but as well slightly less detail, some cound say it sounds now a bit more technical, but the Jensens are now 2 hours in the amp, so let's break them in...maybe they need less time than the blackgates, but I guess they need more than 2 hours.
My question to Mr. PAss: how small could the 220uf caps really be if I would like to change them against MKPs ?
Well...this is a shocking dead-silent amplifier. You don't hear anything. Not from the amp, not from my 95db Speaker. The only think you hear is music.
With this silence as a backround, it seems to do an even better job to model all the details.
I am not yet sure how the JEnsens compare to the Panasonic TSHA in CRC. It could be that the character of the amp changed a bit onto a drier direction, before it had somemore body, but as well slightly less detail, some cound say it sounds now a bit more technical, but the Jensens are now 2 hours in the amp, so let's break them in...maybe they need less time than the blackgates, but I guess they need more than 2 hours.
My question to Mr. PAss: how small could the 220uf caps really be if I would like to change them against MKPs ?
