F5 power amplifier

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T

tonimxp

Member
Joined 2007
How to obtain more warm sound

This is the Papa's Way

"Alternatively, you can increase the value of the Source resistors to 1 ohms,
and increase the value of the feedback resistors from 2 X 100 ohms and 10
ohms to 1 X 100 ohms and 22 ohms.

The lower amount of feedback will warm the sound up, and you can keep
increasing proportional values in the feedback loop if you wish".
Please about Source resistor values is there a correlation with the power out or not?

If yes how it change?

Antonio
 
S

superR

Member
Joined 2006
This question has been asked many times, but since I am having trouble sourcing the 2sk and 2sj's, I am looking for substitutes.

I have read that J175 and J111 should be accepted replacements, but I want to verify.
The same holds for the ZTX's. I can only source ZTX651 and ZTX751.

Are these part ok to use without reducing the performance "greatly"?
 
jackinnj

jackinnj

Member
Joined 2002
tech-diy.com
superR said:
This question has been asked many times, but since I am having trouble sourcing the 2sk and 2sj's, I am looking for substitutes.

I have read that J175 and J111 should be accepted replacements, but I want to verify.
The same holds for the ZTX's. I can only source ZTX651 and ZTX751.

Are these part ok to use without reducing the performance "greatly"?
Click to expand...

LSK170 is a direct substitute for 2SK170 and is in current production. BF862 is an RF N-Channel device, surface mount and in production. 2N5457, 2N5460 are around from time to time -- they are old parts often with the identification painted rather than lasered or silked onto the body -- pinout is a bit different and gm a lot lower, so you have to match. There are surface mount versions of these in current production.
 
Corpius

Corpius

Member
Joined 2011
ce-designs.net/
Started to make a parts list for my F5 on this rainy evening. Just wondering.. Are metal-film resistors preferred over wirewound types for the 3W resistors? ...and why exactly?

The wirewound's have a very low temperature coefficient's (ppm) compared to the metal film types. Most of them also have a smaller tolerance, down to 1%. When I search for parts used in other builds I often see the Panasonic metal film 3W resistors being used, just like in the original F5. The have a large temperature coefficient's (300 ppm) and tolerance of 5%.

I read somewhere that wirewound's have a large inductance compared to metal film oxide type. Probably also when compared to Metal film types. Are resistors with low inductance preferred over ones that have a larger inductance, but lower temperature coefficient?

Ah yes, almost forgot. Do they need to be closely matched for both channels?

p.s. only talking about the the 3W resistors here
 
Root2

Root2

Member
Joined 2010
Corpius said:
Started to make a parts list for my F5 on this rainy evening. Just wondering.. Are metal-film resistors preferred over wirewound types for the 3W resistors? ...and why exactly?

The wirewound's have a very low temperature coefficient's (ppm) compared to the metal film types. Most of them also have a smaller tolerance, down to 1%. When I search for parts used in other builds I often see the Panasonic metal film 3W resistors being used, just like in the original F5. The have a large temperature coefficient's (300 ppm) and tolerance of 5%.

I read somewhere that wirewound's have a large inductance compared to metal film oxide type. Probably also when compared to Metal film types. Are resistors with low inductance preferred over ones that have a larger inductance, but lower temperature coefficient?

Ah yes, almost forgot. Do they need to be closely matched for both channels?

p.s. only talking about the the 3W resistors here
Click to expand...

Try resistors wire wound but in Bi-Fillar format to reduce the small amount of inductance, Welwyn (TT group) do these and Sanyo .
 
T

tonimxp

Member
Joined 2007
How to obtain more warm sound

This is the Papa's Way

"Alternatively, you can increase the value of the Source resistors to 1 ohms,
and increase the value of the feedback resistors from 2 X 100 ohms and 10
ohms to 1 X 100 ohms and 22 ohms.
The lower amount of feedback will warm the sound up, and you can keep
increasing proportional values in the feedback loop if you wish".

Please a question...

Please about Source resistor values is there a correlation with the power out or not?

If yes how it change?
 
A

AndrewT

R.I.P.
Joined 2004
The higher the Source Resistor the more voltage across it will be dropped for that current value.

This means a slightly lower maximum power than for a standard Rs.
As speaker impedance is increased to say 15ohms or 30ohms (headphones) the less current passes through the Rs and thus the less effect that high Rs has on maximum output power.

But lower impedance draws more current and the higher the power lost in Rs compared to standard. 4ohms speakers will suffer a proportionately bigger loss in maximum output power.
 
T

tonimxp

Member
Joined 2007
AndrewT said:
The higher the Source Resistor the more voltage across it will be dropped for that current value.

This means a slightly lower maximum power than for a standard Rs.
As speaker impedance is increased to say 15ohms or 30ohms (headphones) the less current passes through the Rs and thus the less effect that high Rs has on maximum output power.

But lower impedance draws more current and the higher the power lost in Rs compared to standard. 4ohms speakers will suffer a proportionately bigger loss in maximum output power.
Click to expand...

Many thanks AndrewT for your reply and your explenation!

For you is possible to change only feedback net with 100R/22R? to obtain more 2° harmonic distortion prevalence and accordingly more warm sound?

I would like to get something near to 'Aleph 30 but with more muscles on the bass range.
Thanks again

Antonio
 
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