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Speaker amps for headphones - Page 11

post #151 of 2933
Instead of resistors, can we use the attenuators recommended in the Magni thread:
 
 
Do they serve the same purpose of presenting the amp with a load? Or do they work in a totally different way?
 
Thanks!
post #152 of 2933
Quote:
Originally Posted by rexirius View Post

Instead of resistors, can we use the attenuators recommended in the Magni thread:
 
 
Do they serve the same purpose of presenting the amp with a load? Or do they work in a totally different way?
 
Thanks!

Attenuator is a RCA plug with resistors inside it, similar result. You need a resistor network for tube amp regardless.

 

Edit for clarity/safety.

 


Edited by khaine1711 - 5/7/13 at 2:30pm
post #153 of 2933

One method attenuates input gain and the other attenuates output level, so there's a difference.

post #154 of 2933

I'm thinking about getting an adapter for a Pioneer M-22 that is due to arrive in a couple days, but I've read that I need an amp with a common negative ground to be able to drive single-ended headphones safely. The M-22 is a dual mono design, but I see that the negative outputs are connected to earth (I think?), based on the schematic on the service manual here: http://www.hifiengine.com/library/pioneer/m-22.shtml. Does that mean it has a common negative ground?

post #155 of 2933
Quote:
Originally Posted by Tachikoma View Post

I'm thinking about getting an adapter for a Pioneer M-22 that is due to arrive in a couple days, but I've read that I need an amp with a common negative ground to be able to drive single-ended headphones safely. The M-22 is a dual mono design, but I see that the negative outputs are connected to earth (I think?), based on the schematic on the service manual here: http://www.hifiengine.com/library/pioneer/m-22.shtml. Does that mean it has a common negative ground?

 

One way to check is with the amp power disconnected, check for continuity between the negative terminals of the speaker out. But if you use something like this it would not matter because they would be separate anyway.

 

post #156 of 2933

Some solid state amplifier topologies apparently do not like driving high impedance.  I have a Carver M-200t (Magnetic Field Power Amplifier) that goes into overload protect without a load on the outputs.  I've got resistors on order and will give it a shot with a pair of HP-1's.  

 

Anyone familiar with these old Carver amps?

post #157 of 2933
Quote:
Originally Posted by potterma View Post

Some solid state amplifier topologies apparently do not like driving high impedance.  I have a Carver M-200t (Magnetic Field Power Amplifier) that goes into overload protect without a load on the outputs.  I've got resistors on order and will give it a shot with a pair of HP-1's.  

 

Anyone familiar with these old Carver amps?

 

Begin Here http://thecarversite.com/shell2.htm

 

The service manual is available as well. They have a forum which will probably hold the answers to any questions you may have.

post #158 of 2933
Quote:
Originally Posted by Hutnicks View Post

 

Begin Here http://thecarversite.com/shell2.htm

 

The service manual is available as well. They have a forum which will probably hold the answers to any questions you may have.

Thanks!

post #159 of 2933

Quote:

Originally Posted by potterma View Post




Some solid state amplifier topologies apparently do not like driving high impedance.  I have a Carver M-200t (Magnetic Field Power Amplifier) that goes into overload protect without a load on the outputs.  I've got resistors on order and will give it a shot with a pair of HP-1's.  



 



Anyone familiar with these old Carver amps?





I ain't too familair with the old Carver amps, I think they used a Switch Mode Power Supply and a Switching Amplifier?



A Solid State amp that doesn't like to run Open Circuit (i.e. a very high impedance load) is rather unusual.



 



Using a pair of 10 or 20 Ohm resistors in parallel across the outputs should solve your problems.


Edited by Chris J - 11/19/13 at 1:48pm
post #160 of 2933
Quote:
Originally Posted by Chris J View Post

I ain't too familair with the old Carver amps, I think they used a Switch Mode Power Supply and a Switching Amplifier?

A Solid State amp that doesn't like to run Open Circuit (i.e. a very high impedance load) is rather unusual.

 

Using a pair of 10 or 20 Ohm resistors in parallel across the outputs should solve your porblems.

I believe you are correct about the switch mode amplifier.

I'm sure a bit of parallel resistance will make all good.

post #161 of 2933

Been thinking about the simple resistor network and the impact of changing the resistor values.

 

 

  +   ----- ------┐--- ----R2--- ------┐
         R1         R3
  -    ---- ------┘--- ---------- ------┘

 

So,

R1 is the parallel resistance across the speaker taps

R2 is a series resistance

R3 is the impedance of the headphones

 

Initial assumption: R3 = 125 ohms (Yamahas) with 3 W into the headphones

Vary R1 and calculate the equivalent impedance seen by the amp, the current through each resistor, voltage across and power dropped by each resistor.

Then, select an R1 and Vary R2.

This assumes pure resistive loads (no capacitance or inductance)

 

 

R1, Ω R2, Ω R3, Ω Requiv, Ω I1, A I2, A I3, A V1, V V2, V V3, V P1, W P2, W P3, W Ptot, W
4 125 125 3.9 9.68 0.155 0.155 38.73 19.36 19.36 375 3 3 381
10 125 125 9.6 3.87 0.155 0.155 38.73 19.36 19.36 150 3 3 156
16 125 125 15.0 2.42 0.155 0.155 38.73 19.36 19.36 93.75 3 3 99.75
20 125 125 18.5 1.94 0.155 0.155 38.73 19.36 19.36 75 3 3 81
10 25 125 9.4 2.32 0.155 0.155 23.24 3.87 19.36 54 0.6 3 57.6
10 50 125 9.5 2.71 0.155 0.155 27.11 7.75 19.36 73.5 1.2 3 77.7
10 75 125 9.5 3.10 0.155 0.155 30.98 11.62 19.36 96 1.8 3 100.8
10 150 125 9.6 4.26 0.155 0.155 42.60 23.24 19.36 181.5 3.6 3 188.1

 

If anybody sees any stupid mistakes, let me know!

post #162 of 2933

The only mistake I can spot is assuming I have any idea what the #$%! all that means... :P

post #163 of 2933
Quote:
Originally Posted by potterma View Post

Been thinking about the simple resistor network and the impact of changing the resistor values.

So,
R1 is the parallel resistance across the speaker taps
R2 is a series resistance
R3 is the impedance of the headphones
Initial assumption: R3 = 125 ohms (Yamahas) with 3 W into the headphones
Vary R1 and calculate the equivalent impedance seen by the amp, the current through each resistor, voltage across and power dropped by each resistor.
Then, select an R1 and Vary R2.
This assumes pure resistive loads (no capacitance or inductance)

If anybody sees any stupid mistakes, let me know!

Interesting stuff.


Power into the actual load, the headphones, should never be more than 100 mW intoa typical headphone, in fact, 10 mW is far more reasonable.
Then work back from there.
If a speaker load is actually necessary ( and it usually isn't in SS amps, but may be useful in tube amps) R1 should be 8 or 10 Ohms, 4 Ohms is a bit excessive..........

Edit:
sorry about deleting the tables, my iPad made a mess out of my original post!
Edited by Chris J - 5/24/13 at 10:51am
post #164 of 2933
Thread Starter 

You can more independently manipulate the impedance the headphones and amps see, as well as attenuation, by adding another parallel resistor after R2 and then another series resistor after that. 

post #165 of 2933
Quote:
Originally Posted by Operakid View Post

You can more independently manipulate the impedance the headphones and amps see, as well as attenuation, by adding another parallel resistor after R2 and then another series resistor after that. 

 

After much experimentation, that is the same configuration I ended up with, based on a previous reference to a circuit by Fulvio Chiappetta.

 

The first parallel resistor being a 10Ω & 33Ω in parallel, the second section in series consisting of two paralleled 220Ω, with one routed through a switch so it can be lifted out of the circuit, this way I can choose between 220Ω or 110Ω, essentially giving me a high or low gain. Followed by a 33Ω in parallel, and finally to a 12Ω in series.

 

 

I have found this set-up to sound just amazing with my freshly rebuilt Sugden P28 or Robertson Forty ten and I'm finding it difficult to pull myself away from listening. Now I have to make the difficult decision on which of my headphone amps has to go.

 

 


Edited by kozmo - 5/24/13 at 12:43pm
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