[rexirius]

Instead of resistors, can we use the attenuators recommended in the Magni thread:
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=266-244
 
Do they serve the same purpose of presenting the amp with a load? Or do they work in a totally different way?
 
Thanks!

 

[khaine1711]

Quote:

Instead of resistors, can we use the attenuators recommended in the Magni thread:
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=266-244
 
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.
 

 

[grokit]

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

 

[Tachikoma]

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?

 

[wuwhere]

Quote:

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.
 

 

[potterma]

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?

 

[Hutnicks]

Quote:

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.

 

[potterma]

Quote:

 
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!

 

[Chris J]

Quote:

Originally Posted by potterma /img/forum/go_quote.gif




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.

 

[potterma]

Quote:

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.

 

[potterma]

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!

 

[Theogenes]

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

 

[Chris J]

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!

 

[Operakid]

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. 

 

[kozmo]

Quote:

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 [size=9pt]Fulvio Chiappetta.[/size]
 
[size=9pt]The first parallel resistor being a 10Ω & 33[size=x-small]Ω in parallel, the second section in series consisting of two paralleled 220[size=x-small]Ω, with one routed through a switch so it can be lifted out of the circuit, this way I can choose between [size=x-small]220Ω or [size=x-small]110Ω, essentially giving me a high or low gain. Followed by a [size=x-small]33Ω[/size] in parallel, and finally to a [size=x-small]12Ω in series.[/size][/size][/size][/size][/size][/size]
 
 
[size=9pt][size=x-small][size=x-small][size=x-small][size=x-small][size=x-small]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.[/size][/size][/size][/size][/size][/size]