Noise! In building and hearing the DCB1, I realized how important it was to keep the noise level low in all small signal equipment. This is where it can have the greatest affect. I am now trying a tube pre with a regulator from Salas that dropped the noise floor by about half.
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I thought that followers in general had low noise because they had no gain?
I'm surprised you have a tube pre that has lower noise than the B1.
The THD should be very low since there is 100% feedback. There should only be the characteristic noise of the device since the gain is less than 1. They do make low noise mosfets but I don't know how they compare to jfets. In the tube world it was good to use a low gain, high transconductance type of tube for a follower. The higher the transconductance the better the drive and the lower the output impedance. I guess this applies to jfets and mosfets also but I'm no expert.
MOSFETS are much noisier than JFETs in general. In a line buffer, that can be of minimum relative consequence, given the signal level and lack of gain while the MOSFET's higher transconductance benefits Zo, and THD as the signal level rises in peaks. TO-220 and TO-247 devices have way too high input capacitance to be useful here driven from a practical value pot, I have stashed away some BS170 MOSFETS though to experiment with some day. Only problem is to find nice solid TO-92 sinks widely available, since to realize the gm benefit, bias should be appreciably high, at least 100mA. Now imagine the ridicule if I will ever come up with a DC-BS buffer.
MOSFETS are much noisier than JFETs in general. In a line buffer, that can be of minimum relative consequence, given the signal level and lack of gain while the MOSFET's higher transconductance benefits Zo, and THD as the signal level rises in peaks. TO-220 and TO-247 devices have way too high input capacitance to be useful here driven from a practical value pot, I have stashed away some BS170 MOSFETS though to experiment with some day. Only problem is to find nice solid TO-92 sinks widely available, since to realize the gm benefit, bias should be appreciably high, at least 100mA. Now imagine the ridicule if I will ever come up with a DC-BS buffer.
I would think that a depletion mode MOSFET would be easier to use in the B1.
Ha !
(even prettier is shaving the body to the bare minimum thickness, and/or encase it into a larger high thermal epoxy body)
Patrick (EUVL) developed a rather good higher current buffer running about 250mA called the"DAO Buffer (Taylored) with the Lu1014 jFets plus cascode - driver for the AKG k-701 headphones - extremely good, simple device especially with the Shunt Regs, but don't know if it's actually a B1 variant ....
voltage measurements
All,
I apologize if these measurements exist in this long thread. I am (finally) getting around to completing my B-1 with Pass Boards. I didn't burn anything up on initial power up (at least no smoke)... but I'm not getting anything from the output... save for some very faint audio. (yes, it is connected to my power amp)
Can anyone tell me where I might find voltage measurements at some points in the circuit so that I may trouble shoot and identify where I might have made a mistake? It seems silly that it's not working given the simplicity of the circuit and the great board. Alas... obviously I've done something incorrectly.
I have a 24 volt supply. I know the current draw of the circuit is approximately 20 mA. The voltage drop across R1 doesn't tell me anything, i.e. no stable measurement with my DVM. The power indicator LED lights up just fine.
Thanks for the help.
Ryan
All,
I apologize if these measurements exist in this long thread. I am (finally) getting around to completing my B-1 with Pass Boards. I didn't burn anything up on initial power up (at least no smoke)... but I'm not getting anything from the output... save for some very faint audio. (yes, it is connected to my power amp)
Can anyone tell me where I might find voltage measurements at some points in the circuit so that I may trouble shoot and identify where I might have made a mistake? It seems silly that it's not working given the simplicity of the circuit and the great board. Alas... obviously I've done something incorrectly.
I have a 24 volt supply. I know the current draw of the circuit is approximately 20 mA. The voltage drop across R1 doesn't tell me anything, i.e. no stable measurement with my DVM. The power indicator LED lights up just fine.
Thanks for the help.
Ryan
a lot of details about hardware build of a B1 Buffer
Just finished a fully differential version of the B1 Buffer. Details about design, execution, and how it sounds are posted at
Audio Equipment
It sounds wonderful. Much improved over a passive attenuator we were using before this.
Just finished a fully differential version of the B1 Buffer. Details about design, execution, and how it sounds are posted at
Audio Equipment
It sounds wonderful. Much improved over a passive attenuator we were using before this.
Great! I am thinking about going transformer i/o, but unbalanced. Did you consider any other transformer manufacturers like Lundahl or Cinemag?