Hello,
I have been using this pre amp for a LONG time and during the years i made some improvements.
I did use a Tango permalloy output transformer np216N right from the start.
The Allen Wright shunt was installed after a few months. Recently i added a Guido Tent shunt to give a very good 15 volts to the Allen Wright shunt.
Last week i switched from LM350 heater supply to those from Rod Coleman.
The next step is finding a replacement for the 300 ohm cathode resistor from Kiwame.
Audio Note tantalum could be nice. In the most expensive range only 330 ohm available. The cheaper ones also come in 270 ohm.
Will the change from 300 to 330 ohm or 270 ohm have a bigger influence than using a better resistor?
It would have been nice to find an identical value.
Could one say that a lower value will change the sound into a more dark sound and the higher value will have the opposite effect? Right now the sound is well balanced.
By the way this design won a contest in japanese MJ magazine.
Any suggestion would be welcome, Eduard
I have been using this pre amp for a LONG time and during the years i made some improvements.
I did use a Tango permalloy output transformer np216N right from the start.
The Allen Wright shunt was installed after a few months. Recently i added a Guido Tent shunt to give a very good 15 volts to the Allen Wright shunt.
Last week i switched from LM350 heater supply to those from Rod Coleman.
The next step is finding a replacement for the 300 ohm cathode resistor from Kiwame.
Audio Note tantalum could be nice. In the most expensive range only 330 ohm available. The cheaper ones also come in 270 ohm.
Will the change from 300 to 330 ohm or 270 ohm have a bigger influence than using a better resistor?
It would have been nice to find an identical value.
Could one say that a lower value will change the sound into a more dark sound and the higher value will have the opposite effect? Right now the sound is well balanced.
By the way this design won a contest in japanese MJ magazine.
Any suggestion would be welcome, Eduard
Attachments
What effect do you suppose this will have on the preamp?
Just about all of the signal current will not flow through that resistor; it's there to set the DC bias. There's a part sitting right next to it that's handling almost all of the AC current until you get down below most musical reproduction.
The heater supplies are also not in the signal path, the LM350's are quite up to the job.
My thoughts exactly, the place where you may gain something is the bypass capacitor on the cathode of the 5687. (Really good electrolytic or combination of several plus films - experiment to find what works best)
If you are up for a major challenge and some slight inconvenience consider fixed or LED bias.
A really good stepped attenuator is another area where you can make a worthwhile improvement depending on what you've got in there now.
I am a huge fan of the Rod Coleman regs, but their benefits are only audible in DHT and DHP where the filaments are actually in the signal path. They will do no harm, but they will not effect any improvement.
Improvements in the B+ supply will pay off, possibly the Salas SSHV might be an improvement over what you've currently got.
If you are up for a major challenge and some slight inconvenience consider fixed or LED bias.
A really good stepped attenuator is another area where you can make a worthwhile improvement depending on what you've got in there now.
I am a huge fan of the Rod Coleman regs, but their benefits are only audible in DHT and DHP where the filaments are actually in the signal path. They will do no harm, but they will not effect any improvement.
Improvements in the B+ supply will pay off, possibly the Salas SSHV might be an improvement over what you've currently got.
One should also be suspicious of high end, high price iron without much in the way of measurements or detailed specifications. I can remember a prior thread about a 2A3 amp using some 2.5K Hashimoto transformers and the builder being annoyed at the LF performance. It turns out that for $500 he only got 6.5H of primary inductance 
It wouldn't shock me to find that the Lundahl LL2765/30 has better bandwidth (especially down low) than your Tango OPT's for about 1/8 the price.
It wouldn't shock me to find that the Lundahl LL2765/30 has better bandwidth (especially down low) than your Tango OPT's for about 1/8 the price.
Hello,
The Tango is a fine output transformer.
In some of my gear i did replace the Tango choke input with a Lundahl ( with more Henry because thjey were available). And the Lundahl was better eventhough the Tango was designed for choke input.
The cap is already a black gate.
The 300 ohm is less important than the same resistor in a 300B power amp?
I always wanted a remote control for volume so it could be nice to combine this.
Greetings, Ed
The Tango is a fine output transformer.
In some of my gear i did replace the Tango choke input with a Lundahl ( with more Henry because thjey were available). And the Lundahl was better eventhough the Tango was designed for choke input.
The cap is already a black gate.
The 300 ohm is less important than the same resistor in a 300B power amp?
I always wanted a remote control for volume so it could be nice to combine this.
Greetings, Ed
R kiwame sounds just fine and cheap mode, nichicon FG , elna silmic can sound better than an old dry BG .
avoid fixed bias , led or battery bias never sound right with this tube ( i tried dozen of solutions on an audio note tube transformer output stage) an upgrade with the 10K volume pot can help too , a Transformer voulume control too ( Tribute , silk , etc..)
avoid fixed bias , led or battery bias never sound right with this tube ( i tried dozen of solutions on an audio note tube transformer output stage) an upgrade with the 10K volume pot can help too , a Transformer voulume control too ( Tribute , silk , etc..)
Hello,
The black gate is old but it has been used in this amp a long time.
I was not sure about fixed bias too.
The original design had 10K but mine uses a higher value. It could be 50K or 100K. Now it has 2 seperate volume controls and it allows a nice adjustment between the two channels. In the past i used a 24 step se selector with resistors but the steps were sometimes to big to get left right at the same level.
Greetings, Eduard
The black gate is old but it has been used in this amp a long time.
I was not sure about fixed bias too.
The original design had 10K but mine uses a higher value. It could be 50K or 100K. Now it has 2 seperate volume controls and it allows a nice adjustment between the two channels. In the past i used a 24 step se selector with resistors but the steps were sometimes to big to get left right at the same level.
Greetings, Eduard
They serve about the same purpose. The amount of AC signal current going through the resistor depends on how large the cathode bypass cap is and the frequency of the AC itself. Unless designed specifically not to, the cap handles nearly all of the signal current.
Hello,
If they have the same purpose then changing them might be an improvement!! In the eighties la maison de l'audiophile in Paris did start talking about using non inductive wirewound resistors for the cathode of their 300B amps. At that time they were talking about more audiofoolish things that later become more common in audiophile circles.
I remember the review of their Hiraga amp in a German magazine ( the kind that gives good reviews to the companies with lot of pages for advertisements) . They thought their coffee was drugged because the image so holographic.
Will try to find some nice 300 ohm resistors.
Just did buy an avc at Dave Slagle.
Greetings, Eduard
If they have the same purpose then changing them might be an improvement!! In the eighties la maison de l'audiophile in Paris did start talking about using non inductive wirewound resistors for the cathode of their 300B amps. At that time they were talking about more audiofoolish things that later become more common in audiophile circles.
I remember the review of their Hiraga amp in a German magazine ( the kind that gives good reviews to the companies with lot of pages for advertisements) . They thought their coffee was drugged because the image so holographic.
Will try to find some nice 300 ohm resistors.
Just did buy an avc at Dave Slagle.
Greetings, Eduard
Inductance in a wirewound resistor will lead to increasing impedance ats the frequency of AC across the resistor increases. In the case of a very inductive wirewound resistor bypassed with a capacitor, the inductance of the resistor is of very little consequence (but those who don't know better will feel better about their project because they used non-inductive resistors).
A 150k and 10/250v capacitor driving the base of a 2N5551 eliminated all the B+ noise from the voltage tripler I used in SX-780 to Drive 15Ma at 135v to 6922 preamp stage leaving 3v p-p noise and 20v dc drop across the transistor. No L-C-L-C stage required.
here you would need a 500v Transistor or Darlington to work
here you would need a 500v Transistor or Darlington to work
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.