Yes, I don't see why my statement would not be true in that case. A mechanical contact is removed from the path but the signal is still developed across a semiconductor that is not electrically isolated from the source or from the following stage.
Anyway, I'm with Andy. I do all my attenuation digitally.
Hi folks,
Thank you for information about the tubes especially for Andy and Mogglia who share their experience with the tubes they recommend. Very inspiring. It's also inspire me to try other DHT tubes as well, especially the triode one.
After I read some of the former info in this thread, I also realized that sooner or later I must face investment on filament bias. Either for upgrade for the system (better performace) or fixing the hum problem which usually came from the heater. So maybe I will try 46, 26 or 10Y in further days. Right now still focus with my RE144 preamp project......
Thank you for information about the tubes especially for Andy and Mogglia who share their experience with the tubes they recommend. Very inspiring. It's also inspire me to try other DHT tubes as well, especially the triode one.
After I read some of the former info in this thread, I also realized that sooner or later I must face investment on filament bias. Either for upgrade for the system (better performace) or fixing the hum problem which usually came from the heater. So maybe I will try 46, 26 or 10Y in further days. Right now still focus with my RE144 preamp project......
Hi Thomas,
Thanks for you explanations. I am clear now about volume control issue. Yes, it's not about DHT issue. It's more about the signal path issue. Lucky me, some weeks ago I just bought Tribute AVC from swap meet. I plan to replace the blue 100K ALPS in my preamp.
By the way, I see some difference approach here as I saw TVC and AVC implementation. I saw TVC and AVC got so low impedance value such as 10K or 33 ohm. Will be any siginificance problem when an AVC replacing a potentiometer as is?
Regarding your comment before, about Tribute lineout with secondary acts as vol control. Does it means you combine lineout trany with volume control at the output path?
How is the sound impression compared when the volume control installed as conventional way?
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Hi Thomas
yes you hit the nail. Nowadays Linestages didn't need such high gain and to increase the gain of the Phonostages to the level of a CDP (region of +6dBu / ~ 1.55Vrms).
Another thought, why not implementing the gain of the Linestage into the Power Amplifier and use a TVC as stand-alone Volume Controller like in Studios?
BR
Joao
Hi!
You cannot replace a potentiometer with a TVC in every case. I found lower impedance TVCs to generally sound better. Many sources cannot cope well with TVCs even those rated as 10k impedance.
That's why I would never use a TVC at the input of the linestage or as a stand alone attenuator, unless you are sure all your sources can drive the inductive load. That's why I put the TVCs at the output of teh linestages, so all sources are decoupled from this rather difficult load.
Hi!
I have built 10Y linestages both ways. In the article below I posted a listening report from someone who compared both:
VinylSavor: 10Y Line Preamplifier Follow Up
Best regards
Thomas
You cannot replace a potentiometer with a TVC in every case. I found lower impedance TVCs to generally sound better. Many sources cannot cope well with TVCs even those rated as 10k impedance.
That's why I would never use a TVC at the input of the linestage or as a stand alone attenuator, unless you are sure all your sources can drive the inductive load. That's why I put the TVCs at the output of teh linestages, so all sources are decoupled from this rather difficult load.
Hi!
I have built 10Y linestages both ways. In the article below I posted a listening report from someone who compared both:
VinylSavor: 10Y Line Preamplifier Follow Up
Best regards
Thomas
Thanks 12. I had to laugh though. While I was reading your response I remembered I bought a Prometheus a number of months ago and dropped my plans to build a LightSpeed.......
I would really like to try the 26 preamp. I had a John Hogan 300B for 7 years. The drive tube was the 26 and it sounded fantastic. I have the Pete Millete Low-Mu pre amp now, but would like to compare the 26 with it and the 12B4.
If you did that, wouldn't you just end up with a three stage amp....or possible a 4 stage amp?
I quad-amp my system so my line stage/pre amp needs to be separate.
Hi Thomas
I forgot to mention. Thanks for the correction. And yes I agree that lower impedance of AVC / TVC sounds better.
BR, Joao
Yes what is the problem with a 3 stage phono - which reaches the signal level of a CDP - and with a 3 stage power amp?
In general it's the same as you have a lower gain phono and power amp and a separate line stage. I Like Thomas mentioned, dealing with impedances you can lower the impedance of the AVC / TVC (for example 60Ω output of the source > 600Ω TVC > 10K input impedance of the amplifier). You'll find this in studio gear!
BR, Joao
Hello guys,
Can you please critique my HT PS circuit below. Corrections and suggestions are most welcome. I am new to this and trying the best I can to learn in order to prepare myself to build the Type 26 preamp. Apologies for the quality of the pic.
Raw DC supply for the filaments coming soon after I completed this.
Thanks and regards,
Abe
Can you please critique my HT PS circuit below. Corrections and suggestions are most welcome. I am new to this and trying the best I can to learn in order to prepare myself to build the Type 26 preamp. Apologies for the quality of the pic.
Raw DC supply for the filaments coming soon after I completed this.
Thanks and regards,
Abe
An externally hosted image should be here but it was not working when we last tested it.
Hi Abe,
20uF is rather high for the first C with the AZ1 rectifier. I would use a max of 3uF here for best results. Just increase the secondary voltage of your transformer and you will have better regulation this way.
-MW
AZ1 or any other mesh rectifier will sound better than GZ34. I have a variety of sockets in my PSU so I can try out different rectifiers. I couldn't tell any difference between the meshies, but they all sounded better than the plain ones like the 80/5Y3. Not night and day, since there's a lot of stuff after them, but enough to be audible and for me to have a preference.
You don't need to run the 26 so hot, but it's up to you. I use a 150v glow tube (0D3) instead of the voltage reg for instance. In that case the glow tube and both 26s would show a current of max 60mA but that's before the regulator not after it - after it would be max. 15mA depending where you run the 26s.
Agree on small first cap. Up to 1uf really.
For the filament supply I recommend pure choke input or small cap in range 100-660uF, which can be used to tune the output voltage. And using a choke something like a Hammond 159ZC. Then at least 20,000uF smoothing. Caps should be rated 1.5 times the expected output voltage of your raw filament supply to cope with the voltage off load. Rod has recommended JMS transformers, but that's in UK. you could find something similar in the USA.
http://www.jmsonline.co.uk/index.php?cPath=22&sort=2a&page=1
You don't need to run the 26 so hot, but it's up to you. I use a 150v glow tube (0D3) instead of the voltage reg for instance. In that case the glow tube and both 26s would show a current of max 60mA but that's before the regulator not after it - after it would be max. 15mA depending where you run the 26s.
Agree on small first cap. Up to 1uf really.
For the filament supply I recommend pure choke input or small cap in range 100-660uF, which can be used to tune the output voltage. And using a choke something like a Hammond 159ZC. Then at least 20,000uF smoothing. Caps should be rated 1.5 times the expected output voltage of your raw filament supply to cope with the voltage off load. Rod has recommended JMS transformers, but that's in UK. you could find something similar in the USA.
http://www.jmsonline.co.uk/index.php?cPath=22&sort=2a&page=1
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Hi Andy,
Okay, let's see if I understand you correctly.
With the arrangement I posted, the Shunt Regulator will draw 20mA by itself and will drop 50V. If I operate the two 26 tubes at a total of say 15 mA, with 135V at the plate,the model that I should have as main PSU should only show 35 mA of load?
thanks!
Abe
Okay, let's see if I understand you correctly.
With the arrangement I posted, the Shunt Regulator will draw 20mA by itself and will drop 50V. If I operate the two 26 tubes at a total of say 15 mA, with 135V at the plate,the model that I should have as main PSU should only show 35 mA of load?
thanks!
Abe
Hi Abe,
Please connect the shunt regulator + to the dc supply + (ie, the top, or hot end of the LL1660 OT primary). Connect the shunt reg GND to 0V or GND. The shunt reg stabilises voltage by diverting current to GND.
The CCS should drop 25V to 35V minimum.
When you have a shunt regulator, the passive power components can be reduced to CLC - eg 1uF-2H-30uF. A good shunt regulator is VERY effective in removing ripple.
Please connect the shunt regulator + to the dc supply + (ie, the top, or hot end of the LL1660 OT primary). Connect the shunt reg GND to 0V or GND. The shunt reg stabilises voltage by diverting current to GND.
The CCS should drop 25V to 35V minimum.
When you have a shunt regulator, the passive power components can be reduced to CLC - eg 1uF-2H-30uF. A good shunt regulator is VERY effective in removing ripple.
A 0D3 should draw about 22.5mA - that's what's recommended. Here's a draft version of a 26 preamp using the LL1660/5mA. You can play around with the cathode resistor size depending on how much you starve the 26 filaments, e.g. between 0.85A and 1A.
Attachments
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Thank you Andy, and thank you Rod! I will try to build the preamp this way. I leaning towards battery bias, but it is good to learn about filament bias as well.
Rod, the CCS and Shunt Regulator on my schematic is the one from K&K and is already combined.
In the schematic that Andy posted, regarding the CCS, should I just aim for 150V raw DC supply or 200V is fine and just adjust the current as required?
Thanks!
Abe
Rod, the CCS and Shunt Regulator on my schematic is the one from K&K and is already combined.
In the schematic that Andy posted, regarding the CCS, should I just aim for 150V raw DC supply or 200V is fine and just adjust the current as required?
Thanks!
Abe
Hello Andy, Rod,
Can you please take a look at these schematics. The 1st includes the main PSU and the second one is a schematic for the filament using Rod's Shunt Regulator.
All suggestions and corrections are most welcome! Thank you very much!
Abe
Can you please take a look at these schematics. The 1st includes the main PSU and the second one is a schematic for the filament using Rod's Shunt Regulator.
All suggestions and corrections are most welcome! Thank you very much!
Abe
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
