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LD2+ Revisit of Mu follower

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Posted on May 27, 2011 at 06:49:38
IDM
Audiophile

Posts: 15
Location: Newcastle upon Tyne UK
Joined: January 14, 2005
I have a LD2+ with grid chokes and I have just done the ultrapath mod which I am extrmely pleased with.

I am now contemplating the Mu follower change but looking through this forum there are two versions (that I can see). The first involves the use of mica caps (10nf and 7.5nf) and was I believe first put forward by Thorsten. There is also an alternative which Brian seems to have posted that looks like it has the 2 halves of the 6SL7 in parallel with a 10M45s CCS on the top. Which is believed to be the better or if they are both good but different what are the plus and minus points of each.

Thanks in advance
Ian

 

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RE: LD2+ Revisit of Mu follower, posted on May 30, 2011 at 23:50:05
Thorsten
Manufacturer

Posts: 4162
Location: Somewhere nice on planet dirt
Joined: September 25, 1999
Hi,

Actually both the Hybrid Mu-Follower and the original are mine.

Hard to say which is the better choice...

Both have things to recommend them. The original all tube one is more purist, the hybrid one has more driver, much lower output impedance and lower distortion...

Not even shure which I would build myself, TBH.

I'd probably myself build a hybrid Mu-Follower using a D3a as lower tube, but that's just me.

Ciao T

Ciao T

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?

 

RE: LD2+ Revisit of Mu follower, posted on August 19, 2011 at 14:12:51
driguy
Audiophile

Posts: 192
Joined: June 18, 2002
I have done the CCS mod and I definitely prefer it. Thorsten hit the nail on the head. It is less of a "traditional" tube sound but it seems to have more resolution and haze around the music. Also, it you do it cascade the 10M45's. This will net you even more openness. I just did it 2 days ago (why did I wait so long?) and I am surprised at the improvement.
Gary Pimm's website has a good explanation about CCS's. Why and how they work. Explanations as to why they are more linear and why the drive is better. See the link. He also explains why cascading them helps. It is cheap and easy to do but do not forget to change the dropping resistor that feeds the CCS (original I think is 62k). I wound up using about half that. It may vary according to which generation of LD you have. Very easy to undo except for maybe the soldering on the tube socket itself.
Best of luck.
Tony

 

RE: LD2+ Revisit of Mu follower, posted on August 19, 2011 at 14:15:11
driguy
Audiophile

Posts: 192
Joined: June 18, 2002
I meant more resolution and LESS haze and IF you do it.
Tony

 

RE: LD2+ Revisit of Mu follower, posted on September 13, 2011 at 13:45:43
IDM
Audiophile

Posts: 15
Location: Newcastle upon Tyne UK
Joined: January 14, 2005
Hi Tony,

Thanks for the information. I have rebuilt the LD2+ using the traditional mu follower and it is a huge step forward from the original version.

I am however intending to have a go at the parallel 6sl7 with a 10M45 CCS. As far as I can see from previous posts, all that needs to change is the cathode resistor needs to be increased to 1K5, the tubes paralleled and the 10M45 to receive the full 400V B+ with the potentiometer adjusted to give 2mA of current.

I don't understand your comment about the dropping resistor feeding the CCS (62K). Have I misunderstood something?

Thanks
Ian

 

RE: LD2+ Revisit of Mu follower, posted on September 13, 2011 at 14:33:25
driguy
Audiophile

Posts: 192
Joined: June 18, 2002
I forgot that I replaced my power supply transformer in order to get more B+ voltage for my EML 300b XLS tube. Of course, a dropping resistor is still used and the original 62k may still be the correct value. My notes show that it should set the voltage at about 390V with the original transformer which is fine. Be aware the the maximum rating on the 10M45 is 450V. Like most silicon products, the CCS does not like to have it's limits tested repeatedly. Watch the voltage after the dropping resistor when you start the unit up. Be sure you have the 300b installed when you test it to get the proper readings. You will most likely see a voltage spike that goes above your final setting by a fair amount. No need to worry too much but a little added resistance to ensure long life is not too bad. Personally I would not set the quiescent voltage below 375.
Second note: If you use a pot to set the CCS I would chose a setting that you like and install a high quality resistor that matches your setting. 2mA requires about a 1500 ohm resistor according to the spec sheet. You will notice a change in sound with different settings as per a previous post on the subject. I believe the poster wrote that more current resulted in a slightly harder sound.
Third note: I would highly recommend cascading the 10M45's. As per my previous post this is a significant improvement for very little money. I just did this after a couple of years with just one so I was very familiar with the sound. A no-brainer IMO. It increases the PSRR so that the output to the tube is a purer DC. It acts closer to having a separate power supply for the driver with less interaction with the output tube power supply. S/N ratio for that stage is better as well. Purchase some extra 10M45's so if they do fail you have them on hand and your amp is not out of service. I was glad I did. I think I had my voltage a little too close to the limit as I only measured the static voltage, not the voltage spike at startup.
Fourth note: If you really want to go to the end of this path you can go to a shunt regulator for the driver tube. I did this last week and the results are very good. I will post soon about the results and the installation with a picture. It is more difficult by far but it really separates the power supplies to a higher degree. Chassis space is the limiting factor on this upgrade as the photos will show.

 

RE: LD2+ Revisit of Mu follower, posted on September 14, 2011 at 00:46:19
IDM
Audiophile

Posts: 15
Location: Newcastle upon Tyne UK
Joined: January 14, 2005
Hi,
your notes and thoughts are really helpful. I realised where the 62K came from almost as soon as I clicked on post message!

I will try and get some spare 10M45's but this appears difficult in the UK!

I look forward to your further info on shunt regulation as I would like to get the very best out these great amplifiers.
Cheers
Ian

 

RE: LD2+ Revisit of Mu follower, posted on September 19, 2011 at 23:52:25
IDM
Audiophile

Posts: 15
Location: Newcastle upon Tyne UK
Joined: January 14, 2005
Hi Thorsten,

Thanks for the advice, I built the original version as I had the mica caps to hand.

I am however thinking of trying the CCS version using 10M45. I also note your comment about the improvement of using a D3A pentode in triode mode as the driver. I found this post from you which appears to explain the process:

http://db.audioasylum.com/mhtml/m.html?forum=DIYHiFi&n=4263&highlight=d3a+ccs&search_url=%2Fcgi%2Fsearch.mpl%3Fsearchtext%3Dpiezo%26forum%3Dpi

In the text you say change the 62K resistor in the B+ for 3k3, I am not sure if this is meant for just the version with anode resistor or is necessary for the 10M45 CCS as well. I would be grateful if you could clarify.

Also I noticed you mention the possible use of a C3G driver (I know different base) some people think it is better than the D3A. Do you have an opinion, which would you try first?

Thanks
Ian

 

RE: LD2+ Revisit of Mu follower, posted on September 22, 2011 at 02:39:04
IDM
Audiophile

Posts: 15
Location: Newcastle upon Tyne UK
Joined: January 14, 2005
I think I have answered my own question, as it suddenly dawned on me that the reistor has to go from 62K to 3K3 because the current draw is going up to 10mA therefore the voltage drop across the 62K resistor would be way too high.

 

RE: LD2+ Revisit of Mu follower, posted on October 23, 2012 at 13:48:52
Tre'
Industry Professional

Posts: 11954
Location: So. Cal.
Joined: February 9, 2002
"Be aware the the maximum rating on the 10M45 is 450V."

That's 450v across the device. There can be more than 450v at the input to the device as long as there is less than 450v across the device.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

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