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DIY ultimate AS M60

2.106.156.53
Posted on April 1, 2012 at 09:02:58
kbsp

Hi

I've tried for years to avoid building OTL amps but I've reached the point of no return. Can't get the OTL magic sound out of my head after I borrowed a S30 from a friend!

Schematic: My starting point is the M60 MKII.3+PSU schematic provided by Ralph.
Chassis: Will be based on the concept of the Thorens TEM3200 (the picture)
Coupling capacitors: will be Vcaps.
Transformers: Will be custom wounded with static shielding and 2x6.3V windings for the driver tubes (as I've 12SX7), properly higher voltage for output stage (to make better filtering possible)
I'll place measurement sockets at every cathode resistor in the output stage (integrated tube tester... ;-)

So far so good.


I've seen the modifications by Paul Speltz at http://www.paulspeltz.com/tweaks/index.html and consider the PSU mod and later the SLCF (which my RTP3D preamp do have so I'll just connect it directly to the circlotron).

For the ultimate M60 OTL what can I optimize?
1) Chokes?
2) Regulators for the driver stage?
3) Any ideas to lower the overall distortion without adding more feedback?
4) Anyone made a tube failed detector with LED indicators for OTLs?

/Kim

 

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RE: DIY ultimate AS M60, posted on April 1, 2012 at 11:47:16
lone gunmen


 
"Everything should be made as simple as possible, but not simpler."--Albert Einstein

 

RE: DIY ultimate AS M60, posted on April 3, 2012 at 08:44:42
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Cool! I like the vertical orientation, but where will you put the power tubes? On top seems best.
I implemented SLCFs in my highly modified Atma-sphere MA240s, and I've been listening to it for several months now. Although I made several other mods at the same time, I believe the SLCF is a noticeable improvement vs just having a CCS on each CF/driver. I used a K&K Audio mini-cascode kit for each CCS and an ECC99 as the upper voltage strap tube. Allen Wright remarked to me that all tubes sounds best but if you don't have the space (as I don't) then best to use solid state CCS and tube voltage strap. My amps are also a bit unique in that I have a separate SLCF driving each of the four output tubes, which are now type 7241 milspec triodes. This enables me to bias each output tube separately. These amps bring me as close to Nirvana as I have ever been in audio. (Stock MA240 used six 6C33C outputs; I just converted over to 7241s.)

 

RE: DIY ultimate AS M60, posted on April 4, 2012 at 08:06:54
kbsp
 Yes, the power tubes will be placed on top. I'm not sure about the signal tubes yet, properly inside.

Glad to see you like the SLCF. I'll use an all tube version but not likely in the first version of the amp which will be more like the original M60. I like to hear if any changes to the original design are an improvement or not.

I like you multi bias output arrangement but think it's not needed using 6AS7s?

Have you done anything do improve the performance of the gain stage?

 

RE: DIY ultimate AS M60, posted on April 4, 2012 at 08:34:00
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 In production amplifiers, Atma introduced the low-value cathode resistors on each output tube, to mitigate the possible compromise associated with mismatching among 6AS7s. When the amp is using more than six output tubes per channel (i.e., an MA1 or higher power Atma amp), it really is impractical to have separate driver stages. However, if you are going to use only four 6AS7s, I don't know why the benefit of separate biasing would be any less than for 6C33Cs or 7241s.

In my input voltage gain stage, I am using dual-differential cascode, a la the stock topology, but built with type 6900 triodes. (I had them in my stash, so why not?) More readily available 5687s or 7119s would be just as good. To use any of the above tubes, you need to increase the current draw drastically. For a CCS on the dual-differential cascode, I use an ECC99 configured in cascode. The bipolar supply of my MA240s gives +/-400V, which is a worthwhile increase in voltage vs the M60, which I think gives +/-300V. The ECC99-based CCS will be better able to deliver the needed current to the 5687/7119, if you can manage tne +/-400V supply. I don't use any voltage regulators, not because of any philosophical objection to them. I also do not use zeners to set the grid voltage of the upper tube in the dd-cascode, just a voltage divider network with the usual bypass capacitor(s). I figure that if the HV is unregulated then fixing the V on the grid can cause more problems than it solves. Also, I don't like zeners.

 

RE: DIY ultimate AS M60, posted on April 4, 2012 at 11:54:12
bebe


 
Thanks for the pic have you got to hear the..Thorens TEM3200 if so what did you think

 

RE: DIY ultimate AS M60, posted on April 4, 2012 at 13:29:31
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 Lew, if your CCS is really working properly then you will see a slight improvement in performance by locking that upper grid voltage even if the B+ is unregulated- the zener works well for that. If you are worried about noise its easy enough to bypass it or isolate it with a PI network.

 

RE: DIY ultimate AS M60, posted on April 4, 2012 at 18:12:10
Banat



Hi kbsp !

Don`t know did you allready read the article from Big DIY Audio site or not , but there you can find many useful information related to DIY Atmasphere M60 OTL Amp.

BTW , Regardless to electric & sound performance of hybrid Circlotron power Amp Thorens TEM3200 , that Thorens mechanical enclosure design always remind me litle on design from early era of big PC enclosures ,
but that`s only just my personal view.
Any way ,it is my personal opinion that original Atmasphere M60 compact chassis design is the best solution even for DIY for many legitimate reason ,like antimagnetic chassis material , right logical layout of electronic components on the top of the chassis and with same right layout logic under the chassis , all toghether with very good unit ergonomics and with overall very nice unit aesthetic experience , etc ...

Best Regards !


 

recommendations for parts?, posted on July 17, 2012 at 01:08:55
kbsp
 Any recommendations for parts for my OTL build?

1. Caddock MP930 resistors for load and cathode? Or MILLs MRA5?
2. Which resistors for signal path?
3. Brand and type of capacitors for the PSU? Polypropylene bypass?
4. Coupling caps will be VCap CuTF.
5. Wire? Jena Labs? anticables for circlotron?
6. Anything else?

I'm open for your suggestions. :-)

 

RE: recommendations for parts?, posted on July 17, 2012 at 16:43:20
tyu
Audiophile

Posts: 963
Joined: April 19, 2011



Looks like your on track.....It like with the Circlotron it all good... I have a MA1 i diy 5years ago...parts can make a diffs...but with the Circlotron power Amp ...
I know you are someone could make them sound bad....
But i have got one to sound bad yet!....
So you know good parts...I dont care for the mills but thats me.
I Diy my MA1 on the older stock amps M60s ...with dail 7watt 5% 5ohm res...from digkey for 75cent ea.an with Zeners...thay were 40cent ea...... I would get these amps or amp going...then i would go for better parts....just my 5cent.....You should hear these OTLs on these Apogee Stages...Wow...have fun...goodluck

 

RE: DIY ultimate AS M60, posted on October 9, 2013 at 11:11:57
kbsp
 I'm about to assemble my version of a DIY M60 OTL.

Here is a small teaser:




And before you ask, I'll not sell PCBs nor the design. I spent countless of hours designing the PCBs and the chassis I ended up with because I couldn't afford the original M60s from Ralph.

If I had the money no doubt I would had bought an original Atma-Sphere M60! :-)

More in a few weeks...

 

RE: DIY ultimate AS M60, posted on October 9, 2013 at 11:48:18
tyu
Audiophile

Posts: 963
Joined: April 19, 2011
 Vary cool look!................more pic?
thanks

 

RE: DIY ultimate AS M60, posted on October 9, 2013 at 11:55:51
kbsp

Another teaser...

 

RE: DIY ultimate AS M60, posted on October 9, 2013 at 12:13:51
kbsp

The other side...

 

RE: DIY ultimate AS M60, posted on October 12, 2013 at 07:21:29
kbsp

My DIY M60s will look like the 3D model when finished (hopefully)

 

A little progress..., posted on December 2, 2013 at 09:07:58
kbsp
 The first channel will soon be ready:


 

RE: A little progress..., posted on December 2, 2013 at 14:20:14
tyu
Audiophile

Posts: 963
Joined: April 19, 2011
 thanks for more pic..............looks great..

 

RE: A little progress..., posted on October 11, 2015 at 22:09:29
Satelliteman
Audiophile

Posts: 122
Location: Napier - The Art Deco City of the world
Joined: May 21, 2006



Nice work on the DIY AS M60 , Im about to try mine soon on some DIY ESLs .
Is there a photo of the finished pair ?
Cheer Stu

 

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