DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 15 Jun 2019, 18:40

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 247 posts ]  Go to page Previous  1 ... 21, 22, 23, 24, 25  Next
Author Message
 Post subject: Re: 6EM7 power amp
PostPosted: 25 Nov 2013, 23:19 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5104
Location: Australia
I decided to pimp Abstinence:

1 - Remove 22uf electros as first cap in PS and replace with 4uf\400V Russian PIO and snub with 0.1uf\630V poly
2 - Place to 100ohm\5W resistors between power tranni and rec. tube plates (control surge)
3 - Reduce last filtering\limiting R in PS to compensate for 100ohms on plates
4 - Replace orange drops with Russian Teflon 0.033uf\400V inter-stage caps
5 - Snub 100uf NP bypass caps (Ck) with 0.1uf polies.
6 - Replace the $24 5Y3 rec. tube with the $200 Sophia Electric mesh plate.
7 - Added sound deadening (bitumised Al) to bottom plate

I couldn't mount the 4uf cap direct to the bottom of the top plate so now is sits atop a Woodfords bourbon American Oak cork top. I had to reduce the HT to 260V and current to 88mA. Max mA for the Sophia is 90mA. I realise I am running it near max but I was not prepared to drop the HT anymore. Tube and caps are new so need some time. Sounds excellent though, lot clearer with much better sound stage. The giant Sophia is only a few mm from the power tranni but you can put the back of your finger on the tube. It is hot but not burning. Not worried.
Attachment:
UnderNew.jpg
Attachment:
Sophia.jpg
Attachment:
AbstinenceSophia.jpg


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 26 Nov 2013, 16:25 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5104
Location: Australia
I meant to include this image as part of the upgrade (pimping) I made to Abstinence. While I had the amp apart I added some bitumised heavy Al foil to the bottom plate for resonance and vibration control. Before I added the foil I held up the bottom plate by one of the brass cones and rapped it with my knuckle. It rang like an out-of-tune bell. I then applied the foil. The difference was huge. This time it just made a dull thud. No ringing and no vibration and barely any sound at all.

Usually I apply this stuff (comes in three sizes on a roll) before testing the enclosure, lid, bottom plate, top plate or whatever for ringing. I got quite a shock just how effective it is. It takes seconds to apply and is cheap when bought in bulk. You can see here also I add soft foam pads to the large heavy locking end for the brass cones. They came with the cones for other purposes but I like to use them here once more to add more dampening in the cone feet.
Attachment:
BottomPlate.jpg
Attachment:
Bottom.jpg


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 20 Dec 2013, 20:57 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1583
Location: US Pacific Northwest
So, I had a snow day today and I've been cleaning up some amp designs to keep busy. To make a long story short, I've redesigned the circuit for the 6EM7/6EA7 amp. Of course, most people (especially Mark) will probably ask "Why?". The answer is that there were a couple of things that I didn't like about the original amp design. Not major problems mind you, just little things that kept nagging at the Engineer in me every time I looked at the design.

First, I didn't like how close the design point was to the maximum plate dissipation of section 2. The tube limit is 10W and the original design point was 9.8W. This left precious little margin if a power supply was a little over voltage or a cathode resistor a little low in value. So I've optimized the output stage design to reduce the plate dissipation to 9.0W (leaving a 10% margin) while retaining the output power and slightly improving the distortion characteristics. I also took the opportunity to improve the overdrive characteristics of the power stage to make it a little smoother in marginal overdrive conditions.

Second, I was just not happy with the gain and distortion characteristics of the driver stage. Ever since I designed it (September 2011), I've felt that the sensitivity of this amp was a little bit low; requiring a full 2.0v peak to attain full power. So I've redesigned the driver stage to improve gain and lower distortion. I've also included an option for a bypassed driver stage. In the new design, the amp requires only 1.72v peak to reach full power with the driver cathode unbypassed and only 875mV peak to achieve full power if the driver cathode is bypassed. The bypassed and unbypassed distortion numbers have also decreased from 2.5%/1.3% full swing to 1.6%/0.8% full swing. This change will make the amp sound a little cleaner.

So here is the new schematic:
Attachment:
Schematic_v2.jpg

The changes are not dramatic. The power stage has a new bias design with a little larger biasing resistor and a reduced bypass capacitor. Everything else about the power stage remains the same. In the driver stage, the biasing and load are different. It's only two (or three if you bypass the cathode) components but I think the changes really improve the design.

The only thing to watch with the new design is the Miller capacitance of the driver stage with a bypassed cathode. If you choose this option, be careful that the output impedance of whatever drives the amp is not so high that it begins to impact the high frequency response. With a CM of 194µµf the limit on the grid circuit total impedance presented to the grid is ≤41kΩ. With the 100kΩ potentiometer as shown, the max driver impedance is ≈64kΩ in this configuration.

As always, questions and or comments are more than welcome.


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 20 Dec 2013, 21:42 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5104
Location: Australia
Due to the fact I was giving a demo of my 2-way inexpensive speakers to the Melbourne Audio Club a few night back, my system, was not setup the way I like. Though I enjoyed the 12" stereo subbies being driven by Abstinence (independent 200hz passive low pass filter) , the best setup is the subbies driven from their own 50W class D amp and 52hz electronic Xover and Abstinence only concerned with the 2-ways.

After the big changes I made to Abstinence just prior to preparing for the demo, I didn't get a lot on time to listen to It with all it's upgrade parts including the Sophia Mesh Plate rec. tube. System is back to normal now and I'm just starting to appreciate what an incredibly clear and gorgeous sounding amp this really is. Vocal tracks I have played in the past and know well, take on a whole new life. The upgrades are definitely worth while. Where I would never tell Matt how to design a tube amp or even what layout should look like or wiring method should be used I will suggest some components I think have really stepped an already good amp up one full notch.

If you can afford it the Sophia Mesh Plate 274B (about $220 shipped), 4uf Russian PIO\400V first cap in the PS, NP caps for bypass snubbed with 0.1uf polies, 0.033uf Russian Teflon inter-stagecaps, 20H choke, shock mount power tranni and choke and lastly fine wire-wrap wire for signal connection from RCAs to driver triod. I believe these components have resulted in a dead quiet amp (average 1mVRMS of noise) and it's almost surreal clarity. Look forward to you build Matt.

Two days back it was 40C here. Today a lot cooler.

_________________
Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 20 Dec 2013, 22:10 
Offline

Joined: 20 Sep 2008, 19:49
Posts: 171
Location: Montreal, Canada
Hi Matt,

Thanks for the new schematics. I have a bunch of 13FD7 (very similar) so I might give it a try and hope it works, I will store your schematic in a safe place.

Rgds,
Eric

_________________
DIY SS Amp : LM3875 GC | TA2024 | TA2020 (AMP-6) | TA2022 | Amp Camp Amp | JLH
DIY Tube Amp : RH84 SE | 6V6 SET | 13FD7 SET (Chinook) | 807 UL SE | 6BQ5 Class A PP UL | 6LR8 SE
DIY Spkrs : Cyburgs Needle | MLTL (FE206E) | CSS EL70 BR | Open Baffle (Alpha 15A + FE206En) (in process...)
DIY Pre-Amp : MooseFET.
To come : MLTL (CSS enabled EL70) + more tube amp...


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 21 Dec 2013, 00:57 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5104
Location: Australia
I see Matt has increased the inter-stage cap up from 0.022uf to 0.047. I knew I could go larger than 0.022uf but went mean-way between the two limits. I would still suggest a Russian Teflon inter-stage. I originally had orange drops which I think we all agree are very good but the Teflons (first time I have ever used them) I KNOW are better. I think I paid less for these extremely heavy, steel cased Teflons than orange drops. If you go with 0.033uf you will have more bass than you can handle. My system, Abstinence goes down to 40hz easy. Bigger is not always better in this case.

Owing to the fact I bought a NOS\NIB pair of RCAs and 10 single Samsung 6EM7s I'm sure there is another amp out there. I have managed to get ride of 6 tubes so far ($6 each) and in the end I may just keep one pair. Maybe with the next amp I can sell it with spare tubes to use some up.

_________________
Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 03 Mar 2014, 06:29 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5104
Location: Australia
A friend did a frequency plot of Abstinence. Nice and flat all the way out. Right down to around 13Hz. Distortion levels were high at around 3%+
Attachment:
AMP.jpg


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 03 Mar 2014, 06:54 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Sweet! :thumbsup:

3% is quite nice, since most triode designers rate their amps at 5 or 10.

Gotta love that tube, mate! :D

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 03 Mar 2014, 14:28 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5104
Location: Australia
Geek wrote:
Sweet! :thumbsup:

3% is quite nice, since most triode designers rate their amps at 5 or 10.

Gotta love that tube, mate! :D

I thought it too high but you make me feel better now. It definitely does sound like 3%.

_________________
Projects:”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp | "LeManja” - hybrid tube and chip headphone amp


Top
 Profile  
 
 Post subject: Re: 6EM7 power amp
PostPosted: 03 Mar 2014, 17:32 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
That's because SS marketing has told us that unless an amp has 0.00000000001% THD, it's garbage ;)

A great way to learn the sound of distortions is dial up a certain THD on a SET, SEP, PP triode and PP pentode and play a familiar piece (female vocals pref. because of spectrum).

3% on a SET is pretty easy on the ears because it'll be mostly 2H.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 247 posts ]  Go to page Previous  1 ... 21, 22, 23, 24, 25  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 14 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy