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 10 Dec 2019, 00:07

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 34 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
 Post subject: Tube Buffer Amp
PostPosted: 13 Nov 2012, 15:08 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi,

I am currently using a digital 31 band graphic eq betwean my cd player and SE valve ampliier. I am using my eq to remove room resonance with excellent succes. The graphic eq uses XLR's for input and output and because of this I have to use a sound craft mixing desk as I can connect it to the graphic using the XLR's. I would like to remove the mixing desk from the audio path and use something else such as a tube buffer amp or some kind of passive preamp using transformers.

I had thought about connecting the graphic eq directly betwean the cd player and amp but doing this will have terrible impedance miss match as the cd player has a high impedance output and the graphiq has a low impedance input.

Any suggestions on what to do would be very gratefull.

Thanks

Phil


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 13 Nov 2012, 15:56 
Offline
User avatar

Joined: 05 Nov 2010, 21:07
Posts: 702
Location: South East US - Tennessee
How about the suggestions made here: viewtopic.php?f=5&t=4078

You basically just need impedance matching transformers. It would be the simplest approach. The more complex the route, the lesser the return in "investment". While a tube buffer would inject certain "tube ambiance". You will need to know the impedances of the equipment being matched, regardless of approach.

_________________
The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 13 Nov 2012, 17:02 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi Les,

I was thinking of using impedance matching transformers as suggested in that post. I was going to put them in a solid state preamp that I was going to build for my solid state amp but after getting my valve amp to work and replacing all the cheap parts with good quality items i've ended up with an amp that sounds superb compared to my solid state power amp therefore I'm going to concentrate on my valve set up.

The impedances of the equipment are :-
CD Player - 47Kohms @ 1Khz
Valve Amp - 47Kohms
Graphic EQ Input - 22Kohms @ 1Khz
Graphic EQ Output - 100ohms @ 1Khz

Thanks again

Phil


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 13 Nov 2012, 23:58 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
A 6SN7 or 6FQ/CG7 cathode follower will do you nicely :D

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


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 14 Nov 2012, 02:50 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi Gregg,

Thanks for yor suggestion, do you have a circuit diagram that I can look at?

Phil


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 14 Nov 2012, 10:06 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Here's the one I use. Unconditionally stable and one tube for stereo! Good for miniature 6FQ7/6CG7 too.
Attachment:
6SN7_CF.png

For 6SL7 or miniature 5751, use 820 ohms instead of 4.3K on the cathode.

There's lots more like it on Google Images, if you want to use another type.

Cheers!


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


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


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 14 Nov 2012, 13:28 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi Gregg,

Thanks for posting that schematic. I have two questions:-

1. Does this circuit add any gain?
2. Should this buffer amp go betwean the cd player and graphic eq or betwean the graphic eq and amplifier?

Sorry for all the questions.

Thanks for your help :up:

Phil


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 14 Nov 2012, 18:20 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
No problem!

1) Nope. Gain is about 0.95 actually. And given the very high dynamic range, a volume control isn't needed.

2) Anywhere you need a buffer. I find it handy for testing crappy big-box SS gear as my tube preamps have trouble driving 2K input impedance ;)

I forgot to mention the heaters of the buffer.... don't ground them. Either let them float with a noise bleed capacitor, or lift them 40V or so above the cathode (exact amount depends on the HV you use).

Cheers!

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


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 15 Nov 2012, 07:57 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi Gregg

Thank you very much for your help. Is there an equation that I can use to work out the heater bias?

Thanks again

Phil


Top
 Profile  
 
 Post subject: Re: Tube Buffer Amp
PostPosted: 15 Nov 2012, 08:40 
Offline
User avatar

Joined: 14 Feb 2010, 13:13
Posts: 663
Location: Lisbon, Portugal
The heater bias voltage is generally about 1/3 of your HV.


Cheers,

Miguel


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 34 posts ]  Go to page 1, 2, 3, 4  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 19 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