DIY Audio Projects Forum
 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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 18 Sep 2014, 22:44

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 249 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8, 9, 10 ... 25  Next
Author Message
PostPosted: 11 Mar 2012, 10:53 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 2379
Location: Arizona, USA
Hi Rather nice build. It is interesting that the layout of the phono section is really quite close to the same as mine. Some things just work that way. It is toward the front in the photos of the insides of my integrated preamp (digital remote, line stage and phono sections). The PS and actual inputs are under the screens. Since the photo I have upgraded all the coupling caps to Auricaps and Jantzen Silver Z caps. The RIAA network is on a plug in so I can fiddle with it easily. The DIP switches allow for different values of phono cartridge loading. Yes tube rolling the input tube will alter the RIAA curve. I find that generally it shifts the whole curve up or down in frequency, but generally maintains the shape. The value of the first resistor is based on the anode resistance of the first stage and the input resistor of the second. with a 470K on the second grid to ground and a grid stopper of 22K, the value of the resistor is 89K minus the anode resistance of the SRPP. With most 12AX7 types and brands this will put it in the range of 68K to 73K. With the JJ ECC83 Gold pin tubes it works out to just under 71K.
Attachment:
Pre inisde with covers2.jpg

I did not add in the additional time constant as measurements indicated it was not needed. Adherence to the standard was at the limits of may ability to measure accurately. (BTW, the best way I found to do this was with a DSO in spectrum analyzer mode).

Good listening
Bruce


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


_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 11 Mar 2012, 17:23 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 3773
Location: Australia
Unique looking - nice job.

_________________
Projects: "Parley" - Tube preamp with Pass B1 buffer | "VoXConcentriC" - Beyma high efficiency 12" speakers | "Black Lace" - all Ozzie tube 6V6 Power amp - old school
Website: [ retro-thermionic ]


Top
 Profile  
 
PostPosted: 08 Apr 2012, 15:24 
Offline
User avatar

Joined: 14 Feb 2010, 13:13
Posts: 616
Location: Lisbon, Portugal
You mention somwhere that the 3rd stage / output tube is optional.

I wonder if the output signal is enough to drive 5751 tubes?

What capacitor should be used?

I´m talking about an Oddwatt KT88 amplifier.


Cheers in advance,

Miguel


Top
 Profile  
 
PostPosted: 08 Apr 2012, 21:04 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 2379
Location: Arizona, USA
Hi Miguel, It should be able to drive the 5751s easily. I would use a .47uf poly from the cathode of the upper triode in the second SRPP to the output. The output should then go to the input grid resistors of the 5751. They ought to be the same 100K as in the amp schematics. A resistor of about 1K to perhaps as much as 4.7K should be included as grid stopper to insure stability. If you switch the phono section off, then I would want to have a 1m resistor from the ground to the output side of .47 capacitor. This will discharge it when it is not connected to the next stage.

The deletion of the one tube section does make the circuit simpler and easier to build and perhaps slightly quieter. In my three prototypes they are so quiet that any improvement is unlikely to be noticed and only with rather sensitive test gear even measurable. Mine are all now just barely above the residual noise in my shop. The deletion will increase the output impedance of the phono section to about 15K which is fine for Oddblocks, but may be too high for SS amps. The cathode follower drops this value to below 500 ohms.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 23 May 2012, 01:15 
Offline

Joined: 26 Apr 2012, 06:52
Posts: 2
hello to you all. i'm new to valves and am interested in this phono pre amp. i was wondering how the heaters are connected up to the valves and where the second channel is connected to the ECC81 valve. thanks for your help Sean


Top
 Profile  
 
PostPosted: 24 May 2012, 21:55 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 2379
Location: Arizona, USA
Hi, The heaters are powered off a low voltage winding in the power transformer that is rectified by a full wave bridge filtered and then reduced to 6 volts DC. The heater circuit is not grounded. There is a dc reference voltage applied to it of approximately 70 volts. This protects the tubes from failure due to excessive heater to cathode voltages (can occur during start up and operation) and has a side benefit of reducing noise in the circuit.

The halves of the ECC81 are independent and one triode section is used for each channel. No magic involved just a straight forward cathode follower application to translate the high impedance of the previous gain stage to a low impedance output.

If I missed what you were asking (always possible) ask again.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 25 May 2012, 06:12 
Offline

Joined: 26 Apr 2012, 06:52
Posts: 2
Thank you Bruce. best wishes Sean


Top
 Profile  
 
PostPosted: 27 Jun 2012, 22:34 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 2379
Location: Arizona, USA
Hi Everyone... an update. Use JJ ECC803S gold pin tubes for the SRPP stages. They have a smoother overall sound than the ECC83S. Also if you need LOMC capability I found that Lundhal input transformers work rather well and preserve the S/N ratio at -90dbv.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 28 Jun 2012, 07:22 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 3773
Location: Australia
gofar99 wrote:
Hi Everyone... an update. Use JJ ECC803S gold pin tubes for the SRPP stages. They have a smoother overall sound than the ECC83S. Also if you need LOMC capability I found that Lundhal input transformers work rather well and preserve the S/N ratio at -90dbv.

Good listening
Bruce

LOMC?

_________________
Projects: "Parley" - Tube preamp with Pass B1 buffer | "VoXConcentriC" - Beyma high efficiency 12" speakers | "Black Lace" - all Ozzie tube 6V6 Power amp - old school
Website: [ retro-thermionic ]


Top
 Profile  
 
PostPosted: 28 Jun 2012, 09:10 
Offline
User avatar

Joined: 14 Feb 2010, 13:13
Posts: 616
Location: Lisbon, Portugal
I guess it stands for Low Outuput Moving Coil (LOMC) which are considered phono cartridges with output voltage below 0,5mV.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 249 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8, 9, 10 ... 25  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google Adsense [Bot] and 2 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 / Opamp Projects :: DIY Phono Projects :: DIY Cable Projects :: HI-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy