Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th October 2012, 03:20 PM   #1
50AE is offline 50AE  Bulgaria
diyAudio Member
 
Join Date: Jul 2011
Location: Sofia, Bulgaria
Default DAC direct out, not enough gain, help me build a driving stage.

I'm using the AKM4396 DAC direct out without any cap, canceling the +2,5VDC offset with more (-2,5V) bias on the input tube.

The problem is, the direct out unbalanced outputs about 1V maximum and this is not enough. The driver is E180F. The stage gain is about 44. -44 volts aren't enough to drive the output tube 6P45S. I need -75V swing there for full output.

I can get interstage transformers to use the balanced output and hence get 2V, which fixes my problem, but I don't have money now to get high quality ones. This way I will get rid of the offset as well, two birds with one stone.

So I came up with the idea of two stage drivers. The problem is, I want it to be direct coupled, no cap in the way. But doing so, I have to cathode bias the second tube with much voltage to cancel the 1st stage anode voltage.

... so I have to put a cathode capacitor which I don't want to do. I hate cathode bypass.
... I cannot make fixed bias
... I cannot put cathode battery bias (too muc batteries)
... I cannot use cathode resistor only, the gain will be too low, the output impedance will be very high and won't drive the 6P45S
... Or I can buy a higher gain penthode like D3A, but I don't have time and money to do so now.


So what can I do? This is where your help comes.

I could:

1. Use LEDS, if 12V or more ones exist, I could make a chain
2. Use zeners, which I heard that are noisy, except lower voltage ones I heard, from whom I could make a chain
3. Use voltage regulator tube?

http://store.picbg.net/pubpic/EF/D6/...9da052efd6.PNG

Last edited by 50AE; 12th October 2012 at 03:23 PM.
  Reply With Quote
Old 12th October 2012, 04:24 PM   #2
diyAudio Member
 
Join Date: May 2010
Hi high gain,
Gain at 44 looks as triode connected E180F. For more gain and keep at one gain stage, you can connect the E180F as pentode and much more gain.
Ra 10kohm, Ia 15mA, you'll roughly double your gain. If that's too much go for s lower Ra.

Best regards
Karsten
  Reply With Quote
Old 12th October 2012, 05:50 PM   #3
50AE is offline 50AE  Bulgaria
diyAudio Member
 
Join Date: Jul 2011
Location: Sofia, Bulgaria
The problem is, it will be have very high output impedance, not sure if will drive the 6P45S well, which has high miller in triode mode.

Also I don't like the look of pentode curves
  Reply With Quote
Old 12th October 2012, 09:56 PM   #4
diyAudio Member
 
Join Date: May 2010
Hi,
Output imp will app same as the value as the Ra.

Best
Karsten
  Reply With Quote
Old 13th October 2012, 10:08 PM   #5
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
You can use my shunt-cascode circuit.

With E180F [triode connected] S ~21mA/V
Use load resistor 10K.

Gain ~ 210

No cathode capacitor needed.

Sound easily beats 2-stage driver.
Attached Images
File Type: jpeg shuntcasc_300B.jpeg (80.5 KB, 91 views)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FS - $150 - Monica 2 DAC (USB + Coax) + SS I/V Gain Stage ianp Swap Meet 0 15th August 2011 10:18 PM
DAC - tube gain stage w/ AC heaters regal Tubes / Valves 5 26th August 2008 12:30 PM
problems when driving a p3a direct from CD player Mark25 Solid State 1 18th November 2006 02:16 PM
Direct driving of GM70 by one ECL86 ??? noyan Tubes / Valves 9 20th February 2005 07:27 AM
Tubes for direct-driving ESL Prune Tubes / Valves 32 14th March 2004 02:59 PM


New To Site? Need Help?

All times are GMT. The time now is 04:05 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2