 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
69.156.196.162
In Reply to: RE: Modified Futterman OTL amplifier posted by cellai@space.it on June 02, 2008 at 04:44:44
.
Follow Ups:
And this is the power supply schematic.
Can someone here help me out. I am looking for readable schematics for this amp.Can't clearly read these that is posted here. I am looking for part 1 of 2, part 2 of 2 and power supply.
I will be glad to deliver the schematic.
By the way, other inmates have replicated the project and a new post will be likely published in June (after final 'tweaking') by one of those builders.
Best Regards
Luca
ecc230
Thank you.
My e-mail is vejbaek@webspeed.dk
Best Regards
Henrik
Done.
ecc230
PLEASE HELP
IF IT PASSIBLE SEND ME A CLEAR COPY OF THIS PS SCHEMATIC
I try to constuct this amp.
Antony
All information has been forwarded to your mail address.
Please confirm reception.
In case of AC heating see also:
http://db.audioasylum.com/cgi/m.mpl?forum=tubediy&n=176304&highlight=eco+solution&r=
Best Regards
ecc230
Hi Folks: Sorry to clutter the thread, but I too would like a
clear copy of this schematic. A couple of the email addresses for sources on this thread seem blocked or no longer working. Thanks in advance. WS
The files have just been sent to your private mail.
Best Regards
Luca
ecc230
And this is the second part of the schematic.
This is to provisionally post the main schematics (1 of 2).
Please e-mail me a clearer image of the schematics.
Do you have different or same value of plate and cathode resistor in phase splitter (can't read clearly in your schematic)? Because it can make a lot differences as this elimatated a lot extra global NFB that degraded the sonic, especially the upper treble and also speed. As your driver is quite simialar to old rca otl amp. http://www.miduho.com/jp/st/amp-kairo/rca/OTL%20Amplifier/rcaotl.gif it has 56K and 33K in phase splitter. Near very other otl amps use Gobal NFB in one way or another or NFB in the driver stage though, can you test is it better?
The old 'rca otl amplifier' is very similar to the 1954 'Dickie & Makowsky scheme' I had used for the otl guitar amplifier that I have posted here some months ago.
It has about 40 dB of negative feedback (as a matter of fact the final stage made of 12AT7, 6SN7 and 3X-6080 has unitary gain because the output signal returns directly to the cathode).
I have noticed that so much negative feedback results in weird effects in case of hard clipping.
This is the main reason why I have tried to trade in more gain (from the very same tubes) in exchange for a lower negative feedback.
In my proposed scheme (I will be glad to send better jpeg files at the e-mail address of your choice) the open loop gain (@ 8 Ohm)is about 116 (23*1.8*14*6.5mA/V*4*8) whereas the closed loop gain is about 16.
To me this give the best sonic results with my speakers (ESB 7/08, four way Italian floor speakers manufactured in 1989).
Coming to your question the plate resistor of the first triode from the left is 27K (with a current of 2.2 mA) and its cathode resistor (i.e. NFB resistor) is 10K.
You should see here the input phase splitter of the 'modified Futterman schematic'.
There is also a second phase splitter (see the second triode from the left, 33K plate and cathode resistors, 2.5 mA) but its function (in tandem with the following 6SN7 tube differential amplifier) is only to boost the differential drive of the totem pole (4X) 6080 tubes (originating from the 27K plate resistor) to up to 135 V p-p.
The reason why many OTL schematics with 6SN7 differential drive and 6080 tubes exhibit a 18K plate resistor lies in this basic fact: there is no way to have 135 v P-P in the load with a different plate resistor.
Can OTL amp really good guitar amp? I am too interested. The clipping distortion and recovery is not the same as transformer output, but may be I can do something about it if you email the schematic to my email address. I think there are ways to make the clipping better 1)configure the amp in voltage follower instead of cathode follow mode, in the rca otl I believe it is in already in voltage follow mode which is prefered(?) 2)use positve feedback to ensure sufficient gain even at clipping and also can have better damping factor with lesses negative global feedback. 3) allow driver to clipp first before the output by shunting across the 2 plates of driver (2nd tube 6SN7 with 18K plate resistor) with a variable resistor say 250K-B or suitable choke.
For driver level it's 160V P-P in upper arm and 120V P-P in lower arm. The gives 40V P-P or 25W into 8 ohms or 80V P-P or 50W into 16 Ohms. Like flaw in old Willaimson amp, this old otl amp may have same flaw, the cathode bias resitor my be too low a value which I hope it may be verified.
I think the present OTL amplifier scheme (one channel) could be a good OTL amplifier too (with clean channel only).
In fact the design comes out from my previous experience with the construction of an OTL guitar amplifier.
Just add a 12AX7 input gain stage to boost the guitar pick-up signal to about 1V.
Likely due to the generous power supply I have noticed no weird effects (even under severe clipping) and the distortion comes out softly (when approaching overdrive).
The 500 VA transformers (not a VA less!) should also guarantee plenty of 'sustain' to your guitar.
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
