Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Tubes and Hybrids => Topic started by: Steve Conner on February 04, 2011, 10:34:33 AM

Title: LND150 tube emulator attempt.
Post by: Steve Conner on February 04, 2011, 10:34:33 AM
OK, so following the recent discusion on FET-based tube emulators, I did some more work on my own ideas. Friday afternoon at work, and all that.  ::)

First I took the dual gate MOSFET cascode one and compared it against a Mullard ECC83. After some playing with the component values, they gave similar traces, but it was extremely temperature-sensitive. Someone had borrowed the heat gun, but there was no need for it: even breathing on the MOSFET caused about 10V shift in drain voltage. That made me think that the variation between different MOSFETs would be even worse.

So, I tried the LND150 in a circuit somewhere between the Trioderizer and the scalable diode. It worked surprisingly well. The clipped waveforms were as good, if not better than the dual gate circuit, and temperature stability seemed much better. Also, the component count is lower.

The major drawback is that it leaks DC out of its "grid". In conjunction with the usual 1M grid-leak resistor found in a tube circuit (well, 910k, as I ran out of 1Ms) this creates the positive voltage needed for the LND150 to have the right bias point. But tube circuits often use a volume control, or a different value to 1M, as the grid leak.

So, I'm working on that one. For now, this circuit would only be usable in a design that took the DC into account: it might not work if you just plugged it into a tube socket.

The scope shots show the LND150 circuit working alongside the Mullard ECC83, also set up with a 100k plate and 1.5k cathode resistor. Both are running off the same 250V supply. Top trace is the input signal, and the bottom two are the outputs from the ECC83 and LND150. I will leave you all to figure out which is which. :)

To paraphrase the Monty Python sketch, "Bring out your FETs!"
Title: Re: LND150 tube emulator attempt.
Post by: rowdy_riemer on February 04, 2011, 10:55:53 AM
The major drawback is that it leaks DC out of its "grid".

Do you think the gate insulator might be damaged?
Title: Re: LND150 tube emulator attempt.
Post by: Steve Conner on February 04, 2011, 11:00:48 AM
No. It does it on purpose, because I stuck some resistors from drain to gate.

See this article for why I put the resistors there: http://www.radiomuseum.org/forum/the_trioderizer_a_solid_state_triode.html

They also help the LND150 to bias up hotter than it otherwise would, especially since it needs resistance in its source to bring its gm down in line with a 12AX7.
Title: Re: LND150 tube emulator attempt.
Post by: KMG on February 04, 2011, 11:37:00 AM
At the first waveform can be seen that the FET cut-off "sharper" than the tube. I solved this problem by placing GE diodes in the source of FET.
There is no information in LND150 datasheet about gate-source protective zener. Negative half-wave may exceed maximum gate-source voltage specification.
Title: Re: LND150 tube emulator attempt.
Post by: J M Fahey on February 04, 2011, 12:53:07 PM
Good, cool discussion  :tu: :tu:
Title: Re: LND150 tube emulator attempt.
Post by: rowdy_riemer on February 05, 2011, 12:32:15 AM
No. It does it on purpose, because I stuck some resistors from drain to gate.

See this article for why I put the resistors there: http://www.radiomuseum.org/forum/the_trioderizer_a_solid_state_triode.html

They also help the LND150 to bias up hotter than it otherwise would, especially since it needs resistance in its source to bring its gm down in line with a 12AX7.

Duh!! I thought you were talking about leakage through the gate.  :duh
Title: Re: LND150 tube emulator attempt.
Post by: KMG on August 10, 2011, 03:15:36 PM
Continue the story
1-st stage of JCM 800 (2k7/0.68u, 100k)
Left - 12AX7, right - LND150 (with different component values of course)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/1T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/1T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/1F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/1F.JPG)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/2T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/2T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/2F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/2F.JPG)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/3T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/3T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/3F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/3F.JPG)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/4T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/4T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/4F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/4F.JPG)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/5T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/5T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/5F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/5F.JPG)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/6T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/6T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/6F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/6F.JPG)
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/7T_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/7T.JPG) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/7F_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/dc/7F.JPG)
“See the cat? See the cradle?”


Schematic of test equipment.
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/LND150s.jpg)
Title: Re: LND150 tube emulator attempt.
Post by: J M Fahey on August 10, 2011, 07:39:57 PM
*Very* good  :tu: :tu: :tu: :tu: :tu:
Can you please add the driving voltage on each step?
Thanks.
PS: I would love to see what comes out of a 2nd stage, when the first is overdriving and providing all it can (200Vpp or thereabouts?)

PS:Just in case I forgot to say so earlier:  :tu: :tu: :tu: :tu: :tu:
Congratulations.

PS2: I guess it's already beyond the "attempt" stage, isn't it?  ;)
Title: Re: LND150 tube emulator attempt.
Post by: Kaz Kylheku on August 11, 2011, 01:46:34 AM
All that's left to say is: bottle it and sell it.  ;D
Title: Re: LND150 tube emulator attempt.
Post by: KMG on August 11, 2011, 12:35:27 PM
Quote
Can you please add the driving voltage on each step?
I don`t remember values, but they was the same for both stages (tube & fet).
Quote
I would love to see what comes out of a 2nd stage, when the first is overdriving and providing all it can (200Vpp or thereabouts?)
Will be, wait some time.
Title: Re: LND150 tube emulator attempt.
Post by: joecool85 on August 12, 2011, 08:19:47 AM
All that's left to say is: bottle it and sell it.  ;D


Agreed!
Title: Re: LND150 tube emulator attempt.
Post by: KMG on August 21, 2011, 08:38:18 AM
Actually the basic stage.
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/St_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/St.pdf)

RG (with interstage circuits) and RP are original (from tube schematic).
Q1, Q2, ZD1 and R1 is Q3 gate protection, in the first stage is not used, just put in 20V zener at gate.
R2 determines the smoothness of "grid" limitation, R3 voltage at which it occurs.
R4 determines the gain at low frequencies, R5 - gain above the cutoff frequency, C2 - the cutoff frequency.
C1 simulates the Miller effect  (0-100pF, depending on the gain of the original stage and presence of capacitor in the cathode).
VBIAS for JCM800 got the same for all stages "-2.75V"
JCM800 using LND150
(http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/1_st_ver/brdtop_th.jpg) (http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/1_st_ver/brdtop.jpg)
Reamp sample
http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/s/8-Southern%20LP.mp3
Title: Re: LND150 tube emulator attempt.
Post by: KMG on August 28, 2011, 08:46:22 AM
While testing I found that there is no need in additional gate protection, only high voltage diode in source chain.
So, the basic stage for lnd150 is the following
(http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/St1_th.jpg) (http://milas.spb.ru/~kmg/files/projects/dualrectifier/test/lnd150/St1.pdf)
Comparative samples of "glass" JCM8000
(http://milas.spb.ru/~kmg/files/projects/jcm800mv/tube/brdtop_th.jpg) (http://milas.spb.ru/~kmg/files/projects/jcm800mv/tube/brdtop.jpg)
And SS (last version) JCM8000
(http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/brdtop_th.jpg) (http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/brdtop.jpg)
http://milas.spb.ru/~kmg/files/projects/jcm800mv/jcm800_fet_vs_tube.zip
Title: Re: LND150 tube emulator attempt.
Post by: Ilya-v on March 20, 2012, 04:22:51 AM
Bump.

KMG, this will revolutionize the guitar world.

Can you please elaborate on the final gain stage and what each component does?

Thank you.
Title: Re: LND150 tube emulator attempt.
Post by: KMG on March 20, 2012, 06:32:57 AM
There the full final design of LND150 JCM800 & answers to some questions
http://www.ssguitar.com/index.php?topic=2006.msg15734#msg15734
Title: Re: LND150 tube emulator attempt.
Post by: Camembert on December 22, 2017, 06:37:13 AM
Hello,

Can someone explain why, in the final version of this circuit, there are two diodes in parallel between gate and source, in stead of a single one?
Title: Re: LND150 tube emulator attempt.
Post by: Katoda on December 22, 2017, 07:20:10 AM
My guess would be that it's just easier to solder, but two diodes would conduct twice the current, so I'm not really sure.
Title: Re: LND150 tube emulator attempt.
Post by: Camembert on December 22, 2017, 09:28:59 AM
You are right about twice the current of course, but there is not a wholotta current flowing there.
I did find out that when you put two diodes in parallel, the voltage drop across the pair is slightly smaller than across a single diode. Maybe that is good for something.
But actually, I think my problem is that I don't really understand the "grid" limiter thing of wich the diodes are part...
Title: Re: LND150 tube emulator attempt.
Post by: blackcorvo on December 22, 2017, 01:24:36 PM
You are right about twice the current of course, but there is not a wholotta current flowing there.
I did find out that when you put two diodes in parallel, the voltage drop across the pair is slightly smaller than across a single diode. Maybe that is good for something.
But actually, I think my problem is that I don't really understand the "grid" limiter thing of wich the diodes are part...

After reading on the link posted at the end of pg1 of this thread, what I understood is that the source diodes are there to help shape the clipping curve for the stage, as well as act like a protection circuit against overvoltage between source and gate. I might be mistaken, however.
Title: Re: LND150 tube emulator attempt.
Post by: Katoda on December 23, 2017, 06:52:43 AM
You are right about twice the current of course, but there is not a wholotta current flowing there.
I did find out that when you put two diodes in parallel, the voltage drop across the pair is slightly smaller than across a single diode. Maybe that is good for something.
But actually, I think my problem is that I don't really understand the "grid" limiter thing of wich the diodes are part...

The diode conducts when there is a voltage greater than cca 0.7V across the conducting direction.  So when the signal swings in the positive direction, voltage on the source rises. If the source voltage is then greater than 0.7V  to base, the diode clips the signal. The 1k resistor limits the current through the diode, making the knee of the clipping softer.

It simulates the asymmetry of valve clipping.

I hope I'm not completely wrong, somebody please correct me if I am.
Title: Re: LND150 tube emulator attempt.
Post by: phatt on December 23, 2017, 09:15:28 AM
Look at the transfer curves shown here;
http://www.radiomuseum.org/forum/the_trioderizer_a_solid_state_triode.html
posted by Steve Conner on previous page.

The diodes are not causing distortion like a dirt pedal which just clips the audio, they are shifting how fast the Fet reacts (for want of better teck terms) .
As mentioned in the above link Fets gain curve goes straight up as do Pentodes whereas triodes the transfer is much slower to react and never quite gets there.
Pentodes were invented to overcome the limitations of triodes.

As to the Q; why 2 diodes in parallel,,, I dunno. Maybe KMG will see this and respond. He may have mentioned it in a another posting but too late now I'm off for sleep.
Phil.
Title: Re: LND150 tube emulator attempt.
Post by: Camembert on December 24, 2017, 05:24:15 AM
Well, I have been reading a bit about grid current and tubes and diodes, and the most shocking thing I learned is that this 'threshold' where the diode starts conducting doesn't exist! actually, it's a smooth exponential curve with a knee. Beyond the knee the diode starts to conduct 'a lot'. Before, it conducts little, but it does. Now,the grid current is in the order of microamps, so this all takes place way before the knee. And different diodes can behave differently in this region.
When I played with this in SPICE it appeared that two bav70 diodes in parallel behave very similar to a single 1N4148, wich was used in the first version of the circuit. So maybe the answer is quite simple: our KMG ran out of 1N4148 diodes and started using the parallel bav70's  as equivalent circuit..
Anyway, although I have no definite answer to my question, I learned a lot by investigating. Thank you guys for your kind replies.