Mesa Tremolo LDR type?

AdmiralB · 09-20-2007, 09:07 PM

I'm fiddling with getting more depth out of a Tremoverb's tremolo. The LDR - LDR21 on the schem - seems to be the area of focus. But I've never seen anything like it before, it's not a Vactrol, it's a barrel-shaped thing about 3/8" in diameter - circular in cross-section, not a flat oval like Vactrols - and about a quarter-inch long. The only markings on it is the number "217" in (fairly) large white ink.

Any ideas?

tbryanh · 09-23-2007, 04:39 AM

I have heard Mesa orders them special made in batches of 1000.

If you want to buy 1000, I can dig up the manufactuer's name for you.

If you want only one or two, you probably have to go to Mesa or one of their authorized repair centers. I don't know if they will sell them to you or not.

AdmiralB · 09-24-2007, 02:37 PM

Thanks!

tbryanh · 09-25-2007, 01:26 AM

Actually, if that is for a tremelo, it might be similar to the one Fender uses. The one Fender uses is easy to get.

tbryanh · 09-25-2007, 01:31 AM

I was thinking about the typical LDR Mesa uses in their Triaxis and other amps to control patching and presets. The LDRs for those are custom.

I am not sure about the Tremelo one. I think Fender uses a neon bulb and LDR that are shrink-wrapped together. I do not know what Mesa uses for their Tremelo.

Sorry, I may have given you incorrect info.

I am getting deep into the Triax schemat at this point, so I sorta had a one-track mind.

AdmiralB · 09-25-2007, 01:46 AM

Nah, the TOV trem circuit is a 555 timing chip driving an LDR. The Fender unit is high-voltage, the Mesa is 12V. It's not like anything I've seen.

Don Moose · 09-25-2007, 01:56 AM

Quote:

Originally Posted by tbryanh

I am getting deep into the Triax schemat at this point, so I sorta had a one-track mind.

Unless you have the secret magic pages about how the LDRpots work, you need a copy of US Patent 5,208,548.

Hope this helps!

tbryanh · 09-25-2007, 02:42 AM

Thanks for the patent info.

I plan to build an amp similar to the Triaxis that uses standard potentiometers and rotary switches instead of LDRs.

I want to add some ideas of my own also.

I am impressed at how the amp can be configured into the equivalent of 3 or 4 amps by switching in different cathode bypass capacitors, different tone stacks, and extra stages as needed.

I think it is the most advanced amp of its kind, and people like it well.

I am not going to use op amps in the signal path for the EQ. That is one of the complaints about the amp. If you drive it too hard, the op amps give nasty distortion unexpectedly.

I am going to make a tube version or the EQ circuit.

As far as the LDRs go, I want to eventually go down that road, but for now, it is not an obstacle. I am not going to use them.

Don Moose · 09-25-2007, 12:27 PM

Quote:

Originally Posted by tbryanh

I am not going to use op amps in the signal path for the EQ. That is one of the complaints about the amp. If you drive it too hard, the op amps give nasty distortion unexpectedly.

I am going to make a tube version or the EQ circuit.

You might look at the transistor-driven EQs on the Mk series. No complaints that I'm aware of with that circuit. The tough part is sourcing the inductors (and finding room for them).

Best of luck - that's quite a project.

clintronics · 09-25-2007, 06:21 PM

tbryanh · 09-26-2007, 12:56 AM

Quote:

Originally Posted by Don Moose

You might look at the transistor-driven EQs on the Mk series.
Best of luck - that's quite a project.

Thanks. Yeah, I saw those. In fact that is the one I want to convert to tubes.

Any ideas on how to make a tube version of it?

Don Moose · 09-26-2007, 03:08 AM

Quote:

Originally Posted by tbryanh

Any ideas on how to make a tube version of it?

Well ... you'd need to rescale the impedances for tube use.

Other than that, I'm out of my depth.

Good luck!

Enzo · 09-26-2007, 05:53 AM

Look up active filters in a tube reference like the RDH.

Alf · 09-26-2007, 06:50 PM

Have a look at the "Acoustic GT 100" amp , it has a tube eq .
I know because I own one.

Alf

Gregg · 09-26-2007, 09:20 PM

There's a long thread in Theory and Design section called "LDRs as pots" where these so called LDR pots are discussed.

tbryanh · 09-27-2007, 02:05 AM

Quote:

Originally Posted by Enzo

Look up active filters in a tube reference like the RDH.

Sorry for being ignorant, but what is RDH?

Thanks

Don Moose · 09-28-2007, 01:28 AM

Quote:

Originally Posted by tbryanh

Sorry for being ignorant, but what is RDH?

I believe it's 'Radiotron Designer's Handbook' - the sourcebook for tube design engineering. There are a couple of complete copies online, but I don't recall where.

tbryanh · 09-28-2007, 02:43 AM

Quote:

Originally Posted by Don Moose

I believe it's 'Radiotron Designer's Handbook' - the sourcebook for tube design engineering. There are a couple of complete copies online, but I don't recall where.

Oh yeah, I have the free PDFs of that book. I will check it out. Thanks

09-20-2007, 09:07 PM	#1
AdmiralB Member Join Date: Jun 2006 Posts: 102	Mesa Tremolo LDR type? I'm fiddling with getting more depth out of a Tremoverb's tremolo. The LDR - LDR21 on the schem - seems to be the area of focus. But I've never seen anything like it before, it's not a Vactrol, it's a barrel-shaped thing about 3/8" in diameter - circular in cross-section, not a flat oval like Vactrols - and about a quarter-inch long. The only markings on it is the number "217" in (fairly) large white ink. Any ideas?

09-25-2007, 06:21 PM	#10
clintronics Member Join Date: Aug 2007 Location: Richmond, VA Posts: 72	old fax from mesa RE: LDRs

09-26-2007, 06:50 PM	#14
Alf Senior Member Join Date: May 2006 Location: Netherlands Posts: 123	tube eq Have a look at the "Acoustic GT 100" amp , it has a tube eq . I know because I own one. Alf

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09-23-2007, 04:39 AM	#2
tbryanh Senior Member Join Date: Apr 2007 Posts: 403	I have heard Mesa orders them special made in batches of 1000. If you want to buy 1000, I can dig up the manufactuer's name for you. If you want only one or two, you probably have to go to Mesa or one of their authorized repair centers. I don't know if they will sell them to you or not.

09-24-2007, 02:37 PM	#3
AdmiralB Member Join Date: Jun 2006 Posts: 102	Thanks!

09-25-2007, 01:26 AM	#4
tbryanh Senior Member Join Date: Apr 2007 Posts: 403	Actually, if that is for a tremelo, it might be similar to the one Fender uses. The one Fender uses is easy to get.

09-25-2007, 01:31 AM	#5
tbryanh Senior Member Join Date: Apr 2007 Posts: 403	I was thinking about the typical LDR Mesa uses in their Triaxis and other amps to control patching and presets. The LDRs for those are custom. I am not sure about the Tremelo one. I think Fender uses a neon bulb and LDR that are shrink-wrapped together. I do not know what Mesa uses for their Tremelo. Sorry, I may have given you incorrect info. I am getting deep into the Triax schemat at this point, so I sorta had a one-track mind.

09-25-2007, 01:46 AM	#6
AdmiralB Member Join Date: Jun 2006 Posts: 102	Nah, the TOV trem circuit is a 555 timing chip driving an LDR. The Fender unit is high-voltage, the Mesa is 12V. It's not like anything I've seen.

09-25-2007, 02:42 AM	#8
tbryanh Senior Member Join Date: Apr 2007 Posts: 403	Thanks for the patent info. I plan to build an amp similar to the Triaxis that uses standard potentiometers and rotary switches instead of LDRs. I want to add some ideas of my own also. I am impressed at how the amp can be configured into the equivalent of 3 or 4 amps by switching in different cathode bypass capacitors, different tone stacks, and extra stages as needed. I think it is the most advanced amp of its kind, and people like it well. I am not going to use op amps in the signal path for the EQ. That is one of the complaints about the amp. If you drive it too hard, the op amps give nasty distortion unexpectedly. I am going to make a tube version or the EQ circuit. As far as the LDRs go, I want to eventually go down that road, but for now, it is not an obstacle. I am not going to use them.

09-26-2007, 05:53 AM	#13
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,318	Look up active filters in a tube reference like the RDH.

09-26-2007, 09:20 PM	#15
Gregg Senior Member Join Date: May 2006 Posts: 212	There's a long thread in Theory and Design section called "LDRs as pots" where these so called LDR pots are discussed.

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