JLM 60Watt Power AMP Kit

Support for JLM Audio Kits

Moderator: Joe Malone

kevanatkins
Posts: 4
Joined: Fri Aug 25, 2017 6:14 pm

Re: JLM 60Watt Power AMP Kit

Post by kevanatkins »

kevanatkins wrote:
Joe Malone wrote:
kevanatkins wrote:Yikes. I didn't get a notification about your reply. Anyway...

I haven't made much headway since. There's no link on the mute terminal. I've attached some photos.
You must fit the link between mute and -V to turn the amp ON. Without the link you will be in mute so will never get anything out of the amp.

Also for full gain NO resistor should be fitted to the volume terminals. Shorting the vol +/- turns the volume right down.
Fitted the link and removed the resistor. Still nothing.
Oops. Nevermind. My fumbling about putting the link in and taking out the resistor loosened the power connection. PEBCAC! Everything works now.

Thanks Joe!

User avatar
Joe Malone
Site Admin
Posts: 1631
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

kevanatkins wrote:
kevanatkins wrote:
Joe Malone wrote:
You must fit the link between mute and -V to turn the amp ON. Without the link you will be in mute so will never get anything out of the amp.

Also for full gain NO resistor should be fitted to the volume terminals. Shorting the vol +/- turns the volume right down.
Fitted the link and removed the resistor. Still nothing.
Oops. Nevermind. My fumbling about putting the link in and taking out the resistor loosened the power connection. PEBCAC! Everything works now.

Thanks Joe!
Cool great to hear :-)
Joe :-)
JLM Audio
Capturing Audio without Injury

rtchau
Posts: 7
Joined: Thu Nov 03, 2016 12:22 pm

Re: JLM 60Watt Power AMP Kit

Post by rtchau »

Joe Malone wrote:
rtchau wrote:
Joe Malone wrote:
HI Richard
If the volume pot is turned fully down does the amp motorboat?
Hi Joe,

No - it only seems to go bananas after the volume pot is turned up past 50%, prior to that it starts to hum after 10-20%, and nothing at 0%.
OK what value is the volume pot? If 10k log connect a 4.7k resistor between the center wiper and 0v and retest to see if pot can get to 100% with only hum.
Hi Joe,

Sorry for the huge delay - we've moved house and I've changed jobs, so it's been busy times.

I did what you suggested and connected a 4.7k resistor between the centre wiper and 0v - however for simplicity of testing, I connected it directly to the terminals on the PCB on 0v and where the centre wiper joins the PCB (+in).

The motorboating is gone, but replaced with a hum that seems to change from low to high pass depending on volume (higher freq passing at low volume, lower frequency passing at high volume) - it seems I've created a sort of Franken-EQ shaper with the 10k pot :P

Cheers,

Richard

rtchau
Posts: 7
Joined: Thu Nov 03, 2016 12:22 pm

Re: JLM 60Watt Power AMP Kit

Post by rtchau »

One other thing I've noticed is trouble with clearance between the capacitors on either side of the LM3886 and the heatsink that it's bolted to... is there a trick to mounting the LM3886 on the board that I missed, so that it has better clearance and the capacitors aren't making contact with the heatsink? I saw another build on this thread where the plastic on one of those caps had worn through.

frazzman
Posts: 8
Joined: Wed Jan 25, 2017 1:01 pm

Re: JLM 60Watt Power AMP Kit

Post by frazzman »

Hi Joe,

I have 2 of these power amps running happily in bridged mode using a 2x18 160VA toroid.

I’d now like to use this power amp to drive 2 passive speakers.

So my question is, are there any issues with “converting” this to dual mono, but leaving the toroid as is (2x18)?

As I understand it, a 2x25 is what your spec calls for when running 2 independent channels / unbridged?

Cheers

User avatar
Joe Malone
Site Admin
Posts: 1631
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

frazzman wrote:Hi Joe,

I have 2 of these power amps running happily in bridged mode using a 2x18 160VA toroid.

I’d now like to use this power amp to drive 2 passive speakers.

So my question is, are there any issues with “converting” this to dual mono, but leaving the toroid as is (2x18)?

As I understand it, a 2x25 is what your spec calls for when running 2 independent channels / unbridged?

Cheers
Using the 2 x 18vac into 8ohm speakers will just limit the power to some like 40w.
If using 4ohm speaker you will still get the 68w with the 2 x 18vac transformer.
Joe :-)
JLM Audio
Capturing Audio without Injury

JGale
Posts: 4
Joined: Thu Dec 19, 2019 5:13 am
Location: United States

Re: JLM 60Watt Power AMP Kit

Post by JGale »

Hello All.

I have built this AMPkit successfully (+/- 34V rails) and it sounds glorious. I am using it as an FRFR loudspeaker speaker for a Tech21 PSA-1 guitar preamp fully balanced including effects loop. I play mostly clean guitar and the AMPkit delivers the goods.
AMPkit2.jpg
It is however, not very loud. AMP at max volume is on the very low end of "turn-that-down." The amp it replaces, a Tech21 Power Engine 60 (+/- 40V rails, LM3875), was at the high of said scale at 50% volume, and it was exceedingly, horribly noisy! The AMPkit is supremely quiet.

After reading through the forum, I thinking my options for greater volume are as follows:
1. Convert input to SE @ 60W and use a Regurgitator for input conversion.
2. Convert to 120W bridged. Keep the balanced input.
3. Convert to SE @ 120W bridged and use a Regurgitator for input conversion.

Will one of the Dingoes suit me better?
Can any of these input devices be used to increase the apparent loudness of the amp for guitar work?

I would like to entertain the use of an active EQ in the future (the original had a TMB active stack), but have yet to find a circuit board. I assume that the Dingo would be the board to handle this additional circuit?

Finally (maybe), can the Trek2 heat sink be used with the AMPkit? They are the right dimension for my chassis.

Thanks in advance. This Forum has been a great education.

Jim Gale
Roanoke, US
You do not have the required permissions to view the files attached to this post.

User avatar
Joe Malone
Site Admin
Posts: 1631
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

Yes regurg kit is made to do bal in to bal out with up to 18dB gain. The 60w amp kit is a slave amp hi made to take high line level. Most guitar amps are actually a preamp with amp.

If using our 60w amp kit you can get more gain from the amp by making the 1k resistor small value. Also if not using the volume control on the amp kit use the volume+/- as the audio input instead to get a few dB more gain from the amp.

Best to use a preamp and work out the amount of preamp gain you needed to get the level you want and let me know the amount if extra dB you need so I can suggest the best solution.
Joe :-)
JLM Audio
Capturing Audio without Injury

JGale
Posts: 4
Joined: Thu Dec 19, 2019 5:13 am
Location: United States

Re: JLM 60Watt Power AMP Kit

Post by JGale »

Thank you Sir.

The PSA-1 is a 1U rack mount analog guitar modeler with parallel/series loop and stereo, balanced, XLR (600ohm) and 1/4” TRS (1Kohm) output jacks at -10dB. A pad for each set raises the output to 0dB.

http://www.tech21nyc.com/archive/psa-1/

The PSA-1 literature lists the overall available output at +10dB, which I believe unless you “kill dry” the effects loop in parallel. The last control on the front panel is output Level which in most amp models is at or near 75%.

I just made the SE mod to the AMPkit, linking out the two 10K resistors on the PCB. We’re getting closer! Nice increase in volume. Can we double that and stay with balanced input?

I’m assuming, (and you know what that means… :shock: ) a small dB increase via the PCB resistor, coupled with the small increase using volume as inputs would keep the chip happy and the needed Regurgitator levels low allowing some wiggle room?

My goal is to write this up for others to follow simply. A large percentage of these PE60s have this noise problem. A 60W setup would be made simple by reusing the existing heat sink and purchasing the parts (assembled) from JLM. There is currently zero out there on rebuilding these powered speakers.

In my case, after I locate the proper heat-sinks, I intend to bridge two AMPkits to 120W.

UPDATE 21JAN20: I had a chance to sit down today with an old Strat, my favorite oldfenderampmodel and this AMPkit today. Slight boost in front. Pedal only has +10dB and I'm guesstimating this was set ~+3-4dB. Nice increase in volume. Nice dynamics. This little beast can take a wallop. I agree with earlier assessment, "pristine sound, well designed, grunt." Perhaps we are not so far off a solution with balanced input.

UPDATE 26JAN20: I wired a second 8ohm speaker in parallel. Still running SE input only changes to the board. Four ohms is definitely the way to go! The 60W AMPkit handled it easily.

Thanks for your patience. After all this I think I’m clear about my questions pre-order.

UPDATE 14FEB20: Order up! Decided to keep it simple. 120W balanced with a DIngo pup handling loop duties. Even found an active CABSIM that reportedly runs on 16V. Watch this space!

UPDATE 26FEB20: Kudos to the Australian Post! Left Australia on 2/19, arrived Appalachia US 9/22, on a Saturday. That's fast.

Thanks very much for all the learning!

JGale
Posts: 4
Joined: Thu Dec 19, 2019 5:13 am
Location: United States

Re: JLM 60Watt Power AMP Kit

Post by JGale »

They're here, and they're beautiful! Tiny little masterpieces.
Pre-built because my hookup skills are excellent.
PowerEngine60.gif
Now the fun begins.
You do not have the required permissions to view the files attached to this post.

Mattsoniclab
Posts: 3
Joined: Sat Aug 13, 2016 2:38 pm

Re: JLM 60Watt Power AMP Kit

Post by Mattsoniclab »

Hi there.
Some advice please.
Would this transformer be suitable for two amp kits?:

https://nz.rs-online.com/web/p/toroidal ... s/1234025/

thanks!
Matt

User avatar
Joe Malone
Site Admin
Posts: 1631
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

Mattsoniclab wrote:
Thu Jul 02, 2020 6:31 pm
Hi there.
Some advice please.
Would this transformer be suitable for two amp kits?:

https://nz.rs-online.com/web/p/toroidal ... s/1234025/

thanks!
Matt
Hi Matt Yes that transformer is perfect for 2 amps not running in bridge mode.
Joe :-)
JLM Audio
Capturing Audio without Injury

Post Reply