NAD: MonoPrice ProAudio 611815

[1FretLess]

Found a 15% off coupon and combined w/sale price
I could not pass it by...

Was expecting to hate on the Seventy 80 but i'm lettin' it break in....

It really is based on the Laney Cub 12R!

Not much time to bench out the schema
of course this is without the Laney reverb iC and I'm
curious about the verb driver for this little tank.

Word is if you mount it with standoff's instead of the foam
the tank is usable - I have an old tank around I hope to
cycle in.

Most interestingly you can bypass the FX/Verb circuit
and have pure analog wiring input to output.

Sweet and most surprised


Got Tone for Ruby's too..

 

[eS.G.]

SO........I am glad SOMEONE finally snagged one fo these as I have been looking at them and looking at them and ALMOST hit the "buy it now" several times .....

So what the verdict?
How about some sound bites???


What was the final delivered $$???

I gots ta know man......they look groovy for the price I have seen

 

[1FretLess]

170.00 to the door

the 70/80 is fine for what i got it for
(bedroom levels) it gets harsh loud.

Likely toss something else in eventually

not a bluesbreaker or anything but
plenty loud thats for certain
- the low input is all i seem to use
and still toneful

pressboard (hardened tho') back and
the tolex aint so bad....

twas a steal for certain

plenty of reviews on youtube ;-)

 

[eS.G.]

Well done a good tube amp with a 12 AND reverb for under 200.00 is ALWAYS a good thing

Congrats

 

[BGood]

12" Seventy 80 ? I like them, got two with my Super Champs and I like the deep and rich tone they provide. But they are in closed back cabinets with portholes. It might depend on the amp driving them, because it wasn't great with a Micro Terror.

 

[DPaulCustom]

Nice looking lil amp, & a good price as well.
BGood makes a good point about the amp driving the 70/80s.
I picked up a pair on the bay, & put them in an open back 2x12 cab to use with my modded Valve jr.
They're definitely more suited to a 'brighter' amp. Worth mentioning, at bedroom levels, it's gonna take a long time for them to break in.

Congrats on the new amp & enjoy!

 

[1FretLess]

thanks for the encouragement!

actually seems to be running fine
the 70/80 is not nearly as bad as
the webz proclaim - sounding better
anyway (or im used to it now!)

drives my 2x12 really -really- well
Eminence pair (greenback clones)

another mod in order to run the internal
w/external 16 ohm cab ....

cant wait to dig into it but basically an
impulse buy puts her on the back burner
for awhile - could not find any gut shots
when looking and I wanted to post some
(since you guys roll like that !)

Keep on Pickin'

 

[DPaulCustom]

thanks for the encouragement!

actually seems to be running fine
the 70/80 is not nearly as bad as
the webz proclaim - sounding better
anyway (or im used to it now!)

drives my 2x12 really -really- well
Eminence pair (greenback clones)

another mod in order to run the internal
w/external 16 ohm cab ....

cant wait to dig into it but basically an
impulse buy puts her on the back burner
for awhile - could not find any gut shots
when looking and I wanted to post some
(since you guys roll like that !)

Keep on Pickin'

I don't think they're bad speakers, but the Vjr is dark by nature. Even with all the mods I've done, it still tends to lean on the bass a touch.
Glad the new amp is working out for you, Enjoy

 

[1FretLess]

+8 Output Modification:

Issue: Internal speaker is switched OFF when an external cab (load) is plugged into the amp

Desired Operation: Allow the internal speaker to be active when an external load is connected

Concerns: The internal speaker circuit is wired in PARALLEL with the output jack
This puts the amp in an unstable condition with certain external loads

Consider:
On the surface a simple jumper across the switchjack (+) lugs would enable the internal speaker to be connected and operate if a jack is inserted (jumping the switched function) But some attention toward the loads to be to driven (8/ohm leslie -or- 4~16/ohm cab) leads to some interesting problems with this quick and simple fix. The catch being the default circuit places the internal driver in PARALLEL with loads that are attached via the jack. In simplistic terms if we plug in an 8ohm load, with the 8ohm internal speaker (in parallel), the transformer winding “sees” around 4ohm – well below our impedance threshold.

Ohms Law and all!

A Possible Resolution:
To safely operate other external sources, the internal speaker should be placed in SERIES (+8) with the loads presented at the jack. Now we can simply add eight (8ohm) to any additional impedance plugged in. If the circuit can be converted into a series connection, a single 8ohm external load (cab) would be seen by the amp as a 16ohm load, operating within design confines. To drive a little 2x12 that has switching between 4~16ohm – we can connect up as a 4ohm load and present around +/-12ohm to the transformer and operate within the 8-16 ohm threshold. Brilliant!

Intentionally forcing the load UP provides a level of safe impedance loads with many standard configurations with the exception being a 16ohm external load falling above the output range (24ohm) but still not placing the power tubes in an unstable condition by falling below the 8ohm floor. This configuration would provide hardly any power output but would not immediately damage the tubes. If a load of 16ohm is expected, then adding a speaker switch to the circuit would be a relevant and necessary option to disable the internal speaker


A look at the hardware and the intended plan:

Not fond of crossing the ground plane with signal (keep 90’ angles!) and using the jack in such a round robin fashion. I’ll argue with you the possibility of introducing noise into the signal and also the re-use of the SPK1 or positive (+) spade terminal (again crossing the ground plane). However, the factory connections are maintained and I do not intend to provide for switching, and just following the +8 rule when connecting loads. Line noise that may accumulate (if any) has not been audible – with no apparent loss in output, tone, or signal quality.

 

[1FretLess]

What’s Going On in the Circuit:

The signal(s) from the secondary enter the board in the lower Left of this graphic. The positive going signal slides to the right to tap the Feedback jumper and up across a resistor then to the (un-switched) Jack TIP lug. If there is no jack present the signal travels up the lug’s switched contact to the SPK1 (+) output terminal. The signal returns thru the SPK2 (-) terminal to the ground bus and the negative going secondary. If a jack is inserted, the “switch” is lifted from the SPK1(+) terminal breaking the signal flow and disabling output to the internal driver.

Notice the jack’s [switched] RING lug (upper right) is not connected to the circuit at all.

The +8 modification is a play on how the signal passes thru the switching 1/ 4” jack. After freeing the jacks RING lug from the ground plane, the wiring can be modified to “run the loop” around the switched jack circuit (yellow wire) if nothing is connected. The positive(+) going signal exits the jack on the un-switched RING Lug (lower right).

Plugging into the jack will then “switch” or disable the top contacts (yellow wire is now out of the circuit) and signal flows to the jack tip – thru the load - out the Ring lug – then into our internal speaker (+) then returning back to the ground plane.

To switch the circuit, a SPDT (Single Pole Dual Throw) switch can be used. The RING Lug (+line) runs to the center pole on the switch. One pole would connect to the positive going (+) internal speaker lead, the other pole connects to some point on the ground plane (-) to give the external load a path to ground.


Time to Void the Warrantee!

Using a small router bit in a drill press to isolate the negative Jack Lug and the Positive speaker lead



The final Circuit Modification:

There were about 4 different ways to provide for running both an external cab and the internal speaker for this little circuit board. I settled on this variant because this is a fixed “bedroom” amp that I just want to hook up either a 4 or 8 ohm external load. The switch was not necessary for my purpose but adding the switch makes for a much more flexible platform when hooking up to different cabinets.

At last I’ve got the RoTo/Leslie running along with the amp!

… Yeah gonna be awhile till I post back the next episode of the Warrantee Breaker !


What could possibly be next??
Presence Control on the feedback loop?
Fx Loop Bypass (Pure Analog!)?
Reverb Circuit Volt Mod?

Cheers!

 

[1FretLess]

A preliminary Reverb circuit schematic



some minor details - SMD cap's dont have codes
so some cap values are missing.

R34 (not shown) is a 3watt 220 ohm resistor. :-)

pretty standard recovery circuit ought to drive several
different tanks with hardly any changes to the circuit needed

Cheers!

 

[1FretLess]

Coming together!

 

[1FretLess]

Make the new tank usable

 

[eS.G.]

I am curious to see how these hold up----because I have been very interested since I first saw one.

Any sound clips????
Or comparisons to other tube amps in tone etc???

 

[1FretLess]

I am curious to see how these hold up---

Any sound clips????
Or comparisons to other tube amps in tone etc???

It hit my price point for the most part
and internally really good - el-power etc.

the chasis paint/screening is so so and
have a few bubbles from poor prep or
moisture. Tolex is interesting but not
well executed so seams show etc.
a power tube was cracked at delivery
but intended on re-tubin' anyway

i was after function tho'
the pots are light (feeling) and the
arrangement is weird but after a few
tweaks (i've been postin here) its a
workable low priced tube amp

the circuit is a lot like a Fender Deville
so if your familiar - almost the exact same
fx/verb circuit. it is a Laney and brings that
level of component quality (boards - hardware-
interconnects etc.) But the cab/chasis is asian
and brings that quality.

again I hit it for the price and the gamble worked
for me because its a basic circuit and going in was
expecting to modify some.

still needs a Screamer out in front
but she has great gain control...

the stock verb is a must swap (20-30$)

so im around 200 bills but had parts around
(speaker so add another 50! ohh and the JJ's)

sorry i've no sound clips to share
am actually rebuilding things due
to some unexpected gear loss
during my last residence move.

just dont have the tools now

thanks tho for checkin' in

hopefully helpful for someone
in the future anyway!

 

[eS.G.]

Yes......I truly do not NEED another amp----but I have been watching these since they first popped up ---I mena the sum of the parts for the price sure seem a Hell of a deal.

 

[1fender]

So did you do anything to the reverb circuit except put in the MOD Reverb Tank? Was it a 8EB2C1B?

Simple switch out?

Someone suggested that the stock reverb was 600 ohms and the 8EB2C1B is 800 ohms. So they suggested putting ahigh gain/ low noise 12AX7 tube in V2 position to regain some of the gain that is lost by using an 800 Ohm reverb in place of a 600 Ohm reverb and lower the noise of the reverb circuit.

Your thoughts? If correct which tube would you recommend?

 

[1FretLess]

So did you do anything to the reverb circuit except put in the MOD Reverb Tank? Was it a 8EB2C1B?

Simple switch out?

Someone suggested that the stock reverb was 600 ohms and the 8EB2C1B is 800 ohms. So they suggested putting ahigh gain/ low noise 12AX7 tube in V2 position to regain some of the gain that is lost by using an 800 Ohm reverb in place of a 600 Ohm reverb and lower the noise of the reverb circuit.

Your thoughts? If correct which tube would you recommend?

I approached it with a transformer twixt the out and the tank
Played for a spell with a few mods to drive the tank harder
But ended up using the stock circuit - the recovery circuit
Suits the tank fine but needs driven a bit more -
- a 2 spring unit might serve better

The driver / recovery are digital

 

[1fender]

So it is fine to just switch it out with new plugs that fit the MOD unit and nothing else? What about the difference in ohms and the idea of a better tube in the V2 position?

I am not an expert in schematics so looking at the amp from the back, which of the 3 preamp tubes is V2?

 

[1FretLess]

A final schema