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Messages - joecool85

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Amplifier Discussion / Re: Krell amplifier repair
« on: November 19, 2020, 11:50:55 AM »
Great job!

Amplifier Discussion / Re: Amp help for a(n old) newbie
« on: November 05, 2020, 08:56:15 PM »
Being a Fender tube amp, resale is pretty great.  You could definitely get a few hundred dollars for it and turn around to buy a new amp.  That said, this amp should last...forever-ish?  Maybe some tubes here and there, but not bad.  If you like the sound, I'd recommend keeping what you have!  :dbtu:

Schematics and Layouts / Re: Pignose amp?
« on: November 03, 2020, 11:41:45 AM »
Without a schematic I'm not entirely sure what they have going on there.  But one thing I can tell you, a little bit of contact cleaner (I use Deoxit) will most likely fix your issue.  Put the contact cleaner onto a 1/4" plug, work it in and out a few times and try again.

Thanks joecool,

(I got stuck in progress…)

My concern about the speaker-swap came from an exchange here (although some years ago) that the Vox Mini3 is (was?) peculiar about it and would fry the preamp if particular care wasn’t given (like, the ground was not really a ground, etc.) Is this still a problem with the new issue of Mini3-G2?

Other concern – widely shared and confusing – WHY, oh Why can’t be Lithium batteries used? The dire warning on the Mini states “use only alkaline AA batteries”. Will it go "pooof" if I use a Lithium battery, output almost exactly matching that of the Mini’s switching power’s? My Lithium cell is 12v-3A (nominal) center positive, the Mini is 12v-1A (nominal?).
Is the pack of 6 x 1.5v AA (9 volts) better? I produce seemingly unending heaps of dead AAs week after week…
In general, perhaps a modern, universal battery powering system should be developed and employed (and it appears that the Lithiums is the way) instead of the clumsy, inefficient and expensive 4-6-8 x AA alkalines?
Paul Gabor

It depends on the voltage of your lithium ion cell.  Normally they are 3.7v/cell, bringing it to 11.1v or 14.8v to be on either side of "12v."  If it is 11.1v, then that's fine.  If it is 14.8v, it may or may not be fine.  I would say check the voltage of your power adapter - if it is higher than or the same as your charged li-ion pack, go ahead and hook it up to your 12v input.

Either way, without looking at the inside to trace circuit, I would not recommend connecting anything higher voltage than 9v to the battery hookups as this is what it was designed for.  Higher voltage will need to go through the 12v input.

11.1 or 14.8

The Newcomer's Forum / Re: Soldering Station
« on: October 20, 2020, 10:02:49 AM »
I use the Weller WLC100.  It's a 40watt setup, not temperature controlled per-se, but you do have the dial which controls the wattage (and hence temperature) really well.  They go for $40-$60 USD depending on where you find it.

Guitar News / Vox Valvenergy - NuTube pedals are finally out
« on: October 15, 2020, 11:51:54 AM »
For just under $200 USD, you can get a Vox Valvenergy pedal onto your pedalboard.  The concept is that using a "NuTube," which is effectively a small flourescent tube, will bring you "real tube" sound.  Is it worth it?  Does it work?  Not sure, but if I see one in a local guitar shop I'd sure try it out.  They look cool, and the concept is great.  It sure is expensive though...

Of note, this technology has been in a handful of their amplifiers for months now and they do have fairly good reviews.

Guitar News / Puzzle shaped pedals to get rid of cables? Check!
« on: October 13, 2020, 08:42:28 PM »
Puzzle Effects has come up with a prototype effects pedal case that snaps together like puzzle pieces and uses a 3 conductor connector to hook them together.  Power up one pedal, they all have power.  Plug your guitar into the pedal on the right, your amp on the left and proceed to rock on!  No patch cables!  The coolest part is that if you only have one pedal, you can always use the in/out jacks on the top like normal and just have a weird shaped pedal on your board!  No price yet as these are prototypes, but they sure do look interesting!

Guitar News / Rock out with your blocks out - LEGO Stratocaster and amp!
« on: October 13, 2020, 08:37:54 PM »
LEGO has decided to release a fan design again, this time of the Stratocaster as well as an amp (Frontman 65R is my guess).  It looks really cool, and honestly, who doesn't love LEGO?   :tu:

If it's released soon enough, it'll be on our list for Yule this year!

Guitar News / Re: More class D love - GPA-100 from Harley Benton
« on: October 01, 2020, 03:22:45 PM »
Something odd about this amp. The blurb here says '130 watts into 8 ohms or 210 watts into 4 ohms,' however the rear of the amp shows the power consumption - 230 v ~50Hz 0.6A which equals 138w . So how can you get 210 watts from a 138w supply >>100% efficiency. Even 130w from 138w is 94% just about achievable for Class D amplification.

My guess is that because the 210 watts at 4 ohms is only a peak rating, the PSU can supply it for a few ms, maybe even a few hundred ms.  Nominal RMS wattage will be roughly half that most likely, settling in at around 100 watts.  Assuming that is the case, that would be well within the limits of Class D amps.

That said, it would probably benefit from a larger PSU...or simply not driving it to the max.

Guitar News / More class D love - GPA-100 from Harley Benton
« on: September 29, 2020, 08:46:45 PM »
Harley Benton has just released the GPA-100, a 210w (at 4 ohm) class D amp that can fit in your pocket.  For $77 you get a three band eq and a master volume.  While I don't have any experience with the brand, for the money, I'd honestly give it a try!


I am new here, looking for someone that may be able to help me first identify, and then maybe figure out a way to fix the circuit board on a small portable amp I have had since I was a kid.

Attached are a couple of pictures.  It has 1/4" input on the left side, 9v mini power in on the back, and 6 C-cell battery holder inside, and a 1/4" speaker out on the back.

(hope that's how you attach files...)

With 9V in I can measure voltage part way through the board, but the voltage get lost in the middle. 
Speaker does produce some hum/static with power on and touching the input jack.
Guitar signal in does not make it to the speaker, but pushing audio from a iphone into the in jack does make it out of the speaker but very quietly. Adjusting the amp volume in this case distorts the signal but does not increase it's volume.

Any insights appreciated.

Best regards,

To post an image, you need to use these "attachments and other options" link below the window where you post.  Then you can upload an image.

Tubes and Hybrids / Re: What to do with this old Pye radio?
« on: September 21, 2020, 09:32:40 AM »
BTW the volume pot is 1M ohm which is not ideal as its 'off' from 1 to 9 and everything happens from 9.1 to 10. Can I improve that by adding resistors in parallel?

Sent from my SM-A505FN using Tapatalk

This isn't due to the pot being 1M, but rather the taper.  Sounds like you have a linear pot instead of audio taper.  This can be solved with a resistor from wiper (center lug) to ground, between 10% and 20% of pot value.  So 100k to 200k would suffice.

Tubes and Hybrids / Re: VHT Classic 18 Preamp Modification
« on: September 21, 2020, 09:20:23 AM »
From what I can tell the circuit only utilizes one side of at as 3 pins are just left floating..
And I figured the power for it on the schematic is 'IC1-2'??

You should be looking for IC4 (or IC4a/b).  I'm only seeing IC4 at the beginning of the schematic, makes me wonder if there is a typo there.  How many IC's do you see on the PCB?  My guess is that IC4 (the one you are trying to disconnect) is still connected at one or more of the pins and causing an issue.

To keep it simple, I suggest trying the mod this way (cut trace on red line, add jumper on green line):

Tubes and Hybrids / Re: What to do with this old Pye radio?
« on: September 16, 2020, 09:04:17 PM »
It's been a while but this is going to be a powered speaker and maybe guitar amp. It has some of the lovely old radio sound due to the speaker and the enclosure even if theres no valves in the signal path. On the right is a whopper of a volume/tone/power switch. Pot seems noisy but I will definitely use the on/off element. The front panel lights up with good old fashioned incandescent bulbs. I plan to leave the chassis intact and in situ.  Should I discharge the old capacitors for safety?

Sent from my SM-A505FN using Tapatalk

If the old caps haven't been powered up in years, you're fine.  If more recently, stick a multimeter across and see how many volts are sitting there.

Also, how do you like that Kemo brick amp?  They look neat, but I haven't tried them myself yet.

Hi Everyone,

I'm new in these hallowed halls and learning the rites, so have mercy...

In the age of "The Club Goes to the Street" I decided to build (assemble) the World's Greatest Street Sound System - under $ 100, weight 11 lbs., battery-run, pretty and disguisable.  I might need some advice... I'm a musician; I guess breadboards are for toast, no?

To a test I'd like to start with replacing the speaker in my recent issue Vox MINI2, 3Watt street amp. Also, take the whole thing out of it's cute, "boutique" enclosure. Then progress will follow to yield the above superlative.

I've learned (here) not to mess lightheartedly with that speaker-swap in this amp, so it still works. But the sound it does is not what I want. If possible I'd like to test it with 2 x 4" (5)", 90-SPL Visaton speakers - or better. Can this be done, and if yes, why not? (I understand Ohms, but there's more involved here).

Any advice pertaining to this and, consequently, to the Miracle Mini Monster System that will quickly follow is greatly appreciated.



There really isn't more to it than ohms as far as what is safe to connect to the amp.  I'm not sure what it has stock, but assuming 8 ohm (please check this), then you could use two 4 ohm speakers in series, or two 16 ohm in parallel.  If you are trying for more volume, I recommend at least 93 db/watt SPL, but ideally 96 or greater.  Is there a reason for only going with 4 or 5" speakers?  This keeps you pretty limited.  Once you get to 8", things start to open up substantially for great SPL as well as sound quality across the frequency spectrum.

Good luck and welcome!

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