coldsteal2

yea it would be great to have a mid EQ for the
clean channel

dont forget for the combos puting in a V-30 really
improves the tone

__________________


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Arcarix

CS2-
Could you post some sound clips of yours with the V30's ?
THX

Peter

Funny thing, I tried a celestion vintage 30 (chinese) in my avt50 (from avatar sound). I didn't like it - it was way too efficient, mid-rangy, and directional, so I couldn't turn up the amp without blowing out my ears, and standing in front of it could kill you. I found the amp didn't sound right turned down so low either; you need to turn it up somewhat to get a good sound. Opening up the back 1/3 helped, but it was still way too honky. I replaced it with a 4 ohm celestion g12m70. If you play rock and blues, this is the speaker for you. Much much much better, IMHO. The only other thing I may eventually try is putting an aluminum dome on the g12m70. Cheers!

Peter

john_lisi

So Peter,are the stock speakers designed to have a scoopy mid? If so what you are telling is is that a new speaker can drastically improve the mids.Also is there a way to change the treble value because I have it on 0-2 and it's still too bright ( with a les paul to boot) with a strat it would be unbearable.I like the amp but with a few changes it could sound stellar.....

brecab

Hi Peter, My name is Fred and I realize this is an old thread from march, but I am really interested in your mods for the avt50. I have one and I love it, but it's just not quite as versitile as it could be. Your mods would definitly address the issues I have with the amp. I'm not a tech as far as electronics goes but I do all my own guitar electronics so I can usually figure out schematics and am real adept at what it takes to do whatever work on the chassis that needs to be done. You may have a kit already, I don't know but I would definitly be intersted in one, even if it is just the directions and schematics and a parts list if your not set up for parts yet.

Peter

I liked the sound of the stock speaker, but it couldn't handle the power. A half hour playing purple haze and hey joe on 10, and it popped; go figure. Smelled like a barbeque. As for treble, that's the reason guitars have tone controls. Mid shift also helps dramatically. Cheers!

PETER

AVT50 mods link:
Marshall AVT50 Mods

Peter

reply to Adam's email:

Dear Adam, I will experiment with shipping overseas. I will not be sure of the cost until I have produced my first batch, shipping will be whatever the cost is (not in my control), plus perhaps a modest handling fee (yet to be determined). The circuit boards will come pre-soldered. Since the number of features will affect cost, the number of features will be based on what people are willing to spend. Initially, I will custom add features by order to help determine the final kit form/cost. These features will definitely be a part of the kit:

1. Clean channel mid range control
2. 25% pre amp tube gain boost footswitchable for channels 1 & 2 with silent switching & pedal LED (you will have to modify your pedal, and the pedal jack will have to be replaced on the back of the amp with a special one, along with a new secondary jack, I will provide the parts, the 4 conductor wire, and detailed instructions)
3. Mid frequency shift control channel 2 (6 positions, including original unmodified channel 2 amp tone)
4. A few higher wattage and voltage components


I have not tried adding the mid-shift to the clean channel yet, but I have the parts, I just haven't had the time. I haven't seen if the master volume is feasible yet. I don't have sound clips yet either, but the mid-shift on CH2 is dramatic and a key feature. As for tube boost the amp sounds stock, but when you add boost, the tube adds even order harmonics, and sounds like any breaking up tube amp, depending on gain setting (I scoped the results, and they clearly show I am bringing the tube into natural tube saturation/compression).

Whew! I hope this answers your questions! I am leaving on vacation now for about 20 days. I am posting this on the site. Cheers!

Peter

Arcarix

Hi Peter,
Just my prefs on your proposed mods.....

1. Definitely want that
2. Definitely want that
3. I rarely use chan. 2, so not a biggie for me.
4. Never a bad idea, I can deal with that

Could you include a diagram for the ext. spkr cab jack? Or maybe a photo? Anyone that can do these mods as proposed should be able to do that with just simple instructions.

dnz.mtn

hey Peter,

i'm planning to buy an avt-50. The first thing i'll do is adding a midrange control for the clean channel. i haven't gone thru all the posts, so i'm not sure if you already provided a diagram for the modification. i'd be happy if you could send me such a diagram...
thanks
deniz

Arcarix

Hi!
I tried changing spkrs from stock to Eminence Patriot 'Red white and Blue', which is an 8 ohm 120 watt spkr. Although it sounds good when some volume is applied (also use Boss effects in the effect loop - GE7 with mids up, slight compression w/CE3, and slight CS3 delay instead of reverb), I don't think the power/tone potential of the amp is being used to best advantage with this spkr.Any thoughts on this setup would be appreciated, as well as your thoughts on impedance matching (8 ohm spkr to 4 ohm amp). Thanks, still looking forward to getting your mods!
Arcarix

Pete240885

Miss matched impedance WILL kill your amp

Peter

Dear all, I am back. Progress report: I have successfully produced my first circuit boards, though not for the AVT50 yet (these will be next, I am currently modifying the design for the AVT50 board a bit more, and improving my procedures for making circuit boards). I have had to face some challenges. I am awaiting parts I ordered for the AVT50 mods. I have ordered enough parts for about 13 kits. Some of the parts I am searching for are a bit hard to find - I may have to alter my designs a bit if I can't locate them. I plan to have the kits out before the end of 2008. Thanks for everybody's interest.

Dear Arcarix: the extension speaker jack mod is the easiest part of the kits, when installing tube gain. Have no fear, instructions will come with the kits. As for the speaker, I am using a 4 ohm celestion g12m70, which, IMHO, matches up with the amp beautifully. As for speaker impedance, using a speaker rated at a higher impedance than the amps is harmless, but if you run an 8 ohm speaker in a 4 ohm amp, your power gets cut in half. if you run a 16 ohm speaker in a 4 ohm amp, your power gets cut in 4. 4 ohm speaker with 4 ohm amp=100% of your power. WARNING: NEVER USE A LOWER IMPEDANCE SPEAKER THAN THE AMPS IMPEDANCE RATING, AS THAT WILL CAUSE SEVERE DAMAGE TO THE AMP.

PETER

Pete240885

I studied amplifier design in the seccond and third years of my degree, this does not agree what i've been taught.

If the power is not being fed to the speaker then it is being dissapated inside your amp, therefore an impedance missmatch, be it too high or too low, is bad.

PaoloJM

This seems to be a bit of a grey area. This is my understanfing:

Amp type and Class bias are effected slightly differently by load mismatch.

In a Class A biased amplifier mismatched load does not cause power dissapation problems.
Power dissipation is maximum in Class A when the amp is idling. A change in load simply rotates the load line either way and does not cause additional power dissipation. With a signal applied a lower load (assuming it's not a large mismatch) will not cause any problems but may noticably affect the frequency resposne. A higher load may cause higher than expected signal voltage peaks which, if above the limits of the valve/transistor or OT (if present), could cause problems. Power delivered to the load will be reduced.

In Class AB a load mismatch is more serious. A lower load is never a good idea in Class AB as you will most likely cause excessive power dissipation in both the valves/transistors and OT (if present). It effectivley rotates the load line right above the max dissipation level. A higher load may also cause problems with excessive signal voltage peaks.
However most good amps are desined with valves/transistors and OTs (if present) that are rated well above the max voltages expected and a higher load (again within reason) can usually be tolerated but will cause reduced power and changed frequency response.

In short, a higher load is ok but not ideal in both Class A and AB.
A lower load is ok with Class A but definitley not in Class AB and solid state amps are designed to drive multiple different loads ( 4, 8 or 16ohm) but will put out maximum power to a certain specified load.

This is based on my reading so far from sites like The Valve Wizrd, Electronic Circuit Theory text books, RCA manuals and a Designing Solid State Amplifiers pdf book that I downloaded.

However I may have interpereted some of this info incorrectly, does anyone have a definitive answer on this?

__________________
www.youtube.com/paolojm

Pete240885

There is a genereal rule of thumb that will change the way you look at this:

Solid State amplifiers will GENERALLY survive an open circuit (extreme high impedance) but not a short circuit (extreme low impedance)

Valve amplifiers will generally GENERALLY survive a short circuit , but not an open circuit.


Note the word generally, this indicates that this is not always the case, now considering that an impedance miss-match is simply a less extreme version of the above two scenarios, it should be fairly clear that an impedance miss-match (either higher or lower) is not good for your amp.

Peter

NEWSFLASH: I added a 6 position rotary mid-shift switch to my clean channel yesterday. The amp produces a world of new tones now. Today, I had the house to myself, so I took out a Les Paul Deluxe [gibson mini humbucker pickups with alnico magnets, which make the guitar sound between a les paul and a fender strat] and rocked out. With tube boost off, and gain at 5, the amp sounds sweet and clean, for chording and rhythm. With tube boost kicked on, mid-shift set to stock setting, bass at 10, midrange at 5, treble at 8, gain on full, volume at 3/4, the amp really rips, but the highs could kill you. I rotated the mid- shift switch 4 clicks, moving the highs deep into the mid-range, fattening up the tone significantly, and making the sound less ear damaging as a bonus. It really hummed, with sweetly beating frequencies. Powerful sound, and singing leads. I couldn't stop playing. Pure tube sound heaven. A very satisfying mod. A huge improvement in this amp's clean channel flexibility, at any gain setting.

Colbebi

I have two questions for this group:
1. When switching channels (both with footswitch and on the front panel) of my AVT50, the volume spikes very high for a brief moment, then returns to normal. It is quite alarming and can wake the rest of the house when I play late at night. Does anyone have ideas what might be causing this and how I might fix it?
2. Can someone tell me how to bias or adjust the gain of the preamp tube?

Thank you!

Peter

Quote:
Originally Posted by Vince
Hi Peter!
I am interested in your mods for the valvestate amps. I am getting ready to purchase one so of course I am looking around to see how to get the most out of them...

Thanks!
Vince

Great! I have ordered key parts for 13 kits. Some parts, I am scrounging for. When I'm ready, whoever money-orders me first will get them (I am putting out a chunk of change to do this). These amps are capable of great tube sound. Mine is awesome. Thanks for your interest, Vince!

Peter

Peter

Quote:
Originally Posted by formercakid
You seem to have a very high knowledge level of amp electronics and amp speaker selection. Can you give me a suggestion for a speaker to replace the stock speaker in the DSL-201(201 IS THE 20 WATT MODEL)?

I do know amps, but nah, I only know a thing or two about speakers, especially, I know when it sounds good. The Vintage30 sounded bad in my avt50 (in my opinion), and the 4ohm celestion g12m70 works great with the amp. A friend of mine favours old JBL speakers with alnico magnets and aluminum domes, but good as they are, they may not be to all tastes; they sound INCREDIBLE distorted, but are not as sweet as some clean, though they handle massive power and are of very high quality. I am thinking about trying replacing the paper dust cap in the center of my g12m70 with an aluminium one - I bet it will make this amp sound deadlier. Cheers!

Peter

Voland

Hi everyone

I have an issue with my AVT50 - when I turn it off, I sometimes (80% of the time) get a loud pop from the speaker.
As far as I know, the cause for this is the discharge of the capacitors, which still have some charge on them. Does anyone have an idea how to fix this problem?

Cheers

Peter

Usually, solid state amps pop when you turn them on. Last time I had a problem with an amp popping when turning it off, one of the capacitors had a cold solder joint. Re-soldering the capacitor fixed the problem.

Troubleshooting: [if you don't know how to do this safely, or if you don't have the skills to do it, go to a technician, even if the amp is un-plugged, capacitors can hold enough charge to hurt you, especially the main filter caps] - I would start by opening up the amp, turning it on, and poking around, using a stick (or other non-conductive probe). Push and tap on components to see if you can find one that causes noise/crackling (out the speaker). Try pulling out the tube, and seeing if you still get the pop - if you don't, you know it is in the circuit before the tube, if you do, it is after the tube. If that doesn't reveal the problem, try dis-charging the electro-lytic caps, and re-soldering them. It could be a non-polarized cap causing the problem as well. If that doesn't work, you may be looking for a bad cap or cold solder joint, I am guessing. Best of luck. Please let me know if this helps.

Peter

RMiller

Hello Peter,

I am vary interested in your Mod Kit, how much will it cost to order a kit and is this something anyone can do or will a tech have to do the mods? Please email me the info at 59elcamino@earthlink.net. Thanks

Arcarix

>Peter
You still around?

Voland

How did you manage to increase the gain by that much? - I've tried to increase my preamp gain by adding a 4.7 uF capacitor in parallel to the first cathode resistor(R29 on the official schematic), which kinda improved the distortion, but it's nowhere close the 25% you're talking about. I didn't actually measure anything though. Cheers, Ivan

Martdogplay

Hi Peter,

I am interested in purchasing your mods for my amp.Please email me with pricing and availibility. To rocket1101149969@sbcglobal.net

Martdogplay

Hi Peter,

I would like to add a selectable ohm switch for the output of the amp,like the old ones 4,8, and 16 ohms.Can you send me info and pictures on how to do that.

Thanks,
Marty

Fixr1984

I think I figured out the mid shift and made both channels have a footswitchable gain boost.
I have to play my amp a little bit more to see if the values I chose are worth keeping before I put everything back together.

Peter

Sorry, Marty, the old amps had output transformers with coil taps for various impedances, these amps don't.

Peter

I designed all of my mods for the AVT50 combo, and would like to make sure they are compatible with the head. Would anyone out there be willing to send me some high-resolution digital photos of the inside of an AVT50H head? Many thanks.

Fixr1984

I have the head version. Are you looking for up close parts of the board? Certain parts of the inside? The whole thing? Let me know I can get you some pics. Maybe we could trade some mod info. I am currently doing mine but with a 4 position switch and was curious to what values you chose. Also what value you used for the gain boost. I definatly have boost but wasn't sure if I went to the full potential.

Jason