I am trying to contact the author of the VC508 mod. discussed on guitarnuts.com.. I have numerous questions. There is no contact or email address on that site. I assume the author is John S. Atchley, but have not been able to acquire an email for him. Perhaps he wants to be inaccessible. If someone knows who the author is and how to contact them, please let me know with a post or email. Thanks !!!
Hi, I am new here. I finished the Crate VC-508 mod this weekend. I added a few little changes to tame the noise, and now you have to get your ear up into the grill to hear hum, and the hiss is now inaudible. The changes are as follows:
1. Hiss Mod: Replace the TL072 Op amp with an NE5532 Op amp ($1.50 approx). 2. Hum: I wrapped the twisted leads from the transformer secondary with copper tape, soldered to maintain electrical connection. Then, from the middle of each cable bundle, I soldered a wire that terminates at the ground lug (star grounding). I then wrapped the wires in electrical tape, and routed the bundles close to the chassis edges, so that they only crossed over the circuit board near their termination point. 3. Volume Control: I needed to drill a new hole in the chassis anyway, so I drilled one approximately 2" to the right of the power cord (looking from the back) and relocated my power switch to that location. It is much more logical to put a power switch there, than a volume control. I used the shielding/grounding stated above to protect the leads to the new volume control, now located where the power switch used to be. 4. Mechanical Noise: For speaker rattle, I removed the grill, and put some pieces of rubber under the places where the screws go in. And for that other rattle; this is a big one. My experience with EL84 based amps, has been that filament rattle is an issue with this tube. To prove the point, I separated the chassis from the speaker/cabinet and the rattle stopped. With all of the extra reonance from the harmonics, this happens even at low volumed. I tried 3 different EL84 tubes, but there was no difference. For me, the answer will probably be an extension cabinet, but that cuts down on the coolness factor. Has anyone had good results with a remedy for the tube rattle?
Post by lockingnut on Nov 19, 2006 10:37:58 GMT -5
Laserdog - I'm new here too, was nosing around and found you've mod'd your Crateamp. I have both Crate V16 & V32 Palomino's, and love them. For me they are a "no-brainer", bang for the buck.
I notice hum and hiss in mine too, especially after they warm up good. I wonder if your mods would help. Some of the "white noise" I hear are the Groove Tubes which I will replace with JJ's soon. I found the same TL072 OP amp in the V32 as your 508 and suspect it's in the V16 as well.
Was there anything else you had to do, in changing that op amp? (R or C change?) Is it a direct replacement in Crate's circuit? What kind of improvement did you notice? Are there any other gimmicks that you've come up with for these amps?
One amp is still in warranty but I don't care, the reason they're so attractive to me is that I can mod them without loosing an investment like with a Badcat. Being a tech, I'd rather fix it myself than ship it out.
Like I said I love these amps. I've had Fenders, Traynor YCV80, and a Cybertwin and for what I do the Crate wins hands down. I still stand amazed, who would of thought. . . . . a crate??
Always short across the filter cap with a screwdriver before putting your hands inside an UNPLUGGED tube amp.
The NE5532 Op Amp is the one used in Hi Fi preamps and Studio mixers, Headphone amps and such. It is a Low Noise, High Slew Rate (fast rise times= accurate fidelity) version of the 4558. The TL072 is a J-fet input Op Amp with standard noise and slew rates, but they can be a little "iffy" around AC fields (such as the ones around the twisted wires inside a tube amp). The Op Amp is simply set up by the ratio of resistors at the input and in the feedback loop, so no changes are required for a replacement that requires no change in gain. The NE5532 is pin-compatible with the TL0-72. Simply replace the TL072 with the NE5532. Be sure to mark pin 1 on the circuit board before removing the old Op Amp. Route all twisted pairs so that they follow along the chassis for as much of the distance as possible. Use hot glue to affix. This may be all you need to do on the newer Crate amps, as I'm sure they've had an earful by now about the VC-508. I bought a JJ EL-84 tube, and a Calrad L-Pad to install over T'Giving weekend. The JJ tube is supposed to be more rugged and cut down on filament rattle.......The L-Pad is so I can knock off a couple of db, and maybe that will help with cabinet vibrations as well. I know the L-Pad is resistive, but if it is set to 25% of attenuation or less, the bulk of the load would still be reactive, so it should be no worse than a power soak at lower atten. levels. I can still hear a faint hum if I get my ear up to the speaker, but no hiss. This is with the gain at 7 and the new master volume at around 7. It would be possible to further reduce hum by adding 2 more 100uf, 450 volt caps in parallel with the one on the circuit board, but the law of diminishing returns applies because the amp is quiet, now. Filament rattle is the thorn in my side at the moment.....for this to be the killer recording amp that I know it can be, that must be dealt with. I will report back after the new tube is in place.....
Post by lockingnut on Nov 23, 2006 12:58:06 GMT -5
Thanks laserdogs. That's the green light I was waiting for. I'll let everyone know how it works out. I dunno when I'll get it done, I'm off tomorrow but have an evening gig, will use most the day. My V16 has more 60hz hum than the V32, but less hiss. I'll try twisting and rerouting the wires while at it. Thanks, Don
I was coming down with the flu on T'giving, so I didn't finish the mods. They are done now, and wow! The new JJ El84 is very fat and doesn't rattle like the other (three different ones) El84's I tried. I added a 30 watt Calrad L-Pad and I can set it down to "3" without noticing a difference in the sound. If I go below "3' it gets fuzzy, but that lets me run the (new) master vol. at around "9" or so. I set the Gain at around "6". This really kicks as, now. Still no hiss...... I am looking forward to recording with it! If I record something, I'll put it on my HTTP server, and post the URL. BTW, the LASERDOGS CD is at KINESISCD.com. I just finished a CD with CANVAS called "Digital Pigeon" - out soon (Canvasproductions.net). I just checked out the final cover art and it rocks. On this CD, I contributed songwriting, about half of the lead vocals, background vocals, and a couple of guitar solos. It will also be at Kinesis, CD Baby and Amazon. I suspect it will be in stores around early March. Later!
Laserdogs - I've been busy too, haven't replaced that OP amp yet but I did get Tesla NOS EL84 tubes for the V32 and like you said, Wow! Just the change from GT's is amazing, now reminds me of a Traynor YCV80 I used to have, cleans to die for. (BTW the overdrive on that amp was usless.) Traded it in on the V32 and am way happier, the overdrive approaches that of boutique amps. (least it does for me). I haven't had time to listen real close, life is happening constantly. The new tubes did not fix the hiss, but I didn't expected it to either. I've never noticed any tube rattling in either the V16 or 32. Sounds like you're busy recording and doing fun stuff. I play at church and fill in for a bud in his band from time to time, am starting to look for a band who needs some guitar help. Want to get more involved, if life will let me.
It's now ok for treeble, i've found some tricks with my effects pedals.
but I got another issue!
i'm french and my amp is an US v58...
so i need to change the transformers and buy a transformers for use with the 220V in europe...because in the v58 we can't modify this one like with the v508 by moving the Ac swicth wire to 220V position.
does anyone knows the specs of this kind of transfomers?
i just need to know the out voltage frome these transformers.
Yes i was gueesing too but in my amp there is only 2 wire on the multi tap, not 5 like the photos in the website of the vc508. but this thing which look like a hub is still here.
What i understand about this is that , CRATE with this v58, dont modify the circuit board at all (so the hub is stille here), but put just a 110 Volt transformer in the Us Model, and a 220v in the european model.
.......... so i need to change the transformers and buy a transformers for use with the 220V in europe...because in the v58 we can't modify this one like with the v508 by moving the Ac swicth wire to 220V position.
does anyone knows the specs of this kind of transfomers?
i just need to know the out voltage frome these transformers.
OK, so no one else has coughed up what you're looking for, I decided to cast around the net, and what do ya know, none other than John Atchley hisownself has a schematic of the VC-508 on his site. That's the closest I can find to the VC-58, sorry.
That particular schematic tells me that you'll need a transformer that has 300vAC for the secondary voltage. Bear in mind that there is also a low-voltage secondary, approximately 6.3vAC, for the tube filaments and the digital control circuitry. You should read all of John's notes, you'll find information on separating those last two power sources, i.e. individual transformers for each. That might affect the parts that you buy for your update.
Rule #1: All Lives Are Final. Make sure that the life you have just been issued is appropriate for your needs, before departing the womb.
Rule #2: In case you don't like the life you have, see Rule #1.
Ted Weber makes some pretty good transformers for Fender champ type amps that would probably work for you. One, in particular, the Weber part number "W022772INT" has 220v in, and 600v, and 660v output taps. Since the output is diode rectified, it should supply the roughly 300 volts DC that the Crate amp uses:
Please visit the sites below, and listen to some of my music. For those who ask (email me) , I will provide a free mp3 of a new October Tree song (using my '67 SG played through my modified Crate VC-508).
I have a crate vc 508 that i'm looking to mod. Does anyone have the original mod guide? is no longer a working link. I have seen this guide linked to on a bunch of other forms so it must be good stuff.
I tried the waybackmachine and no luck. I did find some other resources and put together a list of modifications for my VC508 I would like to discuss. Should I post my mods on this thread or create a new one? Thanks.
Should I post my mods on this thread or create a new one? Thanks.
Either way is fine. If this were a more recent thread, I'd say create your own thread so as to avoid confusion, but since you've resurrected this ancient thread and since it's about the same amp, no problem either way.
First off I am new to the form and this is my first amp mod project so please be patient with my ignorance. I have a Crate VC508 that is supper noisy so my first priority is to reduce the noise. While researching mods I have found ways to modify the tone of the amp. My goal is to make the tone more "bluesy". Mods 1-5 are from Verne Andru and I saw mod 6 on this form. Below are links to the original schematic and the modifications I am thinking about doing. Please let me know what you think of these modifications and if they will have the desired effect. Thanks for the help.
1. Replace TL072 op-amps with NE5532. (Page 1 of VC508 Schematic with Mods)
-The amp is really noisy. Replacing the op-amps with higher quality ones to bring down noise.
2. Remove C9. (Page 2 of VC508 Schematic with Mods)
-Take off some high end from the tone.
3. Remove C12. (Page 3 of VC508 Schematic with Mods)
-Tone knob currently works as a mid scoop. I read that removing C12 will make it work like a high cut tone knob. I'm thinking of also removing C10. Any ideas on what C10 is doing and what I would gain/lose from shorting it?
4. Replace 1.5 kOhm resistors R10 and R15 with 680 Ohm resistors. Replace 0.047 uF cap C8 with 0.068 cap. (Page 2 of VC508 Schematic with Mods)
-Adding bass and mids to the amp tone.
5. Remove C2. (Page 1 of VC508 Schematic with Mods)
-I read this would help remove "buzziness". To me it looks like remove this cap would reduce higher order harmonics from op-amp stage but I'm not sure. Would like to get some opinions on this.
6. Replace R16 with a 250 kOhm audio taper pot. (Page 3 of VC508 Schematic with Mods)
-Adding this as a master volume control so I can get some pre-amp tube distortion at lower volumes. The pot is one I already have. Is audio taper OK here or would linear taper make more sense?
Post by thetragichero on Sept 13, 2020 20:34:50 GMT -5
1. sure might be worth it. fet op amps can be noisy
2. yes that tiny bypass cap passes a bunch of high frequency trash past the tone control
3. i would try just removing c9 forest, see how you like the tone control at that point. removing c12 looks like the pot would blend between a 720hz and 140hz low pass filter. 720hz is right between 13th and 14th fret of a guitar's high e string, but it's not like they drop off a cliff so you should still get most of the full range of the guitar. shorting c10 would short your signal to ground at one end of the pot's travel. you could try removing c10 and leaving c12
4. reducing r10 and/or r15 is going to drastically change the bias point of the tubes. i wouldn't do that. 100k/1k5 is standard for many guitar amps because it's close to dead central, great for most amplification purposes. 680 ohm cathode resistor will actually decrease bass response (albeit by an imperceptible amount)
for our intents and purposes both of these cathodes can be considered fully bypassed
c8 and c14 to 68nf? sure, that's the case old orange and matamps used for coupling caps. might give ya a little more beef
5. this capacitor in the op amp feedback loop both provides stability from oscillation and cuts highs. don't remove it
6. yes you can replace r16 with a 250kA pot as a master volume. I'd place a large resistor (2M2) from the wiper to ground in the event that the pot wiper fails. I'd love if you could throw ~1k5 grid stopper between the volume and pin 2. might be okay without it but if you experience blocking distortion that could be the cure (just had a similar issue following vibro champ schematic too closely on a build)
oh and thank you for posting a schematic! I'm way more willing to look through and type a lengthy response if i don't have to search around for your schematic lol
Thank you much for the notes. The 2M2 resistor from the wiper to ground is a great call out. I have two 1M I can put in series for that. I had to look up grid stopper. From what a read here, the trick is to get it as close as possible to the grid pin (pin 2 in this case). I also read Fender uses 1.5K with 6L6 and Marshall uses 5.6K with EL34. I have an EL84 so I went with 5.6K but I'm guessing the resistor value dose snot matter that much.
I and going to do Step 1, then listen to the amp, then proceed with Step 2. If you could look over the schematic to see if I put the grid resistors in the correct place it would be much appreciated.
Replace TL072 op-amps with NE5532. (Page 1 of VC508 Schematic with Mods)
Remove C9. (Page 2 of VC508 Schematic with Mods)
Replace 0.047 uF caps C8 and C14 with 0.068 caps. (Page 2 of VC508 Schematic with Mods)
Remove C10 if I still don't like the tone knob. (Page 2 of VC508 Schematic with Mods)
Replace R16 with a 250 kOhm audio taper pot. (Page 3 of VC508 Schematic with Mods)
Add 2 MOhm grid to ground resistor. (Page 3 of VC508 Schematic with Mods)
Add 5.6 kOhm grid stopper resistor. (Page 3 of VC508 Schematic with Mods)
I removed C9, changed coupling caps C8 and C14 with 0.068 caps, and changed the op-amps. I put in a socket for the op-amps and tried it with the stock and new IC. Both sound the same to me. No difference in noise. The amp is less noisy that before but I think that is because of removing C9.
When I increase the "volume" pot which controls the pre-amp tube gain, I get a 60hz hum proportional with the volume level and independent on the op-amp gain. Guitar plays over the hum but it's a decent volume with the input shorted. Any ideas on how to get rid of that hum? There is a ~10 VAC wire that crosses the amp. I pushed it off the PCB but it did not help. Will shielding this wire make a difference at such a low voltage? The >300 VAC lands on the PCB the same side as the transformer. Only thing it is crossing is the rectifier before the filter caps. Can it cause the hum if it is not directly over the signal? Thanks for the help.