blackheart strange volume control

[lnatcbass]

I've had an ongoing problem with a blackheart little giant I've had for a little over a month. I had always thought it had too much treble, and after trying to overload the input stage with a clean signal from a zoom b2, I noticed a different problem as well, but the timing was probably a coincidence. I wonder if these 2 problems are related.

With the volume on zero, there is a significant amount of signal being sent to the speaker (vintage 30 12"), I would guess it is approximately the volume you'd expect if the volume was up to 1 or a little more. The sound is clean if you pick one string, but sounds distorted if you play a chord. The most unusual thing is that as you turn the volume knob up, the sound level coming from the speaker actually gets quieter and more distorted until it is almost non-existant at around one on the volume knob. After that the distortion starts to clean up and volume increases fairly rapidly, until at 2 and a half the volume it sounds like a normal amp.

I've tried to go the warranty repair route, but after dropping it off at the store for five days they gave it back saying that that's just the way they are.
I've done some repair work to another tube amp I have but I'm certainly no expert. Any thoughts? I suspect perhaps a grounding issue or is it possible the rectifier for the DC filaments is in backwards suppling 6 vdc to ground? Another fellow thought it sounded like a bad filter cap connection in the preamp.

[lnatcbass]

I suppose if the rectifier was backwards the 6.3 vdc would just short to ground and I wouldn't have the heaters working. Scatch that idea, I guess I should think before I speak. I suppose the impression I get is that the pot sweeps past full ground at one on the knob and then somehow the signal is reintroduced as the pot is turned fully off.

[Enzo]

The heaters work or they don't, if the rectifier was funny, they either would quit, or not and maybe add some hum. WOuld have zero effect on the volume control and treble-ness.

Search for discussions involving crosstalk. I suspect there is some crosstalk out of phase with the main signal at that volume control. At zero, all you hear is the crosstalk. As you turn up, the main signal grows, and since it is out of phase with the crosstalk, they cancel. When you turn the knob up to the point where the main signal is at the exact level of the crosstalk, they cancel completely and you get no sound, Then turning up further, the main signal drowns out the crosstalk.

Now in this amp, it might be normal, or there could be a problem in the circuit. I am not familiar with the amp.

[lnatcbass]

Thanks for the reply Enzo.
Out of phase crosstalk definately makes a lot of sense. The Blackheart Little Giant is a singled ended el84 with one 12ax7. Despite the fact that the store said it was normal, I haven't heard any other mention of it from other owners, and there are definitely lots of glowing user reviews for the amp. A subsequent email from the manufacturer said that is not normal, only a few amps have been reported with it, but they don't know what the problem is. Another singled ended El84 amp I did some work on with the same topology has only a tiny fraction of the crosstalk my blackheart has. Is crosstalk all that common? A lower frequency, out of phase crosstalk would also explain why the amp sounds thin even at louder volumes.

I thought I was the only person on the planet with the problem. I'm sure searching for "crosstalk" will help alot.

Thanks again
Jamie

[Mars Amp Repair]

Hello Jamie,
Crosstalk as you are speaking is probably caused by a ground path that is creating a ground loop or possibly a path to the next stage through the ground of say the volume pot.

The amp may have a design issue where the grounding of the preamp is actually going to a higher current ground path from other stages theyby creating this out of phase 'feedback' path to the preamp ground path.

If you can, try to reroute the grounding of the preamp stage to some other point. Sometimes you can just connect a wire to the preamp grounding point & just touch it to other grounding spots to try & circumvent the offending ground loop. You might have to cut the trace (if it's a circuit board) & reroute once you find a better grounding spot. A high gain audio signal tracer can sometimes 'hear' the signal on the ground line & help you isolate the issue.

Not an easy thing to find...it usually take a bunch of experimenting...but if there are others of the same model exhibiting the same symptoms, you're probably looking at ground path design issues.

glen

[lnatcbass]

Hey Glen,
No one else seems to be have mentioned having the same problem with this amp as I am. I asked someone else from another post, and they said they may get some small amount of signal throught the amp if they have a preamp hooked up (I assume something like a pod). My guitar is just a Fender Squire with some single coils, so it doesn't really have a high output either.
The fact that its a hard thing to track down probably puts it out of my league, (and I'm trying not to void the warranty) and also probably explains why the service department told me its just the way they are, although an email from loud technologies said the problem wasn't typical. I'm going to guess I'll have similar difficulties they next time I take it in for warranty work.
I did notice it for the first time after trying to overload the preamp stage with a zoom b2 multi effects pedal. Everyone I've talked to has said that that shouldn't hurt anything, but I'm wondering if I could have blown something in the front end that would account for an increased amount of crosstalk.
Here's a link to the schematic. http://www.rowbi.myzen.co.uk/Blackhe...2020070611.pdf

Thanks again for all the responses guys!

[Rick Erickson]

Try a different brand of 12AX7. I have seen Fender amps do this with the old EI brand 12AX7's that Groove Tubes sold as 7025's. Replacing them with a Chinese or other brand would solve the problem. The crosstalk in this instance was actually occuring inside the tube, from one triode to the other.

RE

[lnatcbass]

When I first noticed it I tried two different gt mullard type 12ax7's, a sovtek and the original chinese 12ax7. I also swapped el84's but no luck.
I Also just hooked up my old single ended el84 amp to the cab I'm playing the blackheart through (aside from a reverb and trem and single tone pot, very similar schematic) for a comparison, and the old amp has a small amount of signal getting through in the high input but none in the low input. I think the signal getting through on my old amp isn't crosstalk but rather caused by the pot not shuting off completely, because the signal is completely clean, and the tone pot affects the sound. Also when you turn up the volume, it immediately gets louder in a smooth manner, with no volume drop or distortion. The old amp also sounds WAY nicer, and much louder with much nicer mids.
I just did my own very limited troubleshooting, with the blackheart by checking all the connections that are supposed to go to ground with a multimeter and they seem fine. I also gave everything a poke with the amp on and couldn't find any obvious loose connections. The only thing that looked suspect was a slight burn on R6, but it's resistance measures fine and is probably just a burn from a soldering iron. The distortion of the crosstalk sure sounds like a bad component though.

[52 Bill]

When you went back to the dealer that told you that this was normal, did you see any more of these on the showroom floor?

If there were, did you try one of the other ones to see if they did this as well?

[lnatcbass]

Ya, thats the problem Bill, they seem to be back ordered everywhere so I've got nothing to compare it to, other than a response I got from another owner that said he didn't have the issue, and no mention of the problem from any of the many others that have reviewed the amp.

[lnatcbass]

Very lucky today. Found a store where a Crate rep had left a combo version (store said it wasn't even theirs, they're still waiting for some to come in). This amp I tried worked perfectly, and I didn't have to turn the treble down near as much as my amp when I played a guitar similar to mine. Different cab and speaker though obviously. At least now I know there is definately something funky with mine. Time to try the warranty route again. If I get any luck I'll post the results 'case anyones interested.
I'm quite positive enzo is right about the out of phase crosstalk. That would explain some missing mids. It would also explain why at the lowest point of volume on the volume knob, a little over 1, there is only distortion. the clean signal from the output tube cancels everything in the crosstalk but the distortion. The level of crosstalk on my amp when volume knob is on zero is approx. the level of the good amp on about one or maybe one and a half.

[OldFarb]

Warranty

I would appreciate a report on your quest for warranty with Crate. I bought a Blackheart and Palomino from GC a few months ago. Neither came with a warranty card, so I emailed Crate for the warranty card or online registration information. I never received an answer.

[lnatcbass]

Despite the confusion about whether or not my amp's problems are typical (I think partially the fault of the retailer I bought from, which isn't an authorized Crate service centre), I must say I've been very happy with the support from Loud Technologies (distributor of Crate and other brands). I've made some phone calls and emails and they've been prompt and very fair with their responses. I mentioned that I couldn't find any place to register the amp on line and they said not to worry about it. When I gave the serial number, they knew I bought it at Steve's Music, took down my name and address and even sent out some new tube's when I said I wasn't happy the the amps' tone before I discovered the real problem.
In the last set of emails, they just advised me to bring the sales receipt for the warranty repair. Try emailing guitarampsupport@loudtechinc.com or calling 1-866-858-5832. You probably already know but the blackheart web site is blackhearteng.com or blackheartamps.com

[Noviz]

Similar problem with Blackheart Little Giant

I may have the same problem with my Blackheart Little Giant head as the one lnatcbass describes, though perhaps to a lesser degree. My amp is a couple of months old, and I always found it strangely trebly. I have to turn down the treble to about 2 or less in order to get a pleasant tone out of my SG as well as my Telecaster. There is a slightly painful biting sizzling going on in the highs when I play chords. (It may be distortion, but perhaps it is just rich in overtones. Maybe this is a good thing. My ears don't like it, though.) I also noticed that when turned to zero, there is still a signal to the speaker, though I have to go home and check whether I get the strange phenomenons described when I slowly turn the volume up to 1, then 2.

This said, I like the overall sound of the amplifier when I turn the treble down. I play it through the Blackheart cabinet with the stock Eminence speaker.

Did you find out more about your problem? Fix it?

[Noviz]

I've checked the volume thing. No, my amp seems to behave well volume-wise as far as I can tell. But did you find out whether your two problems were related? The very strong treble output is a feature of this amp? I have read posts where people talk about turning the treble down, say bass 5-10 (10=full), middle 5-10 and treble below 2, and even fiddling a little with the guitar tone control in order to get their desired tone. Is it so that some of us have a "screamer variety" of amp or are all this way?

(Oh, and I have swapped the tubes. Replaced the stock chinese ones with Tung-Sol and Mullard reissue, which seemed to make the tone fuller, but there are still unpleasant ringing overtones.)

And, sorry, yes I am a newbie. Please feel free to ignore me.