DB728 Troubles........Help Needed

[g4string]

Ok, Here is the scoop. I have a used 728 I bought used from the Bass Emporium a few months ago. Since I didn't have the preamp and cab I wanted to use with the 728 at the time, it sat in my closet until I got everything I needed. So, everything I needed is here and I plugged it in. Sounds good.......but one major problem.......the amps seems to break up way before I think it should be distorting.

I am using a Demeter VTB201S as a preamp and a Berg NV610 as the cab. I isolated both the Berg and 201S as suspects. At a low level the 728 wouldn't break up. If I turn the gain up to about 3/4 and the volume on the 201S to about 3/4.......it breaks up. When I played through the amp with my band at rehersal.......the gain structure was about the same as I mentioned previuosly........the same thing happened.

This thing was shipped from Texas to Illinois in non-original packing. Maybe a tube(s) got damaged in shipping? maybe it needs to biased. I opened the top of the amp and did the tap check with the amp on to see if I got any pinging sounds when a taped on the tubes.....nothing there (still could have a bad tube(s). I called Aguilar and they stated that this thing should get pretty damn loud before the amp starts to break up. From the high regards of many here at TB, I was expecting the same.

All of you 728 users, how loud can you get before your amp breaks up? What is your gain structure set-up? Any suggestions or thoughts on my 728. I just wanted some of your comments before I send the amp in to have the tubes tested and re-biased.

 

[g4string]

come on.......somebody here uses a 728

 

[Psycho Bass Guy]

Maybe a tube(s) got damaged in shipping? maybe it needs to biased.

Mine came biased WAYY too cold and did exactly what you describe. Get your amp baised for full output by a tech. They'll also be able to tell you if anything else is wrong with your amp.

 

[marc40a]

No experience w/ the 728 but I have had a similiar experience with a product from the Bass Emporium.

Never again.

 

[g4string]

No experience w/ the 728 but I have had a similiar experience with a product from the Bass Emporium.

Never again.

They told me the amp I bought just had new tubes installed and biased by Aguilar. When I opened the cover, the tubes didn't look new and there was a sticker from an amp repair shop from Austin Texas on the back panel. Maybe they lied to me? I dunno. I think I am going to buy some new tubes and bias the amp myself. I am pretty handy with a multi meter so I should be able to figure out how to bias the tubes with a little research and a phone call to Aguilar.

Marc - Do you mind telling me what happened with you when you bought an amp at BE? Just curious.

 

[Psycho Bass Guy]

I think I am going to buy some new tubes and bias the amp myself. I am pretty handy with a multi meter so I should be able to figure out how to bias the tubes with a little research and a phone call to Aguilar.

Try rebiasing the tubes that are in there first. Chances are whoever unloaded the amp did so because they thought it needed new tubes, when it probably only needs a rebias.

 

[marc40a]

Bought that floor model demo DB-680 listed on Bassgear. The "when it's gone, it's gone" one w/ the free used footswitch thrown in.

It arrived with an output issue and no footswitch.

Got the output issue fixed by Aguilar under warranty - great customer service by the guys at Aguilar.

While it was off being serviced I contacted the Emporium about the footswitch. First via email.... unreturned

I called and was told that Mr. F was "out of the country."

He answered when I called the next day.

Mr. F said that I got the "other" demo model, the "one without the footswitch." He said I could send it back if I wanted. I told him it was being repaired @ Aguilar and left it at that. He wasn't very concerned.

I got the vibe that he lied right to me over the phone. I'm no fool. He seemed pretty proud of himself when he came up with the "two demo" story.

The only thing that kept me from sending it back was that I did get it for a good price w/ a full warranty. He knew that. Shipping back and forth would've almost been the price of the $71 footswitch.

I just walked away. The guy is a total cockroach in my book.

 

[JGR]

I have a pair of DB728's and they are very loud and fairly clean. I would say your bias is definitely off. I bought both of mine used, and the bias was off in both.

You can actually bias them very easily and safely yourself if you have a digital multi-meter.

Attached are the bias instructions from Aguilar. If you look inside the amp, to the right there is a circular cut-out, the same size as all of the ones that all of the filter caps are poking through, with three small metal prongs sticking up (bias test points). The center is ground and the left and right ones correspond the each side of the power section. Assuming you have 120V coming in from your wall, let the amp warm up for 20 minutes to sabilize. Set your DMM to DC mV. Put the red lead to the left test point and the black lead to the center test point. You want a reading of 120mV. You adjust via the small blue trimmer pot inside the amp using a tiny screwdriver. After you do the left side, repeat for the right side. Wait a few minutes and do it again until you get a farily close and consistent reading for both sides.


PM me if you need more info and I can walk you through it.

JR

 

[tombowlus]

I also own a DB 728 and it gets stupid loud without breaking up. I would definitely recheck the bias to confirm.

 

[g4string]

Bought that floor model demo DB-680 listed on Bassgear. The "when it's gone, it's gone" one w/ the free used footswitch thrown in.

It arrived with an output issue and no footswitch.

Got the output issue fixed by Aguilar under warranty - great customer service by the guys at Aguilar.

While it was off being serviced I contacted the Emporium about the footswitch. First via email.... unreturned

I called and was told that Mr. F was "out of the country."

He answered when I called the next day.

Mr. F said that I got the "other" demo model, the "one without the footswitch." He said I could send it back if I wanted. I told him it was being repaired @ Aguilar and left it at that. He wasn't very concerned.

I got the vibe that he lied right to me over the phone. I'm no fool. He seemed pretty proud of himself when he came up with the "two demo" story.

The only thing that kept me from sending it back was that I did get it for a good price w/ a full warranty. He knew that. Shipping back and forth would've almost been the price of the $71 footswitch.

I just walked away. The guy is a total cockroach in my book.

Marc - Did you buy the 680 a month or so ago. They had one on their website acouple of months ago when I bought my 728. It was listed as new. That sucks dude. I was trying to get the 728 that was in the classifieds at TB for soo long. But the guy wouldn't move on the price and was never around to ship or for me to pick up so I said **** it and ordered the one at BE. I thought it was a good deal being that it had new tubes - I guess I thought wrong. Hopefully a re-bias is all it needs. I still might order new tubes just for the hell of it. We'll see.

 

[g4string]

I have a pair of DB728's and they are very loud and fairly clean. I would say your bias is definitely off. I bought both of mine used, and the bias was off in both.

You can actually bias them very easily and safely yourself if you have a digital multi-meter.

Attached are the bias instructions from Aguilar. If you look inside the amp, to the right there is a circular cut-out, the same size as all of the ones that all of the filter caps are poking through, with three small metal prongs sticking up (bias test points). The center is ground and the left and right ones correspond the each side of the power section. Assuming you have 120V coming in from your wall, let the amp warm up for 20 minutes to sabilize. Set your DMM to DC mV. Put the red lead to the left test point and the black lead to the center test point. You want a reading of 120mV. You adjust via the small blue trimmer pot inside the amp using a tiny screwdriver. After you do the left side, repeat for the right side. Wait a few minutes and do it again until you get a farily close and consistent reading for both sides.


PM me if you need more info and I can walk you through it.

JR

JR - thats funny becuase I just ran across that info yesterday while doing a search on power tubes for 728. I do have a digital Fluke meter. Basically all I need to be concerned with is checking for 120mv at each test point to ground - correct? I thought biasing a tube amp would be quite the operation - this seems to easy. BTW, thanks for the info!!

 

[JGR]

JR - thats funny becuase I just ran across that info yesterday while doing a search on power tubes for 728. I do have a digital Fluke meter. Basically all I need to be concerned with is checking for 120mv at each test point to ground - correct? I thought biasing a tube amp would be quite the operation - this seems to easy. BTW, thanks for the info!!

Yup, just make sure your meter is set to DC millivolts. Assuming you have 120V or close coming in from your wall, you can easily bias the amp to Aguilar's specs. They, as well as a lot of newer amps, use 1 ohm resistors on the power tube pin to ground so that V=I. Since they know the plate voltage in the amp, they can spec a voltage(current) draw based on whatever static dissipation they would like to run the tubes at (usually 65-70% of max). Simple and effective.

As they say in the tech sheet, it is more important to get the each side as close as possible rather than hitting the 120mV exactly. Just take your time - it's sort of iterative - do one side, then the other, than back to the first side... until you get a farily stable reading. Those little trim pots have quite a range on them so don't be alarmed if you have to give them quite a few turns. Give the amp a bit of time to warm up, and to stabilize in between iterations, and you should be good to go.

Cheers,

JR

 

[jfiles]

Bought that floor model demo DB-680 listed on Bassgear. The "when it's gone, it's gone" one w/ the free used footswitch thrown in.

It arrived with an output issue and no footswitch.

Got the output issue fixed by Aguilar under warranty - great customer service by the guys at Aguilar.

While it was off being serviced I contacted the Emporium about the footswitch. First via email.... unreturned

I called and was told that Mr. F was "out of the country."

He answered when I called the next day.

Mr. F said that I got the "other" demo model, the "one without the footswitch." He said I could send it back if I wanted. I told him it was being repaired @ Aguilar and left it at that. He wasn't very concerned.

I got the vibe that he lied right to me over the phone. I'm no fool. He seemed pretty proud of himself when he came up with the "two demo" story.

The only thing that kept me from sending it back was that I did get it for a good price w/ a full warranty. He knew that. Shipping back and forth would've almost been the price of the $71 footswitch.

I just walked away. The guy is a total cockroach in my book.

Hi,

I just read these messages and wanted to weigh-in on these. I am always bummed when I hear that customes have a bad experience, whether with us or someone else. The DB728 was a used consignment amplifier which we got from a very good customer who had bought a set of tubes from us a month earlier. He told me that he installed the new power tubes in the amplfier before bringing in to us for consignment. I took him a his word and still believe him. That may be my bad for not pulling the amplifier apart, but when we played it here in the store it sounded correct to me. Sadly, this is first time that I have heard about this.

I did talk with marc40a the day after I got back from Germany. I had two DEMO Aguilar DB-680 preamps. One had a "used" footswitch and that unit was sold. I sold the second unit to marc40a about a month or so later and he did call me about some tube issues with the unit. I offered for him to return this preamp, but was told that it was at Aguilar. My offer still stands to return the unit and I will gladly refund the shipping. Just give me a call.

Again, everyone is wecome to their opinion, and their opinion of me, but I have done a lot of business with a lot of TBers and always try to do my best. Sometimes I goof up, but please let me try and resolve whatever issues there are. I love this business and I have been in retail since 1974. I am trying hard to do a good job and want to be around for many, many more years with a lot of you as satisfied customers.

Thanks for allowing me to respond.

John Files

 

[WovenGraphite]

The DB 728 has a preamp tube 12AX7 and a 12AU7 as splitter tube. You can check those as well. Try to replace the AX7 just in case before touching the bias.
If the triodes are very high gain you could overwhelm the power amp section. See if you can replace just that one with a known AX7 of yours.

Also if you have an active bass, connect it directly in the input... that can tell you if the DB has (or not) bias issues.

Also, from experience the 201S can be very very hot so you could only crank it up to half and then crank up the db all the way.

Have you actually opened the cover? When I received mine, it's the first thing I did as tubes had moved out of their sockets.


That thing in a NV has a probably monstrous tone!

 

[WovenGraphite]

JR - thats funny becuase I just ran across that info yesterday while doing a search on power tubes for 728. I do have a digital Fluke meter. Basically all I need to be concerned with is checking for 120mv at each test point to ground - correct? I thought biasing a tube amp would be quite the operation - this seems to easy. BTW, thanks for the info!!

Yeah but let it warm up for a good 30mn first... it keeps moving otherwise.
Hey... I am the one who scanned that page!

 

[tombowlus]

Bought that floor model demo DB-680 listed on Bassgear. The "when it's gone, it's gone" one w/ the free used footswitch thrown in.

It arrived with an output issue and no footswitch.

Got the output issue fixed by Aguilar under warranty - great customer service by the guys at Aguilar.

While it was off being serviced I contacted the Emporium about the footswitch. First via email.... unreturned

I called and was told that Mr. F was "out of the country."

He answered when I called the next day.

Mr. F said that I got the "other" demo model, the "one without the footswitch." He said I could send it back if I wanted. I told him it was being repaired @ Aguilar and left it at that. He wasn't very concerned.

I got the vibe that he lied right to me over the phone. I'm no fool. He seemed pretty proud of himself when he came up with the "two demo" story.

The only thing that kept me from sending it back was that I did get it for a good price w/ a full warranty. He knew that. Shipping back and forth would've almost been the price of the $71 footswitch.

I just walked away. The guy is a total cockroach in my book.

Whoa, I must have skimmed over this post before. I have no affiliation or connection with Bass Emporium whatsoever, but I have bought several things from John, including my DB 728 and the foot controller for my DB 680. He has always offered excellent customer service (based upon my experiences, which were mostly over the phone/internet). It sounds like some breakdown in the communication between the two of you. I hope that if you both can talk it through, that you will be happy with the end result.

Again, I have no 'special relationship' with Bass Emporium or John Files, but since your experience was so different from mine, I'd like to propose the notion that he is not, in fact, a cockroach, and that that perhaps you two just got your wires a bit crossed. I mean, a guy who owns and operates a bass-only store that does most of its business over long distance isn't going to risk potentially ruining his reputation over a freakin' foot pedal!

Just my two cents. I hope you can resolve your situation amicably.

Tom.

 

[Pickebass]

I personally have bought quite a few things from John and have had EXCELLENT customer service. I drive the extra distance because I have had great customer service.

The 728 problem is probably related to biasing. The amp is stupid loud. I have run the amp previously with a demeter and various 410 and 810 cabs and it's incredible.

I truly have to say I am suprised by your experience with Bass Emporium. I have been shopping there for over 5 years and have never had a problem

 

[g4string]

I brought my multi meter to rehersal last night and re-biased the amp. As was expected, the bias was way off. One side was right around 120mv while the other was around 60mv. I matched both sides to 120mv and gave her a test run. The distortion got a little better but its still there. Another thing I noticed is that the low end has no tightness to it. It sort of sounds plumpy?? Keep in mind I haven't tested any tubes yet. I think at this point it sounds like a tube issue. I will be ordering tubes this weekend unless somebody else has any suggestions.

 

[DB5]

I truly have to say I am suprised by your experience with Bass Emporium. I have been shopping there for over 5 years and have never had a problem

+1

 

[JGR]

I brought my multi meter to rehersal last night and re-biased the amp. As was expected, the bias was way off. One side was right around 120mv while the other was around 60mv. I matched both sides to 120mv and gave her a test run. The distortion got a little better but its still there. Another thing I noticed is that the low end has no tightness to it. It sort of sounds plumpy?? Keep in mind I haven't tested any tubes yet. I think at this point it sounds like a tube issue. I will be ordering tubes this weekend unless somebody else has any suggestions.

It very well may need new tubes then. The only other thing I can think of is that you may need to use a lower bass setting on your preamp than you are used to - the DB728 has a massive abundance of low end capability that can pummel any cab into submission...

One of mine has the original tubes in it. I retubed the other one with Winged C 6550's with great results.

Good luck!

JR