Need help with broken Ashdown Elec Blue 130 bass amp

[smackoj]

I am going to try and be succinct. I am working on a 2002-04 Ashdown Electric Blue 130 ss amp. The traces on the power pcb started coming up, deteriorating so I decided to scrap the power section, bought a TDA8954TH mono chip amp and hook it up to the Ashdown preamp section. I thought the preamp was working fine but here is the problem. I have the chip amp installed and it's running as should BUT when I connect the preamp wires to it amp works but bad buzzing sound. I believe the signal from the preamp is not right but not sure how to measure the preamp output? I tried to measure vdc on the preamp output leads but not having luck getting any kind of accurate reading. I tested the output leads from the chip amp to the speaker and recorded -0.03 vdc and +0.025 vac. Any suggestions?  NOTE: the chip amp has a stereo input and a mono output. And the Ashdown schemo is not the exact same model but close. I couldn't find the exact schemo.

[shooter]

what's the chip expecting for an input, signal vac?
the one I have expects ~ 1vpp
still looking for a good "tap" from your SS pre

[smackoj]

I don't know what it expects Shooter. From China with no instructs, no schemo. the only thing I have is those few pics from the ebay ad and the info they give regarding the transformer requirements.

P.S.  I found the datasheet for the TDA8954 chip. The problem may? have something to do with the MODE selector. If you look at the picture you will see 2 sets of 2 solder pads labeled MUTE and STANDBY. They are between the power block and the audio input connector. I am not sure if those two Modes are suppose to have an ON-OFF switch or not?   Attached link to the data sheet.
https://pdf1.alldatasheet.com/datasheet-pdf/view/726690/PHILIPS/TDA8954_15.html

[shooter]

you get a scope yet ?
start with the chip and find out "how it sounds".
jack in different "sources", like phone, or mp3, or old cd player, something with a volume control.  These are "typically" line out signals, ~~ 1Vac p-p.

now try an old record player, maybe non humbucker guitar, these are low level signals that "need" preamped to drive a PA section.

[smackoj]

Looks like we both posted at the same exact time. I am trying to figure out if the MUTE and STANDBY switches need to be installed?
I need to rig some kind of adapter because the amp only has a 3 pin plastic input connector

[shooter]

my guess is NO, but it is from C town 

this will spin your head for awhile, but if you "get this", you can throw out the broke box and create a new "thing"

http://www.rason.org/Projects/bipolamp/bipolamp.htm

so far the biggest problem with your broke amp, there appears to be a NFB from speaker back to the input.  without it working, it';s hard to know what to expect.

[smackoj]

Tested with an Ipod and working perfect. Don't know what is funky with the preamp. I will pull it down and see if it is something easy. I am suspicious of the Post EQ vol control. It has always been scratchy and popping no matter how much cleaner I use. If not, more trash for the junk man on Tuesday.   
Thanks mucho Shooter

[shooter]

unless you have time AND money, keep the box, PS and you're ready for SS scratch build 
good luck

[smackoj]

I have tried every grounding scheme I can think of and the buzz remains. I plugged a guitar in and the guitar freqs are loud and clear but the background buzz hangs on. I wonder if I should try some simple R and C filter between preamp and the amp? I do not have a scope to isolate the noise freq. Any suggestions?

[PRR]

You have given no information about power supply, for power amp or for preamp.

I even asked my dog, but he says "incomplete information".

[smackoj]

The preamp is powered by the orig. Ashdown PT that gives 17-0-17 vac. The high voltage winding on the orig. was too much 63-0-63 vac so I added a second transformer that gives 28-0-28 which is in the recommended range. The orig. had 2 separate sets of line voltage in and step down voltage out so I removed the high power supply lines and secondary connectors for that part of the transformer. I am using the same 3 prong supply line to feed both PTs.

[shooter]

The high voltage winding on the orig. was too much 63-0-63 vac

ok I'm lost
too much for what, your chip?

where are you "plugging in", your original, or hybrid combo of chip and broke ashdown?

[smackoj]

Yes the chip wants apprx 28vac x 2. I have both PTs taking wall juice through the orig 3 prong plug and just split the + and - so it feeds both PTs. I am going to add a couple pictures. Maybe that will help.  Thanks Shooter and PRR

[PRR]

The new(?) power transformer is nearly touching the preamp board. That can't be good. Looks like you could slide it back and see if it makes *any* change.

The preamp-poweramp signal line practically rubs the PT and that can't be good either.

The yellow wire from the PT should go *direct* to the green power screw-block. Not detour through case ground. The power amp board corner ground can go to the chassis screw.

[smackoj]

I will make changes as suggested. Thanks amigo

[smackoj]

Changes made and the Beast has been tamed! Thanks so very much amigos.
Jack D  Colorado

[shooter]

Are you using the pre to drive the chip?
If so, can you scratch up your schematic to show where you grabbed the signal?
If not, glad you're workin n happy!

speaking of Colorado.......I need to catch up 

[smackoj]

Yes Shooter the Ashdown preamp is driving the chip. I have the schemo for the preamp. I will load it here. I used the same three pin jack you see close to the bottom right labeled Sig to Pwr Amp (It is a 3 pin connector but only has 2 wires connected to it). Sorry I don't know how to 'scratch' on these pdf files.

[shooter]

ah more sense than the 1st schematic