I"m running about 4v right into my guitar amp(as measured with my dmm which strumming My onboard preamp has 20x gain and pickups put out over 200mv) I then have a Tube pre in my amp that puts out over 20v with the gain maxed into the eq section and then into the TDA7293 Power amp and I haven"t had any problem with clipping or anything and no tripping the speaker protection relay (has a threshold of 2v dc at the speaker terminals) ....

I dont have a clue why that is , I haven"t had the amp up to 10 (plenty loud enough to jam on 5) so it might clip at a higher volume ...... I have run my hefty guitar signal into the TDA7293 but it was barely audible so I don"t know what is up with Chipamp input voltage sencitivity specifications but for me I have allways had to put a much higher voltage into them , maybe it has to do with RMS voltage or something ....

If it is a solid state amp you could put power resistors in series with the speaker , if you have an 8 ohm speaker putting a 8 ohm resistor in series will halve the output power , you could also use a L-Pad or a rheostat .....


Cheers

Actually I can"t remember if it was exactly 1v but it was some low voltage ....


this is the module I was talking about

http://cgi.ebay.ca/2-100W-4-TK2050-Class-D-Audio-Amplifier-Board-improved_W0QQitemZ250524283772QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a5469337c


if you go down and look at "Warning #3" it says not to use a Preamp because to high a input voltage will fry the chip .....

Quote from: joecool85 on November 03, 2009, 11:39:36 AM

Quote from: Minion on November 01, 2009, 11:40:00 AM
One thing about useing a Class D amp that I don"t like is that many have a certain threshold for the input signal , if you excede that threshold you fry the amp , some of them it is as low as 1v , and seeing as my Guitar by it"s self puts out up to 4v it allways seemed unsuitable .....


Cheers

Interesting.  I hadn't heard about this, however, I don't know much about class d amps on the whole anyway.

Yea , I was looking at getting one of those 4 x 100w tripath Class d modules from sure electronics for a quad ouput bass amp I wanted to build but after a reading the documentation for the modules it had a warning about excedeing a 1v input voltage and that it could results in failure ... I suppose you could build some sort of voltage divider network to bring down the input voltage to a reasonable level for the class d amp ....

You can also make a low voltage Tube preamp , I have the plates in one of my hybrids running off of 40v , that way you can use the Chip amp PSU to power the plates and just get a 12v Adapter to run the heaters and you don"t have a 200V signal going into your chip amp .... I just have a buffer after the tube stage then going into a 15 band EQ and into a TDA7293 , sounds great ....

One thing about useing a Class D amp that I don"t like is that many have a certain threshold for the input signal , if you excede that threshold you fry the amp , some of them it is as low as 1v , and seeing as my Guitar by it"s self puts out up to 4v it allways seemed unsuitable .....


Cheers

I"m pretty sure that when talking about chip amps the differance between and Dual mono and a stereo chip amp is that a Dual Mono with have a seperate power supply and Transformer for each channel were a stereo will use the same PSU and transformer for both channels ... the advantage of Dual mono is that there is no Crosstalk between channels and the grounding is easier , the disadvantage is that Dual mono takes up more space in your chassis and is heavier and nearly twice as expensive ......


Cheers

Well here is one I did a year or so ago ..... I might have posted it here before ....



It is a PAiA "Stack In a Box" tube guitar preamp kit that is modded to provide 10x more Gain than stock and with better opamps .....

the Preamp then goes into a 15 band graphic eq (consumer gear) and then into a TDA7293 100w Mosfet Power amp chip ......

It sounds freaking awesome and loud as hell .....

I"m now working on a dual channel Tube/solid state hybrid amp with a 5 band eq for each channel and each channel can be used independantly with 2 seperate guitars or can be run in Paralell with a single guitar , each channel can also be summed at the output so the same signal goes out the two LM3886 chips or can be done independantly in stereo ......

Cheers

Actually there are a lot of designs out there that use the 12ax7 with voltages as low as 12v , or use 12v AC and use a Voltage doubler to get about 32v for the Plate , that 12v ac can also be made into a Half wave voltage doubler to give +/-15v DC for solid state stuff like opamps .....

So you can concieveably Build the Tube pre , solid state/Stompbox curcuits and Power amp with a Transformer at 18v ,0v ,18v at 200Va and a 12v tap at 15Va ......

Cheers

Yea , I use a PAIA Kit for a preamp also and it sounds great, did some mods on it to get a more screaming metal sound and then run that through a 15 band eq into a 100w Mosfet power amp ....

here"s a pic ...



I also just designed a PCB for the PAIA Kit so I can etch my own anytime I want ....

I"m building another one accept this one has a dual mono 50w output with a 4 band Parametric EQ , Might just go stereo all the way and use 2 EQ"s and 2 PAIA Kits and a foot switch to switch between the channels and go switch between Stereo and dual mono .....

Cheers

I can"t really post guts pics as I would have to take it appart and it would still be difficult as there isn"t really any room with the pannels off to get a good pic but I could post some schematics...

Here is a schematic for the preamp section...

http://www.paia.com/prodimages/siabsch.pdf

I used fet input opamps and configured it for 10x as much gain than as shown...

the EQ Section is actually consumer gear that I integrated into the unit...

For the Power amp section I used a TDA7293 100w Mosfet Power amp IC , it is the same curcuit in the data sheet under "Figure 1" .....

http://www.datasheetcatalog.org/datasheet2/9/0ozxelyhtgfl5jsx9108fj3sqq3y.pdf

The Preamp runs off of a 12v Power trsnaformer (the Tubes run off of a CMOS Hex inverter to ramp the plate voltage up to 45v dc)

The power amp section runs off of a 2x28v 200Va power transformer giveing me 2x42v dc and has 20,000uF of capacitance per rail (40,000uF total) and uses a 15a Bridge rectifier.....

the amp has a bit of turn on thump but is increadably quiet for a high gain amp (very little humm).....


Cheers

Generally how you bias an opamp depends on it"s configuration...For a Non-inverting configuration can you bias the Non-inverting input of the opamp or you can bias it at the end of the Feedback loop...For an inverting configuration you can bias it through the Non-inverting input through a resistor.....


Cheers

Hi Folks, I just wanted to post my latest Guitar amp build for you guys...

It is Parts DIY Kit, Part Consumer gear and part Totally DIY...

It is a 100w Head , it has a Fet opamp front end driveing a 12ax7 Tube preamp with speaker simulators and Ballanced DI Output and effects loop and polarity switches and some other features (it is a Modded PAiA Kit), it has a 15 band EQ with High pass/Low pass and Notch filters , and a 100w DMOS Output stage....




It sounds Freaking awesome , especially for a heavey sound , lots of Harmonics ....


Cheers

Hi,The reason I don"t ahve any BD140 PNP"s is because were I live there is only one electronics store and it has very limited selection and everything is about 20X the price of what I would find on-line but If I buy on line I have to pay huge Shipping fees which are generally at least twice the Price of the order for such small quantities.....

I get a lot of my Parts from dismantleing broken or obsolete audio and Video equipment so I usually just make do with what I have.....


Thanx

Hi, I have allready considered that Project , But don"t have the right Parts (I guess I could replace the BC549/559 with the BC550/560 but I don"t have any BD140 but maybe I can use a BD139 and switch the Emitor and collector or maybe just use the Tip31/32??)

I actually don"t need any special features accept it being clean and loud as I can allready design the Preamp stage with overdrive and tone controlls useing Ic"s.......


Thanx