Nice stuff about thermal transfer from the ESP site. Thanks

:tu:

<notice the size of the heat sinks>

They appear on the 'too small' size to me. Is that what you mean by "look at the size" ?

sorry about having to hear it 2 or 3 times. I thought that 2 pairs = apprx 100 watts. I get it now; equals apprx 50 watts.

I'm ok with not building this 'too far gone' design. No sweat  :tu:

thanks for the 'clean up' job. I think I'll just try to find a better design. I don't really want a 50 watt amp and I get lots of practice soldering with my pedal projects. I keep lots of spare 'recycled' transformers and other parts around so I won't be buying any of those pieces NEW.

Have any forum contributors used the BD249 and 250 chips in a good design?

thanks amigos    :tu:

Wow! great input friends. I don't really care about the pcbs I bought from the 'masked man' in Thailand cuz those can be plunked in the pot. I do, however wish to build a nice power amp and I have lots of parts left over. I couldn't find the 2955 and 3055 chips with the newer style package so I bought these chips:  BD249C and BD250C. I bought 2 pairs so I have 2 of each. I bought the listed BD139 and BD140 driver chips and I have quite a good selection of single and dual op amps. Would anyone like to offer a suggestion  on what design I could/should build that would work good with these particular transistors?  Note: I had seriously looked at the ESP 100 watt board before I bought these boards. I guess with my Gear Acquisition Syndrome habit of late, I just wanted a simpler, less parts count idea to start. Live and learn as the old farts like to say.

For those readers that may want to scope the original schemo, here is a better viewable copy that I added some highlighted parts to 'make it easier' to see/read.

thanks again friends, lots of good info. I appreciate it.   

I bought a PCB for a diy 100 watt amp off a guy on ebay. I had some questions about mounting the transistors and I posted the schemo on Hoffmanamps.com forum which I follow and contribute to. I got a response from PRR who is one of the moderators saying "that amp is a cummy design that should be put in the trash"  I'm paraphrasing here. I would still like to have a go at it since I already bought power chips and driver chips and lots of 2 watt Rs. I'm putting the link on here to the discussion over at Hoffman's and would appreciate any other, 2nd or helpful opinions about what I would need to change or add to operate this amp safely?  thanks friends  :tu:

http://el34world.com/Forum/index.php?topic=17002.0

Sorry about the very poor quality of the schemo.

I am the Proud owner (what?) of a Crate DT50C that I bought mostly because it came with 2 nice MIE Celestion 10s. It hummed badly and one of the two inputs was inoperable. I replaced the power filter caps and it had little to no effect on hum. Then I did as others have suggested, thorough inspection and re-flowed the solder joints on everything I could get my solder tip close enough to especially around the input jacks, potentiometers and power supply. I also had a Native American medicine man perform an exorcism on the demon spirits that typically haunt Crate equip. Wala, it only hums 1/3 as much and I use it as a backup at church. One great thing about this amp is that I don't worry that someone will steal it and I can torture it with any combination of pedals and gain settings without worrying if it blows up.    :loco

ok, thanks for the tips fellas. now I have to find 3 men and a dog to move this thing home so I can snoop around on it!!!

heavier than Lulu after an 'all you can eat' buffet.

8|

<what is the goal you are trying to achieve with the help of a transformer?>

I guess it's kind of hard to describe my 'goal' because it seems I got a little confused with all the options for preamps-boosters-di boxes available today. My original idea, after building Senor Phatt's Phabbtone preamp, was to adapt it so it could be used with an acoustic guitar (reference the latest discussion under the "Phabbtone" thread on this forum). But, not just any acoustic-electric guitar, but one fitted with a 'wood block' sound board pickup, aka piezo pickup. This type of pickup, as I now know, wants to see an input impedance of about 1 M to 3.3 M. 

So, I guess I thought that trying to convert the preamp to a preamp/di box made sense and a few of the designs I found use transformers in conjunction with the FETs or Op Amps. I presumed that this type of device was better when using a transformer to adjust the impedance? And that is how I arrived at this place where I'm talking about a DIY preamp plus DI box. I know we talked about using a buffer which would take the place of matching Z with a jfet or IC chip. However, I have always been intrigued with transformers carrying guitar signals and it just drove my imagination to seek that as a remedy rather than a FET buffer. I am also starting to build a Roly designed GroMo aka Gronk o Matic. I will pass along what works and what doesn't work so good as time and parts allow.  :tu:

thanks amigos

thanks for the really helpful and interesting info. I am going to have to do some reading on trannies before I can expect to reach my goal. Transformers seem somewhat mystical and I don't want to waste money doing garage 'experiments' with bunches of them.

adios for now friends.  jack :tu:

roly; thanks. yeah, I thought the 'guitar' cable etc were just CAD design add-ons but it took a while to get a clear picture with them on the schemo. I have a couple other projects to finish then I will give your CR circuit a go. looking forward to testing it on this particular application.

thanks again,  jack

earlier in this thread Phatt suggested using Roly's adjustable CR circuit to find the right impedence match for a passive pickup acoustic guitar. I have studied this schemo enough to know that the input side confuses me. The 'guitar', 'pickup' and 'cable' don't usually get shown on a schemo. If I want to build this circuit, do I just start the build at the 'input' as I would normally on a pedal build or am I not reading this right?

thanks friends; simple FET buffer makes lots of sense. I have a few already made laying around I will scrounge up and give 'em a whirl.

question; does the piezo type 'transducer' (passive) have a hi Z?

gracias again

smacko jack     

thanks g1, that helps a lot. I wondered about the 'hi' and 'low' tags? my Normal ch. has the low input that acts right. If the hi input on that ch is working correctly, then it was designed to have a MUCH higher signal because the hi input is pretty darn quiet and wimpy?

the 2nd (reverb) channel has low output from both Hi and Low input jacks. I have not pulled the chassis out for quite some time to have a look. I have just been using the Low input on the Normal ch.

thanks for the help senor.

smacko jack

hi friends; I thought maybe a new thread was warranted instead of jumbling up the earlier thread on Phatt's Phabbtone (a real peach of a design IMO). I was asking how to get the Phabbtone in use as a preamp for an acoustic guitar with a passive transducer inside it. These wood block pickups (I use a Schatten built in Canada) only put out a few mv so most of the preamps and some of the DI boxes aren't easily compatible.

Here are a few schemos and a great website review of 2 of the Radial Engineering DI/preamps on the market. I found these in search of an answer to my original question (can I mod Phatt's Ptone to work with 'quiet' acoustic pickup?). The Firefly DI by Radial sounds fab even on my laptop 'crap can' spkrs!  But, the bad news is they sell for 600 USD, yikes!

So, please read, review, and join in if you know how WE might be able to build a better mousetrap or DI box.  :tu:

Radial DI reviews here:  http://www.acousticguitar.com/Gear/Reviews/Radial-PZ-Deluxe-and-Firefly-Review