Hi friends; A very long time away so apologies. I did a quick cleanup on this Randall RG75D model SS amp. Built in China with one 12" spkr. This amp is almost silent at idle but start playing thru it and it sounds poor with some kind of high freq noise on every note. I checked the speaker wires and there is .25 vdc on them at idle. Is that enough dc to cause a problem? thanks amigos

Hi friends; It's been a very long time away. A lot of things got put on hold including amp repairs. I have been working on a Peavey Ecoustic 112 amp lately. Everything is running smooth and quiet except the reverb which is important for the new owner. I have reverb when I turn the pot up but I also get like a 60hz hum. I tried re-soldering, cleaning the pot, switched out the tank with 2 diff ones but nothing quiets it down? Does anyone have a suggestion? Looking through the Peavey Forum I found evidence that Peavey amps are known for noisy reverbs. Someone on there suggested using an isolation transformer which I have not tried.

I have worked on this GK 200GT for a little too long and believe the 1976 "boat anchor" output transformer is bad. Rather than searching for a replacement, I would  like to replace the whole power amp board with a chip amp, either class AB or D. The problem I have, if it is actually a problem?, is that the preamp section which I like a lot, except for the "Current Limiter" pot, has a negative -8.7 vdc signal wire to the power amp board. Is that too much voltage and needing to be changed to a positive voltage before using a chip amp power board? I believe the preamp is working correctly but I am not sure because the schemo is hard for me to read and not sure if the signal from R85, the reverse 10k pot called "Current Limiter" is showing a negative voltage feed to the power amp? Review of the Owner's Manual shows that the Current Limiter function is to change the power output of the amp (I would just as soon remove it). Would anyone care to look at this and offer suggestions?  thanks

I received a GK Gt2000 to try and repair. I have not been able so far to find a schematic for it. It uses two pcbs: 50015C pwr amp, and 50016A preamp. Everything on this amp is pretty straight forward except it uses 2 large transformers; One is obviously the power supply and it tests good. The 2nd one is on the other end of the chassis and 2 of it's secondaries go to the 2 pwr transistors (collector?). I am not sure what I am suppose to see coming off the secondaries. Someone has re-wired things inside and they had the positive lead to this 2nd transformer coming off the + pin of the bridge rectifier which is obviously DC volts going in the 2nd trans. Any help would be appreciated.

Jack D

I have a 1979 Premier P50R ss amp and I would like to put a fx loop between the preamp and the power amp. Does anyone have a good, working example / schematic they could post?  Here's a picture of the little amp. It only makes about 10 watts so I would like the option of bypassing the preamp and seeing what kind of power and tones I can find using other pedal type preamps. Thanks 

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 

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

Sorry about the very poor quality of the schemo.

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. 

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