ODS 102 HRM

[ic-racer]

Basically this is just a re-working of the ODS 101 HRM schematic with some small additions that I wanted in my build. As I understand 101 HRM was very close to the real thing, likewise this should be very close. I added things to 101, like the Jazz/Rock switch and 12v power supply. Other places I changed things based on some of those HRM innards pictures that have been posted (like the 100R tail on the HRM stack).

One curious thing I did change from 101 is the clean channel plate resistors. Since I am eventually going to build this amp, I want it to be different from my others. I used 100k on my #124, and my Fender has 100k clean and 220/150k on the OD. So, on this one I wanted to try 220/150k on both clean and OD.I guess I'll hear what that sounds like when I finish.

Just for the record this schematic is suppose to show an Overdrive Special with Skyliner tone stack, 'regular' PAB, an independent master circuit, a HRM post OD tone stack and an EL34 100W output section and a 'regular' Non-bluesmaster, PI.

I suspect there may be a number of little errors at this point.

[ic-racer]

See latest file below...

[tubedogsmith]

Great stuff!! Did you want the treble cap to be .02?

[ic-racer]

Great stuff!! Did you want the treble cap to be .02?

No. Thank you for catching that one. I am sure there are others.

[Guitarman18]

ic-racer, it's great that you are doing this. If you are going to include the notes that appear at the bottom of the ODS-101 HRM schematic, it would be nice to have No.4 edited to say that the slope resistor is most often carbon film and if possible, list the composition of the various other key resistors. Having said that, there doesn't always seem to be a difinitive pattern with regard to MF/CF application amongst HAD and the forum's most knowledgeable members.

[ic-racer]

ic-racer, it's great that you are doing this. If you are going to include the notes that appear at the bottom of the ODS-101 HRM schematic, it would be nice to have No.4 edited to say that the slope resistor is most often carbon film and if possible, list the composition of the various other key resistors. Having said that, there doesn't always seem to be a difinitive pattern with regard to MF/CF application amongst HAD and the forum's most knowledgeable members.

I had thought that a separate document with notes would be best, but the way things get scattered on the internet, having notes on the schematic is probably best.

Yes, a description of the components would be good. I can say I have never seen pictures of a de-gooped HRM so I'll either follow the notes on 101 or go with what you guys suggest. I guess this is the perfect place to discuss such things

[dogears]

Pretty close. I had this exact amp open. In the 220s... It had a 47pf bright on clean master. It had 150K grid resistor on OD2. And 500pf HRM treble cap. You have a typo.....

IMO, this circuit needs the 150K grid resistor... All the late model HRM amps with this topography, have it. To the best of my knowledge.

[ic-racer]

Thank you. Changes made.

[Guitarman18]

ic-racer,
Are 1N4007 diodes still used in the FWR bypassed with .01mf caps? I've noticed that in the pictures posted by ayan and Funk, they used the same 4 diode setup, but I assumed (probably wrongly) that they must be FRED's or something.


Cheers, Paul.

[dogears]

The late model amps I have seen all had the .01uf ceramic bypass caps on the diodes.

I use cheap ultra fast soft recovery diodes in TO-220 packaging. Almost like a Fred but for little more than a 1n4007

[kleinm]

The late model amps I have seen all had the .01uf ceramic bypass caps on the diodes.

I use cheap ultra fast soft recovery diodes in TO-220 packaging. Almost like a Fred but for little more than a 1n4007

For amps, I use something similar, but in a DO-41 package. Mouser no. 512-UF4007. Good stuff.

BTW, most excellent schematic. Thanks for sharing your work, ic-racer!

[ic-racer]

The late model amps I have seen all had the .01uf ceramic bypass caps on the diodes.

I use cheap ultra fast soft recovery diodes in TO-220 packaging. Almost like a Fred but for little more than a 1n4007

For amps, I use something similar, but in a DO-41 package. Mouser no. 512-UF4007. Good stuff.

BTW, most excellent schematic. Thanks for sharing your work, ic-racer!

And thank you guys for help on the diodes!

[ic-racer]

I posted some PC boards that are based on this schematic in the files section.

[ic-racer]

Updated the schematic to reflect some subtle details I figured out from the HRM pictures posted by resophonic1.

(Latest file further down in thread...)

[dogears]

Your 91K and 110K PI plates are reversed

In addition, the only confirmed bypass cap on OD2 is a 1uf. In this particular HRM incarnation.

Updated the schematic to reflect some subtle details I figured out from the HRM pictures posted by resophonic1.