5F10 Harvard Triple Inputs

[ToneMerc]

I've seen references around the internet that each of the 3 inputs on the 5F10 has a different response or even gain. Other than some perception, I don't see how thiis is possible with the way that are wired. It appears that the first jack electrically is no different from the third.

Am I missing something here?

http://www.prowessamplifiers.com/schema ... matic.html

http://www.prowessamplifiers.com/schema ... ayout.html


TM

[martin manning]

Am I missing something here?

Yes ;^)

Input 1 parallels all three 68k = 22.6k. No attenuation, HF roll-off is at ~75kHz, and the ground reference is through the guitar.
Input 2 Parallels two 68k and leaves one to ground. Attenuation is -3.5dB
Input 3 has 68k in series and 34k to ground. Attenuation is -9.5dB

Ignoring the guitar cable and pickup impedances, inputs 2 and 3 will have the same HF roll-off as input 1.

[ToneMerc]

Am I missing something here?

Yes ;^)

Input 1 parallels all three 68k = 22.6k. No attenuation, HF roll-off is at ~75kHz, and the ground reference is through the guitar.
Input 2 Parallels two 68k and leaves one to ground. Attenuation is -3.5dB, and HF roll-off is at ~46kHz.
Input 3 has 68k in series and 34k to ground. Attenuation is 9.5dB, and the HF roll-off is at ~23kHz.

Thanks Martin I knew you would set me on the right path . I could see that the inputs were in parallel, but I was missing the fact that they have different references to ground. So, 3 jacks it is then.


TM

[martin manning]

So you have one of these under-way? What did you decide on for the PT? BTW, I would put a 1M across input 1 so as to get a good ground reference.

[ToneMerc]

So you have one of these under-way? What did you decide on for the PT?

Yep, ready to drill some black G10. I ordered a PT fom Heyboer similar to what was discussed in the other thread. However, it's setup for 125V, 3A rectifier winding, filament winding with a CT and it there's extra low current 6.3V winding.

I started to throw out a group buy option, but since the price break was at 5 units and there were no responses to your mention of a group buy, I figured the interest level in a 5F10 was low. Also, there were some unknowns to this PT so I did not want to get into a situation of having 5 transformers that in hindsight should have been ordered differently.

I'm trying to get a repro chrome chassis, if that option falls through I will most likely use the Weber 5F2A and drill additional holes.

TM

[martin manning]

You probably saw the build on the web using a Weber 5F2-A chassis? That seemed to work out fine. How did you spec the HT voltage?

[ToneMerc]

You probably saw the build on the web using a Weber 5F2-A chassis? That seemed to work out fine. How did you spec the HT voltage?

Yes, saw that exact one. For cosmetic purposes it will work better for the inputs than the Mojo model because its only labled "instruments". Whereas, , the Mojo one is labled 1 & 2, which would look funky with a third jack. However, I am almost certain that the Weber chassis is drilled for 1 inch octal sockets, whereas the Mojo takes the Belton sized octal. I'm also thinking about attempting to bypass all the middle men and go straight to China for a chassis.

With 125V primary: 282 @ 95mA

Considering my summer months line voltages are around 123.5 and winter months are in the 124.5-125.5 range, this should get the plate voltage in the no more than +2% range of the schematic I'm hoping.

TM

[wyatt]

I believe that kit-bashed Havard used the older Weber Princeton chassis. I sure wouldn't want to try to drill and punch extra holes in the newer stainless-steel Weber chassis.

[Gordie]

I built a Weber 5F2H (harp amp) and I was afraid of trying to tool the stainless, but it's not hard to drill. I did resort to getting a machine shop to make a large hole for an additional octal socket for the pre-amp. I don't know whether that was money well spent, as the holes I drilled for mounting the choke and Output Xformer went easily without finishing my drills...

[ToneMerc]

I built a Weber 5F2H (harp amp) and I was afraid of trying to tool the stainless, but it's not hard to drill. I did resort to getting a machine shop to make a large hole for an additional octal socket for the pre-amp. I don't know whether that was money well spent, as the holes I drilled for mounting the choke and Output Xformer went easily without finishing my drills...

I'm using the s/s Weber chassis as well and I agree, not nearly as difficult as I was lead to believe it would be.

TM

[martin manning]

Good to know that the Weber SS chassis is easy to machine. Does it seem to be of good quality in general? I've considered their Fender-style slant-front chassis as an alternative to Mojo.

Note I had to back-pedal (a little) on my analysis of the 5F10 triple inputs... edited the post above to correct it.

[LeonC]

I've seen references around the internet that each of the 3 inputs on the 5F10 has a different response or even gain. Other than some perception, I don't see how thiis is possible with the way that are wired. It appears that the first jack electrically is no different from the third.

Am I missing something here?

http://www.prowessamplifiers.com/schema ... matic.html

http://www.prowessamplifiers.com/schema ... ayout.html


TM

Martin's explanation is great. Someone asked a similar question on the gear page a while back. My explanation took a different tack.