Paging Dogears 200V Question

[paddy]

Hi Dogears

I've seen a few posts where you recommend tweaking the power
supply resistor string to achieve 200 volts on the plates of V1.
Can you tell me if this relevant to all models,including mine?
I have built the '97 ODS and currently have the following voltages:

B+1 455
B+2 454
B+3 436
B+4 389
B+5 372

V1b 235
V1a 262
V2b 228
V2a 244

Many thanks for any help
Cheers
Paddy

[dogears]

Hi Paddy,

First of all, something is wrong with V1a. The voltage is WAY high. I would raise the string from 12k and 10k ( I think) to 18k and 4.7k, or maybe even the Hybrid A string but with a 2.2k at the end. Most importantly, hang a 150k from the last resistor in the string to ground. This loads the B+ and simulates the FET that is in all Dumbles. It also will lower your B+ about 20v or more..... Try adding it before messing with string values. But, you also have to figure out why V1a is high. Check your plate and cathode resistors. I always measure.....

Hi Dogears

I've seen a few posts where you recommend tweaking the power
supply resistor string to achieve 200 volts on the plates of V1.
Can you tell me if this relevant to all models,including mine?
I have built the '97 ODS and currently have the following voltages:

B+1 455
B+2 454
B+3 436
B+4 389
B+5 372

V1b 235
V1a 262
V2b 228
V2a 244

Many thanks for any help
Cheers
Paddy

[paddy]

Thanks for the quick reply Dogears
I thought the v1a plate voltage was high.
I built as per the "97 rev 1.2 schematic,unfortunately it shows
a 3k3 cathode resistor.I dropped this value to 2K2(as shown in
other schematics) and the plate voltage has now dropped to 237 Volts.
v1b plate is now 232 volts and B+5 is 370.

I will try your suggestions on the supply string resistors and get
back with the results.

Many thanks
Paddy

[paddy]

Hi Dogears
i have placed the 150K at the end of the resistor string to ground
and now have 203 volts on v1b plate and 208 volts v1a plate.
are these voltages close enough to your 200 volt target?

thanks for all the help

cheers
paddy

[dogears]

Yes! Very good..... Should be so much sweeter sounding. No??

Fwiw, I use RN65 Vishay Dales for plates

V1a 221k/3.32k
V1b 150k/2.21k

V2a 182k/2.74k
V2b 120k/1.8k

Hi Dogears
i have placed the 150K at the end of the resistor string to ground
and now have 203 volts on v1b plate and 208 volts v1a plate.
are these voltages close enough to your 200 volt target?

thanks for all the help

cheers
paddy

[dogears]

Paddy,

If you built the 97, you must fix a few problems with the schematic.

The HRM treble cap is a 500pf. The CL2 grid bypass cap is a 500pf. The pre OD netwrok is 470k w/47pf bypass into a 200 k (schematic says 120k) into a 25k trim w/ 4.7k tail

Try these changes.

If you have a non HRM build then we really need to fix stuff....

[paddy]

Thanks for the tips Dogears

The amp sounded a little sweeter after the changes to get the v1
voltages correct.
I will try the other changes you've suggested.
Unfortunately i wont be able to try the Vishay Dales.I live in Tasmania,
a small island state of Australia,getting parts here is a real problem.
I've spent a fortune on shipping for this build already.
I really envy you guys in the U.S. seems you can lay your hands on just about anything!
Thanks once again--i'll get back to you with the results

cheers
paddy

[paddy]

Hi there Dogears

I made the following changes that you suggested and the amp sounds great!

CL2 grid resistor bypassed with 470pF(didn't have a 500pF)

I/P to OD1 470k//47pF into 200k into 22k pot(no 25k available)
with 4k7 tail.

It sounds fantastic but like everyone else i am willing to accept any more tips if you have them.
just a couple more questions if you can spare the time?

1. I currently have .047uF coupling cap after OD1 what are your thoughts

2. I have no bypass cap on the OD Level pot " " " "

3. I have .01uF Mid cap on the input tone stack and have seen many
recommendations for .047uF. How will this effect the tone on this build
which started out as the '97 ODS and looks now to be the TR
Emerald Pro?

Once again
Many,many thanks
Cheers
Paddy

['67_Plexi]

Paddy,

I could buy some RN65's for you the next time I put an order in and then send them across. You can just pay me via Paypal. I put orders in twice a week so it's no biggie to add a few more. Just let me know what values and how many.

Alan.

[dogears]

I have a .047 after V1b

The OD1 network is a .0022uf into 100k into 250ka pot. (HRM amps!)

Did you change the HRM treble cap??? Must be 500pf (or 470pf if none available)\

You said you built the 97... I assume you have HRM... No?

I have no bright cap on OD 1M master

I like the .01uf midcap

Did you adjust your HRM with the PAB boost on?? Only sounds amazing that way.

Hi there Dogears

I made the following changes that you suggested and the amp sounds great!

CL2 grid resistor bypassed with 470pF(didn't have a 500pF)

I/P to OD1 470k//47pF into 200k into 22k pot(no 25k available)
with 4k7 tail.

It sounds fantastic but like everyone else i am willing to accept any more tips if you have them.
just a couple more questions if you can spare the time?

1. I currently have .047uF coupling cap after OD1 what are your thoughts

2. I have no bypass cap on the OD Level pot " " " "

3. I have .01uF Mid cap on the input tone stack and have seen many
recommendations for .047uF. How will this effect the tone on this build
which started out as the '97 ODS and looks now to be the TR
Emerald Pro?

Once again
Many,many thanks
Cheers
Paddy

[dogears]

I must CLARIFY! This is NOT an Emerald Pro!! That is based on the 97 and the incorrect values. My research and testing has absolutely nothing to do with the Emmy. My changes make it further from the Emmy...

[paddy]

Hi guys
firstly let me say that is a most generous offer on the RN65's Alan,
if you would like to send me a pm with approximate price,i will see
how many i can order.big thanks.

Dogears,i made a mistake in my last post. i should have said i have
.022uF after OD1(schematic shows .0022uF) don't know how i ended up
putting .022uF in that position--i think i was in a hurry to finish the amp
with wife nagging me to mow the lawns and kids wanting to play ball!
anyway i will swap to .0022uF and see what happens

I have .047uF after CL2 just like you

I had already changed the HRM treble cap to 470pF

Yes it is HRM and yes i have only adjusted the HRM tonestack in PAB mode

I totally agree with you when you say the O.D channel only sounds great
in PAB mode.I am only a beginner at guitar and i can only assume that
when playing out,the idea would be to play with no boost and then switch
to PAB during a lead break. is this correct? and if so,have you found a way to make the non boost mode sound better?

I currently have .01uF at the P.I. input and two schematics for the '97
one shows .01 and the other .022 which do you recommend?

as always,
your help is greatly appreciated.

cheers
paddy

[Bob-I]

Interesting.... I spoke with Scott (dogears) yesterday. He told me that using the dropping resistor, the FET load simulation, sounded better than adjusting the string.

I made the following adjustments.

Initially I had this string....

Primary filters 2 - 100uF 350V caps -> choke -> 2.2K -> 12K -> 1.5K -> 1.5K -> 1K

The results of that string are that both V1 and V2 are very close to 200V, about 198 on V1 and 203 on V2.

So I added a 150K resistor to ground from the last node in the supply and lowered the 12K to 8.2K. The voltages remained almost identical.

The tonal results were quite suprising. Overall the amp is smoother and the notes bloom more. The feel is "softer" if that makes since. I feel that there's less distortion and more of a singing... grainy quality.

And I was happy with this amp before. Thx Scott!!!