Dsl40CR CIRCUIT QUESTIONS

Robi mi

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Hi Guys!
I bought a DSL40CR to play around with modding etc. I have great resaultes with the usual mods, but i have a question about 2 parts of the ciurcuit that I can't understand the pourpose of, and I consider changing:
1 - the resonance circuit looks very complex to a normal one. +Why it has HT on it? (Photo attached)
2. What is the pourpose of all the circuit in front of the master volume controls? (Photo)
 

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tschrama

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1. Tr1 with Tr6 simulate an inductor. It’s a inductor based resonance circuit.

2. no idea. Might be just a bandlimmited gain stage to get the voltage swing up again after the FX level. Cannt see from the tiny schematic snippet. Please post complete schrmatics.
 

Robi mi

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Full schematics uploaded

1. Tr1 with Tr6 simulate an inductor. It’s a inductor based resonance circuit.

2. no idea. Might be just a bandlimmited gain stage to get the voltage swing up again after the FX level. Cannt see from the tiny schematic snippet. Please post complete schrmatics.
 

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SkyMonkey

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Please be aware that those are incomplete schematcs from 2015, 3 years before the 40CR was released.
There are probably multiple revisions since those prototype drawings were leaked.
 

Max Gahne

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TR2 is a buffer and TR3 is a common emitter amp, a gain stage. I think the DFX IC puts out a weak signal that has to be increased before the phase inverter. The same design is used in the DSL20 which I have and made a lot of experiments with. I've experimented with bypassing the buffer but reversed that. The highs are thin without the buffer. I have changed the bias and lag capacitor on TR3 which I like a lot better. I left that mod in.

The HT goes to TR1 and TR6 which make a gyrator. Look that up, it's an impedance thing for the resonance circuit. I haven't messed with that as I haven't been using resonance.

Also like @SkyMonkey says it's an old schematic. I found lots of component value differences between my new DSL20 and the old schematic I have. Also some of the value differences are suspicious like they came from simply running out of one value and putting in the next closest value they had on hand.
 
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Robi mi

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TR2 is a buffer and TR3 is a common emitter amp, a gain stage. I think the DFX IC puts out a weak signal that has to be increased before the phase inverter. The same design is used in the DSL20 which I have and made a lot of experiments with. I've experimented with bypassing the buffer but reversed that. The highs are thin without the buffer. I have changed the bias and lag capacitor on TR3 which I like a lot better. I left that mod in.

The HT goes to TR1 and TR6 which make a gyrator. Look that up, it's an impedance thing for the resonance circuit. I haven't messed with that as I haven't been using resonance.

Also like @SkyMonkey says it's an old schematic. I found lots of component value differences between my new DSL20 and the old schematic I have. Also some of the value differences are suspicious like they came from simply running out of one value and putting in the next closest value they had on hand.
thanx alot! this is exacty the info I needed!
can you explain how to do the TR3 mod? what it does?
 

Max Gahne

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I don't want to steer you into messing with TR3 without thinking about it. My mod works with all the changes I made in my amp's pre amp and tone stack. And also the DSL20 has a completely different pre amp as it is, just 4 gain stages whereas the DSL40 has 5 gain stages and a buffer. And lastly I'm an old boomer and play like one and tuned my DSL20 to work for my style which might be different from your's. I will say that from my own experiments I wouldn't change TR2 and I wouldn't change the attenuator ( R139, R44 and RL2.2 ) that is after TR3. I did experiment with bypassing the attenuator but it makes the red channel volume control hard to use at bedroom volume. I wouldn't change that and reversed mine back to stock. On TR3 I experimented with the emitter ( R52, C46 which set TR3's gain ) but reversed it back to stock because the tube phase inverter liked that best. The only mods I kept were to the bias and lag capacitor network ( R13, R53, C43, C27 ) which you might not like, again it works with what I did upstream and my own tastes. I experimented and in the end removed R13 and left that open, removed and jumper'd C27, changed R53 to 470K and C43 to 180pf ( 500V or bigger ). Basically I simplified the circuit so that I only had C43 to experiment with - a smaller C43 will be brighter, bigger less bright. But I wouldn't recommend doing any of that because depending on what you've already done and your own tastes you might be reversing all that back. What I was after was to make the top end less sizzly and metallic sounding and the high mids less - I don't know how to describe the sound but stock the high mids didn't work with my tastes. I posted a vid of me playing it down in the cellar a few days ago and you can hear it.
 
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Robi mi

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Your a brave soul!
My DSL40CR sounds so great I cant imagine modding it!
What are you attempting to achieve if I may ask?
i bought that amp as a relatively cheep modding platform for learning. and i needed a portable amp for gigging.
i already did some mode to it: changed the classic gain channel tone stack to quality caps, reduced the gain and tuned the bright caps.
 


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