Hello-
I have poured over the You Tube Fryette two videos on finding ultimate tone for DR-103. If anyone else has watched these and tried to glean information can you please comment on my conclusions? I went back to the Mark Huss site and verified the documents, just trying to make sure I followed video correctly.
1. The mod work done was based on layout for "Early-70's Four-Input Preamp" Rev 1.4
2. The corresponding schematic to above layout is "Mid-70's Four-Input Preamp" which is labeled as "Drawing Rev 1.4 Mark Huss"
3. Just to be sure -- the audio signal is passed around the voltage regulator cathode follower. The techs discussion of that confuses me, but layout and drawings indicate signal is NOT passed through the cathode follower.
Thanks!
Fryette Videos on DR-103
Moderators: pompeiisneaks, Colossal
Re: Fryette Videos on DR-103
I apologize in that I made an error in regards to the schematic that matches the layout shown in video. I got a good look at the layout shown in video. It is marked "Rev 1.4" The tech in video stated that he was going to modify the DR-103 to match that layout. To me, then, the layout is THE determining thing so I tried to find the matching schematic. It appears the correct one, at least in everything after the tone stack, is "Early 70's Linked Input Preamp" Rev 1.0 Note that the signal IS passing through the cathode follower. So this video has me very confused. Does anyone know what circuit ended up being used?
Re: Fryette Videos on DR-103
I did a few mods on my DR504 clone based on what I learned in those videos. I originally went with the late-style phase inverter which passed no signal on through the CF, but I was convinced to try the other style after seeing those. I agree that the version Fryette used in those videos seemed to use the same circuit as Mark Huss' Rev 104 mid-70s linked input preamp from the tone stack forward (which is also the same circuit as the "Early 70s Linked Input Preamp" for the part of the circuit in question). After combing through the video, I'm thinking the input stage uses the conventional Hiwatt split cathode input stage (220K/2K2+47nF on Bright and 220K/2K2 [non-bypassed cathode] on Normal; link for anyone interested: https://hiwatt.org/Schematics/DR_PreLinkedInput_v1.gif). That's based on the stickers' labels from 20:00 to to 20:35 in the second video in the series (again, for anyone else no familiar: https://www.youtube.com/watch?v=xXfplMsVwVk).
So on the whole, I gather the circuit Fryette went with is more or less identical to the Mojotone schematic: https://www.mojotone.com/Amp_Kits/Briti ... 50_SCH.pdf
So on the whole, I gather the circuit Fryette went with is more or less identical to the Mojotone schematic: https://www.mojotone.com/Amp_Kits/Briti ... 50_SCH.pdf
Re: Fryette Videos on DR-103
I posted this earlier in the VOX/Hiwatt section and will post here also if OK -
Thought I would pass this along -
I stumbled upon the 3 very informative Hiwatt DR-103 videos by Steve Fryette. They are pretty long but it was worth the time to study them. He tells of his favorite version of the last gain stage and DC coupled bias regulator triode. What is revealing is when he does a frequency response test of a DR-103 both before and after he implements his version of the bias regulator triode. Also the playing samples done both before and after are convincing.
Mr. Fryette implements the bias regulator triode circuit very much like the "Early 70's Linked Input" preamp schematic as shown on the Mark Huss site. Regarding the last gain stage and cathode follower regulator of this preamp schematic only 1 resistor value is different, the 560K from C/F grid to ground is changed to a 680K. Per Mr. Fryette, in regards to C/F circuit, the keys to getting best tone are two things:
1. The audio signal is passed through the bias regulator triode to the 12AT7 phase inverter.
2. The values of the C/F voltage divider resistors are critical as they form a frequency compensation network in combination with the 0.02 coupler/bypassing capacitor. He prefers the 1 Meg/680K divider.
Some other bits of info I picked up from the videos:
1. Mr. Fryette likes the Hiwatt tone stack and never discusses any changes. He held up a hand drawn DR-103 schematic that is his favorite and I noticed his tone stack is the version with 22K resistor between treble and mid pots. I have seen a 220K resistor in that spot on another Hiwatt schematic.
2. He uses no larger than 0.047 cathode bypass capacitors, in combination with 2.2K resistors, in first and third gain stages. Second gain stage is 1K unbypassed.
3. EL-34 biasing is important in that he demands that factory (warm) biasing be used. He removes the voltage doubler mods if present.
4. He adresses the blocking distortion that can occur in DR-103 versions that do not have grid stopper resistors for second gain stage.
Just thought I would pass along what I learned from these videos.
Thought I would pass this along -
I stumbled upon the 3 very informative Hiwatt DR-103 videos by Steve Fryette. They are pretty long but it was worth the time to study them. He tells of his favorite version of the last gain stage and DC coupled bias regulator triode. What is revealing is when he does a frequency response test of a DR-103 both before and after he implements his version of the bias regulator triode. Also the playing samples done both before and after are convincing.
Mr. Fryette implements the bias regulator triode circuit very much like the "Early 70's Linked Input" preamp schematic as shown on the Mark Huss site. Regarding the last gain stage and cathode follower regulator of this preamp schematic only 1 resistor value is different, the 560K from C/F grid to ground is changed to a 680K. Per Mr. Fryette, in regards to C/F circuit, the keys to getting best tone are two things:
1. The audio signal is passed through the bias regulator triode to the 12AT7 phase inverter.
2. The values of the C/F voltage divider resistors are critical as they form a frequency compensation network in combination with the 0.02 coupler/bypassing capacitor. He prefers the 1 Meg/680K divider.
Some other bits of info I picked up from the videos:
1. Mr. Fryette likes the Hiwatt tone stack and never discusses any changes. He held up a hand drawn DR-103 schematic that is his favorite and I noticed his tone stack is the version with 22K resistor between treble and mid pots. I have seen a 220K resistor in that spot on another Hiwatt schematic.
2. He uses no larger than 0.047 cathode bypass capacitors, in combination with 2.2K resistors, in first and third gain stages. Second gain stage is 1K unbypassed.
3. EL-34 biasing is important in that he demands that factory (warm) biasing be used. He removes the voltage doubler mods if present.
4. He adresses the blocking distortion that can occur in DR-103 versions that do not have grid stopper resistors for second gain stage.
Just thought I would pass along what I learned from these videos.